Senior Welding Inspector Guide Book

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WORLD CENfRE FOR MATERIALS JOINING TECHNOLOGY

Copyright o 2002, TWI Limited

Training & Examination Services

Granta Park, Great Abington

Cambridge, CB 1 6AL, UK

SENIOR WELDING INSPECTION (WlS 10)

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Section

Title

1)

Terms & Definitions

2)

Duties & Responsibilities

2a)

Duties of a Senior 'Welding Inspector

2b)

QA/QC

3)

Welding Imperfections

4)

Mechanical Testing

5)

Welding Procedures/Welder approval

6)

Materials Inspection

7)

Codes and Standards

8)

Welding Symbols on Drawings

9)

Introduction to 'Welding Processes

0)

Manual Metal Arc Welding

11)

Tungsten Inert Gas Welding

12)

Metal Inert/Active Gas Welding

13)

Submerged Arc Welding

14)

Welding Consumables

15)

Non Destructive Testing

16)

Weld Repairs

17)

Residual Stress & Distortion

18)

Heat Treatment of Steels

19)

Oxy-Fuel Gas Welding & Cutting

20)

Arc Cutting Processes

21)

Welding Safety

22)

Weldability of steels

23)

Fracture Assessments

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THE WELDING INSTITUTE

Senior welding Inspection General Theory (situations) Paper SWI·Q~S1 1. You are an SWI who has taken over from an SWI who has been on site for a few months. It becomes obvious that there is a complete lack of moral amongst your inspectors but they do not approach you to discuss any grievance. What would be your approach to the situation?

2. You are an SWI responsible for a team of welding inspectors who have been on~site for two months. A welding inspector who has been on site for only one week informs you that the contractor has approached him with an offer of money in return for ). "turning a blind eye" when certain welding work is being performed. Discuss your . course of action.

3. You are the SWI on a pipeline project. The radiographic interpreter informs you that he believes that the same weld has been radiographed with different weld numbers on a number of occasions and the radiographs have been submitted. 'J\/hat action do you take?

4. You are the SWI working on behalf of a client on a project to build an offshore platform. You discover that one of the welding inspectors, supplied from a different agency, who has been on site for one week, does not hold a valid welding inspector approval. State the actions that you would take.

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You visit a fabrication company as an SWI on behalf of a client and you discover in a welders electrode quiver a number of incorrect electrodes among the correct ones which are very different to' those specified for the item being welded. The welder states that he only uses the correct electrodes. State your course of action

6. Question number 6 is a compulsory question for the SWI examination. You are required to visit a site on which your welding inspectors have been involved.

The work concerns the inspection of a welded structure to a specified application

standard and is now completed and ready for final approval.

What questions do you ask, what documents do you review and what inspections do

you require before submitting your inspection report to the authorities concerned?

WIS LO MSR/SWI-Q-S l issue 2 Date: 28/05/03

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Terms and Definitions:

A Weld:

A Joint:

Senior Welding Inspection - Terms & Definitions Copyright © 2002 TWI Ltd

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Types of common welds:

Welds.

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Welds.

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Welds.

Welds.

Welds.


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Welded Closed Corner Joints:

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Welded Closed Corner Joint.

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Welded Open Corner Joints:

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Welded OQen Corner Joint.

A

Welded O.l!en Corner Joint.

A

Welded OQen Corner Joint.


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Terms of a Butt Welded Butt Joint:

Weld zone

= Weld Metal + HAZ

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Root

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A, B, C & 0

Welding Inspection - Duties of a Welding Inspector Copyright © 2002 TWI Ltd

=Weld Toes

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Terms of a Fillet Welded T Joint:

\ In visual inspection it is usually the leg length that is used to size fillet welded joints. It

is possible to find the design throat thickness easily by multiplying the leg length by 0.7

The excess weld metal can be measured by taking the measurable throat reading, then by

deducting the design throat thickness calculated above.

Example:

If the leg length of a convex fillet weld is measured at 10 mm, then the design throat

thickness

>

10 x 0.7 which is 7mm.

If the actual throat thickness is 8.5 mm then the excess weld metal is calculated as:

8.5 -7mm = 1.5mm excess weld metal.


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'Nominal' and 'Effective' Design Throat Thickness:

Same leg length

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"s" = 'Effective' design throat thickness

"a" = 'Nominal' design throat thickness

(deep penetration fillets)

When using deep penetrating processes with high current density it is possible to create deeper throat dimensions. This may be used in design calculations to carry stresses and is a big advantage by reducing overall weight of welds in a large welded structure. Deep throat fillet welds are possible when using high penetration (High current density) processes, such as FCA \V & SAW. This throat notation "a" or "s" is used in BSEn 22553 for weld symbols on drawings throughout Europe.


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Fillet Weld Profiles:

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In joints that are to be dynamically loaded with cyclic stresses, concave fillet weld are preferred to minimise any stress concentrations or sites for fatigue crack initiation. In critical applications it may be a requirement of the welding procedure that the toes are lightly ground, or even flushed i~ with a TIG run, to remove any notches that are present.

Senior Welding Inspection - Terms & Definitions Copyright © 2002 TW[ Ltd

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Effect of a Poor Toe Blend:

A very poor weld toe blend angle 6mm

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An improved weld toe blend angle 3mm ,~~~~atr~%~~~;r1.~t~:tl~~~:!i.;·~

Generally speaking, most specifications tend to quote that "The weld toes shall blend smoothly" This statement can cause problems as it is not a quantitative statement, and therefore very much open to individual interpretation. To help in your assessment of the acceptance of the toe blend it should be remembered that the higher the angle at the toe then the higher is the concentration of stresses, which between 20 0 - 30 0 is almost at a ratio of2:1 A poor toe blend will be present when the excess weld metal height is excessive, however it may be possible that the height is within the given limits, yet the toe blend is not smooth, and is therefore a defect, and unacceptable.

It should be remembered, that effect.


a poor toe blend in the

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root of the weld has the same

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Summary of "Veld and Joint Terms and Definitions:

A Weld:

A Union of materials, produced by heat ancIJor pressure.

A Joint:

A Configuration of members.

A weld preparation:

Preparing a joint to allow access & fusion through the joint

faces.

Types of weld:

Butt. Fillet. Spot. Seam. Edge.

Types of joint:

Butt. T. Lap. Open Comer. Closed Comer.

Types of preparation:

Bevel's. V's. J's. U's. (Single & Double).

Preparation terms:

Bevel angle. Included angle. Root face. Root gap.

Weldment terms:

Weld face. Weld root. Fusion Zone. Fusion boundary.

HAZ. Weld toes. Weld width.

Weld sizing (Butts):

Design throat thickness. Actual throat thickness. Excess

weld metal. Excess root penetration.

Weld sizing (Fillets):

Design throat thickness. Actual throat thickness. Excess weld metal. Leg length.


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Welding positions in accordance with BS EN 287

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PC

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PE Overhead

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PF Vertical upwards

PG Vertical downwards

a) Butt welds

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PF Vertical upwards

PG Vertical downwards


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Welding positions in accordance with BS EN 287 continued

PA

Pipe: rotating Axis: horizontal Weld: flat

PG

Pipe: fixed Axis: horizontal Weld: vertical downwards

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45° Pipe: fixed PFAxis: horizontal Weld: vertical upwards

PC

Pipe; fixed Axis: vertical Weld: horizontal vertical

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Pipe: fixed Axis: inclined Weld: upward

al Butt welds

PB

Pipe: rotating Axis: horizontal Weld: horizontal vertical

PF

PB

PG

Pipe: fixed Axis: horizontal Weld: vertical downwards

PD

Pipe: fixed Axis: vertical Weld: horizontal overhead

Pipe: fixed Axis: horizontal Weld: vertical upwards

Pipe: fixed Axis: vertical Weld: horizontal vertical . b) Fillet welds


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Senior Welding Inspection, Steels - WIS 10 Question Paper (MSR-S-SWI-1) Nam e:

. Answer all questions

1. In accordance with BS 499 what is the weld junction?

a. The area containing HAZ and weld metal. b. The weld metal and parent metal. c. The boundary between the fusion zone and HAZ. d. The part of the weld, which undergoes metallurgical, changes due to heat from welding. 2.

Which of the following are essential factors for lamellar tearing? a. High residual stresses, poor through thickness ductility, existing plate laminations. b. Poor through thickness ductility, fusion face parallel with rolled direction of parent plate, most commonly occurs in butt welds. c. Stress, poor through thickness ductility, fusion face parallel with rolled direction of parent material. d. Tensile stress, deoxidised parent plate, poor through thickness ductility.

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3.

The strength of a fillet weld is primary controlled by the: a. Leg length. b. Weld face. c. Throat thickness. d. All of the above.

4.

Which of the following is not a fusion welding process? a. Thermit welding. b. Electro slag welding. c. Laser welding. d. Friction welding. WIS 10 Qu paper MSR-A-SWI-l issue 3 Date 28/05/03

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Name the fourth weld process crack which has a totally different formation mechanism to HICC, solidification cracking and lamellar tearing: a. Liquiation cracking. b. Re heat cracking. c. Crater cracking. d. Hot tearing. Which of the following will vary the most when varying the arc length using the m.m.a. process? a. Voltage. b. Amperage. c. Polarity. d. Both a and b.. What is another term for suckback? a. Concave root. b. Elongated porosity in the rot area of a weld. c. Lack of root penetration. d. None of the above. Which of the following materials has the poorest weldability? a. Austenitic stainless steel. b. Martensitic stainless steel. c. Carbon manganese steel. d. HSLA steel.

In a fusion weld, which usually has the highest tensile strength? a. Weld metal. b. Parent material. c. Heat affected zone. d. Fusion zone.

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10. An undesirable property of aluminium oxide residue is that it: a. Creates problems when welding in position (vertical, horizontal, overhead). b. Requires more heat to melt it when compared with aluminium. c. Creates problems when welding in position (vertical, horizontal, overhead). d. Decreases weld pool fluidity. e. Both a and b.

11. Which of the following statements is true regarding hydrogen cracking? a. It is a type of hot crack. I

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b. It most frequently occurs in ductile materials. c. It only occurs in the h.a.z of fusion welds. d. It is the most common type of crack encountered in steel weldments.

12. Which material is the most susceptible to re heat cracking? a. High carbon steels. b. Killed steels. c. Creep resistant steels. d. Austenitic steels.

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13. Three essential factors for producing a fusion weld are; Melting, the removal of surface oxide from the joint surfaces and elimination of atmosphere from the region of the arc. Name the fourth? a. The weld must be free from stress. b. The filler material must match that of the weld. c. The completed joint must at least match the mechanical properties required by the specification. d. An arc for a heat source.

WIS 10 Qu paper MSR-A-SWI-l issue J Date 28/05/03

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14. Which arc welding process/technique is likely to be used to repair localised porosity in a weld? a. MMA, PG position. b. Mechanised arc welding. c. Sub Arc. d. All of the above. e. None of the above.

15. A welder qualified in the PG position would normally be qualified for welding: a. All diameters of pipe.

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b. Welding positions PA, PC, PG, and PF. c. In position PG only. d. All pipe wall thickness. 16. Which ofthe following are considered to be heat affected zone cracks? a. Solidification cracks, lamellar tearing and reheat cracks. b. Reheat cracks, Iiquation cracks and solidification cracks. c. Hydrogen cracks, solidification cracks and liquation cracks. d. Re heat cracks, liquation cracks and hydrogen cracks.

c.

17. The h.a.z associated with a fusion zone: a. Cannot be avoided. b. Usually has the highest u.t.s value of the weld joint. c. Is desirable to maintain ductility. d. Both a and b. e. All of the above.

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18. What four criteria are necessary to produce h.i.e.e? a. Hydrogen. moisture, martensite and heat. b. Hydrogen, poor weld profiles, a temperature above 200°C and slow cooling. c. A grain structure susceptible to cracking, stress, hydrogen, and a temperature below 200°C. d. Weld defects, pearlite, hydrogen and a temperature above the material being welded. 19. A carbon equivalent of 0.48%: a. Is high for carbon steel and may require a preheat temperature over 100°C. b. Is insignificant for carbon steel and preheat will not be required. c. Is calculated from the heat-input formula. d. Is not a consideration for determining preheating temperatures? 20. A semi-automatic welding process is best described as: a. The welder is responsible for the arc gap and travel speed. b. The welder is responsible for the travel speed only. c. The welding plant controls both travel speed and arc gap but under constant supervision. d. The welding plant controls both travel speed and arc gap, no supervision required. . .. ~1. Which of the following statements is true?

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a. The core wire of an MMA electrode has a higher melting point than the flux. b. Basic electrodes are preferred when welding is carried out in situations where porosity free welds are specified c. Rutile electrodes always contain a large proportion of iron powder. d. Cellulose electrodes may deposit in excess of 40 ml of hydrogen per 100g of weld metal. 22. Preheat prior to welding: a. Must always be carried put on steels. b. Need not be carried put if post weld heat is to follow? c. Is always carried out using gas flames. d. None of the above. WIS 10 Qu paper MSR-A-SWr-l issue 3 Date 28/05/03

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23. Root concavity may be caused by which of the following: a. Insufficient back purge gas. b. Entrapped gas. c. Slow travel speed. d. Excessive back purge pressure. 24. High phosphorous contents in carbon steels may cause: a. Cold shortness. b. Hot shortness. c. An increase in ductility.

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d. An increase in malleability.

25. If arc strikes are found on carbon steel (carbon equivalent of 0.5%), what undesirable grain structure may be present? a. Perlite. b. Martensite. c. Bainite. d. All of the above are undesirable grain structures in constructional steels. 26. When considering the heat treatment process of tempering: a. This is achieved by slowly heating the material to a temperature between

200DC-650 DC and slow cooling in air.

b. This is achieved by heating the material to around 200 DC and soaking for

approximately 10-12 hours and cooling down in air.

c. Very fast cooling from the austenite region. d. All of the above could give a temper. 27. Which element in steel has the greatest effect on hardness? a. Manganese. b. Chromium. c. Carbon. d. Nickel.


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28. Which of the following units is used to express the energy absorbed by a charpy specimen? a. Joules. b. Newton's. c. Mega Pascal's. d. P.s.i.

29. Which mechanical test(s) can be used to make an assessment of surface breaking defects? \

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a. Bend test. b. Nick-break test. c. Micro test. d. All of the above.

30. Which of the following is the odd one out? a. Neon. b. Xenon. c. Argon. d. Nitrogen.

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11. What does the 70 represent on an E7010 AWS A5.1 classified electrode? a. 70 N/mm2 minimum u.t.s. b. 70 N/mm2 minimum impact strength. c. 70,000 p.s.i. minimum u.t.s. d. 70 p.s.i. minimum yield strength.

32. If a material has a CE of 0.46: a. Post heat treatment would always be necessary. b. It will probably require preheat prior to welding c. The h.a.z. will be very tough. d. All of the above.


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33. Assuming no post-heat treatment has been carried out which of the following is normally the hardest part of a multi-pass butt weld made on low alloy steel? a. The cap. b. The root. c. The HAZ of the cap. d. The HAZ of the root.

34. Which of the following is the correct heat input if the amps are 350, volts 32 and travel speed 310 mm/minute. a. 2.16 kJ/mm. )

b. 0.036 kJ/mm.

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c. 2.61 kJ/mm. d. 0.36 kJ/mm.

35. Assuming that the specification makes no reference to arc strikes, what would you do if you found arc strikes on a fabrication constructed out of high tensile strength material? a. Have the welders re-approved. b. Reject all the areas where the arc strikes occur. c. Have the areas checked for cracking. d. If the specification makes no reference to arc strikes ignore them.

36. Which of the following may be used for the TIG welding of Nickel and its alloys? a. Lanthanum electrode, DC. -ve. b. Cerium electrode, DC -ve. c. Zirconium electrode AC d. Thorium electrode, DC +ve.


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37. Which of the following welding processes uses resistive heating to achieve weld metal deposition? a. Flux-core m.a.g. b. Sub-arc. c. Resistive spot welding. d. Electro slag.

38. What are the possible results of having a lower heat input from the approved

procedure?

a. An increase in hardness, lower yield strength and lack of fusion. b. A reduction in toughness, hydrogen entrapment and an increase in hardness. c. Entrapped hydrogen, an increase in hardness and lack of fusion. d. Entrapped hydrogen, a reduction in carbon content and lack of fusion.

39. A multi-run MMA butt weld made on low alloy steel consists of 5 passes using a 6 mm diameter electrode, a 12 pass weld made on the same joint using a 4 mm diameter electrode on the same material will: a. Have a lower heat input and a higher degree of grain refinement. b. Have a lower heat input and a coarse grain structure. c. Have a lower heat amount of distortion and a higher degree of grain refinement. d. Have a higher amount of distortion and a lower degree of grain refinement.

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40. Which of the following heat treatments may be applied to a material to give maximum toughness values: a. Normalising. b. Tempering. c. Annealing. d. Both a and b. e. All of the above.


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41. The main reason for using a back purge when welding 18-8 stainless steel with the TIG welding process is to: a. Control the root penetration. b. Prevent the formation of a dense oxide layer on the root bead. c. Control porosity in the root bead. d. Improve positional welding.

42. Which of the following would you expect of a martensitic grain structure? a. An increase in toughness and a reduction in hardness. b. An increase in hardness and a reduction in ductility. (

c. An increase in ductility and a reduction in toughness.

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d. An increase in malleability and an increase in hardness.

43. Which of the following reduce the chances of arc blow? a. A change from AC current to DC current. b. A change from DC current to AC current. c. A change from DC electrode +ve to DC electrode -ve. d. A change from DC electrode -ve to DC electrode +ve.

44. When considering the advantages of site radiography over conventional ultrasonic inspection which of the following applies? a. A permanent record produced, good for the detection of defects that do not have significant depth in relation to the x-ray beam and defect identification. b. A permanent record produced, defect identification and not so reliant upon operator skill for the detection of any possible defects present. c. A permanent record produced, good for the detection of all surface and sub surface defects and assessing the through thickness depths of most defects. d. No controlled areas required on site, a permanent record produced and good for assessing the extent of pipe wall thickness reductions due to internal corrosion.


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49. What paper work is required prior to witnessing of mechanical testing? a. Calibration certificates for each test piece. b. Calibration certificates for the test equipment being used. c. Test operator's qualifications. d. Test procedure qualification certificates e. All of the above.

50. When using basic coated electrodes, to keep the weld metals hydrogen content down to scale C:

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a. The electrodes must be used indoors, can only be used in a down hand position and the use of pre-heat. b. The electrodes must be used in a dry condition but never baked, the use of pre heat and used with a short arc gap. c. The electrodes must be used with a short arc gap, the use of a minimum weave and used in a baked condition. d. The electrodes must be pre-baked, used on DC electrode +ve and with a

minimum arc gap.

51. The primary function of the addition of silicon to an MMA welding electrode covering would be to act as: a. A deoxidiser. . b. An arc stabiliser.

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c. A slag-forming agent.

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d. A shielding gas forming agent.

52. Which of the following is most likely to be an essential variable for a welder's

qualification?

a. A change from an electrode to BS EN E46 3 B to an electrode to AWS A5.1 E7018. b. A change of pipe wall thickness by at least 25 mm. c. A change in pre-heat from 50° to 100°C. d. All of the above.

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53. Which of the following are applicable to DC electrode -ve when using the rn.rn.a. welding process? a. A broad heat affected zone, a reduction in hardness and a narrow deep fast freezing weld pool. b. A narrow heat affected zone, fast freezing weld pool and good penetration properties. c. Mechanically and metallurgical no difference to DC electrode -ve. d. Wide shallow weld pools, flat weld profiles and lower hardness values. 54. When welding rimming steel with autogenous TI8 process which of the following problems may occur?

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a. Porosity. b. Lack of fusion. c. Tungsten inclusions. d. Excessive root penetration.

55. In MMA welding process, which of the following flux types gives the deepest penetration? a. Rutile b. Acidic. c. Cellulosic. d. Basic (low hydrogen). (

56. Basic coated electrodes have which of the following properties? a. High mechanical properties may be used to produce welds of high deposition rates and are designed to produce welds of low hydrogen content. b. Friable slag, high mechanical properties and are designed to produce welds of low hydrogen content. c. Ease of use, good stop/starting properties and high mechanical properties. d. High mechanical strength, friable slag and may produce welds of low hydrogen content.


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57. Which of the following is the most likely appearance of lack of root fusion on a

radiograph taken of a single-vee butt weld in C/C Mn steel?

a. A dark straight line with a light root. b. A dark straight line with a darker root. c. A dark root with straight edges. d. A dark uneven line with a light root.

58. Which of the following methods would be the best suited for the detection of lamellar tearing in a fabrication? a. Radiography.

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b. Ultrasonic testing c. Dye penetrant testing d. Magnetic particle testing

59. Which of the following are applicable to fatigue cracking? a. A rough randomly torn fracture surface, an initiation point and beach mark(s). b. A smooth fracture surface, an initiation point and beach mark(s). c. Beach mark(s), step like appearance and a secondary mode of failure. d. All of the above.

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60. Which of the following weld symbols in accordance with BS EN 22553 represents a fillet weld made on the other side?

a.

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b.

c.

d.

:?= ~

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61. A back step welding technique is most often used to? a. Reduce welding time. b. Increases weld toughness. c. Reduce the chances of undercut. d. Reduce distortion.

62. E6013 electrode would most probably-be used for the welding of? a. Low-pressure pipe work. b. High pressure pipe work. c. Vertical down welding on pressure vessels.

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d. Where welds of low hydrogen content are specified.

63. The need for pre heat for steel will be increased by? a. Lower carbon contents. b. A reduction in material thickness. c. Faster welding speeds. d. The use of a larger dlarneter-weldlng electrode.

64. From the following ·electrode coding E50 4 B 160 20 H5, the compulsory part is:

65. When considering radiography using x-ray, which of the following techniques is most likely to be used for a pipe-to-pipe weld (circumferential), 610 mm diameter pipe with no internal access? a. SWSI. b. DWSI. c. DWDI. d. SWSI (panoramic).

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66. What happens to the mechanical properties of carbon steel if its carbon content is Increased from 0.12% to 0.5%? a. The material becomes softer. b. Malleability increases. c. The tensile strength increases. d. Ductility increases. e. None of the above.

67. One purpose of microscopic examination of a welded joint is to establish? ( _)

a. The strength of the weld. b. The number of alloying elements presents. c. The grain size. d. The overall weld toughness. e. All of the above.

68. Which of the following tests would you not expect to be carried out on a welder qualification test? a. Radiography. b. Tensile test. c. Marco.

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d. Bend test.

69. Which of the following can be welded by DC output when using the TIG welding process? a. Copper. b. Commercial pure aluminium. c. Siltcon-alurniniurn. d. Magnesium alloys. e. None of the above.

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70. Which of the following defects is most likely to be missed by visual inspection. a. Cap undercut. b. Centreline crack. c. Lack of interun fusion. d. Lack of root fusion.

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Questions

Terms and Definitions

au 1.

Sketch a single-U butt joint and indicate the following: b: root face

a: root gap

c: included angle

d: root radius

~~

au 2.

Sketch a tee joint, fillet welded and indicate the following a: leg length

b: throat thickness

d: weld toes

c: root

au 3.

Sketch five joint types in addition to a butt weld.

aU4.

Identify the following butt weld features.

~

A: B:

F E

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I~

c:

.C

D:

E:

s-r

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Duties of a Welding Inspector: It is the duty of a welding inspector and Senior welding inspector to ensure that all operations concerning welding are carried out in strict accordance with written, or agreed practices, or specifications. This will include monitoring or checking a number of operations including:

Before welding: Safety: Ensure that all operations are carried out in complete compliance with local, company, or National safety legislation (i.e. permits to work are in place). Documentation: Specification. (Year and revision) Drawings. (Correct revisions) Welding procedure specifications and welder approvals. Calibration certification. (Welding equipment/ancillaries and all inspection instruments) Material and consumable certification Welding Process and ancillaries: Welding equipment and all related ancillaries. (Cables, regulators, ovens, quivers etc.) Incoming Consumables: All pipe/plate and welding consumables for Size, Type and Condition. Marking out preparation & set up: Correct method of cutting weld preparations. (Pre-Heat for thermal cutting if applicable) Correct preparation. (Relevant bevel angles, root face, root gap, root radius, land, etc.) Correct pre-welding distortion control. (Tacking, bridging, jigs, line up clamps, etc.)

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Correct pre heat applied prior to tack welding.

All tack welding to be monitored and inspected

During welding: Pre-heat values. (Heating method, location and control)

In-process distortion control. (Sequence or balanced welding)

Consumable control. (Specification, size, condition, and any special treatments)

Process type and all related variable parameters. (Voltage, amperage, travel speed)

(

)

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Purging gases. (Type, pressure/flow and control method)

Welding conditions for root run/hot pass and all subsequent run, and inter-run cleaning.

Minimum, or maximum inter-pass temperature. (Temperature and controlling method)

Compliance with all other variables stated on the approved welding procedure.

After welding: Visual inspection of the welded joint. (Including dimensional aspects)

NDT requirements. (Method and qualification of operator, and execution)

Identify repairs from assessment of visual or NDT reports. (Refer to repairs below)

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Post weld heat treatment (PWHT) (Heating method and temperature recording system)

Re-inspect with visuallNDT after PWHT. (If applicable)

Hydrostatic test procedures. (For pipelines or pressure vessels)

Repairs: Excavation procedure. (Approval and execution)

Approval of the NDT procedures (For assessment of complete defect removal)

Repair procedure. (Approval of're-welding procedures and welder approval)

Execution of approved re-welding procedure. (Compliance with repair procedure)

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Re-inspect the repair area with visual inspection and approved NDT method. Submission of inspection reports, and all related documents to the Q/C department.

Responsibilities of a Welding Inspector:

'----_1-+ To Observe

)

To observe all relevant actions related to weld quality throughout production. This will include a final visual inspection of the weld area.

To Record ( To record, or log all production inspection points relevant to quality, including a final map and report sheet showing all identified welding imperfections.

To Compare

1-+

' - - - - - - -

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Submit a final inspection report of your findings to the QA/QC department for analysis and any remedial actions.

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The duties and responsibilities of a senior welding inspector The fabrication industry has come to accept the need for a detailed inspection of welding for a combination of two reasons:

1. The quality of a manually made weld id critically dependent on the skill of the welder. 2. Much fabrication is made under sub-contracting conditions.

There has developed, therefore, a system which is quite general, but is more obvious in the fabrication field, of client appointed inspectors who may work independently or alongside the fabricators own inspectors with or sometimes without the full co-operation of the welding supervisors and welders (

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Welding inspection in general sense is the monitoring of the formation of the weld. I.e. materials, equipment, consumables, approvals of staff and procedures, examination of the compilation, i.e. size, excess metal, undercut, surface defects, spatter etc., and the compilation of documents into the fabrication file. Many quality welds are required to be examined by non-destructive testing techniques and operatives with required skills are called in as a required and the senior welding inspector obtains the NDT reports for the fabrication file. The senior welding inspector grade is able to assess and control welding inspection with a wide perspective because of his/her wider qualifications and experience. In addition he/she must have the knowledge of the practice of supervision and to have the necessary personal quality of leadership.

(

It is not possible to be a senior welding inspector without technical knowledge but the quality of leadership is an essential addition. \

It is sometimes said that leadership cannot be taught and there is a lot of truth in this but the ability to lead can be improved by teaching.

Tasks and responsibilities The following list shows the tasks and responsibilities of welding co-ordination personnel, not all the tasks given will necessarily be carried out by the senior welding inspector, the tasks and responsibilities allocated will depend on the contract/project being carried out. Each single activity in the following list may be associated with a number of tasks and responsibilities such as: - specification or preparation; -co-ordination; - control; - inspection, check or witnessing. Where welding co-ordination is carried out by a number of persons, the client will generally nominate the tasks and responsibilities for the appropriate persons. Welding co-ordination is considered to be the responsibility of the manufacturing organisation. For some work activities the co-ordination tasks and responsibilities may be carried out by subcontractors.

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Welding related activities to be considered 1.

Contract review • Meetings. • Welding capability and associated activities of the manufacturing organisation.

2.

Design review • Relevant welding standards. • Joint location with relation to the design requirements. • Access for welding, inspection and testing • Weld joint details. • Quality and acceptance requirements for welds.

3.

Parent material • Weldability of parent material. • Parent material certificates. • Identification of parent material. • Handling and storage of parent materials. • Tractability.

4.

Consumables • Compatibility • Delivery' conditions. • Identification of consumables. • Storage and handling of consumables.

5.

(

Subcontractors· • Suitability of any subcontractors.

6.

Production planning • Suitability of welding procedure specifications (WPS) and welding procedure approval records (WP AR). • Work instructions. • Welding jigs and fixtures. • Suitability and validity ofwelder approvals. • Welding and assembly sequences for the component • Production weld test requirements.

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Equipment

•

Suitability of welding and associated equipment.

• •

Equipment supplies, identification and handling. Calibration of equipment.

Safety

•

Health and safety requirements.

• •

Suitability of working area. Ventilation, extraction etc.

Welding operations ;.~

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•

Issue of work permits,

• •

Issue of work instructions,

•

Preparation of production tests.

• •

Assignment and instruction 0 f welders.

• • • • •

Application of tack welding.

,

-~(

Joint fit up and cleaning.

Welding consumables and auxiliaries.

Application of welding process parameters. Application of any intermediate testing. Application and method of preheating. Application and method of post weld heat treatment. Welding sequences.

10.

Visual inspection .

• • • • 11.

Weld dimensions. Shape, dimensions and tolerances of the welded components. Joint appearance.

Destructive testing

• 12.

Completeness of welding.

Application and records of destructive testing.

Non-destructive testing

•

Application and records of non-destructive testing.

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\-Veld acceptance

•

Assessment of inspection and test results.

•

Weld repairs.

•

Reassessment of repaired welds.

•

Corrective actions

Documentation •. Preparation and maintenance of the necessary records.

The technical skills required by a Senior Welding Inspector are:

1. Knowledge of technology. 2. Knowledge of codes of practice / Normative documents (

3. Knowledge of planning. 4. Knowledge of organisation.

5. Knowledge of auditing

The responsibilities of a Senior Welding Inspector:

1. Supervision 2. Planning

3. Organisation

4. Auditing.

Supervision A supervisor is any person who id given authority and responsibility for planning and controlling the work of others with whom they are in close touch. Supervisor and operatives The difference between a supervisor and an operator is that an operator performs his/her own work but the supervisor gets work done through his operators. Supervisors and managers Supervisors are part of the management structure. The term supervision, however generally implies overseeing and controlling a working group on the spot dealing with situations and details as they arise. The term management implies planning ahead and controlling work more remotely using administrative procedures and reporting systems. The supervisor is in a key position between operatives and management able to encourage smooth

working or cause disruption both wilfully and unintentionally. He/she is also subject to pressure

from both sides that each expects the supervisor to support their views. He/she must seek to earn

the respect and support of managers and operators, carry out sometimes-unpopular orders and

duties at the same time as looking after the group he/she leads.

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Working with others The job of the supervisor is enhanced and becomes more satisfying if he she makes LbC of the assistance of specialist advisors on personnel, work scheduling, work study, finance, etc, thereby allowing him to spend more time on organising and dealing with his/her staff.

Responsibilities of a supervisor A supervisor is responsible for his/her subordinates, the activities and the work place, which he is given formal authority to control, this usually includes: 1. Staff - moral, consultation, discipline, welfare, safety, employment induction, training.

2. Work - maximum economy. 3. Cost - maximum economy. \

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4. Machines and equipment - maintenance, loading, operation. 5. Materials - supplies, suitability, economic use. 6. Workplace - layout, tidiness, good housekeeping. Qualities of a good supervisor Particular circumstances will give different emphasis to the following essential basic qualities required in the good supervisor. I. Technical skill and knowledge - ability to explain why and how jobs are to be performed to eliminate faults, dangerous practices, wastage, to keep up to date. 2. Intelligence - judgment, sound common sense, ability to determine priorities. 3. Drive - vitality, energy, enthusiasm and general good health. Vigour is as infectious as fatigue is demoralising.

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4. Leadership - maintenance of high personal standards, goal setting, trustworthiness, reliability, consistency, fairness, stability, persistence and a sense of humour. Motivation and the supervisor It is very important for a supervisor to take an interest in his/her operators, to try to understand their attitudes and reactions, to treat them in a responsible manner and give respect to their views, efforts and skills. Responsible treatment includes correcting or reprimanding those who fail to respond responsibly. Good operatives expect the supervisor to act justly when dealing with those who do not conform to working requirements.

Staff assessment Linking motivation with responsibility of a supervisor to achieve targets of performance is the

assessment of staff and the development needs of the supervisor's section.

Whatever policy an organisation applies to staff assessment, a supervisor inevitably forms

judgments on varying capabilities and. attributes of his/her operatives. Assessment procedures

only differ in the degree to which they are formalized..

If no other agreed system applies, a supervisor should first decide the factors that are important in

constituting a good worker. These usually include such factors as quality of output, quantity of

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Output, versatility (range of capabilities) co-operation, timekeeping, conduct, relationships with others etc. On the basis of factual records where possible, each operative can be assessed against each factor using for instance a grading scale. Below is an example of a grading scale:

POOR

BELOW AVERAGE

AVERAGE

ABOVE AVERAGE

A simpler three-grade scale may be:

BELOW

AVERAGE

ABOVE

Operatives should be made aware of those factors, which are satisfactory and by discussion methods should be agreed for improving those aspects, which are not satisfactory.

Planning The planning function may be taken to mean the consideration of the necessary arrangements, which must be made from the general notification of the job requirement through to the final advice of completion. It is usual to find that this falls into three stages.

1.

Preparation and dispatch of staff

2.

The inspection and documentation.

3.

• • • • • • • •

Equipment.

•

Welding operations.

Personnel approvals. Procedure approvals. Materials. Consumables. (

Edge preparations. Tacking. Preheats.

Collection of data and certificates.

There are various methods of dealing with the planning function and the three most common are:

1.

Allocate staff on a block basis i.e. send an inspector on to the site and allow and expect

himlher to make a useful return on his/her time.

2.

The use of charts in which each job function is estimated for time. In certain cases this

situation enables a considerable saving of staff and time to be made. But by the

implication the inspector works harder and tends to travel more.

3.

The use of a critical path analysis in which a detailed assessment is made or obtained of

the overall production plan and the inspection function is meshed into this.

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Which of these approaches is used will depend on the nature of the workflow and the number of calibre of the available inspectors and back-up staff. Also critical is the degree of competition. which may be the driving force for economic use of staff hence low tendering. Planning aspects

Planning can be taken to mean to make the general arrangements. There are many ways of increasing productivity. Amongst them, production projects planning id high on the list. Apart from improving the utilisation of resources it also forms the basis for effective production or project control, and thereby reduces the risk of over spending budgets and for failing to achieve delivery targets. Some advantages of planning

C_)

1.

Jobs are planned and issued in correct sequences thereby reducing unnecessary work-in progress and minimising the need for overtime or subcontractors.

2.

Men and machines are supplied with the correct materials and tools at the right time.

3.

The correct quality standards are achieved for minimum cost.

4.

Completed goods are dispatched to customers as promised.

5.

Adequate stock levels of materials and components are maintained.

6.

Greater job satisfaction.

7.

Greater job security.

A sound system of planning should clearly show the stages of manufacture and inspection. It should draw attention to bottlenecks and areas of unused resources, and show what, and Where, additional resources are needed.

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Organisation The organisation function may be taken to mean the fitting of staff to the plan, which must be supervised to completion. In these terms the organisation function means the ability to assess the detailed requirements of the plan and to gauge the ability of individual staff to be technically competent, available and temperamentally able to perform the tasks involved. As a preliminary checklist organisation involves: 1.

How much inspection is required

2.

Total man hours

3.

Number of personnel required

4.

Estimation of job times

5.

Analysis ofjob sequences

6.

Preparation requirements and time

7.

Travel and down time (mobilisation/demobilisation)

8.

Leave time for personnel

9.

Ability of staff

()

Auditing The term audit has been taken from accounting practice and means: I. An overall check of inspection. 2. A detailed check of a very limited area of inspection In the overall check the general content of the fabrication file examined for completeness and

presentation and generally impression is formed as to the visual quality of the product.

For the detailed check the requirements of a very limited zone is examined with great care and (as

appropriate) the code requirements are checked against the documents in the fabrication file.

Definitions • Audit Program: set of one or more audits planned. • Audit Criteria: set of policies, procedures or requirements used as a reference. • Audit evidence: records, statements of fact, which relate to audit criteria. • Audit findings: results of the evidence of the collected audit evidence against audit criteria • Audit conclusion: outcome of an audit provided by the audit team, after considerations of the audit findings.

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Assessments of:

• Staff • Equipment • QA / QC and inspection • Documents • Safety Internal Audits First-party audits are conducted by or on behalf of, the organisation itself for intemal purposes and can form the basis for an organisation's self-declaration of conformity.

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External Audits Second-party audits are conducted by customers of the organisation or by other persons on behalf of the customer. Third-party audits are conducted by extemal independent organisations. Such organisations, usually accredited, provide certification or registration of conformity against documented requirements There are three types of audits currently used in the fabrication industry. I. Pre - production

This is usually undertaken to assess ability in terms of staff and facilities to perform a task. 2. In - production

(

This is to confirm that the welding and related activities are being carried out accordance with the requirements of the applicable procedures and specifications.

111

3. Post - production The objective in this instance is to ensure that the welding and welding inspection are satisfactory. Audits are used to determine the extent to which the quality system requirements are fulfilled. Audit findings are used to assess the effectiveness of the quality system and to identify opportunities for improvement for improvement.

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Concepts relating to an audit

Audit client Organization or person requesting an audit

Audit program Set of one or more audits planned for a specific time frame and directed towards a specific purpose

Auditee Organization being

audited

(-) Audit
Audit criteria / Set of policy procedures or requirements used as a reference

!

Audit team One or more auditors conducting an audit

Technical expert Person who provides specific knowledge of or expertise on the subject to be audited

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Auditor A person with competence to conduct on audit

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~ Audit findings

Results of the evaluation of the collected audit evidence against audit criteria

I

Audit evidence Records, statements of fact or other information, which are relevant to the audit criteria and verifiable

I

Audit conclusion Outcome of an audit provided by the audit team after consideration of the audit objectives and all audit findings

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Knowledge of technology The scope and level of the technical aspects of welding with which the senior welding inspector needs to be familiar are similar to those of the welding inspector with slightly more depth but in addition a good appreciation of NDT is required together with a proven ability in radiographic interpretation. The reason for this is a senior welding inspector on certain projects may also be employed to view radiographs as well as checking the NDT reports and supervising and giving advice to NDT operatives. For all tasks assigned, a senior welding shall be able to demonstrate adequate technical knowledge to enable such tasks to be performed satisfactorily. The following factors should be considered: (

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•

General technical knowledge;

• Specialised technical knowledge relevant to the assigned tasks. This may be attained by a combination of theoretical knowledge, training and/or experience.

Knowledge of codes of practice Neither welding inspectors or senior welding inspectors would be expected to have a detailed recall of the requirements of a code of practice or be expected to write welding procedures. What is expected is at a senior level an appreciation of the commonly used codes and a capacity to give

advise on the application of these documents. The senior welding inspector must be aware of the quality levels required for a particular product and be able to implement the quality requirements of the applicable codes and standards. Such documents include:

\'1

1. Standards for consumables

• BS EN 499 covered electrodes. • BSEN 440 gas shielded filler wires. • AWS A5.1/A5.5 covered electrodes. • AWS A5.8 shielded filler wires. 2. Standards for welding procedure approval • BS EN 287 approval of welding procedures. • ASME IX approval of welding procedures. 3. Standards for welder approval • BS EN 287 the approval of we~ders. • ASME IX

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Standards for quality of fabrications.

•

BS 5500.

•

ASME VIII

_


5. Standards for pipeline construction. •

BS 4515.

•

API 1104

•

B'Gas P2.

It must be noted that standards are merely convenient collections of good practice data, but as a stand-alone document it is not mandatory. If the client who is commissioning the manufacture may incorporate a standard into the specification and therefore the legal contract, but the client may add requirements for the particular component being constructed. Codes and standards plus client requirements control many major fabrications and projects.

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Questions

Terms and Definitions

QU 1.

Sketch a single-U butt joint and indicate the following: a: root gap

lJ

QU 2.

b: root face

c: included angle

Sketch a tee joint, fillet welded and indicate the following a: leg length

b: throat thickness

c: root

d: weld toes

QU 3.

Sketch five joint types in addition to a butt weld.

QU4.

Identify the following butt weld features.

~. )

A: B:

F

c:

C

D:

E:

S-r-

d: root radius

,. v: : /~ " -,

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Quality Quality is a subjective thing, what is quality to one person might not be quality to another person. Quality its self is very difficult to define but the concepts of quality or shown below

r -----

Requirement . . . . Need or expectation that is stated, generally implied or obligatory

--IIIo..

~ Grade Category or rank given to the different quality requirements for products, processes or systems having the same function use

Quality Degree to which a set of inherent characteristics fulfils requirements

Capability Ability of an organisation, system or process to realise a product that will fulfil the requirements for that product.

( ., Customer satisfaction Customer's perception of the degree to which the customer's requirements have been fulfilled. It must be said that these terms although they are all widely used and definitions of their meanings defined in many documents, are not sufficiently precise for really general application. It is not uncommon to find that these functions overlap or that in particular instances QA isplanned and organized as a department, which in practice covers inspection and quality control. Again many manufacturing plants are organized with a Project Office dealing with the aims of quality and an Inspection Office dealing with the attainment of quality.

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Note: quality can be used with objectives such as poor, good or excellent.

Note: inherent, as opposed to assigned, means existing in something, especially as a permanent

characteristic. Note: requirements can be generated by different interested parties. Note: a specified requirement is one which is stated, for example a document Note: when establishing a quality requirement, the grade is generally specified. Note: customer complaints are a common indicator of low customer satisfaction but their absence does not necessarily imply high customer satisfaction. Note: Even when customer requirements have been agreed with the customer and fulfilled, this does not necessarily ensure high customer satisfaction

QAVSQC (,,~

QA applies to all areas, which have an affect on quality and asks the question "has the work been performed correctly?" QC deals with the actual measurement of quality performance, this performance is compared against what is required, and action is taken on the difference and asks the question "is the work been performed correctly?"

QA VS Inspection QA is not inspection. It deals mainly with documentation and must see the entire picture. Inspection is mainly about physical reality, monitoring and measuring basically inspection is a QC tool.

Definitions Relating to Quality Quality Assurance: all those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality or that quality requirements will be fulfilled. (

Quality Control: The operational techniques and activities that are used to fulfil the requirements for quality Inspection: activities such as measuring, examining, testing, gauging one or more characteristics of a product or service and comparing these with specified requirements to determine conformity. Inspection is a tool used for quality control.

Aim of quality assurance The aim of quality assurance is to improve quality whilst keeping costs to an acceptable level. The objectives of a system used to implement quality assurance, i.e. a quality system is to determine and rectify the root cause(s) of any problems, thereby reducing faults and wastage. This will in tum improve quality and reduce costs. The emphasis is on fault prevention rather that detection and cure i.e. it is a lot more cost effective to prevent welding defects from occurring rather than repairing defective welds after- detection.

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Benefits of adopting quality assurance

A properly implemented and managed quality system should:

I. Help to ensure that the company focuses on the market needs and requirements.

2. Make the company more competitive in the market place due to an increased customer confidence in the company's output, i.e. a product or service that a customer wants 3. Lead to a reduction of costs due to a reduction in defective items and wastage 4. Give a measure of performance, which will enable any areas for improvement to be identified. 5. Introduce a more organized way of thinking. 6. Provide motivation, motivate employees provide a better working environment in addition to the product or service output benefits. Quality assurance provides the objective evidence needed to give maximum confidence for quality. Quality assurance should be considered as a management tool when used within an organization. A supplier who implements and maintains a system for assuring quality, is providing maximum confidence to a purchaser, or potential purchaser, that the supplied product or service attains, or is going to attain, its fitness for purpose.

(-)

Concepts relating to quality assurance for measurement process

Metrological confirmation Set of operations required to ensure that measuring equipment conforms to the requirements for its intended use

Measurement process Set of operations to

determine the value of

quality

~ Measurement control system Set of interrelated or interacting elements necessary to achieve metrological confirmation and continual control of measurement process

~

Measurement function Function with organisational responsibility for defining and implementing the measurement control system

•

Measuring equipment Measuring instrument, software, measurement .......... Metrological characteristic Distinguishing features which standard, reference material can influence the results of or auxiliary apparatus or measurement combination thereof necessary to realise a measurement process Senior Welding Inspection - QA / QC Copyright © 2002 TWI Ltd

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Questions Responsibilities and duties of a welding inspector

QU1.

Give the three main responsibilities of a welding inspector:

QU2.

Give three main attributes. which all welding inspectors must possess.

QU3.

The welding inspector should refer to what documents and records.

QU4.

Give six main duties of a welding inspector before welding.

QU5.

Give six main duties of a welding inspector during welding.

QU6.

Give six main duties of a welding inspector after welding

J

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Welding Imperfections: What are welding imperfections? Welding imperfections are material discontinuities caused by, or during, the process of welding. All things contain imperfections, but it is only when they fall outside of a "level of acceptance" that they should be termed defects, as they may render the product defective, or unfit for its purpose. As welds can be considered as castings they may contain all kinds of imperfections associated with the casting of metals, plus any other particular imperfections associated with the specific welding process being used.

:)

We can classify welding imperfections into the following groups: 1)

3) 5) 7)

1)

Cracks Solid inclusions Surface and profile Misalignment

2) 4) 6)

Gas pores and porosity Lack of fusion Mechanical damage

Cracks:

Cracks sometimes oceur in welded materials, and may be caused by a great number of factors. Generally, we can say that for any crack like imperfection to occur in a material, there are 3 criteria that must be present: a) A force

b)

Restraint

c) A weakened structure ( .

Typical types of cracks that will be discussed later in the course are: 1)

Hz Cracks

2)

Solidification Cracks

3) Lamellar Tears

A Material's likelihood to crack during welding can be evaluated under the term Weldability. This may be defined as: "The ease with which materials may be welded by the common welding processes" All cracks have sharp edges, which produce high stress concentrations. This generally results in rapid progression, however this also depends on the properties of the metal. Cracks are classed as planar imperfections as they generally have only 2 visible, or . measurable dimensions i.e. length and depth. Most fall into the defects category, though some standards allow crater cracks.

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Gas pores, porosity and cavities:

Gas pores: Gas pores are defined as intemal gas filled cavities smaller than 1.6mm diameter, which are created during solidification by the expulsion of gases from solution in the solidifying weld metal.

(~)

Porosity: These are gas pores < 1.6mm diameter which are generally grouped together, and may be classified by their number, size and grouping. (i.e. Fine, or coarse cluster porosity) A singular gas filled cavity = or > 1.6mm diameter is termed a "blow hole" Porosity is mainly produced when welding improperly cleaned plate, or when using damp welding consumables. Gases may also be formed by the breakdown of paints, oil based products, corrosion or anti corrosion products that have been left on the plates to be welded.

(' Shrinkage cavity

Hollow root bead

Senior Welding Inspection - Welding Imperfections Copyright © 2002 TWl Ltd

. An isolated internal pore

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Solid inclusions:

Solid inclusions include metallic and non-metallic inclusions that may be trapped in the weld during the process of welding. The type of solid inclusion that may be expected is really dependant on the welding process being used. In welding processes that use fluxes to form all the required functions of shielding and chemical cleaning, such as MMA and Submerged Arc welding, slag inclusions may occur. Other welding processes such as MIG and TIG use silicon, aluminium and other elements to de-oxidise the weld. These may form silica, or alumina inclusions. Any of these non-metallic compounds may be trapped inside a weld during welding. This often happens after slag traps, such as undercut have been formed. Slag traps are mostly caused by incorrect welding technique. Metallic inclusions include tungsten inclusions that may be produced during TIG welding by a poor welding technique, an incorrect tungsten vertex angle, or too high amperage for the diameter of tungsten being used. Copper inclusions may be caused during MIGIMAG welding by a lack of welding skill, or incorrect settings in mechanised, or automated MIG welding. (Mainly welding Aluminium alloys)

( )

Other welding phenomena such "arc blow" or the deviation of the electric arc by magnetic forces, can cause solid inclusions to be trapped in welds. The locations of these inclusions may be within the centre of a deposited weld, or between welds where the result causes "Lack of inter-run fusion", or at the sidewall of the weld preparation causing "Lack of side wall fusion" Generally solid internal inclusions may be caused by:

1) 2) 3) 4) 5) 6)

Lack of welder skill. (Incorrect welding technique)

Poor manipulation of the welding process, or electrode.

Incorrect parameter settings, i.e. voltage, amperage, speed of travel.

Magnetic arc blow.

Incorrect positional use of the process, or consumable.

Incorrect inter-run cleaning.

Surface breaking solid inclusion Internal solid inclusion causing

a lack of sidewall fusion

Internal solid inclusion causing a lack of inter-run fusion

Solid inclusions caused by undercut in the previous weld run

Internal solid inclusion


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Lack of fusion:

Lack of fusion imperfections, are defined as a lack of union between two adjacent areas of material. This may be accompanied, or caused by other imperfections as explained in the last section. Lack of fusion can be considered a serious imperfection, as like cracks, they produce areas of high stress concentration. Lack of fusion, or overlap (a form of lack of fusion) may occur in the weld face area during positional welding caused by the action of gravity and incorrect use of the process.

l)

Arc blow is a prime cause of lack of fusion imperfections, particularly when using high current processes, such as Sub Arc using high direct electric currents. (DC+ or DC -) Lack of fusion may also be formed in the root area of the weld where it may be found on one, or both plate edges. It may also be accompanied by incomplete root penetration. Lack of fusion is also a common imperfection in "Dip transfer MIG welding" of metals over 3mm thickness, especially when welding vertically down. This is caused by the inherent coldness of this form of metal transfer, and the action of gravity. Like solid inclusions, lack of fusion imperfections may be caused by:

1) 2) 3) 4) 5) 6)

Lack of welder skill. (Incorrect welding technique)

Poor manipulation of the welding process, or electrode.

Incorrect parameter settings, i.e. voltage, amperage, speed of travel.

Magnetic arc blow.

Incorrect positional use of the process, or consumable.

Incorrect inter-run cleaning.

Lack of sidewall fusion (Incompletely filled groove in some standards)

(J

Lack of inter-run fusion

I.

\

Lack of sidewall fusion

Lack of root fusion


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Surface and profile:

Surface and profile imperfections are generally caused by poor welding techniques. This includes the use of incorrect welding parameters, electrodelblowpipe sizes and/or manipulation and joint set up. This category may be split into two further groups of weld face and weld root. Surface and profile imperfections are shown pictorially in A & B below:

A: Spatter is not a major factor in lowering the weldment strength, though it may mask other imperfections, and should therefore be cleaned off before inspection. Spatter may also hinder NDT and be detrimental to coatings It can also cause micro cracking or hard spots in some materials due to the localised heating/quenching effect. An incompletely filled groove may bring the weld below its DTT. It is a major stress concentration when accompanied by lack of sidewall fusion. Lack of root fusion causes a serious stress concentration to occur in the root. It may also render the root area more susceptible to corrosion in service

Spatter (.

A

Lack of root fusion


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THE WELDIf\IG INSTITUTE

B: A bulbous contour is an imperfection as it causes sharp stress concentrations at the toes of individual passes and may also contribute to overall poor toe blend Arc strikes, Stray-arcing, or Stray flash may cause many problems including several types of cracks to occur. They can also cause depressions in the plate bringing it below its DTT. Arc strikes would normally be NDT inspected and then repaired. Incomplete root penetration may be caused by too small a root gap, insufficient amperage, or poor welding technique. It also causes high stress concentrations to occur. It also generally produces a weld with less throat thickness than the DTT of the joint. An irregular bead width is a surface imperfection, which is often referenced application standards as. "The weld bead should be regular along its linear length" /

in

Bulbous, or irregular contour

Arc Strikes

<, ~

G)r-~

Poor toe blend

B

Incomplete ro'ot penetration /

(

Undercut: Undercut can be defined as a depression at the toe of a weld in a previous deposited weld, or base metal, caused by welding. Undercut is generally caused by incorrect welding technique, including the use of too high a current for the electrode being used, and the welding position. It is often caused in the top toe of fillet welds when attempting to produce a large leg length fillet weld in one run. Undercut can also be considered a serious imperfection particularly if it is sharp, as again it causes high stress concentrations. It is gauged in severity by its length, depth and sharpness. Fillet welded structures intended for fatigue loaded applications often require the toes' to be lightly ground, or flushed in with a TIG run to remove any toe undercut. Shrinkage grooves: Shrinkage grooves may occurin the root area and are caused by contractional forces pulling on the hot plastic base metal in the root area. It is often mistaken as root undercut.


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Root Run or "Hot pass" undercut


Parent metal, "top,,:e" nn?t

s.> "!i"!iq;:R~~.'.'~

Parent metal, surface undercut

,~

~.

_

._Q~~'~i{'=,.

y

Weld metal, surface undercut

)

Weld metal, surface undercut

t

~"" ".jfj: Shrinkage grooves

(

Root concavity: (suck back) This may be caused when using too high a gas backing pressure in purging. It may also be produced when welding with too large a root gap and depositing too thin a root bead, when the hot pass may pull back the root bead through contractional strains,

. Root concavity Senior Welding Inspection - Welding Imperfections Copyright © 2002 TWI Ltd

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Excess penetration:

Often caused by using too high a welding current, and/or, slow travel speed, coupled

with a large root gap, and/or a small root face for the current or process being used. It is

often accompanied by bum through, which can be defined as a local collapse of the weld

puddle causing a hole, or depression in the final weld root bead.

Root oxidation:

Root oxidation may take place when welding re-active metals such as stainless steels

with contaminated, or inadequate purging gas flow.

Crater pipes:

Often occurs during TIG welding, at the end of the weld run, on final solidification. It is

caused by insufficient filler material to meet the solidification process. It can be

eliminated by careful application of the filler metal, or using a slope out control.

I

\

<:

Crater pipe

Excess penetration, and bnrn tbrougb

/'1',",

Root oxidation in Stainless Steel

To summarize, we can list surface or profile welding imperfections as follows:

(

1)

Incompletely filled grove.

2)

Spatter.

3)

Arc strikes. (Stray arcs)

4)

Incomplete root penetration.

S)

Bulbous or irregular contour.

6)

Poor toe blend.

7)

Irregular bead width.

8)

Undercut.

9)

Root concavity.

10)

Excess penetration/Burn through.

11)

Root oxidation.


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5)


Mec hanical damage:

Mechanical damage: This can be defined as any surface material damage caused during the manufacturing process. This can include damage caused by: 1) Grinding. 3) Hammering. 5) Chiselling.

2) 4) 6)

>

Chipping.

Braking off welded attachments by hammering.

Using needle guns to compress weld capping runs.

As with the stray arcing, the above imperfections can be detrimental as they reduce the through thickness dimension of the plate in that area. They can cause local stress concentrations and should be repaired prior to completing the job.

7)

lVIisalignment:

There are 2 forms of misalignment, which are termed: 1)

Linear misalignment.

2)

Angular misalignment.

Linear misalignment: can be controlled during weld set up by the correct use/control of the weld set up technique i.e. tacking, bridging, clamping etc. Excess weld metal height is always measured from the lowest plate to the highest point of the weld cap.

Linear misalignment measured in:: -

-

-

-

-

-

-

-

-

-

3mm

t-

Angular misalignment: may be controlled by the correct application of distortion control techniques, i.e. balanced welding, offsetting, or use ofji.gs, clamps, etc.

-

-

------

;~-·":"·K'~-:"""'_:-

Angular misalignment measured in degrees

-

-

-~ 15

0

0

Good working practices and correct welder training will minimise the occurrence of unacceptable welding imperfections, or welding defects.


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Summary of Welding Imperfections: Type

Causes/Location

Centreline H2 Lamellar Tears Porosity Gas pore < 1.6mm 0 Blow hole> l.6mm 0 Shrinkage cavity Slag MMAISAW Silica TIG/MAG(Fe steels) Tungsten TIG Copper (MIG/MAG) Lack of side wall fusion (Can be surface breaking) Lack of root fusion Cold lapping Poor toe blend Arc Strikes Incomplete penetration Incompletely filled groove Spatter Bulbous contour Undercut: Surface and root run Shrinkage groove (Root) Root concavity Excess Penetration Burn through Crater Pipes (Mainly TIG) Hammer/Grinding marks etc. Angular Misalignment (0) Linear Misalignment (mm)

Weld Metal Weld Metal & HAZ Base metal Damp electrodes Un-cleaned plates/pipes Loss of gas shield

Group 1) Cracks (Discussed in Weldability)

2) Porosity/Cavities

3) Solid Inclusions

4) Lack of Fusion

5) Surface & Profile

(

6) Mechanical damage 7) Misalignment

Weld metal d:w > 2:1 Poor Inter-run cleaning Slag traps. Arc blow Dipping tungsten in pool Dipping contact tip in pool Arc Blow Incorrect welding technique Incorrect welding technique Positional welding technique Incorrect welding technique Poor welding technique < Root gap/Amps. >Root face Incorrect welding technique Damp consumables Incorrect welding technique Too high an amperage Poor welding technique Contractional forces Too high gas pressure >Root gap/Amps < Root face Incorrect current decay Poor workmanship Poor fit-up. Distortion Poor fit-up. Hi-Low in pipes

Note: The causes given in the above table should not be considered as the only possible causes of the imperfection given, but as an example of a probable cause.


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Questions Welding Imperfections

QU 1.

Give two main causes for the occurrence of a burn through

QU2.

Give two main causes for the occurrence of excessive root penetration on a single

Vee butt weld.

c)

QU3.

Give five defects, which may occur when welding carbon steel using the MMA

welding process with the current setting too low.

QU4.

Give three possible causes for the occurrence of lack of side-wall fusion

(

QU5.

Sketch the following defects a. Lack of root fusion b. Lack of root penetration . c. Incomplete filled groove d. Concave root.

Senior Welding Inspection - QU Welding Imperfections Sec 3 Copyright © 2003 TWl Ltd

170 nOHJas

TWI I[J[JI.

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Mechanical Testing: Mechanical tests are generally carried out to ensure that the required levels of certain mechanical properties have been achieved. When metals have been welded, the mechanical properties of the plates may have changed in the HAZ due to the thermal effects of the welding process. It is also necessary to establish that the weld metal itself reaches the minimum specified values. The mechanical types of properties or characteristics most commonly evaluated are:

Hardness:

The ability of a material to resist indentation.

Toughness:

The ability of a material to absorb impact energy and resist fracture.

Strength:

The ability of a material to resist a force. (Normally tension)

Ductility:

The ability of a material to plastically deform under tension.

To carry out these evaluations we require specific tests. There are a number of mechanical tests available to test for these specific mechanical properties, the most common of which are: 1)

Hardness testing. (Vlckers/Brinell/Rockwell)

2)

Toughness testing. (Charpy V/lzod/CTOD)

3)

Tensile testing. (ReducedlRadius /All weld metal)

Used to measure Quantity.

Tests 1 - 3 have units and are termed quantitative tests.

We use other tests to evaluate the quality of welds 4)

Macro testing.

5)

Bend testing. (Side/Face/Root)

6)

Fillet weld fracture testing.

7)

Butt weld Nick-break testing.

Used to measure Quality.

Tests 4 - 7 have no units and are termed qualitative tests.

Senior Welding Inspection - Mechanical Testing Copyright © 2002 TWI Ltd

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Hardness tests:

Types

0


Used to check the level of hardness across the weld.

f hardness test are:

a)

Rockwell scale.

(Diamond or steel ball)

b)

Vickers pyramid. VPN

(Diamond)

c)

Brinell. BHN

(5 or 10 mm diameter steel ball)

d)

Shore Schlerescope.

(Measures resilience)

Most hardness tests are carried out by (1) impressing a ball, or a diamond into the surface of a material under a fixed load, (2) then measuring the resultant indentation and comparing it to a scale of units (BHN/VPN etc.) relevant to that type of test. Hardness surveys are generally carried out across the weld as shown below. In some applications it may also be required to takes hardness readings at the weld junction/fusion zone. A shore schlerescope measures hardness by dropping a weight from a height onto the surface of a metal and measuring the height of the rebound. The higher the rebound of the weight, the harder is the material. Early equipment was cumbersome, but more portable compared to other hardness testing methods. Equipment is now available which works on the resilience principle, and is the size of a ballpoint pen. This equipment is generally scaled to give hardness values in all of the above scales.

+ + \f o

1

1

r-

2

1

r-

(> Plate


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Toughness tests: Used to check the resistance to impact loading.

Types 0 f toughness test are: a)

Charpy V. (Joules) Specimen held horizontally in test machine, notch to the rear.

b)

Izod. (Ftlbs) Specimen held vertically in test machine, notch to the front.

c)

CTOD or Crack Tip Opening Displacement testing. (mm)

There are many factors that affect the toughness of the weldment and weld metal. One of

the important effects is that of testing temperature. In the Charpy V and Izod test, the

fracture toughness is assessed by the amount of impact energy absorbed by a small

specimen of 10 mm- during fracture by a swinging hammer. A graph can be produced

using temperature as the base. The notch is 2mm deep, 0.25 root radius, and notch e 45 0

(

~WIltl'tIlil · li tili iWilM.V.bl i l·' ' '-' lili:.lie*~'l">~M.• /' (.

_

P"~

10 x 10 mm

Fusion zone & HAZ

Machined notch

Graduated scale of Joules absorbed energy Pendulum locked in position

"

Notch placed to the

rear 0 f the strike

Specimen


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Ductile/Brittle transition curve for a typical ferritic steel

Temperature range-.J

47 Joules

I'"

Transition range

i

M

__ J

Ductile/Brittle transition point

_

28 Joules

I I

I I I I

Energy absorbed (Joules)

I

I I I

-50

-40

-30

-20

-10

0

10

20

30

40

Degrees Centigrade

The curve can be moved by many factors, including alloying & heat input: a)

(\

Alloying:

The curve can be moved to the left by additions of manganese of up to 1.6 %. In other

words the addition of manganese of up to 1.6% has a positive effect on improving the toughness of plain" ferritic steels. Nickel also has a very positive effect on low temperature toughness of steels, however nickel is a very expensive metallic element and is used only where low temperatures are severe. Steels containing 9% nickel have excellent low temperature toughness. Fully austenitic stainless steels show measurable toughness at -270 °C, or a few degrees above absolute zero. b)

Heat input:

The curve can be moved to the right by too high a heat input during the welding cycle. This happens because of the effect called grain growth. At high temperatures, grains grow and fuse together to form larger grains. The amount of energy needed to fracture a large grain structure is much less than a fine grain structure. Hence the need to control inter-pass temperatures.


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3)

Tensile Te st: Used to measure tensile strength (Nzmm'') (Ductility as E %)

Types of tensile tests are:

a) Transverse tensile test:

Reduced section: Used to test the strength of the weldment,

Radius reduced section: Can be used to assess the strength of the weld metal.

b) AU weld metal tensile test: Used to test weld metal for UTS, Yield point and elongation, or E %. Transverse tensile tests are taken across the weld to test the value of tensile strength in this area. A reduced tensile test is the standard test where the specimen is first cut and then reduced to allow a gripping area for the machine with a very low stress concentration. A radius may be cut into the weld to assess the weld metal strength.

)

A transverse tensile test specimen Test gripping area

Weld

Radius (For radius reduced test specimens only)

-, I

/44.~~ .-'

"

Plate

material~/

~ ~0V: ~v:

•

"'.

II>

"

<

50mm

• ......

"

!R:UCed Sectiuu

Elongation marks Failure is generally expected in the plate material, though failure in the weld or HAZ is not reason to fail the test if the minimum specified tensile stress has been reached.

In a Radius reduced tensile test the weld metal is turned down, and so failure would be expected in the weld, due to a smaller CSA. It is sometimes used to show the tensile strength of the weld metal, but it is not very accurate due to the local stress concentrations that are produced. All weld metal tensile tests are carried out by electrode manufacturers to determine weld metal strength, and also ductility as elongation (E%). A deep weld' is made in a plate and then a tensile specimen is cut along the length of the weld, which should contain 99.9% undiluted, or pure weld metal. Prior to the test, marks are made 50 mm apart along the length of the specimen. As the test is being carried out yield stress and fracture stress are recorded and documented. After fracture, the pieces are placed back together and the elongation is calculated from the original gauge length and given as E%


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Macro examination tests: Used to check the internal level of quality in the weld.

...

A macro specimen is normally cut from a stop/start position in the root, or hot pass of a welder approval test. The start/stop position is marked out during a welder approval test by the welding inspector. Once cut, the specimen is polished using progressively finer grit papers and polishing at 90° to previous polishing direction, until all the scratches caused by the previous polishing direction have been removed. It is then etched in an acid solution which is normally 5 -10% Nitric acid in alcohol (carbon steels). Care must be taken not to under-etch or over-etch the specimen, as this will mask the elements that can be observed on a correctly etched specimen. After etching for the correct time, the specimen is then washed and dried. A visual examination should be carried out at all stages of production to observe any imperfections that are visible. Finally, a report is then produced on the visual findings, then compared and assessed to the levels of acceptance in the application standard. Macro samples may be sprayed with clear lacquer after inspection, for storage purposes.

(/

Macro Assessment Table 1)

Excess weld metal height.

2)

Slag with lack of sidewall fusion.

3)

Slag with lack of inter-run fusion.

4)

Angular misalignment.

5)

Root penetration bead height.

6)

Segregation bands.

7)

Undercut


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Bend tests: Used to check weld ductility & fusion in the area under stress.

The former is moved through a guide (guided bend test), or rollers, and the specimen is

bent to the desired angle.

Types of bend test are:

a)

Face bends

b) Root bends

c) Side bends

d) Longitudinal bends

Fonner.

Specimen

Before testing Guide

( )

A guided side bend test

After testing

(

Specimen is bent through pre-determined angle Generally, bend tests are carried out for welder approval tests, though they may also be used during procedure approval to establish good sidewall, root, or weld face fusion. Inspection of the test face is made after the test to check the integrity of the area in test. For materials of greater than 12mm thickness, a slice of 10-12mm is normally cut out along the length and the material is side bend tested. Bend testing is a qualitative method of mechanical testing. Ductility may be observed but is not measured.


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Fillet weld fracture tests. Used to assess root fusion in fillet welds. A fillet weld fracture test is normally only carried out during a welder approval test. The specimen is normally cut by hacksaw through the weld face to a depth (usually 1-2 mm) stated in the standard. It is then held in a vice and fractured with a hammer blow from the rear. Once fracture has been made, both fractured surfaces are inspected for imperfections. Finally the vertical plate X is moved through 90° and the line of root fusion is observed for continuity. Any straight line would indicate a lack of root fusion. In most standards this is sufficient to fail the welder.

Hammer blow Saw cut Line of fusion

c Fracture line

t Full fracture

X

( "

,

~3

B

1

/1.R~f'~ y "Lack of root fusion"

After inspection of both fractured surfaces for imperfections, tum fracture piece X through 90° vertically and inspect the line of root fusion. (Line 2) A Fillet weld fracture test is a .qualitative mechanical test, as we are observing weld

quality.

Senior Welding Inspection - Mechanical Testing Copyright © 2002 TW[ Ltd

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Nick-break tests: Used to assess root penetration and fusion in double-sided butt welds, and the internal faces of single sided butt welds. A Nick-break test is normally carried out during a welder approval test. The specimen is normally cut by hacksaw through the weld faces to a depth stated in the standard. It is then held in a vice and fractured with a hammer blow from the rear. Once fracture has been made then both fractures are turned horizontally through 90° and may then be inspected for imperfections on the fracture faces, as shown below in C.

Hammer blow

Saw Cuts

.D Fracture line

A

B (

Lack of root penetration, or fusion

Inclusions on the fracture line

A butt Nick-break test is a qualitative test, as we are observing quality.

Senior Welding Inspection --: Mechanical Testing Copyright © 2002 TWI Ltd .

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Quantitative and Qualitative Mechanical Testing: Quantitative: We test weldments mechanically to establish the level of mechanical properties of the weld. In such a case we may use the following types of tests:

cJ

1) Hardness: Vickers (VPN)

Brinell (BHN)

Rockwell (Scale C for steels)

2) Toughness:

Charpy V (Joules)

Izod (Ftlbs)

CTOD (mm)

Tensile Strength:

3) N/mm 2 (UK) & PSI (USA)

Transverse reduced & radius reduced.

Longitudinal all weld metal.

Elongation E% may be measured during tensile testing.

(The ductility value often given as a % reduction in area mainly in transverse and short

transverse tensile tests)

All the above tests 1 - 3 have units, and are thus termed quantitative tests.

They are used only in welding procedure approvals.

Qualitative:

We also test weldments mechanically to establish the level of quality in the weld.

In such a case we may use the following types oftest:

( 4)

Macro testing.

5)

Bend testing. (Face. Root. Side. & Longitudinal)

6)

Fillet weld fracture testing.

7)

Butt nick-break testing.

All the above tests 4 - 7 have no units, and are thus termed qualitative tests.

They are mainly used in welder approvals.

Some of the qualitative tests may be used during procedural approval to establish

good fusion/penetration etc.

Senior Welding Inspection - Mechanical Testing Copyright © 2002 T\VI Ltd

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Summary of Mechanical Testing: Name

Property

Units, if applicable

Used mainly for

Welding Procedure tests Welding Procedure tests Welding Procedure tests Measuring Stock materials Welding Procedure tests Welding Procedure tests Welding Procedure tests Welding Procedure tests Welding Consumable tests Welding Procedure tests Welder Approval or Procedure tests Welder Approval or Procedure tests Welder Approval or Procedure tests Welder Approval or Procedure tests

Rockwell scale

Hardness

Qualitative or Quantitative Quantitative

Vickers pyramid

Hardness

Quantitative

Scale C is used for Steels VPN

Brinell

Hardness

Quantitative

BHN

Shore Schlerescope

Hardness

Quantitative

Charpy V

Toughness

Quan titative

Izod

Toughness

Quantitative

Measures Resilience mm Joules. Energy absorbed Ft.lbs

CTOD

Notch Ductility Toughness Tensile Strength Ductility Tensile Strength Ductility Tensile Strength of weld metal

Quantitative

N/A

Qualitative

N/A

Ductility may be observed

Qualitative

N/A

N/A

Qualitative

N/A

N/A

Qualitative

N/A

If applicable

Transverse Reduced Tensile All Weld Metal Tensile Radius Reduced Transverse Tensile Macro Bends Face Root or Side Fillet Weld Fracture T & Lap Joints Nick Break Test Butt Joints


Quantitative

0.0000 mm + a detailed report N/mm- or PSI % Reduction Area L

Quantitative

N/mm or PSI

Quantitative

Elongation % z N/mm or PSI

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Questions

Mechanical Testing

QU 1.

Which mechanical properties can be measured in the all-weld metal tensile test?

QU 2.

What is the purpose of a charpy V-notch test and what units are the results give in

QU3.

Give a brief description of the following mechanical tests

)

a. bend test

QU4.

b. Nick break test

c. Macro

From a transverse tensile test the following information is known. calculate the ultimate tensile strength for the following Maximum load applied: 235 Kilo Newton's Least cross sectional area: 25.20mm x 17.52 mm

Senior Welding Inspection -QU Mechanical Testing Sec 4 Copyright © 2003 TWI Ltd

I.

')

SIUAo.lddu .lapIaA\ pun sampaoo.r.j ~U!PIa A\

(

.

\

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V!lOI.

_


Welding Procedures: What is a welding procedure? A welding procedure is a systematic method of producing a sound weld. For production purposes this is generally held as a written, or a computer generated document.

Testing a weld sample: Most production welding procedures are approved. (They have been thoroughly tested) Having carried out a test weld using the preliminary Welding Procedure Specification (pWPS), the welded specimen is generally sent for visual inspection and non-destructive testing to assess the level of quality. If the test weld passes these tests it may then be sent for any required mechanical testing. The test coupons are cut from the welded test piece from locations that are generally specified in the application standard, and are then sent to a test house for testing. These tests may include quantitative tests such as hardness, toughness or tensile tests, and any required qualitative tests such as macros, bends, or fracture tests.

Documentation: If all the tests have met the requirements of the standard, the procedure will become approved. The Welding Procedure Approval Record *(WPAR) will include all the various welding parameters and test record data. * Also commonly referred to as a Procedure Qualification record (PQR)

From this data a workable document for production welding is prepared and called a

Welding Procedure Specification (WPS). Generally the approved Welding Procedure Specification will have an "Extent of approval" which may include the following variable parameters:

1)

Thickness of plate.

2)

Diameter of pipe.

3)

Welding position.

4)

Material groups.

5)

Amperage range.

6)

Number of runs.

7)

Consumables.

8)

Heat input range. (kJ/mm)

A CSWIP 3.2 Senior 'Welding Inspector would generally witness the welding of the procedure and supervise the subsequent testing ofthe weld.

Senior Welding Inspection - Welder & Procedure Approval 5.1 Copyright © 2002 TWr Ltd

Rev 09-09-02

(

TWI V!7!lI.

_


Welder Approval: A welder approval test is a test of the level of skill attained by the welder. Once a welding procedure has been approved it is then important to ensure that all welders employed using the procedure on a project can meet the level of quality set down in the application standard. Welder approvals are therefore carried-out, where the welders are directed to accurately follow the approved WPS by the welding inspector.

(

)

The test plate, or pipe is then tested for quality using NDEINDT and some qualitative mechanical tests. In general a visual examination is carried out, followed by radiography or ultrasonic testing (depending on the level of skill demanded from the welder) to look for internal imperfections. The specimen may then be cut into coupons for the various qualitative mechanical tests. These tests generally require simple equipment such as a hacksaw, hammer, vice, polishing equipments, and bend testing machine. The mechanical tests of a welder approval may include: a)

Bend tests. (Side. Face. Root)

b)

Fillet weld fracture tests.

c)

Nick Break tests.

d)

Macro Assessments.

When supervising a welder test the welding inspector should:

(

.

1)

Check the welding process, condition of equipment and test area for suitability.

2)

Check that extraction systems, goggles and all safety equipment are available.

3)

Check grinders, chipping hammers, wire brush and all hand tools are available.

4)

Check materials to be welded are correct and stamped correctly for the test.

5)

Check welding consumables specification, diameter, and treatment with WPS.

6)

Check the welder's name and stamp details are correct.

7)

Check that the joint has been correctly prepared and tacked, or jigged.

8)

Check that the joint and seam is in the correct position for the test.

9)

Explain the nature of the test and check that the welder understands the WPS.

10)

Check that the welder carries out the root run, fill and cap as per the WPS.

11)

Ensure welders identity and stop start location are dearly marked.

12)

Supervise or carry out the required tests and submit results to Q/C department.

ACSWIP 3.1 welding inspector may be called upon to witness/conduct a welder approval test, and supervise, or carry out thesubsequent testing of the weld.

Senior Welding Inspection - Welder & Procedure Approval Copyright © 2002 TWI Ltd

5.2

Rev 09-09-02

TWI V!lIJI.

_


A typical welder approval certificate to BS 4872 would contain the following data: I

Organization's Symbol Logo:

tst

!

Welder approval test certificate (BS 4872: Part 1 1982)

Manufacturers name:

Issue No 001

Date of test

9th September 2002

Test piece details: MMA III Ferritic steel 5mm Single V butt. 150mm Overhead. Vertical up. Horizontal vertical. Flat. Axis? inclined 45 Fixed

Test piece position: Fixed/rotated:

:

Welders name & Identity No Mr. A Welder. Stamp 123

XYZ Fabrications Ltd.

Welding process: Parent material: Thickness: Joint type: Pipe outside 0: Welding position:

Test record No 321

!

Extent of approval: Welding Process: Materials Range: Thickness range: Joint types:

MMA Ferritic steels. 2.5 - 10 mm. Butt welds in plate & pipe. 75 - 300mm All except Vertical down. Rutile & Basic.

Pipe outside 0: Welding Position:

Welding consumables:

Consumables: Filler metal: (Make & type)

BOC Fortrex 7018

Composition: Specitication: Shielding gas: Specification number:

Ferritic steel. E 50 5 B 12 H 5 N/A BSEn 499 1994

Weld preparation

(dimensioned sketch)

,~6°i

1.5 - 2 mm

l.5-2mm

T~~

Visual examination & Test results: Visual Inspection: Contour: Undercut: Smoothness of joins:

I1cce;taJle. I1cce;taJle. I1cce;taJle.

l1ue;taJle. /Y,t otttcaJfe l1ue;taJfe

Penetration (No backing) Penetration (with backing) Surface defects

Destructive tests: Macro /Y,t I'efll/iwI

Remarks:

I

I

Side Bend . #It I'efll/iwI

I

I

Tk «Iell «Ia~ 9attel" II'U

Root Bend ..t211~taJle.

I

Fillet fracture #It I'efll/iwI

I

Butt Nick break /Y,t I'efll/iwI

I I MIIMI afool fJI!eQl"Mee MI toe blelfr!.

The statements in this certificate are correct. The test weld was prepared in accordance with the requirements of BS 4872: Part 1 1982. Manufacturers Representative: Mr. A'Representative

II Rtll'«Uftat/H Position. Quality Manager Date: 9th September 2002

Inspecting authority, or test house: · ..............

ABC Inspection Ltd.

It Plut~

······A·············d······ :::::: .. pp~q~~ .::::::

·:CS·Wlp s.r: DO: t:23:. · ..............

Witnessed by:

:::: :~~ ~ ~ ~1~1i::::: Mr. I C Plenty

th Date: 9 September 2002

Senior Welding Inspection - Welder & Procedure Approval Copyright © 2002 TWI Ltd

5.3

Rev 09-09-02

(

TWI V[JI.

_


Questions

Welding Procedures and Welder Approvals

au 1.

State six essential variables in a welding procedure specification

aU2.

What do you understand by the term extent of approval giving four examples?

au 3.

Describe what you understand by a welding procedure specification a welding procedure approval record and a welder's certificate.

aU4.

What are the main reasons for approving a welding procedure and a welder?

au 5.

Give three reasons why a welder may require re-qualification

Senior Welding Inspection - QU Welding Procedures and Welder Approvals Sec 5 Copyright © 2003 TWI Ltd

)

uopoodsnj SIB!.Iarr.w

90 U0!lJaS

TWI

1ll!J1.

_


Materials Inspection: All materials arriving on site should be inspected for: 1) 2)

3)

Size. Condition. Type/Specification.

In addition, other elements may need to be considered depending on the materials form or shape. Most plate materials begin life as a casting, which is then rolled out into plate. Plate is sometimes rolled into pipe and then welded with a longitudinal, or helical seam. Some imperfections associated with rolling are shown below:

Direction of rolling

Larni

/

............................

Segregation

.

~nd

Laminations contain impurities and major inclusions such as slags that solidify in the

ingot.

When rolled out these major inclusions may exist throughout the plate thickness.

Gas pores in the solidified ingot can also cause laminations when rolled out but will

generally 'close up' during the hot rolling process.

Laminations will become thinner as the plate is rolled into thinner sections and will

eventually become invisible to the naked eye in thinner sheet or plate.

Segregation bands occur in the centre of the plate and are low melting point impurities

such as sulphur or phosphorous which have segregated to the centre of the ingot as that

is the last place to cool. Great care needs to be taken when welding low quality steel as

sulphur levels may be present in the steel which cannot be detected by non destructive

testing.

Segregation bands can only be found on etched surfaces and have an appearance

similar to that of a weld HAZ.

Laps are caused during rolling when overlapped metal does not fuse to the base

material due to insufficient temperature, and or pressure.

Senior Welding Inspection - Materials Inspection Copyright © 2002 TW[ Ltd

6.1

Rev 09-09-02

l

TWI 1ll1J1.

_


Plate luspection:

Condition: Corrosion, Mechanical damage, Laps and Laminations.

() Thickness

Size: Length Width

~

I

( .

Other checks need to be made such as heat treatment condition, distortion, tolerance, quantity, storage and identification.

Senior Welding Inspection - Materials lnspection Copyright © 2002 TWI Ltd

6.2

Rev 09-09-02

TWI V!l!ll.

_


Pipe Inspection:

Condition: Corrosion, Mechanical damage, Wall thickness, Ovality, Laps, Laminations.

Type/Specification:

Welded seam

Size: Outside 0

Length

Other checks also need to be made, such as heat treatment condition, distortion, tolerance, quantity, identification and storage.

Senior Welding Inspection - Materials Inspection Copyright © 2002 TWI Ltd

6.3

Rev 09-09-02

TWI V!lOI.

_


Questions

Material Inspection

QU1.

What should an inspector check for when plate materials arrive on site?

QU2.

What is a plate lamination and what inspection method is most suited for the detection of plate laminations

QU3.

What is a lap in steel?

QU4.

What should an inspecting check for when pipe arrives on site?

QU5.

With regards to the materials being used on site which records or standards should be checked and referred to by the inspector

i)

Senior Welding Inspection - QU Material Inspection Sec 6 Copyright © 2003 TWI Ltd

\

;'

sp.mpumg pun sapo.j LO uOHJaS

(

TWI

V!llll.

_


Codes and Standards: A code of practice is generally a legally binding document containing the rules and laws

required to design, and test a specific product, whereas a standard will generally contain,

or refer to all the relevant optional and mandatory manufacturing, testing and measuring

data. The definitions given in the English dictionary state:

A code of practice:

A set oflaw's, or rules that shall be followed when providing a service or product.

An applied standard:

A level of quality, or specification too which something must be tested.

We use codes and standards to manufacture many things that have been built many times

before. The lessons of failures, or under-design are generally incorporated into the next

revised edition.

Typical design/construction codes and standards used in industry include:

Pipe lines carrying low, and high-pressure fluids.

Oil storage tanks.

Pressure vessels.

Offshore structures.

Nuclear installations.

Composite concrete and steel bridge construction.

Vehicle manufacture.

Nuclear power station pipe work.

Submarine hull construction.

Earth moving equipment.

Building construction etc.

'-. ~

Generally; the higher the level of quality required then the more specific is the

code/standard in terms of the manufacturing method, materials, workmanship, testing

and acceptable imperfection levels.

The application code/standard gives important information to the welding inspector

as it determines the inspection points and stages, and other relevant criteria that must be

followed, or achieved by the contractor during the fabrication process.

Most major application codes and standards contain 3 major sections, which are

dedicated to:

1) 2) 3)

Design. Man ufacture. Testing.

Senior Welding Inspection - Codes and Standards Copyright © 2002 TWI Ltd

7.1

Rev 09-09-02

TWI V!lOI.

_


Application codes/standards may not contain all the relevant data required for manu facture, hut 111 a y refer to other app1icab1e standards for special c lcrucn ts. Examples of these are given below:

1) 2) 3) 4) 5)

Materials specifications. Welding consumable specifications. Welding procedure and welder approvals. Personnel qualifications for NDT operators. NOT Methods.

On many occasions the application code/standard will contain it own levels of acceptance, which are drawn up by a board of professional senior engineers, who operate in that specific industrial area, Codes and standards are revised periodically! to take into account new data, new manufacturing methods, or processes that may come into being. If no local legal obligations exist then it is the year of the application code/standard within the contract documents, which becomes the legally binding version. The main areas of responsibility within an application standard is generally divided into:

1) 2) 3)

The client, or customer. The contractor, or manufacturer. The third party inspection authority, or client's representative.

The applied code/standard will form hub of the contract documents hence any deviation, or non-conformance from the code/standard must be applied for by application from the contractor to the client as a concession. Once a concession has been agreed, it must then become a signed and written document, which is then filed with the fabrication quality documents. .


7.2

Rev 09-09-02

TWI VOI.

_


Questions

Codes and Standards

QU 1.

What is the difference between a codes and a standard?

QU2.

In a code/standard, what is the difference between shall and should

QU 3.

What do you understand by the terms: National standard and Harmonized standard

QU4.

As a welding inspector what important information can be obtained form an application code/standard?

QU5.

Is it a requirement for the application code/standard to contain all relevant data required for manufacturing a product? And if not give details of what elements may be missing.

Senior Welding Inspection -QU Codes & Standards Sec 7 Copyright © 2003 TWI Ltd

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_


Weld Symbols on Drawings We use weld symbols to transfer information from the design office to the workshop. It is essential that a welding inspector can interpret weld symbols, as a large proportion of the welding inspectors time will be spent checking that the welder is correctly completing the weld in accordance with the approved fabrication drawing. Therefore without a good knowledge of weld symbols, a welding inspector is unable to carry out his full scope of work. Standards for weld symbols do not follow logic, but are based on simple conventions.

There are many different standards for weld symbols, as most major manufacturing countries have their own. Basically a weld symbol is made of 5 different components, and the following is common to all major standards:

(.)

The arrow line: 1) The arrow line is always a straight and unbroken line, (With the exception of instances in AWS A2.4) and has only 1 of 2 points on the joint where it must touch, as shown below: F.ither/or

2) The reference line:

The reference line must touch the arrow line, and is generally parallel to the bottom of

the drawing page. There is therefore always an angle between the arrow line and

reference line. The point of the joint of the 2 lines is referred to as the knuckle.

c

t/

Either/or

;;:

The symbol:

3) The orientation of the symbol on the line is generally the same in most standards,

however the concept of arrow side and other side is shown differently in some

standards. This convention is explained within the following text for UK., European, and

ISO standards. (AWS A2A convention for arrow and other side follows that of BS 499)

4) The dimensions:

Basically, all cross sectional dimensions are given to the left, and all linear dimensions

are given to the right hand side of the symbols in most standards.

Supplementary information:

5) Supplementary information, such as welding process, weld profile, NDT, and any special

instructions may differ from standard to standard.

Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

8.1

Rev 03-06-05

TWI V!lOI.

_


BS 499 (UK):

The Arrow Line:

a) b) c)

Shall touch the joint intersection. Shall not be parallel to the drawing. Shall point towards a single plate preparation.

The Reference Line: a) b)

Shall join the arrow line.

Shall be parallel to the bottom of the drawing.

Position of Symbols

The position of the symbol is used in conjunction with an arrow line and a reference line

Reference line ~ Other side I

Joint

Arrow line

-,

Arrow side

<,

The position of a weld in a particular joint relative to the parts being joined is indicated by the head of an arrow, this denotes the reference line side of the joint. The side nearer the arrowhead is known as the arrow side; the remote side is known as the other side The symbol is placed below the reference line if the weld (weld face) is on the arrow side of the joint. The symbol is ·placed above the reference line if the weld (weld face) is on the other side. For welds made on both sides the symbols are placed both above and below the reference line.

(

a) To be welded on the arrow side


a) To be welded on the other side

8.2

Rev 03-06-05

TWI V!7!lI.

_


Supplementary symbols Supplementary symbols may be used when a specific external weld profile is required. They are used in conjunction with the relevant elementary symbol.

/

[?

Concave Profile

/

[2J

/

~

Convex Profile

v

/ (

Mitre Profile

Toes Shall be Blended Smoothly


8.3

Rev 03-06-05

TWI VIJI.

_


Complementary indications

Complementary indications are used for the following.

• • • • •

a peripheral weld-a weld made all round a joint. a site weld-not a shop weld. non-destructive testing. welding process. Additional information.

Indication of peripheral weld

Indication of field or site weld

111

Indication of non-destructive testing

Indication of welding process (MMA)

Additional Information, the reference document Is Indicated In the box

Elementary symbols. Each weld may be characterised by a symbol which, in general, is representative of the shape of the weld to be made, or edge preparation to be used, e.g. single-V butt weld. The vertical portion of a fillet weld symbol, single-bevel butt weld symbol must always be placed on the left-hand side. An elementary symbol does not indicate the welding process to be used. Detail with regarding the root gap, root face, bevel angles etc will be stated in the applicable welding procedure specification (WPS). Providing the joint is not to complex, combinations of elementary symbols may be used for welds made from two sides and compound welds, e.g. a fillet weld superimposed on a single bevel butt weld. Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

8.4

Rev 03-06-05

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V!l!ll.

--

_


1. Square butt weld

/

2. Single-V butt weld

3. Single-bevel butt weld

4. Single-bevel butt weld with a broad root face (.

)

/ /

~

______v y

5. Single bevel butt weld with broad root face

6. Single-J butt weld

7. Backing run; or back weld IUSAJ

8. Single-U butt weld (parallel or sloping sided)

(

/ /

~

~

,

9. Fillet weld

/

10. Plug weld

11. Spot weld

Senior Welding Inspection - Weld Symbols or. Drawings Copyright © 2005 TWI Ltd.

8.5

Rev 03-06-05

I

TWI 1[J[l1.


Dimensions Any dimension relating to the cross-section of the weld must be given on the left-hand side of the symbol; distances between adjacent weld elements must be indicated in parenthesis. Butt welds are intended to be continuous and have full penetration along the entire length of the joint, unless dimensional detail specifies otherwise. The cross sectional dimension indicated for a fillet weld is referring to its leg length. When it is desired to indicate the design throat thickness, then the leg length dimension is prefixed with the letter b; the design throat thickness dimension is prefixed with the letter a.

b := leg length (e)

a

=Design throat thickness.

n = number of welds. (e)

I = length of each weld. e = distance between each weld.

I"

I..

e

·1"

• 1..

• 1..

e

I

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.1 .. I

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Welds in line not staggered Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

8.6

Rev 03-06-05

TWI V!lfll.


/fl Single-U

Single-V

/"',

Single-V Butt flush

~

Single-U Butt with sealing

-,

Single-bevel butt

Double-bevel butt

n

~

[ 1 Single-bevel butt Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

Single-J butt 8.7 .

Rev 03-06-05

TWI

V!lOI.

_


BS EN 22553 (ISO 2553) The Arrow Line: b) d) e)

Shall touch the joint intersection. Shall not be parallel to the drawing. Shall point towards a single plate preparation.

The Reference Line: c) d)

Shall join the arrow line.

Shall be parallel to the bottom of the ,drawing.

Position of Symbols

The position of the symbol is used in conjunction with an arrow line and two reference lines

The position of a weld in a particular joint relative to the parts being joined is indicated by the

head of an arrow, this denotes the reference line side of the joint. The side nearer the arrowhead is

known as the arrow side; the remote side is known as the other side

The symbol is placed on the dashed reference line if the weld (weld face) is on the other side of

the joint. The symbol is placed on the continuous reference line if the weld (weld face) is on the

other side. For welds made on both sides the symbols are placed on both continuous and dashed

reference lines or alternatively if the weld is the same both sides there is no need to have a dashed

reference line.

/

---~-----

/---[/7"---- To be welded on the arrow side

To be welded on the other side

---v---- To be welded on both sides


---[/7"---- 8.8

Rev 03-06-05

TWI VllOI.

_


Supplementary symbols Supplementary symbols may be used when a specific external weld profile is required. They arc used in conjunction with the relevant elementary symbol.

'\,

)

Concave Profile

Convex Profile

,~

Mitre Profile


I--I

/

If\:

Toes Shall be Blended Smoothly

8.9

Rev 03-06-05

TWI V!l!ll.

_


Complementary indications Complementary indications are used for the following. • • • • •

a peripheral weld-a weld made all round ajoint. a site weld-not a shop weld. non-destructive testing. welding process. Additional information.

Indication of field or site weld

Indication of peripheral weld

111

Indication of non-destructive testing

Indication of welding process (MMA)

Additional information, the reference document is indicated In the box


8.10

Rev 03-06-05

TWI Vflfll.

_ THE WELDII\JG INSTITUTE

Elementary symbols. Each weld may be characterised by a symbol which, in general, is representative of the shape of the weld to be made, or edge preparation to be used, e.g. single- V butt weld, The vertical portion of a fillet weld symbol, single-bevel butt weld symbol must always be placed on the left-hand side. An elementary symbol does not indicate the welding process to be used. Detail with regarding the root gap, root face, bevel angles etc will be stated in the applicable welding procedure specification (WPS). Providing the joint is not to complex, combinations of elementary symbols may be used for welds made from two sides and compound welds, e.g. a fillet weld superimposed on a single bevel butt weld.

v

Steep Flanked Single-V Butt Weld

/----------

Steep Flanked Single-Bevel Butt Weld

Surfacing

r:":

Removable backing strip

MR

Permanent backing strip

M

11

Edge flange weld

/----------


8.11

Rev 03-06-05

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Square Butt

~

Single-V Butt

/----------

r---

Single-Bevel Butt

y

/-----------

Single-V Butt Weld, Broad Root Face

Single-Bevel Butt Weld, Broad Root Face

Single-U Butt Weld

Backing/Sealing Weld

r:":

Single-U Butt Weld

Fillet Weld

r---

Plug Weld

Spot Weld


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Dimensions Any dimension relating to the cross-section of the weld must be given on the left-hand side of the symbol; distances between adjacent weld elements must be indicated in parenthesis. Butt welds are intended to be continuous and have full penetration along the entire length of the joint, unless dimensional detail specifies otherwise. The cross sectional dimension indicated for a fillet weld is referring to its leg length. When it is desired to indicate the design throat thickness, then the leg length dimension is prefixed with the letter z; the design throat thickness dimension is prefixed with the letter a.

z = leg length

z6a4

(e)

z6a4

(e)

a = Design throat thickness. n = number of welds.

=length of each weld. e =distance between each weld. I

)

4

14

e

_1 4

1

_1 4

_14

e

e

I

_1 4

_1 4

_1 4

I

_1 4

_1 4

_1 4

I

e

-I

e

Welds off set staggered welding

(

I

z6a41"'"

nxI

(e)

z6a4V

nxI

(e)

•

4

14

_'4

I~

~

e

e

_'4

J~

I

_1 4

~

e

_1 4

e

I

J~

-I~

e

.4 e

Welds in line not staggered Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

8.13

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/

__":J _


/'l Single-U

Single-V

(

~

Single-V Butt flush

Single-U Butt with sealing

/_JL __ •

(

Single-bevel butt

Double-bevel butt

----~-~

n

I

Single-J butt

Single-bevel butt Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

~

8.14

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Numerical indication of process No.

Process

No.

Process

I II III

Arc welding Metal-arc welding without gas protection Metal-arc welding with covered electrode Gravity arc welding with covered electrode Bare wire metal-arc welding Flux cored metal-arc welding Coated wire metal-arc welding Firecracker welding Submerged arc welding Submerged arc welding with wire electrode Submerged arc welding with strip electrode Gas shielded metal-arc welding MIG welding MAG welding: metal-arc welding with non-inert gas shield Flux cored metal-arc welding Gas-shielded welding with non-consumable electrode TIG welding Atomic-hydrogen welding Plasma arc welding Other arc welding processes Carbon arc welding Rotating arc welding Resistance welding Spot welding Steam welding

47 48

752 753 76 77 78

Gas pressure welding Cold welding Other welding processes Thermit welding Electroslag welding Electrogas welding Induction welding Light radiation welding Laser Welding Arc image welding Infrared welding Electron beam welding Percussion welding Stud welding

781 782

Arc stud welding Resistance welding

9

Brazing, soldering & braze welding Brazing Infrared brazing Flame brazing Furnace brazing Dip brazing Salt bath brazing Induction brazing Ultrasonic brazing

Lap scam welding Seam welding with strip Projection welding Flash welding Resistance butt welding Other resistance welding processes HF resistance welding Gas welding Oxy-fuel gas welding Oxy-acetylene welding Oxy-propane welding Oxy-hydrogen welding Air fuel gas welding Air-acetylene welding Air-propane welding Solid phase welding: Pressure welding Ultrasonic welding Friction welding Forge welding Welding by high mechanical energy Explosive welding Diffusion welding

918

ll2 ll3 114 115 118 12

121 122 13 131 135 136 14

141 149

15 18

181 185 2

21 22 221 225 23 24

25 29 291 3 31

311 312 313

32 321 322 4

41 42

43 44 441

45

7

71 72

73

74 75 751

91 911

912 913 914 915 916 917 919

923 924 93 94 941 942 943 944 945

946 947

948 949 951 952 953 954

96 97 971 972

Resistance brazing Diffusion brazing Friction brazing Vacuum brazing Other brazing processes Soldering Infrared soldering Flame soldering Furnace soldering Dip soldering Salt bath soldering Induction soldering Ultrasonic soldering Resistance soldering Diffusion soldering Flow soldering Soldering with soldering iron Friction soldering Vacuum soldering Other soldering processes Braze welding Gas braze welding Arc braze welding

* Table 10, This table complies with International Standard ISO 4063 Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

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Complete a symbols drawing for the welded cruciform joint given below: All butt weld are welded with the MIG process and fillet welds with MMA.

1

10

20

35

30

15

) /

All fillet weld leg lengths are 10 mm

BS EN 22553

'!,

( \]

2

,m m_m_mnmb Senior Welding Inspection - Weld Symbols on Drawings Copyright © 2005 TWI Ltd.

8.16

Rev 03-06-05

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as 499 part 2 Fillet Weld Exercise 1. Welded both sides: A continuous concave fillet weld 6mm leg lengths.

2. Welded arrow side: Three Intermittent fillet welds, 6 mm leg lengths, the length of each weld 20 mm, the distance between each weld 30 mm. Welde.d other side: Two intermittent fillet welds 12 mm leg lengths, the length of each weld 30 mm, the distance between each weld 10 mm. Welds to be staggered.

3. Welded both sides. A continuous fillet weld, 6 mm leg lengths, 4 mm throat thickness, welds to be carried out on site.

4. Welded arrow side: Three intermittent fillet welds 10 mm leg lengths, 7mm throat thickness, length of each weld 15 mm, the distance between each weld 25 mm. Welded other side: A continuous convex fillet weld, 15 mm leg length, 10.5 mm throat thickness. Senior WeldingInspection - QU BS 499 part 2 Fillet Welding SymbolsSec 8 Copyright© 2003 TWI Ltd

TWI

V!l!ll-----------


BS EN 22553 Butt Weld Exercise 1. Welded arrow side: Single-V butt weld with permanent

backing strip, flat weld profile.

2. Welded other side: Single-U butt weld, flat weld profile

I

I

I

I

I

I

I

I

I

3. Welded arrow side: Single-V butt weld depth of preparation 10 mm Welded other side: Backing run. (Plate thickness 15 mm.)

4. Welded arrow side: Single-J butt weld, depth of preparation 12 mm with a 8 mm fillet weld superimposed. (plate thickness 15 mm.

. Welded other side: 12 mm leg length fillet weld.

Senior Welding Inspection - QU BS EN 22553 Butt Welding Symbols Sec 8 Copyright © 2003 TWI Ltd

'

60 uon~as

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Introduction to Welding Processes: A welding process: Special equipment used with method, for producing welds. The 4 main requirements of any fusion welding process are:

I:

Heating:

Of high enough intensity to cause melting of base metals and filler metals.

Protection:

Of the molten filler metal in transit and base metal from oxidation, and to protect the heat source and metals from ingress of gases such as hydrogen & oxygen.

Cleaning:

Of the weld metal to remove oxides and impurities, and refine the grains.

Adequate: properties

Adding alloying. elements to the weld, to produce the desired mechanical properties.

Senior Welding Inspection - Introduction to Welding Copyright © 2002 TWI Ltd.

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Rev 09-09-02

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Heating: There are many heat sources used for welding. In fusion welding, the main requirement is that the source must be of sufficient temperature to melt the materials being welded. Combustion of gases: Oxygen & acetylene will combust to produce a temperature of 3,200 "C. Other fuel gases may be used for oxy fuel gas cutting. The intensity of the flame is not as high as other heating methods and so longer time has to be spent to bring the material to its melting point.

(

-,

Electrical resistance: The heat generated by electrical resistance between 2 surfaces is used to produce over 95% of all welds made, in the resistance spot welding process. Electrical resistance is also used as a heat source in the Electro Slag welding process where the resistance is given by the molten slag. This process is classed as a resistive heating process. High intensity energy beams:

We use 3 types of concentrated high intensity energy beams, which are:

1) 2) 3)

Laser. (Light Amplification by Stimulated Emissions of Radiation)

Electron Beam. (Concentrated beam of electrons, generally in a vacuum)

Plasma. (A gas forced through an electric arc to create an ionised gas)

All these welding processes use beams of high energy creating extremely high

temperatures. These energy beams also enable very high welding speeds, which reduce

the amount ofoverall distortion with increased productivity.

Friction:

We can use the heat generated by friction (and pressure) to weld components together.

The joint is made with the materials faces in the plastic state.

The Electric Arc:

By far the most common heat source for fusion welding, the electric arc is utilised in

most of the common welding processes. The electric arc can produce heat of> 6000 °C

with extreme levels of ultra-violet, infrared and visible light. Heat is derived from the

collision of electrons and ions with the base material and the electrode. An electric arc

may be defined as the passage of current across an ionised gap. All gases are insulators

and thus sufficient voltage, or pressure needs to be available to enable an electron to be

stripped from an atom into the next. Once this conducting path or plasma has been

created, a lower voltage can maintain the arc. The voltage required to initiate the arc is

termed the open circuit voltage or OCV requirement of the process/consumable. The

voltage that maintains the arc once it is created is termed the welding, or arc voltage.

The conducting path produced is termed the plasma column.


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Protection: In [V[MA welding, the gas shield is produced from the combustion of compounds in the electrode coating. The gas produced is mainly C0 2 but electrodes are available that produce hydrogen gas, which give a very high level of penetration. In Submerged Arc welding the gas shield is again produced from the combustion of compounds, but these compounds are supplied in a granulated flux, which is supplied separately to the wire. MMA electrodes or SAW fluxes containing high levels of basic compounds are used where hydrogen controlled welding is required. In MIG/MAG & TIG welding the gas is supplied directly from a cylinder, or bulk feed system and may be stored in a gaseous, or liquid state. In TIG & MIG welding we generally use the inert gases argon or helium. In MAG welding we generally use C0 2 or mixtures of C02 or 0 2 in argon.

Cleaning (of surface contaminants): The cleaning, refining and de-oxidation of the weld metal is a major requirement of all common fusion welding processes. As a weld can be considered as a casting, it is possible to use low quality wires in some processes, and yet produce high quality weld metal by adding cleaning agents to the flux. This is especially true in MMA welding, where many cleaning agents and de-oxidants may be added directly to the electrode coating. De-oxidants and cleaning agents are also generally added to FCA W & SAW fluxes. For MIG/MAG & TIG welding wires, de-oxidants, such as silicon, aluminium and manganese must be added to the wire during initial casting. Electrodes and wires for MIG & TIG welding must also be refined to the highest quality prior to casting, as they have no flux to add cleaning agents to the solidifying weld metal.

Adequate properties (from alloying): As with de-oxidants, we may add alloying elements to the weld metal via a flux in some processes to produce the desired weld metal properties. It is the main reason why there is a wide range of consumables for the MMA process. The chemical composition of the deposited weld metal can be changed easily during manufacture of the flux coating. This also increases the electrode efficiency. (Electrodes of > 160% are not uncommon). In SAW, elements such as Ferro-manganese may be added to agglomerated fluxes. It is much cheaper to add alloying elements to the weld via the flux as an ore, or compound. As with the cleaning requirement described above, wires for MIG/MAG & TIG must be drawn as cast, thus all the elements required in the deposited weld metal composition must be within the cast and drawn wire. This is the main reason why the range of these consumables is very limited. With the developments of flux core wires, the range of consumables for FCAW is now very extensive, as alloying elements may be easily added to the flux core in the same way as MMA electrodes fluxes.


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THE WELDING 1t\ISTITUTE

Special Terms Related to Welding Safety: Duty cycle: A Duty Cycle is the amount of current that can be safely carried by a conductor in a period of time. The time base is normally 10 minutes and a 60% duty cycle means that the conductor can safely carry this current for 6 minutes in 10 and then must rest and cool for 4 minutes. At a 100% duty cycle equipment can carry the current continuously. Generally 60% & 100% duty cycles are given on welding equipment. Example: 350amps at 60% duty cycle and 300amps 100% duty cycle.

)

This should not be confused with the term Operating Factor, often wrongly used for Duty Cycle, as they are both measured as a percentage. Operating Factors are mainly used in economic calculations to calculate the amount of time required from a welding process to deposit an amount of weld metal. A typical Operating Factor for MMA would be only 30%

Occupational, and Maximum Exposure Limit (OEL and MEL): Operational, and Maximum Exposure Limits may be defined as a safe, or maximum working limit of exposure to various fume, gases or compounds during certain time limits, as calculated by the Health and Safety Executive or HSE in the UK. The branch of the executive that holds responsibility for this function is known as COSHH or Control of Substances Hazardous to Health. Examples of levels of some fume and gases that workers may be exposed to, taken from Guidance Note EH/40 2002, are given in the table below: Fume or gas Cadmium General Welding Fume Iron Aluminium Ozone Phosgene Argon

Exposure Limit 0.025Mglm J 5Mg/nr' 5Mg/rrr' 5Mg/rrr' 0.20 PPM 0.02 PPM No OEL Value 0 2 air content to be controlled

Effect on Health Extremely toxic Low toxicity Low toxicity Low toxicity Extremely toxic Extremely toxic Very low toxicity

*Note MEL/OEL values given in Guidance Note EH/40 may change annually. The toxicity of these examples can be gauged by the value of exposure limit. Any of the above examples may be present in welding under certain conditions, which will be expanded upon by your course lecturer at the relevant time, though Welding Safety will be discussed fully as a separate subject area. Senior Welding Inspection - Introduction to Welding Processes; Copyright © 2002 TWI Ltd.

Rev 09-09-02

(MVWS VWW) ~u!PlaM J.IV l~law l~nu~w

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Arc Characteristic for MMA & TIG: In MMA & TIG welding, the arc length is controlled by the welder. Whilst an

experienced and highly skilled welder can keep the arc length at a fairly constant length,

there will always be some variation.

When the arc length is increased, the voltage or pressure required to maintain the arc will

also need to increase. This wouldalso reduce the current supplied in a normal electrical

circuit, where the supplied voltage is proportional to a drop in current.

Thus we need to find a way of reducing a large drop in current for the variation in arc

voltage. This is achieved by the use of special electrical components within the

equipment that produce sets of curves as shown below. The graph below shows amperage curve (A) selected @ 100 amps, with the effect of

variation inthe arc gap and voltage.

Note how an increase in arc length increases the area under the graph, which

appears to give an increase in overall heat input. The extra heat is, however,

generally lost in the arc and is not transferred to the weld pool.

Constant Current (Drooping) Characteristic OCV 50-90 volts

...........__

t~

Output Curves for current selector settings: A: 100 Amps. B: 140 Amps. C: 180 Amps

Long arc gap

Normal arc gap.

1.Y' mel

0""

Y

Mug

I.

I

Short arc gap

Arc Voltage Welding Amperage

ABC

A large variation in voltage = Asmaller variation in amperage

Senior Welding Inspection - Manual Metal Arc Welding Copyright © 2002 TWI Ltd.

10.1

Rev 09-09-02

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Manual Metal Arc Welding:

MMA is a welding process that was first developed in the late 19th century using bare wire electrodes.

Definitions: MMA:

Manual Metal Arc Welding. (UK)

SMAW:

Shielded Metal Arc Welding. (USA)

Introduction:

(

MMA is simple process in tenus of equipment and consumables, using short flux covered electrodes. The electrode is secured in the electrode holder and the leads for this, and the power return cable are placed in the + or - electrical ports as required. The process demands a high level of skill from the welder to obtain consistent high quality welds, but is widely used in industry, mainly because of the range of available consumables, its positional capabilities and adaptability to site work. (Photograph 1) The electrode core wire is often of very low quality, as refining elements are easily added to the flux coating, which can produce high quality weld metal relatively cheaply. The arc is struck by striking the electrode onto the surface of the plate and withdrawing it a small distance, as you would strike a match. The arc should be struck in the direct area of the weld preparation avoiding arc strikes, or stray flash on the plate material. Care should also be taken to maintain a short and constant arc length and speed of travel. Photograph 2 shows a trainee dressed in the correct safety clothing, whilst photograph 3 indicates the level of process-produced fume, and the use of a flexible hose extraction system. Little has changed with the basic principles of the process since it was developed, but improvements in consumable technologies occur on a very regular basis.


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Manual Metal Arc Welding Basic Equipment Requirements:

)

1)

Power source TransformerlRectifier. (Constant current type)

2)

Holding oven. (Temperature up to 200°C)

3)

Inverter power source.

4)

Electrode holder.

5)

Power cable.

6)

. Welding visor with correct filter glass rating.

7)

Power return cable.

8)

Electrodes.

9)

Electrode oven. (Bakes up to 350°C)

10)

Control panel. (Amperage & polarity)


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Variable Parameters: 1)

Voltage:

The Arc Voltage of the MMA welding process is measured as close to the arc as possible. It is variable only by changes in arc length. The OCV (Open Circuit Voltage) is the voltage required to initiate, or re-ignite the electric arc and will change with the type of electrode being used. Most basic coated electrodes require an OCV of 70 - 90 volts. Most rutile electrodes require only 50 volts. 2)

Current & Polarity:

The type and value of current used will be determined by the choice of electrode classification, electrode diameter, material type and thickness, and the welding position. Electrode polarity is generally determined by the operation i.e. surfacing/joining and the type of electrode, or electrode coating being used. Most surfacing and non-ferrous alloys require DC - for correct deposition, although there are exceptions to this rule. Electrode bum off rates will vary with AC or DC + or - depending on the coating type and the choice of polarity will also affect heat balance of the electric arc.

Important Inspection Points/Checks when MMA Welding: 1) The Welding Equipment:

A visual check should be made to ensure the welding equipment is in good condition.

The Electrode:

2) Checks should be made to ensure that the correct specification of electrode is being used,

that the electrode is of the correct diameter and that the flux coating is in good condition.

A check should be made to ensure that any basic coated electrode being used has been

pre-baked -to that specified in the welding procedure. A general pre-use treatment for

basic coated electrodes would typically be:

a) b) c)

Baked at 350°C for 1 hour. Held in holding ovens at 150 °C Issued to the welder in a heated quiver (Normally around 70°C)

Vacuum pack pre-baked electrodes do not need to undergo this pre-baking treatment.

If the vacuum seal appears be broken at the point of opening the carton, users should

follow the manufacturers advice and instructions to maintain the hydrogen level specified

on electrode cartons.

The date and time of opening must be recorded to enable re-baking as required.

Senior Welding Inspection - Manual Metal Arc Welding Copyright © 2002 TWl Ltd.

10.4

Rev 09-09-02

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C\\V.lD DI.l) ~U!Pla1\\ s~D l.lauI ualS~un.l 11

uon~as

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Tungsten Inert Gas Welding:

TIG welding was first developed in the USA during the 2 nd world war for welding aluminium alloys. As helium was used as the gas, the process was known as Heliarc.

Definitions: TIG:

Tungsten Inert Gas Welding. (UK)

GTAW:

Gas Tungsten Arc Welding. (USA)

Introduction: TIG welding is a process that requires a very high level of welder skill, which can be gauged in the degree of concentration of the welder shown in photograph 1 above. It is a process synonymous with high quality welds, as shown in application of the offshore powerboat repair in photograph 2. It is considered a comparatively slow process, but with the development of hot-wire TIG (Photograph 3) TIG welding may produce high quality welds with deposition rates higher than SAW. The arc may be struck by using a number of methods, but in cheaper equipment the arc is struck (Scratch start) in a similar way to MMA welding. This can easily cause contamination of the tungsten and weld metal and to avoid this high frequency arc ignition is often used in most equipment to initiate the arc, however high frequency may cause interference with hi-tech electrical equipment and computer systems. To overcome this, Lift arc has been developed where the electrode is touched onto the plate and is withdrawn slightly. An arc is produced with very low amperage, which is increased to full amperage as the electrode is extended to the normal arc length. In contrast with other arc processes, the filler wire is added directly into the-pool separately by the welder, which requires a very high level of hand dexterity and artisan craft skill. TIG is a far more complex process than MMA, with more variable parameters to adjust, and parts to check, and therefore more inspection points for the inspector to meet.

Senior Welding Inspection - Tungsten Inert Gas Welding Copyright © 2002 TWI Ltd.

11.1

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Tungsten Inert Gas Welding Basic Equipment Requirements:

\ )

~

1)

Power source. TransformerlRectifier (Constant Amperage type)

2)


3)

Power control panel.

4)

Power cable hose.

5)

Flow-meter.

6)

Tungsten electrodes.

7)

Torch assemblies.

8)

Power return cable.

9)

Power Control panel. (Amperage & polarity)


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The TIC Torch Head Assembly:

1\

1)

Tungsten electrodes.

2)

Spare ceramic shield.

3)

Gas lens.

4)

Torch body.

5)

Spare ceramic shield.

6)

Gas diffuser.

7)

Split copper collett. (For securing the tungsten electrode)

8)

On/off or latching switch.

9)

Tungsten housing.


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Variable Parameters: t) Voltage: The voltage of the TrG welding process is variable only by the type of gas being used, and changes in arc length as in MMA.

2) . Current & Polarity:

The current is adjusted proportionally to the diameter of the tungsten being used. The

higher the level of the current, then the higher is the level of penetration and fusion that is

obtained.

The polarity used for steels is always DC -ve as most of the heat is concentrated at the +

pole in TIG welding. This is required to keep the tungsten as cool as possible during

welding. AC is used when welding aluminium and its alloys.

i~

3) Tungsten type and vertex angle: The tungsten diameter, type of tungsten, and vertex angle, are all critical factors considered as essential variables of a welding procedure. The most common types of tungsten used are thoriated or ceriated for DC and zirconiated with AC (aluminium alloys) The vertex angle is measured as shown below: Too fine an angle will promote melting of the tungsten tip

The tungsten vertex angle

e When welding aluminium alloys with AC, the tungsten end is chamfered, and forms a ball end during welding.

4) Gas type and flow rate:

Generally 2 types of pure gases are used for TIG welding; namely argon and helium,

though nitrogen is sometimes added for welding copper and hydrogen additions may be

made for austenitic stainless steels (increasing welding speed). The gas flow rate is a

further essential variable of the welding procedure. This will change on joint type and

welding position.

TIG gases are produced in purity of 99.99% and though argon is cheaper than helium

and has higher density than air, it has low ionisation potential, giving relatively shallow

penetration. Helium is more expensive than argon and has a lower density than argon

and air, and higher ionisation potential, giving higher penetration and a hotter arc. This

means practically that the flow rate of helium must be increased in the down-hand

position, and argon increased in the overhead position, for a similar joint design in order

to maintain adequate gas cover of the weld zone. We sometimes mix argon and helium

gases to combine the useful features of each gas i.e. gas cover and penetration.

Senior Welding Inspection - Turigsten Inert Gas Welding Copyright © 2002 TWI Ltd.

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5) Slope in and slope out: Slope in and slope out are variables available on some TIO welding equipments, which can regulate the current climb and decay. This is very beneficial in avoiding crater pipes at the end of weld runs. The slope in and slope out control may be shown 011 the equipment as below:

~Slopeout

Slope in /

During welding it is used to control the rise and decay of the current at the start and end of a weld as shown below:

weldFiniSh~~~ Weld Start (Slope out) (Slope In) 6) Gas cut off delay: The gas cut off delay control delays the gas solenoid shut off time at the end of the weld, and is used to give continued shielding of the solidifying and cooling weld metal at the end of a run. It is often used when welding materials that oxidise at high temperatures such as stainless and titanium alloys. It may be shown on the welding equipment as follows: Gas delay

C) Seconds

7) Pulsed TIG welding variables: The pulse parameters of pulsed TIG are generally adjustable as follows: a) b)

Pulse background current. Pulse duration.

Senior We[ding Inspection - Tungs ten Inert Gas Welding Copyright © 2002 TWI Ltd.

c) d)

11.5

Pulse peak current. Pulse frequency.

Rev 09-09-02

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Important lnspection Points/Checks when TlG Welding: 1) The "Velding Equipment:


2) The Torch Head Assembly:

Check the diameter and specification of the tungsten, the required vertex angle has been

correctly ground, and that a gas lens has been fitted. Check the tungsten protrudes the

correct length from the ceramic, the ceramic is the correct type, and is in good condition.

Gas type and flow rate:

3) Check the correct gas, or gas mixture is being used and the flow rate is correct for the

given joint design and position as stated on the approved welding procedure.

\

)

Current & Polarity:

4) Checks should be made to ensure that the type of current and polarity are correctly set,

and that the current range is within that given on the procedure. These values will be

controlled by, the material type, thickness, and diameter and type of tungsten being used.

5) Other Variable Welding Parameters:

Checks should be made for correct angle of torch, arc gap distance, speed of travel and all

other essential variables of the process given on the approved welding procedure.

In mechanised welding checks will need to be made on the speed of the carriage

mechanism and the speed of the filler wire. Additionally when welding reactive materials

checks will need to be made on purging, or backing gas type and pressures.

Safety Checks:

6) Checks should be made on the current carrying capacity, or duty cycle of equipment, and

that all electrical insulation is sound. Correct extraction systems should be in use to avoid

exposure to ozone and other toxic fumes.

~

A Check should always be made to ensure that the welder is qualified to weld the

procedure being employed.

Typical Welding Imperfections: 1) Tungsten inclusions, caused by a lack of welder skill, too high current setting, and/or incorrect vertex angle. 2) Surface porosity, caused by a loss of gas shield particularly when site. welding, or incorrect gas flow rate for the joint design and/or welding position. 3) Crater pipes, caused by poor weld finish technique, or incorrect use of current decay. 4) Weld/root oxidation if using insufficient gas cut-off delay, or purge pressure when welding stainless steels or titanium alloys.


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Summary ofTIG/GTAW: Equipment requirements: 1) 2) 3) 4) 5) 6) 7) 8)

A Transformer/Rectifier. (Constant amperage type)

A power and power return cable.

An inert shielding gas. (Argon or Helium)

Gas hose, flow meter, & gas regulator.

TIG torch head with ground tungsten, collets, and ceramics.

Method of arc ignition. (High frequency, lift arc, or scratch start.)

Correct visor/glass, all safety clothing and good extraction.

Optional filler metal in rod form, to correct specification.

Parameters & Inspection Points: 1) 3) 5) 7) 9) 11)

Amperage. AC/DC & Polarity. Tungsten type & diameter. Tungsten vertex angle. Gas type & flow rate. Ceramic condition, size and type.

2) 4) 6) 8) 10) 12)

Arc voltage.

Speed of travel.

Duty cycles.

Connections.

Insulation/extraction.

Gas lens.

2) 4)

Surface porosity.

Weld/root oxidation.

Typical Welding Imperfections: 1) 3)

Tungsten Inclusions. Crater pipes.

Advantages & Disadvantages: Advantages: 1) 2) 3) 4) 5)

Disadvantages:

High quality. Good control. All positional. Lowest Hz arc welding process. Low inter run cleaning.


1) 2) 3) 4) 5)

11.7

High skill factor required. Small range of consumables. Protection for site work. Low productivity (o/f). High ozone levels.

Rev 09-09-02

TWI V!lOI.

_


Questions

TIG Welding Process

au 1.

Give three reasons for the occurrence of tungsten inclusions.

au 2.

State the essential welding parameters of the TIG welding process

au 3.

Which electrode polarity is considered essential for the welding of carbon steels? And give a brief description why

aU4.

Which electrode polarity is considered essential for the welding of aluminum? And give a brief description why.

au 5

State the tungsten electrode activators required for the welding of carbon steels and the light alloys

au 6.

Give the main advantages and disadvantages of the TIG welding process

(i

Senior Welding Inspection - QU Tungsten Inert Gas Arc Welding Sec II Copyright © 2003 TWI Ltd

\

(MVWD DVW/DIW) ~U!PlaM SBD aAnJV/l.lauI l~law ZI UOnJas

()

TWI V[JI.

_


Arc Characteristic for MIG & SAW: In MIG/MAG & SAW welding we require different welding equipment than used

for MMA & TIG, as the arc length is controlled by voltage.

To achieve this we require a Constant Voltage (Flat) characteristic power source.

Constant Voltage (Flat) Characteristic .~

OCV

Large arc ga

)

Normal arc gap

A~

,,.

Small arc gapI

.....

~

......

l1li"'"

Arc Voltage

(

\

....

Welding Amperage Small change in voltage = Much larger change in amperage. i.e. 2 volts = 100 amps

When pre-calculating the welding arc voltage from the OCV setting it is considered that 1-2 Open Circuit Volts are lost for every 100 amps of welding current being used.

Senior Welding Inspection - Metal Inert/Active Gas Weldingl2.1 Copyright © 2002 TWI Ltd.

Rev 09-09-02

.

TWI V!lOI.

_


Metal Inert Gas Welding:

(

) MIG welding was initially developed in the USA in the late 40's for the welding of aluminium alloys structures, using argon, or helium gas shielding.

Definitio ns: MIG: Metal Inert Gas (Using an inert shielding gas i.e. argon or helium) MAG: Metal Active Gas (Using active gases i.e. pure CO2, Ar/C0 2 or Ar/0 2 mixtures) GMAW: Gas Metal Arc Welding (Used to describe the MIG/MAG process in USA) FCAW: Flux Cored Arc Welding (Used to describe the flux cored arc process in USA)

Introduction: The basic equipment requirements of MIG/MAG welding differ from MMA and TIG as a different type of power source characteristic is required and a continuous wire (from a spool) is supplied at the welding torch head automatically. The shielding gas is supplied externally from a separate cylinder. A separate wire feed unit, or internal wire drive mechanism is also required to drive the wire electrode. The arc is struck by short circuit of the wire on contact with the work piece, as it is driven by the drive rolls through the liner, and then out through the contact tip. The type of metal transfer that occurs is entirely dependant on gas type being used and amperage/WFS and voltages set. As the electric arc length is controlled by the power source the process is classified as a semi automatic welding process, which may be used manually, fully automated by robotics, or can be simply mechanised by using tracking and/or weaving system. Photograph 1 and 2 show the basic process components and photograph 3 shows simple mechanisation in the overhead position.

Senior Welding Inspection - Metal Inert/Active Gas Weldingt 2.2 Copyright © 2002 TWI Ltd.

Rev 09-09-02

TWI

V!lOI.

_

THE WELDIt\IG 1t\ISTITUTE

Metal Inert Gas Welding

Basic Equipment Requirements:

1)

Power source. TransformerlRectifier (Constant Voltage type)

2)


3)

Power hose assembly. (Liner. Power cable. Water hose. Gas hose)

4)

Liner.

5)

Spare contact tips.

6)

Torch head assembly.

7)

Power-return cable & clamp.

8)

15kg wire spool. (Copper coated & uncoated wires)

9)

Power con trol panel.

10)

External wire feed unit.:

Senior Welding Inspection - Metal Inert/Active Gas Welding 2.3 Copyright © 2002 TWI Ltd.

(

Rev 09-09-02

TWI

V!7!lI.

_


The lVIIG/lVIAG Wire Drive Assembly 1) An internal wire drive system

2) Half groove bottom drive roller.

Senior Welding Inspection - Metal Inert! Active Gas Welding! 2.4 Copyright © 2002 TWI Ltd.

3) Wire guide.

Rev 09-09-02

TWI

17001.

_


The lVnG Torch Head Assembly

I.

1)

Torch body.

2)

Onloff or latching switch.

3)

Spot welding spacer attachment.

4)

Contact tips.

5)

Gas diffuser.

6)

Spare shrouds.

7)

Torch head assembly. (Less the shroud)

Senior Welding Inspection - Metal Inert/Active Gas Weldinl?l2.5 Copyright © 2002 TWI Ltd.

Rev 09-09-02

)

TWI VOI.

_


Immediately on pressing the torch on/off (latching) switch, the following occurs:

a) b) c) d)

The The The The

gas solenoid opens and delivers the shielding gas. wire begins to be driven from the reel and through the contact tip. contactor closes and delivers current to the contact tip. water pump circulates the cooling water. (If required)

Types of Metal Transfer: 1) Dip Transfer:

In dip transfer the wire short-circuits the arc between 50 - 200 times/second. This type of

transfer is normally achieved with CO 2 or mixtures of C02 & argon gas + low amps &

welding volts < 24 volts. Dip transfer is all positional, but with a low deposition rate,

penetration and fusion. This is because of the time when the arc is extinguished and only

resistance heating takes place. It is mainly used for thin sheet steel < 3mm(and may also

be used for positional welding in thicker section). The weld metal is deposited during the

short circuit part of the welding cycle.

2) Spray Transfer:

In spray transfer a continuous electric arc and spray metal transfer is produced. This is

usually achieved with pure argon, or argon CO 2 mixtures and higher amps & volts> 24

volts. With steels it can be used only in down-hand butts and H/V fillet welds, but gives

higher deposition rate, penetration and fusion than dip transfer because of the continuous

arc heating. It is mainly used for plate steel > 3mm but may be have limited use for

positional welding due to the potential large weld pool involved.

\.

3) Pulsed Transfer:

Pulse transfer uses pulses of current to fire a single globule of metal across the arc gap at

a frequency between 50 -300 Pulses/second. Pulse transfer is a development of spray

transfer, that gives positional welding capability for steels, combined with controlled heat

input, good fusion, and high productivity. It may be used for all sheet steel thickness>

1mm, but is mainly used for positional welding of steels> 6mm.

As all the parameters require extremely fine adjustment synergic equipment is normally

used for pulse transfer.

4) Synergic Pulsed Transfer:

Synergic MIG/MAG was developed in the 1980's and uses microprocessor control to

adjust the parameters of the electric arc, in maintaining an optimum conditions for a

selection of wire type & diameter, material and gas. The microprocessor control will

change all other pulse parameters automatically and immediately, for any change in WFS

(Wire feed speed). Equipment may also be used for standard dip, spray and globular

transfer.

5) Globular Transfer:

Globular transfer occurs between dip & spray, but is not normally used for solid wire

MIG-MAG welding, but is sometimes used in FCAW. (Flux cored arc welding)

Senior Welding Inspection- Metal Inert/Active Gas Weldingt2.6 Copyright © 2002 TWI Ltd.

Rev 09-09-02

TWI 1l701.

_


Variable Parameters: 1) Wire Feed Speed:

Increasing the wire feed speed automatically increases the current in the wire.

Wires are generally produced in 0.6/0.8/1.0/1.2/1.4 & 1.6 mm diameter.

Voltage:

2) The voltage setting is the most important setting in spray transfer as it controls the arc

length. In dip transfer it also effects the rise of current and the overall heat input into the

weld. An increase of both WFS/current and voltage will increase heat input. The welding

connections need to be checked for soundness, as any slack connections will give a hot

junction where voltage will be lost from the circuit and will affect the characteristic of the

welding arc greatly. The voltage will affect the type of transfer achievable, but this is also

highly dependant on the type of gas being used.

Gases:

3) C02 gas cannot sustain spray transfer, as the Ionisation Potential of the gas is too high.

Because of this high ionisation potential it gives very good penetration, but also a very

unstable arc and lots of spatter. Argon has a much lower Ionisation potential and can

sustain spray transfer above 24 welding volts. Argon gives a very stable arc and little

spatter, but lower penetration than CO 2 • We mix both argon and CO 2 gas in mixtures of

between 5 - 20% CO 2 in argon to get the benefit of both gases i.e. good penetration with

a stable arc and very little spatter. CO 2 gas is much cheaper than argon or its mixtures.

4) Inductance:

Inductance causes a backpressure of voltage to occur in the wire and operates only when

there is a changing current value. In dip transfer welding the current rises as the electrode

short circuits -on the plate and it is then that the inductance resists the rapid rate of rise of

current at the tip ofthe electrode. This has a main effect of reducing the level of spatter.

Important Inspection Points/Checks when MIG/MAG Welding: 1) The Welding Equipment:


The Electrode Wire

2) The diameter, specification and the quality of the wire are the main inspection headings.

The level of de-oxidation of the wire is an important factor with Single, Double & Triple

de-oxidized wires being available. The quality of the wire winding is also important.

The higher the level of de-oxidants in the wire, then the lower is the chance of occurrence

of porosity in the weld. The quality of the copper coating, and the quality of the wire

temper and winding are also important factors in minimizing wire feed problems.

Quality of wire windings aud increasing costs (a) Random wound. (b) Layer wound.c) Precision layer woun

Senior Welding Inspection - Metal Inert!Active Gas Welding),2.7 Copyright © 2002 TWI Ltd.

Rev 09-09-02

TWI VllOI.

_


3) The Drive Rolls and Liner.

Check the drive rolls are of the correct size for the wire and that the pressure is only hand

tight, or just sufficient to drive the wire. Any excess pressure will deform the wire to an

ovular shape. This will make the wire very difficult to drive through the liner and result in

arcing in the contact tip and excessive wear of the contact tip and liner. .

Check that the liner is the correct type and size for the wire. A size of liner will generally

fit 2 sizes of wire i.e. (0.6 & 0.8) (1.0 & 1.2) (1.4 & 1.6) mm diameter. Steel liners are

used for steel wires and Teflon liners for aluminium wires.

\)

The Contact Tip.

4) Check that the contact tip is the correct size for the wire being driven, and check the

amount of wear frequently. Any loss of contact between the wire and contact tip will

reduce the efficiency of current pick. Most steel wires are copper coated to maximise the

transfer of current by contact between 2 copper surfaces at the contact tip, this also

inhibits corrosion. The contact tip should be replaced regularly.

The Connections.

5) The length of the electric arc in MIG/MAG welding is controlled by the voltage settings.

This is achieved by using a constant voltage volt/amp characteristic inside the equipment.

Any poor connection in the welding circuit will affect the nature and stability of the

electric are, and is thus is a major inspection point.

6) Gas & Gas Flow Rate.

The type of gas used is extremely important to MIG/MAG welding, as is the flow rate

from the cylinder, which must be adequate to give good coverage over the solidifying and

molten metal to avoid oxidation and porosity.

Other Variable Welding Parameters.

7) Checks should be made for correct WFS, Voltage, Speed of travel, and all other essential

variables of the process given on the approved welding procedure.

~

8) Safety Checks:

Checks should be made on the current carrying capacity, or duty cycle of equipment and

electrical insulation. Correct extraction systems should be in use to avoid exposure to

ozone and fumes.

A check should always be made to ensure that the welder is qualified to weld the

procedure being employed.

Typical Welding Imperfections: 1) 2) 3) 4)

Silica inclusions, (on ferritic steels only) caused by poor inter-run cleaning. Lack of sidewall fusion during dip transfer welding thick section vertically down. Porosity caused from loss of gas shield and low tolerance to contaminants Burn through from using the incorrect metal transfer mode on sheet metal.

Senior Welding Inspection - Metal Inert! Active Gas Welding! 2. 8 Copyright © 2002 TWI Ltd.

Rev 09-09-02

TWI

V!lOI.

_


Advantages of Flux Cored Arc Welding: In the mid 80's the development of self-shielded and dual-shielded FCAW was a major step in the successful application of on-site semi automatic welding, and has also enabled a much wider range of materials to be welded. The wire consists of a metal sheath containing a granular flux. This flux can contain elements that would normally be used in MMA electrodes and so the process has a very wide range of applications. In addition we can also add gas producing elements and compounds to the flux and so the process can become independent of a separate gas shield, which restricted the use of conventional MIG/MAG welding in many field applications. "Dual Shield" wires obtain their gas shielding from a combination of flux and separate shielding gas. Most wires are sealed mechanically and hermetically with various forms of joint. The effectiveness of the joint of the wire is an inspection point of cored wire welding, particularly with wires containing basic fluxes, as moisture can easily be.' absorbed into a damaged or poor seam. It is the accepted practise when using basic wires that the first few meters of wire from

the reel is stripped off and discarded as moisture can be absorbed up the length of the wire through the core of flux if incorrectly stored. Baking of cored wires is ineffective and will do nothing to restore the condition of a contaminated flux within a wire. A major advantage of fluxed cored wires is that they produce extremely good penetration.

This is caused by the amount of current density in the wire, or in other words the amount

of current carried in the available CSA of the conductor.

This area is very small in flux-cored wires, in comparison with other welding processes. ( .

MMA 3.25 mm (2) @125 Amps

Solid MIG Wire

Flux Cored Wires

e @180 Amps

2.0mm (} @180 Amps

1.2 mm

~

Wire sheath . carrying current

~

Flux core centre

-----------~

Increasing Current Density & Penetration Power Senior Welding Inspection - Metal Inert!Active Gas Welding}, 2.9 Copyright © 2002 TW[ Ltd.

Rev 09-09-02

TWI V!l!ll.'

_


Summarv of Solid wu- NIlG/MAG GyIA "V: Equipment requirements: I) 2) 3) 4) S) 6) 7) 8)

()

A Transformer/Rectifier. (Constant voltage type)


An Inert, active, or mixed shielding gas. (Argon or C02)

Gas hose, flow meter, & gas regulator.

MIG torch with hose, liner, diffuser, contact tip & nozzle.

Wire feed unit with correct drive rolls.

Electrode wire to correct specification and diameter.

Correct visor/glass, all safety clothing and good extraction.

Parameters & Inspection Points: I) 3) 5) 7) 9) l l)

WFS/Amperage. Wire type & diameter. Contact tip size and condition. Liner size. Insulation/extraction. Duty cycles.

2) 4) 6) 8) 10) 12)

OCV & Welding voltage. Gas type & flow rate. Roller type, size and pressure. Inductance settings. Connections. (Voltage drops) Travel speed, direction & angles.

2) 4)

Lack of fusion. (Mainly dip transfer) Bum through (Using spray for sheet)

Typical Welding Imperfections: 1)

Silica inclusions.

3)

SurfacePorosity.

Advantages & Disadvantages: \

.

Advantages:

Disadvantages:

1) 2) 3) 4) 5)

1) 2) 3) 4) 5)

High productivity (o/f). Easily automated. All positional. (Dip & Pulse) Material thickness range. Continuous electrode.

Senior Welding Inspection - Metal Inert! Active Gas Weldingt2.1 0 Copyright © 2002 TWI Ltd.

Lack of fusion. (Dip Transfer) Small range of consumables. Protection for site working. Complex equipment. High ozone levels.

Rev 09-09-02

TWI V!701.

_


Questions MIG/MAG Welding Process

QU1.

State the possible problems, which may occur when using the dip transfer mode in the MAG welding process

QU2.

State the application areas for the spray transfer mode when using the MAG welding process

QU3.

What power source characteristic is considered essential for a semi automatic welding process and state the current type and electrode polarity

(, ') QU4.

QU5.

State the main variables for the MAG welding process

State the advantages and disadvantages of the MAG welding process when compared to the MMA welding process

Senior Welding Inspection - Qll Metal Active Gas Sec 12 Copyright © 2003 TWI Ltd

)

C\\.vs: ~n!PlaM. JJV pa~Jamqns

£1 nOnJas

TWI

1ll01.

_


Submerged Arc Welding:

SAW or Submerged arc welding was developed in the Soviet Union during the 2nd world war as an economical means of welding thick steel sections.

Definitions: SAW: Submerged Arc \Velding. (UK & USA)

Introduction:

This welding process is normally mechanised and uses a constant voltage power source,

as it is the voltage that controls the arc length. Amperages can range from 100 up to and

over 2,000 amps, which gives very high current density in the wire and deep penetration

and dilution into the base metal.

The arc is struck in the same manner as MIG, which is generally aided by the linear

movement of the electrode tip across the surface of the run on tab, though H/F arc

striking is also possible on some equipment. As its name suggests the arc is submerged

beneath a covering of flux, which is of a granular nature. A flux delivery system must be incorporated into the equipment, which may also be

accompanied by a flux recovery system. It is restricted in position and is generally used

for thickness of over 10mm. Run-on and run-off tabs are normally used on welded

seams, as this allows the welding arc to settle to its required conditions prior to the

commencement of the actual welding seam. The run off plate allows a similar set of

conditions to occur at the end of the weld. Both run-on and run-off tabs are removed after

the weld seam has been completed. The arc is normally formed as the point of the wire

comes into moving contact with the plate. The flux blanket protects 'the arc from

atmosphere and decomposes in the heat of the arc adding alloying elements and de

oxidants to the molten weld metal. The flux also provides a slag, which forms a

protective barrier to the cooling weld in a similar manner to MMA.

Photographs 1 and 2 show a stationary SAW head with rotated pipe, and photograph 3

shows a mobile tractor/carriage assembly, which may be used for welding deck plates.

Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TW[ Ltd '

13.1

Rev 09-09-02

(~

TWI V!JI.

_


Submerged Arc Welding

Basic Equipment Requirements:

'I

1)

Welding carriage control panel.

-'!o

',",,_,i

2)

Welding carriage assembly.

3)

Reel of wire.

4)

Granulated flux.

5)

Transformer rectifier.

6)

Power source control panel.

7)

Power return cable.

8)

Flux hopper.

Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TWI Ltd

13.2

Rev 09-09-02

TWI

V!lOI.

_


Immediately on pressing the switch, the following occurs: a) b) c) d)

The flux is released forming a layer beneath the torch head. The wire begins to feed and strikes the arc. The contactor closes and delivers current to the contact tip. The tractor begins to move. (If mechanised)

Because of the nature of the granular flux, the use of Submerged Arc Welding for positional welding has been restricted to the flat position. However the process has been continually developed and is now capable of certain degree of positional welding, with an addition of some simple extra equipment (i.e. flux dams). Submerged arc welding has many applications, but certain limitations exist other than the positional capability of the process, as with the restriction of full penetration welds from one side without the use of a backing bar or backing strip. One of the most popular applications for SAW is in the welding of "Spirally welded pipe" where a fixed unit is stationed inside the pipe to weld the internal seam with an additional fixed unit placed on the top of the pipe for the outer seam. Full penetration welding takes place as the pipe is spiralled through. Other factors that may need to be taken into consideration are the toughness requirements of the joint, as the arc energy input is comparatively high. Arc blow can also be a major problem as its occurrence due to magnetic field is proportional to the current used and in SAW currents of over 1,500 amps are not uncommon. Arc blow can be minimised by the use of tandem wire systems with the leading wire on DC+ and the trailing wire on AC producing opposing magnetic fields. The use of double, or multi run techniques also has effects on the properties of the weld metal and HAZ. Multi run techniques tends to normalise previous weld deposits and HAZ, giving 'superior properties, The resultant SAW weld metal is difficult to predict, as the weld is made up from 3 elements. A typical set of values is given below, but this can change dramatically with any changes in the welding parameters: 1)

The Electrode. (25%)

.~~\~~t\~:t:~~-J.~~~4,)f::;hl~~;:~£~:!U~~t~~1r.~.;-~'n~~1~:1:~':.:·.;"~~~%t::';:· _ ~

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I I';~

SAW Weld Metal Analysis

~:~~ - ~-

/~

2)

3)

1 1

~

Elements in the flux. (15%)

I ~~ :.

. Dilution. (60%) •.•. ;..

__.

. ..••. '.<;":

The proportion of these elements in the final weld deposit will vary depending on the welding parameters set and a variation in arc voltage will change the arc length and thus affect the amount of flux being melted and overall % of alloying elements in the final weld.


13.3

Rev 09-09-02

TWI VOI.

_


Variable Parameters: 1) Wire Feed Speed:

Increasing the wire feed speed automatically increases the current in the wire. The

density of the current in the wire is dependant on the cross section area of the wire. The

higher the density of the current, then the higher is the level of penetration and fusion that

is obtained.

2) Voltage:

The voltage setting is a critical variable in SAW affecting the bead shape and penetration

profile and is an essential variable of a SAW welding procedure. It also governs arc

length beneath the flux layer and any changes in arc length will radically alter weld metal

composition due to more or less elements from the flux being alloyed in the weld metal.

) 3) Electrode stick out:

This variable parameter is adjusted by adjusting the distance of the welding head

assembly from the work surface. It will affect the arc amperage, as power will be

consumed in the resistance heating of the wire from the tip of the contact tip to the end of

the wire. The electrode stick out dimension should be given on the approved welding

procedure specification sheet.

4) Flux depth:

The flux depth is controlled by the flux feed rate and the distance from the feeding head

to the work surface. The flux depth needs to be sufficiently high to cover the arc.

5) Travel Speed:

As SAW is most often a mechanised process the travel speed can be considered as an

important variable parameter affecting penetration and bead profile.

\

The correct travel speed for the joint should be given on the approved welding procedure

specification sheet.

Important Inspection Points/Checks when Submerged Arc Welding: 1) The Welding Equipment:


2) The Welding Head Assembly & Flux Delivery System: Checks should be made that the diameter, specification of the electrode wire and the specification and mesh size of flux being used is correct to the approved WPS. Checks should also be made to ensure the wire drive system has correct rollers diameter and that the flux delivery system is operational. A check should be made that the electrode stick out dimension is correct, and if using run on and run off plates that these are fitted and tacked in place correctly. Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TWI Ltd

13.4

Rev 09-09-02

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V!lOI.

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3) Current & Polarity: Checks should be made to ensure that the type 0 f current bei ng used is correct and i CDC that the polarity is COlTect and that the current range is within that given on the procedure. Multi wire welding may use both types of current i.e. DC + leading wire with an AC trailing wire as this improves welding times and offsets the effects of "arc blow" If using multi wire process the angle of the trailing wire must also be checked. All parameters should be given on the approved WPS. 4) Other Variable Welding Parameters: Other procedural parameters may include the use of backing bar or backing strips particularly when welding from a single side. In addition to the inspection points mentioned previously checks should also be made to ensure that arc voltage and speed of travel are within the acceptable limits. All these parameters should be given on the WPS.

A typical single sided weld preparation for SAW could look like this:

40-50

A broad root face with no root gap

0

A permanently" welded backing bar.

5) Safety Checks:

Checks should be made on the current carrying capacity, or duty cycle of equipment, and

that all electrical insulation is sound. Correct extraction systems should be in use to avoid

exposure to toxic fumes.

Typical Welding Imperfections: 1) 2) 3) 4)

Porosity from the use of damp welding fluxes or improperly cleaned plates. Centreline cracks caused by high dilution and sulphur pick up or deep and narrow welds (Le. depth/width ratio of>3/2)

Sb.rinkage cavities caused by a weld depth/ratio of > 3/2

Lack of fusion caused by the effects of arc blow.

Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TWI Ltd "

13.5

Rev 09-09-02

TWI V!lOI.

_

THE

WELDI~IG

INSTITUTE

Summary of Sub Arc \Velding: Equipment requirements: 1) 2) 3) 4) 5) 6) 7) 8)

IJ

A Transformer/Rectifier. (Constant voltage type)


A torch head assembly.

A granulated flux of the correct type/specification and mesh size.

A flux delivery system.

A flux recovery system.

Electrode wire to correct specification and diameter.

Correct safety clothing and good extraction.

Parameters & Inspection Points: 1) AC/DC WFS/Amperage. 3) Flux type and mesh size. 5) Electrode wire and condition. 7) Flux delivery/recovery system. 9) Insulation/duty cycles. 11) Contact tip size/condition.

10) 12)

OCV & Welding Voltage.

Flux condition. (Baking etc.)

Wire specification.

Electrode stick-out.

Connections.

Speed of travel.

2) 4)

Solidification, or centreline cracks. Porosity.

2) 4) 6) 8)

Typical Welding Imperfections: 1)

3)

Lack of fusion. Shrinkage cavities.

Advantages & Disadvantages: (

Advantages:

Disadvantages:

1) 2) 3) 4) 5)

1)

Low weld-metal costs. Easily mechanised. Low levels of ozone production. High productivity (o/t). No visible arc light.


2) 3) 4)

5)

13.6

Restricted in positional welding. High probability of arc-blow. (DC+/-) Prone to shrinkage cavities. Difficult penetration control. Variable compositions. (Arc length)

Rev 09-09-02

TWI V!7[JI.

_


Questions Submerged Arc Welding Process

QU1.

State the possible problems when using damp and contaminated fluxes in the SAW welding process.

QU2.

State the two flux types used in the SAW welding process.

QU3.

Generally what power source characteristic is required for the SAW welding process?

QU4.

State three main items of SAW fluxes, which require inspection

QU5.

State the advantages and disadvantages of the SAW welding process

Senior Welding Inspection - QU Submerged Arc Welding Process Sec 13 Copyright © 2003 TWI Ltd

(

M VS ~ DVW/DIW DIL VWlt\1.10J sojqaumsuo.j ~u!PIaM

171 u0!l;,as

TWI V!lOI.

_


Welding Consumables: Welding consumables are defined as all those things that are used up in the production a weld.

0

t'

This list could include many things including electrical energy, however we normally refer to welding consumables as those things used up by a particular welding process.

These are namely: wires

Electrodes

Fluxes

Gases

~

'J.;~

~: ~,,:

~

'1

I; .

. . S"A'U'1' .

i,'

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.::FVStP: .

. 'Fl' .. ,\,;.,.. , ... , llX.'

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:.; ;:::

_

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I.......

U',l

./'

When inspecting welding consumables arriving at site, it is important that they are inspected for the following:

1) 2) 3)

Size.

Type or Specification.

Condition.

Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

14.1

Rev 09-09-02

TWI V!lOI.

_


Consumables for 1VIMA Welding: Welding consumable for MMA consist of a core wire typically between 350 and 450m01 length and from 2.5 - 6mm diameter. Other lengths and diameters are also available. The wire is covered with an extruded flux coating. The core wire is generally of low quality steel (Rimming Steel) as the weld can be considered as a casting, and therefore the weld can be refined by the addition of cleaning, or refining agents in the flux coating. The flux coating contains many elements and compounds that all have a variety of jobs during welding. Silicon is mainly added as a de-oxidising agent (in the form of Ferro silicate), which removes oxygen from the weld metal by forming the oxide Silica. Manganese additions of up 1.6% will improve the strength and toughness of steel. Other metallic and non-metallic compounds are added that have many functions, some of which are as follows:

1) 2) 3) 4) 5) 6) 7) 8)

To aid arc ignition. To improve arc stabilisation. To produce a shielding gas to protect the arc column. To refine and clean the solidifying weld-metal. To form a slag which protects the solidifying weld-metal. To add alloying elements. To control hydrogen content of the weld metal. To form a cone at the end of the electrode, which directs the arc.

Electrodes for MMAJSMAW are grouped depending on the main constituent in their flux coating, which in turn has a major effect on the weld properties and ease of use. The common groups, are given below:

Group

Constituent

Titania Rutile Calcium compounds Basic Cellulose Cellulosic


Shield gas

Uses

AWS AS.1

CO 2 CO 2 Hydrogen + CO

General purpose High quality Pipe root runs

E 6013 E 7018 E 6010

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A Typical BS 639 Specification: Reference given in box letter:

E 51 A)

A) Tensile strength:

Symbol

Min Yield Strength 2 N/mm

I

B 160

B)

C)

2 0 H

E) F) G)

D)

--

B) Toughness:

Tensile Strength

Nzmrrr'

3

Flat Butt & Fillets + HV Fillets.

4 5

Flat Butt & Fillets Vertical Down + positions of symbol 3 Any position not classified by the above.

First Digit 28 J 0 1 2 3 4 5

I

430-550 330 43 380 510-650

51 C) Covering types:

B Basic

BB Basic High Efficiency

C Cellulosic

0 Oxidising

R Rutile Medium Coated RR Rutile Heavy Coated

S Other Types

E) Welding position:

Position

Symbol

All positions

1

All positions except 2

Vertical Down

9

33


Second Digit 47 J

Testing Temperature Not specified +20 0 -20 -30 -40

0

1 2 3 4 5

[ D) Electrode Efficiency: l % Recovery to ~he nearest 10% (> = 110)

I

)

F) Electrical characteristic:

Symbol 0 1 2

3 4 5 6 7 8 9

I

DC Polarity Polarity as recommended + or -

+ + or + + or +

AC Min OCV Not recommended 500CV 500CV 500CV 700CV 700CV 700CV 900CV 900CV 900CV

G) Hy'~rogen Control: H Indicates Low Hydrogen Potential

'I

(


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A Typical Electrode Specification to BSEn 499

(

".

A Typical Electrode Specification to AWS A 5.1

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A Typical BSEn 499 Specification: Reference given in box letter:

E 46 3 INi B

35 38 42 46 SO

Min Yield Strength

Nzmrrr' 355 380 420 460 500

Tensile Strength N/rnm2

E%

440-570 470-600 500-640 530-680 560-720

22 20 20 20 18

5 4

HS

A) B) C) D) E) F) G)

A) Tensile strength: Symbol


B) Toughness at minimum impact energy 47 Joules: No requirement Z

Min

+20 0 -20 -30

A 0

2 3

-40

4 5

-50 -60

6

C) Alloying: (Deposited weld chemical composition) Mn Mo Symbol Ni 2.0 None 0.3-0.6 104 Mo >104-2.0 0.3-0.6 MoMo 104 0.6-1.2 INi 104 1.8-2.6 2Ni 104 >2.6-3.8 3NI 0.6-1.2 Mo INi >104-2.0 0.3-0.6 0.6-1.2 104 INiMo Any other agreed Z composition

D) Covering types: A Acid C Cellulosic R Rutile RR Rutile thick covering RC Rutile/Cellulosic RA Rutile/Acid RB Rutile/Basic B Basic

F) Welding position:

E) Electrical characteristic + recovery % Current type Symbol Recovery % ac +"dc < 105 1 < 105 dc

2 > 105 < 125 ac +dc 3

> 105 < 125 dc

4 > 125 < 160 ac+ de 5

> 125 < 160 dc

6 > 160 ac+dc 7

> 160 dc 8

Symbol I 2

G) Hydrogen Content of deposited weld metal: Max H2 Content Symbol ml/100mgm 5 H5 10 HIO 15 HIS

Position All positions All positions except Vertical Down

3

Flat Butt & Fillets + HV Fillets.

4 5

Flat Butt & Fillets Vertical Down + positions of symbol 3

The strength, toughness, coating of BS 639 plus any light alloying elements of BS EN 499 (If applicable) are the mandatory elements of information that shall be shown on all electrodes. All other information is normally given on the electrode carton.


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Inspection Points for MlVIA Consurnables 1: Size:

Wire Diameter & length. ~

-E

(j"~ ,:, , ' ' -'-~ ~'-i,$_: .•, .~:_.:·,!,#:. !".;: :·.:~.. ~,~.!!, :!,i.::{C~,.~ k .t~ . .;f,t;~_ ;.! _;; ,~~:;it r,.' ,

2: Condition:

Cracks, chips & concentricity.

)

3: Type (Specification):

Correct specification/code.

f@~::?jh?.,.":

";:~

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Checks should also be made to ensure that basic electrodes have been through the correct pre-use procedure. Having been baked to the correct temperature (typically 300 350°C) for 1 hour and then held in a holding oven at 150°C before being issued to the welders in heated quivers. Most electrode flux coatings will deteriorate rapidly when damp and care should be taken to inspect storage facilities to ensure that they are adequately dry, and that all electrodes are stored in conditions of controlled humidity. Vacuum packed electrodes may be used directly from the carton, only if the vacuum has been maintained. Directions for hydrogen control are always given on the carton and should be strictly adhered to. The cost of each electrode is insignificant compared with the cost of any repair, thus basic electrodes that are left in the heated quiver after the day's shift may potentially be re baked, but would normally be discarded to avoid the risk of H, induced problems.

Senior Welding Inspection -Weiding Consumables Copyright © 2002 TWI Ltd

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Consumables for TIG Welding: Consumables for TIG/GTAW consist of a wire and gas, though tungsten electrodes may also be grouped in this. Though it is considered as a non-consumable electrode process, the electrode is consumed by erosion in the arc, and by grinding and incorrect welding technique. The wire needs to be of a very high quality as normally no extra cleaning elements can be added into the weld. The wire is refined at the original casting stage to a very high quality where it is then rolled and finally drawn down to the correct size. It is then copper coated and cut into 1m lengths. A code is then stamped on the wire with

a manufacturer's, or nationally recognised number for the correct identification of chemical composition. A grade of wire is selected from a table of compositions. The wires are mostly copper coated which inhibits the effects of corrosion. Gases for TIG/GTAWare generally inert. Pure argon or helium gases are generally used for TIG welding. The gases are extracted from the air by liquefaction. Argon is more common in air than helium and thus it is generally cheaper than helium. In the USA vast pockets of naturally occurring helium are found and thus helium gas is more often used in USA. Helium gas produces a deeper penetrating arc than argon. It is less dense (lighter) than air and needs 2 to 3 times the flow rate of argon gas to produce sufficient cover to the weld area when welding down-hand. Argon on the other hand is denser (heavier) than air and thus less gas needs to be used in the down-hand position. We often use mixtures of argon and helium to balance the properties of the arc and the shielding cover ability of the gas. Gases for TIG/GTAW need to be of the highest purity (99.99% pure). Careful attention and inspection should be given to the purging of, and the condition of gas hoses, as it is possible that contamination of the shielding gas can be made through a worn, or withered hose. Tungsten electrodes for TIG welding are generally produced by powder forging technology. The electrodes contain other oxides to increase their conductivity, electron emission and also have an effect on the characteristics of the arc. Sizes of tungsten electrodes are available off the shelf between 1.6 - lOmm diameter. Ceramic shields may also be considered as a consumable item, as they are easily broken. The size and shape of ceramic used depends on the type ofjoint design and the diameter of the tungsten.


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Consumables for MIG/lVIAG Welding: Consumables for MIG/MAG welding consist of a wire and gas. The wire specifications used for TIG welding are also used for MIG/MAG welding, as a similar level of quality is required in the wire. The main purpose of the copper coating of steel MIG/MAG welding wire is to maximise current pick-up at the contact tip and reduce the level of coefficient of friction in the liner, with protection against the effects of corrosion being a secondary function.

)

Wires are available that have not been copper coated as the effects of copper flaking in the liner can cause many wire feed problems. These wires may be coated in a graphite compound, which again increases current pick up and reduces friction in the liner. Some wires, including many cored wires are nickel coated. Wires are available in sizes from 0.6 - 1.6 mm diameter with finer wires available on a lkg reel though most wires are supplied on a 15kg drum. Common gases and mixtures used for MIG/MAG welding include:

Gas Type

Used for

Characteristic Very stable arc with poor penetration and low spatter levels. Good penetration Unstable arc and high levels of spatter. Good penetration with a stable arc and low levels of spatter.

Pure Argon

MIG

Pure CO 2

MAG

Spray or Pulse Welding of Steels and Aluminium alloys Dip Transfer Welding of Steels

MAG

Dip Spray or Pulse Welding of Steels

Argon + 5 - 20% CO 2 (

Process

.

Argon + 1-2% O 2

MAG

Senior Welding Inspection -Welding Consumables Copyright © 2002 TW[ Ltd

Spray or Pulse Welding of Austenitic or Ferritic Stainless Steels Only

14.8

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Consumables for Sub Arc Welding: Consumable for Submerged Arc SAW consist of an electrode wire and flux. Electrode wires are normally of high quality and for welding C/Mn steels are generally graded on their increasing Carbon and Manganese content, and the level of de-oxidation. Electrode wires for welding other alloy steels are generally graded by chemical composition in a table, in a similar way to MIG and TIG electrode wires. Fluxes for Submerged Arc Welding are graded by their manufacture and composition. There are 2 normal methods of manufacture known as fused and agglomerated.

1)

Fused fluxes:

Fused fluxes are mixed together and baked at a very high temperature where all the components become fused together. When cooled the resultant mass resembles a sheet of black glass, which is then pulverised into small particles. These particles again resemble small slivers of black glass. They are hard, reflective, irregular shaped, and cannot be crushed in the hand. It is impossible to incorporate certain alloying compounds into the flux such as Ferro manganese, as these would be destroyed in the high temperatures of the manufacturing process. Fused fluxes tend to be of the acidic type, which are fairly tolerant of poor surface conditions, but produce comparatively low quality weld metal in terms of the mechanical properties of tensile strength and toughness.

I, ~,,:.

,~~~

-:'I -~~

.

.' .~

';.

"~::';\":~ ~~.";':;;~:....;:,-:,:.


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THE WELDING 1t\ISTITUTE

Agglomerated tluxes: Agglomerated fluxes on the other hand are a mixture of compounds that are baked at a much lower temperature and are essentially bonded together by bonding agents into small particles. The recognition points of these types of fluxes is easier, as they are dull, generally round granules, that are friable (easily crushed), and can also be very brightly coloured, as colouring agents may be added in manufacture as a method of identification, unlike fused fluxes. Agglomerated fluxes tend to be of the basic type and will produce weld metal that is of much higher quality in terms of strength and toughness. This is at the expense of usability as these fluxes are much less tolerant of poor surface conditions.

, '\>!:.

':". ~

:'i:....

)

;:.it:":·

\

.~:.:

It can be seen that the weld metal properties will result from using a particular wire, with a particular flux, in a particular weld sequence and therefore the grading of SAW consumables is given as a function of a wirelflux combination and welding sequence.

A typical grade will give values for: 1)

2)

Tensile Strength. Toughness (Joules at temp)

2) 3)

Elongation %. Toughness testing temperature.

The re-use or mixing of used and new flux will depend on the class of work being undertaken and is generally addressed in the application standard. All consumables for SAW (wires and fluxes) should be stored in a dry and humid free atmosphere. Basic fluxes may require baking prior to use, and the manufacturers instructions should be strictly followed. On no account should different types of fluxes be mixed together. Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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Questions Consumables

(

QU1.

Why are basic electrodes used mainly on high strength materials? And what controls are required when using basic electrodes.

QU2.

What standard is the following electrode classification taken from and briefly discuss each separate part of the electrodes coding E 80 18 M.

QU3.

Why are cellulose electrodes commonly used for the welding of pressure pipelines?

QU4.

Give a brief description of a fusible insert and state two alternative names give for the insert

QU5.

What standard is the following electrode classification taken from and discuss each separate part of the electrodes coding. E 42 3 1Ni B 4 2 H1

Senior Welding Inspection - Consumables Sec 14 Copyright © 2003 TWI Ltd

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Non-Destructive Testing: NDT, or Non Destructive Testing is used to assess the quality of a component without destroying it. There are many methods ofNDT some of which require a very high level of skill both in application and analysis and therefore NDT operators for these methods require a high degree of training and experience to apply them successfully. The four basic methods ofNDT are: 1)

Penetrant testing.

2)

Magnetic particle testing.

3)

Ultrasonic testing.

4)

Radiographic testing.

( \

A welding inspector should have a working knowledge of all these methods, their

applications, advantages and disadvantages.

NDT operators are examined to establish their level of skill, which is dependant on their

knowledge and experience, in the same way as welders and welding inspectors are examined and tested to establish their level of skill. Various examination schemes exist for this purpose throughout the world. In the UK the CSWIP and PCN examination schemes are those that are recognised most widely.

A good NDT operator has both knowledge and experience, however some of the above

techniques are more reliant on these factors than others.

Senior Welding Inspection - Non-Destructive Testing Copyright © 2002 TWI Ltd

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Penetrant Testing: Basic Procedure: 1)

Surface preparation.

Component must be thoroughly cleaned.

2)

Penetrant application. Penetrant applied and allowed

~o

dwell for a specified time. (Contact time)

3)

Removal of excess penetrant. Once the dwell or contact time has elapsed, the excess penetrant is removed by wiping with a clean lint free cloth, finally wipe with a soft paper towel moistened with liquid solvent. (solvent wipe)

4)

Application of developer. Penetrant that has been drawn into a crack by capillary action will be drawn out of the defect by reverse capillary action.

5)

Inspection.

6)

Post cleaning and protection.

1\ )

Method: (Colour contrast, solvent removable) 1) Apply Penetrant.

C

2) Clean then apply Developer.

3) Result.

I

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Advantage


Disadvantages

1)

Low operator skill level.

1)

Careful surface preparation required.

2)

Applicable to non-ferromagnetic materials.

2)

Surface breaking flaws only.

3)

Low cost.

3)

Not-applicable to porous materials.

4)

Simple, cheap and easy to interpret.

4)

No permanent record.

5)

Portability.

5)

Potentially hazardous chemicals.

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Senior Welding Inspection - WIS 10 Multi - Choice Question Paper (MSR-SWI-PT-1) N arne:

.

Answer all questions t.

What is the flash point of a solvent based product? a. The minimum temperature at which the solvent will be flammable. b. The temperature at which the vapours given off will spontaneously ignite.

l) ~

c. The minimum temperature at which the vapours given off will ignite if source of ignition is introduced. d. The temperature at which the dye in a solvent based penetrant losses its capillary action.

2. What primarily governs the rate (speed) of a penetrant entering a surface breaking discontinuity? a. Viscosity. b. Capillary action. c. Wetting ability. d. How the penetrant is applied.

(. 3. Aluminium alloy test specimens that have been tested with penetrant should be thoroughly cleaned after testing because: a. The remaining toxic residue from the test may react with the aluminium causing a fire hazard. b. The acid in the penetrant may cause server corrosion. c. Any remaining alkaline penetrant will leave a red permanent stain on the surface of the aluminium. d. The alkaline content of wet and most emulsifiers could lead to surface pitting, especially in high humidity environments.

WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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Which penetrant type does not exist? a. Post-emulsifiable fluorescent. b. Post-emulsifiable visible. c. Dual sensitivity penetrant. d. Dry particulate penetrant.

5.

Why is it bad practice to prepare soft alloy surfaces with a wire brush prior to testing with a penetrant test method? a. It may cause damage to the part. b. It may close any surface breaking discontinuities.

)

c. It may contaminate the developer. d. It is not considered to be bad practice. e. Both a and b are correct.

6.

Which of the following NDE method is most likely to detect fatigue cracking? a. Dye penetrant. b. Magnetic particle (a.c. current) c. Ultrasonics. d. It depends on many factors, none of the above can be selected due to the lack of information given. ( -

7.

Which of the following cleaning methods is generally considered unsuitable for pentrant testing without further processing? a. Vapour degreasing. b. Abrasive blasting. c. Solvent cleaning. d. Steam cleaning.


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THE WELDIr'\IG INSTITUTE

8. Which of the following penetrant properties influences capillary pressure? a. Surface tension. b. Wetting ability. c. Dimension of surface breaking flaw. d. All of the above e. Both a and b.

9. Of the following, which are the most important reasons for filtering the UV-A light used for fluorescent penetrant inspection? -,

)

a. To minimise the total light intensity by filtering out the visible light rays. b. To produce better viewing conditions in darkened areas. c. To reduce overall wavelength bands to allow only green fluorescence. d. To prevent personal injury from the more penetrating UV-A rays.

10. How would an ideal emulsification time be established when using post-emulsifiable penetrants? a. By calculation b. By experimentation. c. By measuring the contact angle of the penetrant. (

d. By determining the viscosity of the emulsifier.

11. Generally speaking, which of the following penetrant systems would be the most time consuming to use on the same type of component? a. Solvent based. b. Post-emulsifiable. c. \'Vater-washable. d. All of the above generally would take the same time.


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12. Which of the following may be used to apply penetrant effectively? a. Spray.

b. Immersion. c. Brush. d. All of the above

13. Dry developer should be applied: a. So that a heavy coat of developer covers all surfaces to be inspected. b. So that a light dusting covers all surfaces to be inspected. c. With a dry soft brush, e.g. paint brush. d. By dipping.

14. Which of the following is not considered good practice when penetrant testing? a. Applying emulsifier by dipping. b. Applying developer by dipping. c. Removing water based penetrant by water spray. d. Applying emulsifier by brush.

15. The profile of the meniscus of a penetrant would be: a. Concave when compared to the meniscus of a penetrant with lower penetration. b. Convex when compared to the meniscus of a penetrant with lower penetration properties.

c. Flat. d. All of the above. 16. Why is it advisable to have an UV-A light source installed at the wash station when

using fluorescent penetrant systems?

a. So that the drying stage can be eliminated to save time. b. To increase the bleed out speed of the penetrant. c. To check the effectiveness of the wash cycle. d. To check that the test components have been adequately covered with penetrant. WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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17. Which factor would be used for determining the penetrants contact time required for the test method to be effective? a. Type of discontinuity sought. b. Shape of component. c. Size of component. d. All of the above.

18. Why is the wetting ability a consideration in the design of penetrants? a. Because it has an effect on capillary action. )

b. Because it has an effect on the penetrants coverage of the components surface. c. Both a and b. d. None of the above.

19. Why are contrast penetrants usually red? a. Red provides high definition. b. Red provides high contrast against a white background. c. Red penetrants are more cost effective than other penetrants of different colours. d. Both a and b.

(

20. Which of the following statements is false? a. Penetrant testing can find most types of surface breaking defects. b. Penetrant testing can under most conditions be just as reliable when testing ferritic materials as MPI. c. Penetrant testing can be used to detect fatigue cracks. d. Penetrant testing is less reliable than radiographic testing when attempting to detect minute surface breaking defects.


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21. Which of the following would be the most desirable centre wavelength for the light used in the fluorescent penetrant process. a. 3200A (320nm). b. 3650A (365nm).

c. 4650A (465nm). d. 5960A (596nm).

22. A good commercial penetrant should have a: a. Low flash point. b. High flash point.

c. Flash point less than 55°C. d. A flash point is not relevant.

23. Which of the following materials is often difficult to test with a penetrant test method, due to lack of contrast during final interpretation? a. Ferromagnetic C-Mn steels. b. Aluminium. c. Titanium alloys. d. Cast iron. \.

24. If a penetrant system is halogen free it will contain no: a. Sulphur. b. Dye.

c. Chlorine. d. Solvent.


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25. Which of the following statements is false regarding the use of cracked panels or comparator blocks? a. To establish a standard size of crack, which can be reproduced as, needed. b. To determine the relative sensitivities of two penetrants. c. To determine if a fluorescent penetrant has lost or reduced its fluorescence. d. To determine the degree or method of cleaning necessary to remove penetrant from the surface without removing it from the crack.

26. Which of the following pentrant test methods is the most common found on site work if used on ferromagnetic pipework or pressure vessels?

)

a. Water-washable (Fluorescent). b. Post-emulsifiable (fluorescent). c. Solvent base (contrast) d. Penetrant testing is not used on ferromagnetic materials.

27. When using fluorescent water-washable penetrants, adequate rinsing time is assured by: a. Timing the rinse cycle. b. Scrubbing the part surface. c. Rinsing under UV-A light. ( .. _

d. Using a high-pressure water blast.

28. How long must a penetrant be left on a component before removal? a. As long as possible to ensure good test sensitivity. b. 20 minutes. c. It varies depending on the type of penetrant used, defects to be detected. d. Always between 6 and 20 minutes.

WIS to Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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29. Which of the following are unique to a penetrant test report a. Penetrant used, developer used and dwell time. b. Penetrant used, development time and contrast paint. c. Penetrant used, fluorescent particles and drying time. d. Penetrant used, dwell time and drying time.

30. Which of the following surface breaking defects are best detected using DPI? a. Equiaxed defects. b. Planar defects. (

c. Linear defects. d. All of the above.

(


80f8

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uouaadsu] ;}]JHJUd JHJutluW £1 UO!lJ~S

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5. Materials which are repelled magnetically are called: a. Paramagnetic. b. Diamagnetic. c. Ferromagnetic. d. Non-magnetic. 6. Which of the following NOT method would be best suited for the detection of surface breaking defects on a austenitic steel weld: a. Dye penetrant. b. Magnetic particle (AC current) )

c. Ultrasonic. d. All of the above. 7. Which of the following are unique to a magnetic particle inspection report: a. Dwell time, magnetic ink, contrast paint b. Couplant, magnetic ink, crack detection unit. c. Magnetic ink, contrast paint, crack detection unit. d. Development time, magnetic ink, contrast paint. 8. An ASME penetrameter may be used in MPI: a. To measure test sensitivity.

(' I

b. To detect the direction of magnetic flux. c. To measure black/fluorescent ink suspensions. d. Both a and b. 9. What is the curie temperature of a ferromagnetic material? a. The temperature at which it becomes radioactive. b. The temperature at which it losses magnetism. c. The temperature at which it becomes magnetic. d. None of the above.

WIS 10 Qu paper MSR-SWI-MT-l issue 3 Date: 28/05//03

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10. The build up of a non-relevant indication due to a sharp contour change in the test component is referred to as: a. A defect. b. Furring. c. Magnetic writing. d. None of above. 11. Which of the following are important considerations when carrying out MPI? a. Material type. b. Surface condition c. Type of defects sort after. d. All of the above 12. A 5 turn coil around a part being tested produces: a. A longitudinal field. b. A circular field. c. An intermittent field. d. Both a and b depending on current type. 13. Which of the following MPI test methods may be used for the detection of longitudinal defects on a pipes external surface? a. The threader bar method.

(.

b. Rigid coil method. c. Flexible cable wrapped around the pipe making a coil. d. All of the above. 14. Which of the following is considered the most sensitive test method when using MPI. a. Fluorescent particle, wet method. b. Contrast particle, wet method. c. Dry powder method. d. All of the above are considered to be the same sensitivity.


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15. Which of the following will produce circular magnetism: a. A.C. yokes. b. Passing current through a coil.

c. Prods. d. All of the above.

16. Which of the following methods would be best suited for the detection of surface breaking defects on duplex stainless steel? a. Dye penetrant.

( J

b. Magnetic particle. c. Radiography. d. The method used depends on the procedure requirements.

17. In accordance with the relevant standard, what is the specific percentage of

fluorescent particles to the base:

a. 1.25%.

b. 0.8 to 3.5%.

c. 0.1 to 0.3%. d. 0.3 to 0.8%. 18. When demagnetising a component in situ in a structure that cannot be easily removed from the parent structure, which of the following techniques is normally used? a. Stroking the component in the same direction using an AC yoke. b. Stroking the component in different directions using a DC Yoke. c. Stroking the component in the different directions using an AC. yoke. d. Stroking the component in same direction using a DC Yoke. 19. When using AC. electromagnets, the strength of the magnet shall be assessed by measuring the lifting power. The lifting power shall be equivalent to or not less than: a. 4.5 kg for poll spacing of 300 mm. b. 2.25 kg for poll spacing of 300 rnrn. c. 18 kg for poll spacing greater than 75 mm. d. The sensitivity of AC. electromagnets is assessed using penetrameters. WIS 10 Qu paper MSR-SWI"MT-l issue 3 Date: 28/05//03

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20. A copper bar is placed inside a 5 mm coil, the amperage required to magnetically saturate it will be: a. In the range of 500 to 100 amps. b. Generally less than steel. c. Not enough information given to give a correct value. d. It is not possible to magnetically saturate a copper bar. 21. Which of the following is the most common method for demagnetising a component?

a. AC. b. DC straight polarity. (

c. HW DC d. The above currents cannot be used for dernagnetising. 2?-. What is coercive force? a. The magnetic force required to magnetically saturate a part. b. The magnetic force required to magnetise a part. c. The reverse magnetic force required to demagnetise a part. d. The reverse magnetic force required to cause the poles of a magnet to rotate

180°.

23. How is the strength of a permanent magnet usually measured? a. By lifting a specified weight of any material.

(

b. By lifting a specified weight of steel. c. By ampere-turns. d. By comparing it against the readings of a magnetometer. e. Both a and b. 24. What sort of magnetic field is produced when using a permanent magnet? . a. Longitudinal. b. Circular. c. Reversing poles. d. None of the above.

W£S 10 Qu paper MSR-SWI-MT-l issue 3 Date: 28/051103

5 on

)

TWI

VOL


25. When considering AC. yokes, which of the following is applicable? a. Can be used for the detection of both surface and slight sub-surface defects. b. No power source required. c. Must be used with at least a 400 mm pole spacing to ensure adequate coverage. d. None of the above. 26. An example of an instrument use to determine the direction of a magnetic field is

called a:

a. Burmah-Castrol strip. -,

)

b. ASME penetrameter. c. Berthold penetrameter. d. All of the above. e. None of the above. 27. Why is H.W.D.C. often used with dry powders, as opposed to D.C.? a. Because dry powders are not attracted to leakage fields caused by direct current. b. Because the powder retains a residual field with direct current. c. Because greater powder mobility is achieved on the test surface. d. A.C. of H.W.D.C. is not used with dry powders.

28. When checking a weld for defects with a permanent magnet, the magnet should be

) placed:

a. Transversely over the weld to look for longitudinal defects. b. Longitudinal with the weld to look for transverse defects. c. At 45° to the weld to look for both transverse and longitudinal defects at the same time. d. Normally in positions A and B if specification does not state otherwise. 29. Which of the following statements is always true? a. MPI is better than dye penetrant testing. b. Fluorescent inks used in MPI are always green/yellow. c. MPI'can only be used on ferromagnetic materials. d. All of the above.

WIS 10 Qu paper MSR-SWI-MT-1 issue: 3 Date: 28/05//03

60f7

TWI

VOL


30. Which of the following surface breaking defects are best detected using MPI? a. Equiaxed defects. b. Planar defects. c. All types of entrapped gas defects. d. All surface defects are detected using MPI.


70f7

uouoodsuj J!UOS1Unn £1 UOn;)~S

TWI VOI.

_


Magnetic Particle Testing: Basic Procedure: l)

Test method for the detection of surface and sub-surface defects in ferromagnetic materials.

2)

Magnetic field induced in component. (Permanent magnet, electromagnet (Y6 Yoke) or current flow (Prods).

3)

Defects disrupt the magnetic flux.

4)

Defects revealed by applying ferromagnetic particles. (Background contrast paint may be required)

Method: 1) Apply contrast paint.

( . ?'<";,~-'

I

2) Apply magnet & ink.

,

3) Result.

,

lVi';--'"

Advantage

Disadvantages

1)

Pre-cleaning not as critical as with DPL

1)

Ferromagnetic materials only.

2)

Will detect some sub-surface defects.

2)

Demagnetisation may be required.

3)

Relatively low cost.

3)

Direct current flow may produce Arc strikes.

4)

Simple equipment.

4)

No permanent record.

5)

Possib le to inspect through thin coatings.

5)

Required to test in 2 directions.


15.4

Rev 09-09-02

TWI

VOl.


Senior Welding Inspection - WIS 10 Multi - Choice Question Paper (MSR-SWI-MT-1) N arne:

.

Answer all questions

1. A desirable property of magnetic particles used for the inspection medium for either the dry or wet method, is that they: a. Posses high permeability. b. Posses high retentively. c. Must be non-magnetic d. None of the above 2. The accumulation of particles held at a leakage field on a components surface is called: a. A discontinuity. b. A defect. c. An indication. d. Magnetic writing 3. Which of the following methods my be considered for the magnetic particle inspection of a large casting, both for surface and subsurface defects: a. A.C. yolk b. Permanent magnet. c. D.C. prods. d. All of the above. 4. A magnetising force of one oersted produces: a. 1 gauss. b. 1 Tesla. c. 1 Weber. d. 104 Tesla.


1

on

TWI

VOL


4. Which of the following probes under most circumstances would be best suited for the detection of plate laminations, on thin plate: a. 1.5 MHz twin shear wave, 45°. b. 4 MHz single shear wave, 60° c. 4 MHz twin compression wave. d. 1.5 MHz single compression wave.

5. The number of complete waves which pass a give point in a give period of time (usually one second) is referred to as: )

a. Amplitude of wave motion. b. Pulse length of wave motion. c. Frequency of wave motion. d. Wave length of wave motion.

6. Which of the following are unique to an ultrasonic test report. a. Type of couplant, scanning pattern and attenuation checks. b. Surface preparation, scanning pattern and type of couplant used. c. Pre-cleaning method, probes used and couplant used. d. Calibration, probes used and test sensitivity.

(- 7.

25 million cycles per second can also be stated as: a. 25 kilohertz. b. 250 kilohertz. c. 25 megahertz. d. 2.5 megahertz.

WIS 10 Qu paper MSR-SWI-UT-l issue 3 Date: 28/06/03

20f8

TWI

VOL 8.


In A scan presentation, the amplitude of the vertical indications on the screen represents the: a. Amount of ultrasonic energy returning back to the probe. b. Distance travelled by the probe. c. Thickness of the material. d. Elapsed time since the ultrasonic pulse was generated.

9.

In A scan presentation, the horizontal base line represents the: a. The amount of reflected ultrasonic energy b. Distance travelled by the probe.

( \

c. Elapsed time or distance. d. None of the above.

10. Which of the following are important considerations for the ultrasonic examination of a fusion butt weld a. Material thickness. b. Surface condition. c. Joint configuration. d. Both a and b. e. All of the above.

( 11. Which of the following probe combinations would you expect to be used on a carbon steel weld joining two plates 12mm thick (cap left as welded)? a. 45° single crystal shear wave, 85° single crystal shear wave, 60° single crystal shear wave and a single crystalcompression. b. 45° single crystal shear wave, 70° single crystal shear wave, 60° single crystal shear wave and a twin crystal compression. c. 0° single crystal shear wave, 45° single crystal compression, 60° single crystal compression and a combined double longitudinal wave. d. 45° twin crystal transverse wave, 60° single crystal transverse wave, 70° twin crystal transverse wave and a 00 twin crystal compression.


30r8

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VOL


12. The angle of incidence is: a. Greater than the angle of reflection. b. Less than the angle of reflection. c. Equal to the angle of reflection. d. Not related to the angle of reflection.

13. The gradual loss of sonic energy as the ultrasonic vibrations travel through the material is referred to as: a. Reflection.

J

b. Refraction.

c. Attenuation d. None of the above.

14. The phenomenon whereby an ultrasonic wave changes direction when the wave crosses a boundary between materials with different velocities is called: a. Refraction. b. Reflection. c. Penetration. d. Rarefaction.

(

\ 15. How many echoes would be present on the CRT if a V1 (A2) block is used to calibrate a normal probe 0 to 50 mm, on the 25-mm dimension?

a. 2. b. 4.

c. 8. d. As many echoes as possible to ensure good test sensitivity.


40f8

TWI

VOL


16. The 1.5 mm hole in a V1 (A2) test block may be used to: a. Determine the resolution of the probe. b. Determine the pulse width of the probe. c. Set test sensitivity. d. All of the above.

17. An echo is set at full screen height on' a vertically calibrated CRT, then the sound is reduced by 6dB: a. The echo will drop by 50% of its initial height. b. The echo will drop to 20% of its initial height. c. The echo under most circumstance disappears off the screen. d. The echo will drop to 10% of its initial height.

18. What is the thickness of a V2 (A4) test block? a. 12.5 mm.

b. 20 mm.

c. 25 mm. d. Both a and b e. All of the above.

19. What does 23 mm of Perspex represent in a V1 (A2) block when using compression probes: a. 100 mm of steel. b. 23 mm of steel. c. 50 mm of steel. d. 200 mm of steel.


50[8

\,

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VOL


20. Which of the following NDE methods is best to use when testing ferromagnetic materials? a. Magnetic particle. b. Radiography. c. Ultrasonic. d. All of the above may be used, it depends on many factors.

21. Which of the following statements are true?

!

J

a. The higher the probe frequency the faster the sound travels through a given material. b. The higher the probe frequency the slower the sound travels through a given material. c. The higher the probe frequency the more sound is lost due to attenuation. d. The higher the probe frequency less sound is lost through attenuation.

22. Which of the following wave types travels the fastest in steel a. Longitudinal. b. Shear. c. All wave types travel at the same velocity in steel. d. Longitudinal and shear waves will not travel in steel.

(

,

23. Which of the following single crystal probes would contain the thinnest crystal? a. 2.5 MHz compression probe. b. 5 MHz compression probe. c. 5 MHz angle probe. d. 10 MHz angle probe.

WIS 10 Qu paper MSR-SWI-UT-1 issue 3 Date: 28/06/03

6 of8

TWI

VOl.


24. Which of the following transducers produces the least beam spread in the far zone? a. 1 MHz, 10 mm diameter crystal. b. 5 MHz, 25mm diameter crystal. c. 2 MHz, 25 rnm diameter crystal. d. 5 MHz, 10 mm diameter crystal.

25. Sound attenuation in a material is due to: a. Absorption and scattering. b. Reflection and refraction. c. Density and velocity. d. Density and elasticity.

26. Which of the following probes would be best suited for the detection of near surface plate lamination on 12mm thick plate? a. 5 MHz, twin compression probe. b. 2.5 Mhz, twin compression probe. c. 5 Mhz single 0° probe. d. 5 Mhz twin 60° probe.

27. Calculate the wavelength for a frequency of 4.25 MHz at a velocity of 5800 meters per second: a. 0.73 mm. b. 1.36 mm. c. 0.073 mm.

d.0.136mm.


70f8

(

TWI

VOL


28. Which of the following scan types produces a plan view of any defective areas under test? a. A-scan. b. B-scan. c. C-scan. d. D-scan.

29. When testing a specimen, using a compression probe, a decrease in a wave

frequency (obtained by changing the probe) will result in:

a. An increase in sound velocity. b. A decrease in sound velocity. c. No change in velocity. d. No change in wavelength.

30. Which of the following is acceptable test sensitivity when using a compression probe? a. 2nd BWE 80% FSH at test depth. b. 1st BWE 100% FSH at any depth. c. Echo from 1.5 rnm hole 100% FSH (V1 test block). d. Echo from 5 mm hole 80% FSH (V2 test block).

(

.

WIS La Qu paper MSR-SWI-UT-l issue 3 Date: 28/06/03

80f8

)

(

)

uo!p~dSUI j!qdljJ~OH)U~. ~1 u0!lJ~S

()

..-.-- .... _ - - - - - - _ . _ - - - .._... _.-----_ . . .

_... _..- -._------_. /"

.:»

..

8S 3971

Ifhickness (mm) 1-6

STEP 7-12

13-18

4-10

'WIRE 9-15

~

Image Quality Indicators

15-21

DIN 54 109

WIRE (DIN 62)

6-12 10-16 1-7

~~ 8S EN 462-1 WIRE

8S EN 462-2 STEP/HOLE H1

H5

H9

H 13

W1

W6

W10

W 13 7

0.050 0.063 0.08

7

6

6

5

0.10

5

7

6

4

6

5

3 2 1

0.125

7

4

6

6

3

5 4 3

5

2 1

7

4 3

0.15 0.16 0.20 0.25

4 3

6

7

5 4 3

7

0.30 0.32 0.35

2

5

6

2

2

6

6

2

0040

1

5 4

1

1

5 4

5

1

6

4

3

4

5

2

3

3

3

0.80 0.90

4

1

1.00

0.50 0.60 0.63 0.75

. 7

7

2

2

6

7

2

3

6

6

1

1

5

6

1

1.25

2

5

5

4

5

1.50

1

4 4

3

4

3 2

2 1

1.20

1.60 1.80 2.00 2.50

6 5

3.00 3.20

4

4.00 5.00 6.30

2 1

3 2 1

6

5

1

4 3

3

3 2 1

2

,

1

__ ...

- - - - - - - - _ ... _..

- -- . -_.

TWI

V!7!7I.

- -_ _


Annex B (nonnative) Minimum image qual ity values

Table 13.2 Steplhole IQI

Single-wall technique; rQ{ on source side

Nomlrial Utickncss t

Il1In~e

I'fa,Me B.1 \\fire IQI

(Illal.ity cluss A

Jnrn

up to 2,0 above 2,0 to 3,5

[lImge lllU1Jity class A Numinal thlekncss t. 111m

IQI ~'alue1)

Up to 1,2

W 18

above 1,2 to 2,0 above 2,0 to ;'l,5

\V 17

above 3,5 to 5,0 above 5,0 to 7

\V 15

W 14

above 7 to 10 above 10 to It')

'ltY 13 W 12

above lG to 25

Wll

above 25 to 32 above 32 to 40 above 40 to 55 above 55 to 85 above 85 to 160 above 150 to 250 above 2fJO

WlO

above 3,5 to 6 above 6 10 10 above 10 to 15 above 15 to 24

\\1 16

W7

W4

When using Ir W2 sources, IQI values values can be accepted as fQUQWS;

WO(1iC

than the I~tecl

118

lIll H 12 II 13 H 14

II 15 H 16 1117

H 18

When using Ir Hl2 sources, IQI values W01SC

UI,I.(I

1I11: listed

values can be accepted as fOUI)\\'!;: 10 rom t.) 24 nun: UJl to two values; above 24 nun to 30 mm: up to one value.

Single-wall technique; IQI on source side

10 rmn to 24 111m: up to two values; abovo 24 10m lQ :30 mm: up to one

H7

HID

!)

1)

no H9

WI)

'W5

H4 H5

above 30 to 40 above 40 to 60

above 100 to 150 above 150 to 200 above 200 to 250 above 250 to 320 . above 320 to 400 ahove 400

\V8

110

above 2'1 to 30

above 60 to 100

W9

-~-~

IQI "llluc l )

V'.lIU{l.

1able B.3 Wire IQI Image quality class B

'fuble

Nominal thickne.'iS t

n.is Step/hole IQI

llIlllge tlulllit)' C!l...., 11

Penetrated

Up to 1,5

IQI value l )

thiclme~s In

above 1,5 to 2,5 above 2,5 to 4 above 4 to 6 above 600 8 above 8 Lo 12 above 12 to 20 above 20 to 30

lUllI

I

up to 2,5

HZ

above 2,5 to 0,5 above 5,5 to 9,5

113

H4

above 9,5 to 15

H5

above 15 to 24

116

above 2-1 to "0 above 40 to 60 above 60 to 80

Hi HS

I) \\11(:11

using Ir W:! sources, IQI V;tlll~S worse than

&15 HUll

:t.hu\.'."

to U"S

mm;

above 30 to 35 above 35 to 45_ above 45 to 65

UO

''nhw,:'l C"MI be ;lcce[>lc,l

,L';

ULI! listt1(!

followa;

up to two values;

fJ/", nuu to :!·l hUll.:

IQI value I)

mm

UJllU

unc \·,Lhw.. .

above 65 to 120

above 120 to 200 above 2.00 to 350 above 350

WIg WI8

Senior Welding Inspection - Non-Destructive Testing Copyright © 2002 TWr Ltd

15,1

V.[17

W16 W 15 W 14 W 13

W 12 Wll

W 10 W9 WB W7

W6 W5

When using Ir 192 sources, IQI values worse than Vlllues can be accepted as (ollom;: 12' mm to 40 miu; up to one value. 1)

\

UIC

li>.1.ed

Rev 09-09

TWI V!J[lI.

_

ITable BA ~tp.p/hoIC ror

r TabLe R.l' Step/hole IQI

. l mugc qual it.y d.1.S.Q B Nominal

f:hi.c:kl1'~s;; [

[Q[ vn.Iue

1)

Peue trutcd thickness

tv

rql v:tlue l}

Hun

2,5

1I2

above 2,5 tn 4 above <3 to 12

H3 H4 H5

above 12 to 20

H ty

above 20 to 30 above ;30 to ,10

H7

118

above 40 to 60

H9

above 60 to 80

H 10

above 80 to 100

Hll

above 100 to 150 above 150 to 200

n iz H 1:3

above 200 to 250

lIM

above '1 to g

I) W]l('J1 using Ir 192 sources, IQI values worse than the listlld values can be accepted M (ollow~~

12 mill to '10 mm: UP to one value.

Doubfe-walj technique; double Imnge; IQr on

source side

Table

u.s Wire lQI

lma!:c quality class A Peuetrnted U,icImcs..q to

IQ[ value

mm up to 1,2

(

I

Im:l.':'; [lll,lIlt.)' dass A

mm

Up to


above 1,2 to 2 above 2 to 3,5 above 3,5 to 5 above 5 t.o 7 above 7 to 12 ahove 12 to 18 above 18 to 30 above 30 to 40 above 40 to 50 above 50 to 60 above GO to 8G above S5 to 120 above 120 to 220 above 220 to 380 above 380

W 18 W 17 W 16 W 15 WB VI 13

W 12 Wl1 W 10 W9

Up to 1

H3

above 1 to 2

H4

above 2 to :3,tJ

H5

above 3,5 to 5,5

HG

above 5,5 to 10 above 10 to 18 above 19 to 35

H7

HS FIg

l} ""'hen using Ir 192 sources, IQI values worse than the listed values C~111 be
Double-wall technique; double image; {QI ott 801ll"Ce side Table B.7 Wire IQI linage quality cla... s n Penetrated thickness 'w

fQI value.

mm

UV to 1,5

W19

above 1,5 to 2,5

w is

above 2,5 to 4

\V 17

above 4 to G above 6 to 8 above 8 to 15 above 15 to 25 above 25 to 38

W 16 W 15 W 14 W 13 W 12

above 38 to 46 above 45 to 55 above 55 to 70 above 70 to 100 above 100 to 170 above 170 to 250 above 250 .

Wll W 10 W9

W8 W7 W6

W5

W8 W7 W6

W5 W4 W3

Senior Welding Inspection - Non-Destructive Testing Copyright (;i 2002 TWI Ltd

15.2

Rev 09-09

TWI

V!lOI. !

_

'nlhle U.S StcpAwlc IQl

Tnblc

11H.1~C

lm.l~c

qual ity class 8

Pcuetrated thickness

H1

IQI va lue II

a.io Step/hole [QI lllw.tily cia:,,; A

I'Cllctrlltcd tl'ticknes8 10

IQI \·:l.hl~l)

mm

111.111

up


to 1

above 1 LO 2,5 above 2,5 [0 4 above 4 to () above 6 [0 11 above 11 to 20 above 20 to 35

U2

H3 114 1I5 HI>

H7 US

II Wh~lt It",ingIt 192 scurces, IQI Vllll~.$ WOniC th:.ul the 1c.1ed v,.!ue::i can he 3Cceplcd ~ ColIo\VJI: " nun to II tum: up to QI~ va.lUl!.

up to 2 above 2lO 5 above Gto 9

H3

II ·1 H5

n10 11\

above

I

HG II7

above 1'1 to 22 above 22 to 36 above 3G to 50 above 50 to 80

I

i

HB

U9 HlO

I) \V1l~ft Iltint.:

v.t.lU<'::'

c.ID

(r 19'1 sources, IQI 'i:Ull'!!> \..~ U';'II Ill.: fuiled be ;'l<('c.'P!:l;.-d as folJO\vs::

5 lIInI to 9 111m: up [0 two

Double-wall technique; single or double image; IQI on film side

;iliaI~ 9

\'a1U€S;

mm to 22 lime up to one \-;UI~,

Double-wall tniekness, single or double image; IQI Oil film side

Table B.9 Wire lQI JllInge cluality eless A 'V~lllc

Pelletrated thickness w film

rQ]

Up to 1,2 above 1,2 to 2

W 18

above 2 to 3,5 above 3,5 to 5

Table n.n Wire IQI Xn.IUIN Ilull1ity elass B l~
tltl.ckue!:is

tll

IQ[ vnlue

mill

W 11 W 16

up to l,5

w 19

W 15

abo~

W 18

above 5 to 10

W 14

above 10 to 15

W 13

above 15to 22 above 22 to 38 above 38 to 48 above 48 to GO above GO to 85 above 85 tof25 above 125 to 225

W 12 Wll

""10 W9

\Va W7

1,5 to 2,5 above 2,5 to .. above 4 to 6 above 6 to ]2 above 12 to is above 18 to 30 above 30 to 45 above 45 to 55 above 55 to 70

W 17 W 16

W 15 W 13 W 12

Wll W10

above 70 to 100

\V9

above ~ to 375

W6 W5

above 100 to ISO

\V8

~.bovc

WI}

above 180 to 300

W7 W6

375

above 300

Senior Welding Ir:spection - Non-Destructive Testing Copyright © 2002 TWl Ltd

15.3

(

W 1,4

Rev 09-09

TWI

VIJ[JI.

_


v

500

400~

kV 300I

/ /V

/

zooI

-

~

r-ro-

~

~

f..- ~

r--

I--'

/v ~

I--

~~

-

100I It

70

60

,/]

....

I-'

/

V

V

V ..........

-l-

V .....

••;::1-...

./

./'

......... I

~""-4 I

l--

SO

I

l/'

/

v

V

l---

40

,-

30

zo0

- -' - , C

-r-

1°1

z

:3

"

5 6 7 8910

20

]()

4.Q

50 601{) mm100

21

1 Copper/nickel and alloys

2 St~'Cl 3 TItanium and alloys

.J Alumlnlum and altoy-$ 1) X-r~' voltage 2) Penetrated tllickIll~:;S ~o

Figure 20. Maxlrnwn X-ray voltage for X-ray devices up to tiOO leV as a function of peuerrated thickness and material

•

Table 1. Penetrated thickness range for gamma. ray sources and X.ray equipment with energ}' from 1 Me V and above, for steel, copper and nickel-based alloys Radiation source

Penetrated thIckness, u' nun

Test class A

Tm 170

Yb

1601)

1.£/

Test class B

-s 5

U1

es 5

I s w:=: 15

2s1v:S:12

10 :5 w:S 40 20 s 10 ::; 100

14

2Osw:s90

40:s w s 200 30 s'W =:;; 200

60 S 50 ::;:;

X-ray equipment wtth energy from '1 MeV to 12 MeV

1V~50

'1.02::80

X-nw equipment with energy above 12 MeV

1Q~80

10 ~

Se 752) Ir 192 Co 60 X-ray equipment 'with energy from 1 MeV

$111 S

1lI :5

tV :=:

40 150 180

to 4 MeV

100

I) For aluminium and tit:miurn, the penetrated material thiclmt'_'i5 is 10 mm <: 1(1 -:: 70 null for class A and c1..'\..'>5 B.

2) For aluminium and titaniuru, the penetrated material thi(".kn= Is 35 liull :;: W ,;; iao mm for crass A.


15.4

2,.,

mm < w < 55 mm Ior

Rev 09-09

TWI

1001.

THE WELDING Ir'-,ISTITUTE

Senior Welding Inspection - WIS 10 Multi - Choice Question Paper (MSR-SWI-RT-1) Name:


1. If it were necessary to radiograph a 7-inch thick steel product, which of the following gamma ray sources would most likely be used? a. Co60. b. Ir192.

()

c. Ce137 d. Yb169.

2. The kilovoltage applied to an x-ray tube effects: a. The quality of the x-ray beam. b. The quantity of the x-ray beam. c. Has no effect on subject contrast. d. All of the above.

3. Isotopes of a single element differ only in the number of: a. Protons.

(

b. Neutrons. c. Electrons. d. Positrons.

4. Calcium tungstate screens used in industrial radiography are usually used to: a. Improve definition. b. Improve contrast in the radiograph. c. Decrease exposure times. d. None of the above.

WIS 10 Qu paper MSR-SWI-RT-I issue 3 Date: 28/05/03

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5. The most common causes for excessively high-density radiographs are: a. Insufficient washing and overdevelopment. b. Contaminated fixer and insufficient washing. c. Overexposure and contaminated fixer. d. Overexposure and overdevelopment.

6. Movement, geometry and screen contact are three factors that affect radiographic: a. Contrast. b. Unsharpness.

i

_)

c. Reticulation.

d. Density.

7. The half-life of a source is dependent on; a. It's original intensity. b. The source to film distance. c. The physical size of the isotope. d. The isotope.

8. If a film is placed in a developer solution and allowed to develop without agitation:

('I

a. The radiograph will not show correct contrast. b. It will be impossible to fix the radiograph permanently. c. There will be a general fogging condition over the entire radiograph. d. Bromide streaking may result.

9. When a radiograph of a weld which contains a large, the crack will appear radiograph as:

~n

the

a. A dark intermittent or continuous line. b. A light, irregular line. c. Either a dark or light line. d. A dark rounded indication. WIS 10 Qu paper MSR-SWI-RT-l issue 3 Date: 28/05/03

2of7

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10. Which one of the following persons is allowed to work with ionising radiation? a. An authorised person. b. A qualified person. c. A classified person. d. A radiation person.

11. Which of the following units is used for measuring the amount of absorbed dose? a. Sievert. b. Rem c. Roentgen. d. Gray.

12. Lead foil in direct contact with x-ray film: a. Intensifies the scatter radiation more than the primary radiation. b. Decreases the contrast of the radiographic image. c. Intensifies the primary radiation more than the scatter radiation. d. Should not be used when gamma rays are emitted by the source of radiation.

13. Which of the following defects are likely to be missed using x-ray as the inspection medium? a. Plate laminations, lack of side wall fusion on a single U butt weld and cap overlap. b. Toe cracks, plate laminations and lack of side wall fusion on a single U butt weld. c. Plate laminations, lack of inter run fusion using the MIG/MAG welding process

and cap overlap.

d. All defects are always detected using x-rays.

WIS 10 Qu paper MSR-SWI-RT-l issue 3 Date: 28/05/03

30f7

(

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VOL


14. Which of the following is the most likely appearance of lack of root fusion on a radiograph taken of a single V butt weld? a. A dark straight line with a light root. b. A dark straight line with a root of higher density. c. A dark root with straight edges. d. A dark uneven line with a light root.

15. Which of the following defects would show up as light indications? a. Copper inclusions, slag inclusions and excessive root penetration. ()

b. Tungsten inclusions, spatter and lack of root penetration. c. Tungsten inclusions, excessive root penetration and spatter. d. Excessive cap height, copper inclusions and underflushing.

16. If an exposure time of 3 minutes and 30 seconds were necessary using a 5-metre source to film distance for a particular exposure, what time would be necessary if a 3 metre source to film distance is used and all other variables remain the same? a. 1 minute 43 seconds. b. 1 minute 15 seconds. c. 65 minutes 12 seconds. d. 2 minutes 55 seconds.

(

/

17. In order to increase the intensity of x-radiation: a. The tube current should be increased. b. The tube current should be decreased. c. The test specimen should be moved nearer to the film. d. A lower kilovoltage should be applied to the tube.

WIS 10 Qu paper MSR-S\VI-RT-l issue 3 Date: 28/05/03

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18. Excessive exposure of film to light prior to development of the film will most likely result in: a. A fogged film. b. Yellow stains. c. An increase in film contrast. d. Frilling.

19. The penetrating ability of gamma rays is governed by: a. The isotopes activity. b. Time plus activity.

)

c. The isotopes half-life. d. The atomic number of the element used for the isotope.

20. Two different gamma isotopes of the same activity: a. Will produce different wavelengths of radiation. b. Will produce the same quality of radiation. c. Will produce the same intensities and wavelengths of radiation. d. Will produce only electromagnetic and ionising radiation.

21. A good radiograph is produced using the following exposure conditions, 4 minutes at 3 mAo What exposure time would be needed if the mA were reduced to 2mA? a. 6 minutes. b. 3 minutes. c. 2 minutes. d. 4 minutes.

WIS 10 Qu paper MSR-SWI-RT-1 issue 3 Date: 28/05/03

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22. Reticulation resulting in a puckered or netlike film surface is probably caused by: a. Crimping the film after exposure b. Sudden extreme temperature change while processing. c. Crimping the film before exposure. d. Warm or exhausted fixer.

23. A penetrameter on the film side of the object is used to indicate: a. The size of discontinuities in a part. b. The density of the radiograph.

(J

c. The amount of film contrast. d. The overall quality of the radiographic technique used.

24. X-rays and gamma rays are: a. Corpuscular and ionising radiation. b. Particulate and ionising radiation. c. Particulate and corpuscular radiation. d. Electromagnetic and ionising radiation.

25. The activity of the developer solution is maintained stable by: (

a. Constant agitation b. Maintaining processing solutions within the recommended temperature range. c. Avoiding contamination from the water wash. d. Addition of replenisher.

26. The small area in the x-ray tube from which the x-radiation emanates is called the: a. Focalspot. b. Filament. c. Focusing cup. d. Cathode.


60f7

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27. The absorption of gamma rays from a given source when passing through matter depends on: a. The atomic number, density and thickness or the matter. b. The Young's modulus value of the matter. c. The specific activity value of the source. d. All of the above.

28. The fact that gases, when bombarded by radiation, ionise and become electrical conductors makes them useful in: a. X-ray transformers. )

./

b. X-ray tubes. c. Radiation detection equipment. d. Radiographic film.

29. A graph showing the relation between material thickness, kilovoltage and exposure is called: a. A bar chart. b. An exposure chart. c. A characteristic curve. d. An H & 0 curve.

30. Beta particles are: a. Neutrons. b. Protons. c. Electrons. d. Positrons.


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Ultrasonic Testing: Basic Procedure: 1)

Component must be thoroughly cleaned; this may involve light grinding to remove any spatter, pitting etc in order to obtain a smooth surface.

2)

Couplant is then applied to the test surface. (water, oil, grease etc.) This enables the ultrasound to be transmitted from the probe into the component under test.

3)

A range of angle probes are used to examine the weld root region and fusion faces. (Ultrasound must strike the fusion faces or any discontinuities present in the weld at 90° in order to obtain the best reflection of ultrasound back to the probe for display on the cathode ray tube)

Method: 1) Apply Couplant.

2) Apply sound wave.

3) Result.

Signal rebound from the lack of sidewall fusion

(

Advantage

Disadvantages

1)

Can easily detect lack of sidewall fusion.

1)

High operator skill level.

2)

Ferrous & Non - ferrous alloys.

2)

Difficult to interpret.

3)

No major safety requirements.

3)

Requires calibration.

4)

Portable with instant results.

4)

No permanent record. (Unless automated)

5)

Able to detect sub-surface defects. Measures depth and through wall extent.

5)

Not easily applied to complex geometry.


15.5

Rev 09-09-02

TWI

VOl.


Senior Welding Inspection - WIS 10 Multi - Choice Question Paper (MSR-SWI-UT-1) Name:


1.

Under most circumstances, which of the following frequencies would result in the best resolving power when testing C-Mn steel? a. 1 kilohertz. I

b. 1 megahertz. c. 2 megahertz. d. 5 megahertz.

2.

Which of the following materials of the same alloy is most likely to produce the greatest amount of sound attenuation over a given distance? a. A hand forging. b. A casting c. An extrusion. d. A weld made on a thin plate material.

3.

(

Grass on a CRT display could be caused by: a. A crack. b. A large slag inclusion. c. A coarse grain structure. d. A gas pore.


10f8

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TWI VOI.

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Radiographic Testing:

Basic Procedure:

1)

X or Gamma radiation is imposed upon a test object.

2)

Radiation is transmitted in varying degrees dependant upon the density of the material through which it is travelling.

3)

Variations in transmission detected by photographic film or fluorescent screens. (Film placed between lead screens then placed inside a cassette)

4)

An IQI (image quality indicator) should always be placed on top of the specimen to record the sensitivity of the radiograph.

\,

Method: a)

Load film cassette.

b)

Exposure to radiation.

.---. % Radioactive source

. c) Developed graph.

Developed graph

IQI

~

.,

Film cassette:;::::::+'

Latent, or hidden image

Advantage 1) 2)

Disadvantages

Permanent record. . Most materials can be tested.

1)

Skilled interpretation required.

2)

Access to both sides required.

3)

Detects internal flaws.

3)

Sensitive to defect orientation. (Possible to miss planar flaws)

4)

Gives a direct image of flaws.

4)

Health hazard.

5)

Fluoroscopy can give real time imaging.

5)

High capital cost.

Senior Welding lnspection - Non-Destructive Testing Copyright © 2002 TVV! Ltd

15.6

Rev 09-09-02

"WI}l

SWI) 2

Single~ wall .~.~. ~~......

. Si!1gle\V~ILs}.ngleillulge SWSl panoramic .

sinzle ijllaae SWSl. ~ . ;'.~.~.~~ .. i:? .... . .....

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~~~:~l:~, l~ir~~r' -Film 101's should be placed source side

• 101'5 are placed on the film side • Source inside film outside (single exposure)

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Double wall single image DWSl Identification • Unique identification • IQI placing • Pitch marks indicating readable film length

• iQrs are placed on the film side • Source outside film outside (multiple exposure) • This technique is intended for pipe diameters over 100mm

Radiograph

Co~)'I".I1t02003lWllJd

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Double wall double jmage Ownl elliptical exposure

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Identification • Unique identification

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• IQI placing

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• Pitch marks indicating readable film length

• 10l's are placed on the source or film side • Source outside film outside (multiple exposure) • A minimum of two exposures

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Shot" Radiograph

• This technique is intended for pipe diameters less than 100mm •

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_


Summary of Non Destructive Testing: I

Discipline

Application

Welds/Castings. Surface testing only. All materials can be Penetrant tested. Colour Testing contrast & florescent. Welds/Castings i i Ferrous metals only. ! "Vet & Dry inks. ! Magnetic Yolks. Permanent Particle magnets and straight Testing current AC/DC Welds/Castings. One side access. : Ultra Sonic Un-favoured for large grained structured Testing alloys. I I i.e. Austenitic SIS i Welds/Castings. II Access from both I sides is required. Radiographic All materials. Gamma and X-ray sources of Testing radiation used.

I

J

I

(

)

Advantages Low operator skill level All non porous material surfaces may be tested Low cost process Simple equipment Low operator skill level Surface/Sub surface flaws Relatively low cost Simple equipment

Disadvantages

I

--I

Highly clean the material Surface flaws only Extremely messy No permanent record Fe magnetic metals only De-magnetise after use Can cause arc strikes using straight current technique No permanent record I

Can more easily find lack of High operator skill level sidewall fusion defects A wide variety of materials Difficult to interpret can be tested No safety requirements Req uires calibration Portable with instant results No permanent record Permanent record 0 f results High operator skill level A wide variety of materials Difficult to interpret can be tested Can assess penetration in Cannot generally identify small diameter, or line pipe lack of sidewall fusion** Gamma ray is very portable High safety requirements

** To identify planar or 2 dimensional defects such as lack of side wall fusion, or cracks etc, the orientation of the radiation beam must be in line with the orientation of the defect as shown below, hence if the radiation source is at the centre of the weld then no indication of lack of side wall fusion may be shown on the radiograph.

Lack of sidewall fusion Film Radiation beam

Senior Welding Inspection - Non-Destructive Testing CUlJyri~ht2 2002 TWI Ltd

15.7

Rev 09-09-02

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Dye Penetrant Report Information A report should include the following information as a minimum: • 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 26.

Client. ProjecUContractor. Item number. Weld identification. Weld geometry/set-up. Relevant specifications/procedures. Relevant acceptance criteria. Date of test. Stage of test. Location. Description of equipment used including manufacturer and serial numbers. Background and viewing conditions. Consumables used including manufacturer and batch numbers. Method of application. Dwell time. Pre cleaning method. Sensitivity. Surface condition. Method of reporting defects. Details of any test restrictions. Details of all flaws, which exceed the acceptance criteria. The position of any inspection datum's used and the dimensions of the item under test. Post test cleaning (if applicable). Report number and any report numbers of any complementary inspection reports (if known). Operators name, signature and qualifications.

WIS 10 MSRlMPIIINFO Issue 1 Date: 14/01/02

)

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'

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Radiographic Report Information A report should include the following information as a minimum: •

u

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

(

19. 20. 21. 22. 23. 24. 25. 26.

Client. Project/Contractor. Item number. Weld identification. Relevant specifications/procedures. Relevant acceptance criteria. Date of test. Stage of test. Location. Technique used. Weld geometry/set-up. Details of equipment type (manual external, battery internal crawler), this shall include manufactories name and serial number. Exposure container (where applicable). Tube voltage or source strength. Film type used and the density. Intensifying screens, type and thickness front/back. Shielding (if applicable). Geometric relationship, source/focal spot size, focal film distance, object film distance, radiation angle with respect to the weld and film. Exposure. Material thickness and surface condition. IQI type, size, position and sensitivity. Processing, .manual/automatic, development and fixing temperature and times. Details of any flaws exceeding the written criteria. The positions of any inspection datum's used and the dimensions of the component under test (weld thickness, circumference). Report number and any report numbers of any complementary inspection reports (if known). Operators name, signature and qualifications.

WISI0 MSRlRTIINFOIssue 1 Date: 14/1/02

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THE WELDING INSTITUTE Penetrant Test Report Bad Example 1.

Company Name:

!WI Services

Location:

Melt down power station

Reference No:

MSR 112034

Report Number:

MSR 110365

Parts Tested Product No:

W21R

Stage of Test:

After Hrr

Material Details:

Steel

Surface Cond:

As Welded

D~ t 2.0mm

--+1 l+-

Root Gap: 2.5mm Root Face: 2.0mm Bevel Ang: 20 mm Capping

2.0mm

Test Instructions Test Procedure Number:

MSR 1445610365

Test Procedure I

~enetrant Time

IEmulsification:

5 mins

Test Temp:

28°C

Viewing Conditions:

UV-A

10 mins

Application:

Aerosol

Current Used

100 amps

Consumables Consumable

Manufacturer:

Penetrant: solvent removable contrast

Ardrox

Developer: Dry powder

Ardrox

Remover: water

Test Results:

Crack like indication 1rnrn slight sub-surface 10mm from datum

'~

J

Evaluation of Test Component: Acceptable as to Specifications Requirements Test Operators Name:

M S Rogers

Test Operators Signature:

'lItR~

BRlPT1 issueS Date: 10/06/05

Date of Report: 12112103

TWI

VOl.

THE WELDING INSTITUTE Magnetic Particle Inspection Test Report Bad Example 2.

Company Name:

TWI Services

Project/Client:

MSROil

Reference No:

MSR 1120

Report Number:

MSR 110365

Weld No:

W 23 & W 25 Fabrication number 21A

Surface Condition: as welded Stage of Test:

After HIT

Welding Process: TIG/GTAW

Test date: 3/11/2003

Product Details:

Single - U Butt

Root Gap 2.0 mm

Material Details:

Austenitic/Ferritic SS

Root Face 2.0 mm

Bevel Angle:

70°

Test Instructions Test Procedure Number:

MSR 110365

Scope of Testing:

100%

150 lux

Test Equipment Il)etection Unit:

(j~ Coil

Spacing:

Test Sensitivity:

Prods

Pole/Prod Space: 2m

Viewing Conditions:

10 mm

Wave Form:

Current Used

150 amps per inch of weld

AC+

IPenetrameter Used:

100 amps Gauss Meter

Consumables Consumable

Manufacturer:

Batch Number:

Black Ink

Johnson % Allen

MSR 110012

Solvent

Johnson % Allen

MSR 110456

Post Test Details Demagnetization: DC coil

Test Limitations: N/A

( / jest Results: Slight sub-surface defect detected at 6 o'clock position Gas pore at 20mm from datum Irrelevant indication at 6 o'clock position Weld W 21 Action: All defects detected shall be removed by grinding and cleared with PT. Evaluation of Test Component: Acceptable as to Specifications Requirements Test Operators Name:

M S Rogers


m~~~

BR/MT2 issue 5 Date: 10/06/05

Date of Report: 11/03/04

r"

TWI

VOl.


Ultrasonic Test Report Bad Example 3. Company Name:

TWI Services

Location:

Melt down power station

Reference No:

LOS 26252/P

Report Number:

MSR 110YV65

12/5/2001

Date:

Parts Tested Product No:

RW2-11

Material Thk

3mm

Material Details:

Steel

Surface Cond:

As Welded

D~ t 2.0mm

-+1 k-

Process

MMA root TIGfill

Bevel Ang: 700 Capping

2.0mm

Test Instructions Scope of Testing:

100%

Serial No USN1298

Viewing Conditions:

150 lux

Probe Type

Crystal,~

Frequency

60° Compression

10mm single

4 KHz

45° Shear

10mm double

4 KHz

60° Shear

10mm double

4 KHz

80° Shear

10mm double

4 KHz

Test Procedure Number

MSRlUT/03456

Test Equipment I")etection Unit:

USN 30

l)

Test Sensitivity Angle Probe Scanning:

12 dB above DAC

Compression Probe Scanning:

100% FSH at test depth

Calibration:

o to 200mm from V1 block

rTest Results

(

) No indications found exceeding the limits of the specification

Evaluation of Test Component: Acceptable as to Specifications Requirements· Test Operators Name:

BRlUT3 issueS Date: 10/06/05

M S Rogers

Date of Report: 11/03/04

TWI

VOl.

THE WELDING INSTITUTE Ultrasonic Test Report Bad Example 4.

Company Name:

TWI Services

Location:

Kuala Lumpur to Nowhere Pipeline

Reference No:

LOS 262521P

Report Number:

MSR 110YY65

Date:

12/5/2001

Parts Tested Stage of test

After HIT

Material Thk

3mm

Material Details:

Steel

Surface Cond:

As Welded

D~ t 2.omm-..1 ~

Process

MMA

Root Gap

2.5mm

Bevel Ang: 50° Capping

2.0mm

Material Dimensions: 5mm wall thickness, pipe diameter 36 inch Test Instructions Specification:

(

\

Scope of Testing:

API 1104

100%

Test Equipment

Detection Unit:

ISonatest Sitescan 130

Probe Type

Crystal

Frequency

MAP 45° shear

Single

1.5 KHz

MAP 60° Shear

Single

4 KHz

MAP 80° Shear

Single

4 KHz

MAP 0° Transverse wave

Twin

4 KHz

Test Sensitivity

(

Angle Probe Scanning:

1.5 mm hole 80% FSH

Compression Probe Scanning:

1st BWE 100% FSH

Calibration:

o to 200mm from V1 (A4) block

est Results . APlate lamination detected 450 and 600 probes. 20mm from reference

Tungsten inclusions detected 1OOrnrn X 100mm in area

Lake of sidewall fusion detected

Evaluation of Test Component: Acceptable as to Specifications Requirements Test Operators Name:

M S Rogers


7It~~

BRlUTJ issueS Dale: 10/06/05

1Date of Report: 14/05/01

o

TWI

VOl.

THE WELDING INSTITUTE Radiographic Test Report Bad Example 5.

Company Name:

TWI Services

Location:

Kuala Lumpur to Nowhere Pipeline

Reference No:

PL /177/04

Report Number:

TWI 1/4YT7-04

3/12/2004

Date:

Parts Tested Stage of test

Completed

Details

pipe to pipe

Material Details:

C/Mn Steel

Surface Cond:

As Welded

Material Dimensions:

D~ t 2.0mm

~I

\+-

Process

GTAW

Root Gap

3.0mrn

Bevel Ang: 700 Capping

2.0 mm

IProduct No: SEC 12 W24

25mm WIT, 38' Diameter

Test Instructions Specification:

API 1104

IRadiation Source: Yb 169

Procedure: No

121mr/03 Scope of Testing:

FFD/SFD: 700mm

IQI Type: 12 cu 10

100%

Source Strength:

600000 Mbq

Size of Source: 4 X 2

Sensitivity: 4.5 %

Killo Volts

N/A

Focal Spot Size: N/A

Technique: DWDI

Exposure:

16 Ci Mins

Screen type: Salt

Film Type: Ultra fine grain factor 10

(

Processing Development

FiXing:

Time:

4 to 5 minutes

Time:

6 minutes

Temperature:

200C

Temperature:

20°C

Test Results Shot 1

Density 2 to 3

Sensitivity: 1.9%

reshoot

Shot 2

Density 4%

Sensitivity: 4%

accetable

~hot3

Density 0.2 to 1.0

Sensitivity: 4 wires visible

accetable

Density NA

Sensitivity: no wires visible

reshoot

. Shot 4

Evaluation of Test Component:

Acceptable as to Specifications Requirements

Test Operators Name:

M S Rogers

Date of Report: 03/1212004


m~~

I est operators t.luaIS: A::;N I L:.:!

BRlUT3 issueS Date: 10/06/05

(

TWI

VOl.


Ultrasonic Report Information A report should include the following information as a minimum:

(j

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

(-

./

21. 22. 23.

Client Item number. Weld identification. Relevant specifications/procedures. Relevant acceptance criteria. Operators name, signature and qualifications. Date of test. Stage of test. Location. Flaw detector used (including serial numbers). Details of all probes used including all performance checks and serial numbers. Reference to inspection sensitivities and dB usedfor each probe. Details of all areas where the surface preparation is out of specification. Details of surface condition during test and parent material quality. All attenuation checks/measurements. Weld geometry's and weld condition Details of any areas with limited access. Details of all flaws, which exceed the recording threshold/acceptance criteria. Any flaws exceeding the acceptance criteria limits shall be shown on a drawing. The positions of any inspection datum's used and the dimensions of the component under test (weld thickness, circumference). Flaw sizing technique used. Report number and any report numbers of any complementary inspection reports (if known). Operators name, signature and qualifications.

WISIO MSRlUTIINFO Issue 1 Date: 14/01102

TWI

VOl.


Magnetic Particle Report Information A report should include the following information as a minimum: • 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

Client. Project/Contractor. Item number. Weld identification. Weld geometry/set-up. Relevant specifications/procedures. Relevant acceptance criteria. Date of test. Stage of test. Location. Description of equipment used including manufacturer and serial numbers. Background and viewing conditions. Detection medium including manufacturer and batch numbers. Method of flux generation. Distance between contact areas. Current type used, AC.lDC.lhalf-wave/full-wave rectified. Current used if applicable. Test Sensitivity. Surface condition. Method of reporting defects. Details of any test restrictions. Details of all flaws, which exceed the acceptance criteria. The position" of any inspection datum's used and the dimensions of the item under test. Post test cleaning (if applicable). Report number and any report numbers of any complementary inspection reports (if known). " Operators name, signature and qualitications.

WIS 10 MSRlMPVINFO Issue 1 Date: 14/01/02

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Questions

Non-Destructive Testing

QU1.

Name four NOT methods.

QU2.

State the two radiation types used in industrial radiography and state the advantages of each type

QU3.

Give the advantages and disadvantages of radiography and conventional ultrasonic testing.

QU4.

Give the main advantages and disadvantages of magnetic particle inspection and state at least three methods to magnetise a component.

QU5.

State the main limitations of the dye penetrant inspection method

\,

Senior Welding Inspection - QU Non-Destructive Testing Sec 15 . Copyright © 2003 TWI Ltd

()

)

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S.l!BdalI PIa M

91 uonJaS

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V!lOI.

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weu Repairs: Weld repairs can be divided into two specific areas: I)

Production repairs

2)

In service repairs

1)

Production repair

The Welding Inspector, or NDT operator usualIYlcI~ion repairs during the process of inspection, or evaluation of reports to the code or applied standard. A typical defect is shown below:

".

Before the repair can commence, a number of elements need to be fulfilled: 1)

An analysis of the defect may need to be made by the QI A department to discover the likely reason for the occurrence of the defect (Material/Process or Skill related).

2)

A detailed assessment needs to be made to find out the extremity of the defect. This may involve the use of a surface or sub surface NDT method.

3)

Once established the excavation site must be clearly identified and marked out.

( 4)

An excavation procedure will need to be produced, approved and executed.

5)

NDT should be used to provide confirmation that the defect has been located.

6)

NDT used to establish total removal of the defect

7)

A welding repair procedure will need to be drafted and approved.

8)

Welder approval to the approved repair procedure.

(Normally carried out during the repair procedural approval)

9)

A final method of NDT will have to be identified and a procedure prepared to ensure that the repair has been successfuUy carried out.

10)

Any post repair procedures that need to be carried out i.e. Heat treatment.

Senior Welding Inspection - Weld Repairs Copyright © 2002 TWI Ltd

16.1

Rev 09-09-02

TWI V!lOI.

_

THE WELDIf\IG INSTITUTE

Analysis:

As this defect has occurred in the HAZ the fault could be a problem with either the

material or the welding procedure, however if the approved procedure was followed no

blame can be apportioned to the skill of the welder.

Assessment:

In this particular case as the defect is open to the surface, penetrant testing may be used

to gauge the depth and length a f the defect.

lJ Excavation: As this defect is a crack it is likely that the ends of the crack should be drilled to avoid further propagation during excavation, particularly if a thermal method of excavation is being used. The excavation procedure may also need approval, particularly if it will affect the metallurgical structure of the component i.e. Arc Gouging.

Plan View of defect with drilled ends

\.

Side View of defect excavation

Seruor Welding Inspection - Weld Repairs Copyright © 2002 TW[ Ltd

16.2

Rev 09-09-02

T'VI

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_


Confirmation of excavation: At this stage NOT should be used to confirm that the defect has been completely excavated from the area. Re-welding of the excavation: Prior to re-welding of the excavation a detailed weld procedure will need to be drafted and approved. This is often carried out by the welder to be used in the repair who should then become automatically approved, should the procedure become qualified.

NOT confirmation of successful repair: After the excavation has been filled the weldment should then undergo a complete retest using ~'DT to ensure no further defects have been introduced by the repair. NDT may also need to be further applied after any additional post weld heat treatment has been carried out.

In service repairs:

~

~

Most in service repairs can be of a very complex as the component is very likely to be in a different welding position and condition than it wa ring production. It may also have been in contact with toxic, or combustible fluids hence a permit to work will need to be sought prior to any work being carried out. The repair welding procedure may look very different to the original production procedure due to changes in these elements. Other factors may also be taken into consideration, such as the effect of heat on any surrounding areas of the component i.e. electrical components, or materials that may become damaged by the repair procedure. This may also include difficulty in carrying out any required pre or post welding heat treatments and a possible restriction of access to the area to be repaired. For large fabrications it is likely that the repair must also take place on site and without a shut down of operations, which may bring other elements that need to be considered. Repair of in service defects may require consideration of these and many other factors, and as such' are generally considered more complicated than production repairs.

Senior Welding Inspection - Weld Repairs Copyright © 2002 TWI Ltd

16.3

Rev 09-09-02

UOIlJ01SIU pUB SSaJ1S IBnpISa}[ L1 nOI1Jas

(j

TWI

V!7I.


The degree of distortion that occurs is dependant on the ability of the material to resist these stresses and deformation. It is this deforn1ation that produces distortion of a product. Distortion, like the overall pattern of residual stresses can be very complex, however we can show the three basic directions of distortion exaggerated as follows:

Longitudinal distortion

(

Transverse distortion

(

t Angular distortion

tii

:..

~~".,.

----.

~\:_<:i~.

.

Senior Welding Inspection- Residual Stress and Distortion 17.2 Copyright © 2002 TWI Ltd.

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The volume of weld metal in a joint will affect the amount of local expansion and contraction, hence the more volume of weld metal then the overall amount of distortion wi II be higher. Preparation angle of 60°

~ =:

Preparation angle of 40° ,

(0

(~~ ,

...,' '." '!.~·~'·'~~~.'_·'-:i::~ ...-~,,:~ ~

':1

Preparation angle of 0° .·':::':':f}'f{~~,:

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(

"';:{.

The effect of expansion and contraction causing distortion during welding can be graphically seen when gas welding 2 free plates together, as the plates tend first to move apart and then back together and then apart again and finally change direction once again and move together. This effect is caused by what is called the reversal of stresses, where expansion and contraction are taking place as the weld cools and each weld element acts as a fulcrum for the following element upon contraction. As progression is made down the weld the weld becomes fixed in a final position and is restrained from further movement by the previous length of weld, as shown below:

I) Plates are 2) Welding begins 3) Fulcrum effect. 4) Fulcrum reversal. 5) Final position. with contraction. unrestrained.

~ :'.' ,,' ,., ..

. : :: , . .

l~.r-

" · · , · D :.,..;...:.:

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~.

.

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Senior Welding Inspection - Residual Stress and Distortion 17.3 Copyright © 2002 TWI Ltd.

Rev 09-09-02

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To counteract the effects of expansion contraction and distortion we can carry out one 0 f' the following techniques:

Offsetting: Offsetting means to offset the plates to a pre-determined angle to allow distortion to take place, with the final position of the weld being that required. Examples of this are shown below:

~

' ·'<. :" : . , o ~''''':'':''''

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..

,'"

~:

;,t..::....:..

~

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f 5'·«·
The amount of offsetting required is generally a function of trial & error, but if there are many numbers of components to produce it can be an economical method of controlling distortion.

Back-step welding and balance welding: These 2 methods of distortion control use a special welding technique, or welding sequence to control the effects of distortion. Examples are given below:

Back-step welding

Balance welding of a pipe butt weld Weld

~~ ""\'--.

C

Weld 1 from A-B Weld 3 from B C

Senior Welding Inspection - Residual Stress and Distortion 17.4 Copyright © 2002 TWI Ltd.

Weld 2 fromC-D Weld 4 from D-A

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Clamping Jigging and Tacking: In clamping and jigging, the materials to be welded are prevented trorn moving by the clamp or jig. The advantage of using a jig is that elements in a fabrication can be precisely located in the position to be welded and can be a very time saving method of manufacturing high volume products. On most occasions the components are accurately positioned by the jig and then tacked in position to prevent movement, then the jig is removed to allow full access for welding. The use of clamps, jigs, strong backs, bridging pieces, and tack welds will severely restrict any movement of material, and so reduce distortion, this however will also increase the maximum amount of residual stresses. Pictorial examples of some of these methods are shown below: a)

Summary of Residual Stresses & Distortion:

\

1)

Residual stresses are locked in elastic strain, which is caused by local expansion & contraction in the weld area.

2)

Residual stresses should be removed from structures after welding as they may cause Stress Corrosion Cracking to occur, and can compound with applied stresses. They may also affect dimensional stability, when machining a welded component.

3)

The amount of contraction is controlled by: The volume of weld metal in the joint, the thickness, heat input, joint design, and the coefficient of conduction.

4)

Offsetting may be used to finalise the position of the joint.

5)

If plates or pipes are prevented from moving by tacking, clamping or jigging etc (restraint). then the amount of residual stresses that remain will be higher.

6)

The movement caused by welding related stresses is called distortion.

7)

The directions of contractional stresses and distortion is very complex, as is the amount and type of final distortion, however we can say that there are 3 directions:

I

a) Longitudinal

b) Transverse

c) Short transverse

8)

A high percentage of residual stresses can be removed by heat treatments. Ultrasound has also been used in the stress relieving of fabrications.

9)

The peening of weld faces (With the use a pneumatic needle gun) will only re distribute the residual stress, and place the' weld face in compression.

Senior Welding inspection - Residual Stress and Distortion 17.5 Copyright © 2002 TWI Ltd.

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Questions

Stress and Distortion QU1.

What causes residual stresses in a welded joint?

QU2.

State three directions which residual stresses form in a welded joint

QU3.

Give four methods of controlling distortion

QU4.

Sketch "a balanced welding technique

QU5.

State four factors. which affect distortion

-,

(, )

,

r

Senior Welding Inspection - QU Stress and Distortion Sec 17 Copyright © 2003 TWI Ltd

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slaalS jO mounaarj, lBaH

81 nOllJas

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Heat Treatment of Steels: All heat treatments are basically cycles of three elements, which are: a) Heating.

b) Holding, or Soaking.

c) Cooling.

Q,l

b. Holding

... I..<

:::l ~

I..<

c. Cooling

Q,l

c.

5 Q,l

Eo-<

Time

We use heat treatments to change properties of metal, or as a method of controlling formation of structures, or expansion/contractional forces during welding. In heat treating metals and alloys there are many elements for the welding inspector to check that may be of great importance, such as the rate of climb and any hold points in the heating cycle. The holding or soaking time is generally calculated at 1hour for every 25mm of thickness, but this can vary. Heat treatments that are briefiy covered in this section are as follows: 1)

Annealing

2)

Normalising

3)

Hardening

4)

Tempering

5)

Stress relieving

6)

Pre-heating

The methods/sources that may be used to apply heat to a fabrication may include: a) b) c)

Flame burners/heaters (Propane etc.). Preheating.

Electric resistance heating blankets. Pre-heating & PWHT.

Furnaces. Annealing. Normalising. Hardening. Tempering.

The tools that an inspector may use to measure the temperatures of furnaces and heated

materials may include.

a) b) c) d)

. Temperature indicating crayons (Tempil sticks). Pre-heating. PWHT.

Thermo-couples. All heat treatments.

Pyrorneters (Optical. Resistance. Radiation.). Furnace heat treatments.

Segar cones. Furnace heat treatments.

All heat treatment records are an important part of the quality documentation.

Senior Welding Inspection - Heat Treatment of Steels Copyright © 2002 TWI Ltd

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Annealing:

Full Annealing UCT LCT

Annealing for steels Annealing is a heat treatment process that may be carried out on steels, and most metals that have been worked hardened or strengthened by an alloying precipitant, to regain the softness and ductility. In the latter case we generally refer to solution annealing. In work hardened non-ferrous metals, annealing is used to re-crystallise work-hardened grains. When annealing most work hardened non-ferrous alloys the cooling rate is not always critical, and cooling may be rapid without forming any hardened structures. In steels we can carry out 2 basic kinds of annealing:

a) b)

Full Annealing (Including Solution Annealing) Sub Critical Annealing

In full annealing of steels the steel is heated above its UCT (upper critical temperature) and allowed to cool very slowly in a furnace. This slow cooling will result in a degree of grain growth, which produces a soft and ductile structure. There are no temperatures that can be quoted for annealing steels, as this will depend entirely upon the carbon content of the steel. The DCT range ofP.lain Carbon Steels is between 910 -723°C, however the temperature is mostly taken to 50°C above the calculated UCT to allow for any inaccuracies in the temperature measuring device. Plain carbon steel of carbon content of 0.2% would have an annealing temperature in the region of 850 - 950°C The solution annealing of some metallic alloys may require a rapid cooling rate. In sub critical annealing the steel is heated to temperatures well below the lower critical temperature (723°C). This type of annealing is similar to that used with non-ferrous metals as it is only the deformed ferritic grains that can be re-crystallised at these lower temperatures. The term annealing generally means to bring a metal, or alloy, to its softest and most ductile natural condition. In steels this also means a reduction in toughness, as the resultant large grain structure shows very low impact strength.

Senior Welding Inspection - Heat Treatment of Steels Copyright © 2002 TW[ Ltd

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".,

Normalising:

2)

i.

~."':

UCT Cooling in still air

Normalising is a heat treatment process that is generally used for steels. The temperature climb and holding may be exactly the same as for annealing, however the steel is removed from the furnace after the soaking period to be allowed to cool in still air. This produces a much finer grain structure than annealing and although the softness and ductility is reduced, the strength and hardness is increased. Far more importantly the toughness, or impact strength is vastly improved.

3)

Hardening:

UCT

Rapid cooling

In the thermal hardening of steels the alloy must be taken above its VCT as with all the heat treatment processes discussed thus far, and soaked for the same period. The major difference is in the cooling cycle where cooling is generally rapid. For plain carbon steel, the steel must have a sufficiently high carbon content to be hardened by thermal treatment, which is generally considered as > 0.3% carbon. Alloy steels containing carbon contents below 0.1 % with added Mn. Cr. Mo. or Ni. Etc. can be made much harder by thermal heat treatment. Some steels are specially designed to produce hardness even at very slow rates of cooling, and are included in a group of steels called Air Hardening Steels. The cooling media for quenching steels is very important; as if the steel is cooled too quickly then the thermal shock may be too rapid and cause cracking to occur in the steel. Brine is considered to be the fasted cooling media followed by water and then oil.

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4) Tempering:


Fe steel temper colours:

1 2r'C_ Tempering range 220 - 723°C 240 0 e 220 0 e

Tempering is a sub critical heat treatment process that is used only after hardening has first been carried out. Hardening will leave some steels very hard, but also very brittle.

Balance of properties, after Hardening.

Balance of properties after a temper at 350°C

o ~

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Balance of properties after a temper at 720°C

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The softness, anel far more importantly the toughness, is of very low values after thermal hardening, and the term temper really means to balance. When tempering steel we re balance the properties of excessive hardness and brittleness by decreasing the hardness and increasing the level a f toughness. The process of tempering the hardness commences measurably at around 220°C and continues up to the LCT, or 723°C. At this point most of the extra hardness produced by thermal hardening has been removed, or fully tempered, but the fine grain structure produced by the hardening process will remain, giving the steel good toughness and strength. This is the mechanism used to give good toughness, and strength to Q/T steels.

5)

Stress relieving, or PWHT:

\ The purpose of stress relieving is to relieve internal elastic stress that has become trapped inside the weld during welding. The procedure of heat, hold and cool is the same as all other heat treatments however special heating curves are required when stress relieving some types of steels, particularly Creep Resistant Steels. In stress relieving the steel may be heated between 200-950 °C depending on the steel type and the amount of stress that is to be relieved. To understand what happens during stress relieving there are a number of terms that require to be defined:

Yield Point (Re) This is the point where steel can no longer support elastic strain and becomes plastically deformed i.e. plastic strain occurs. This means that the steel will no longer return to its original dimensions. The residual stresses that are contained within steels after welding are all elastic, with the remaining stresses having been absorbed by plastic movement of the steel (Distortion). The stress/strain diagram of annealed low carbon steel below shows this point: Yield Point

' / Failure point

CIl

CIl

~ ......

(/)

• Elastic strain

Plastic Strain

When steel is heated the yield point is suppressed, which means that the elastic strain shown above will now start to. become plastic strain. The higher the temperature, then generally the more elastic strain will be converted to plastic strain, or plastic movement.


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It is generally accepted that lip to 90 0ft) of residual welding stresses can be plastically relieved during this process. ThLS change is shown diagrammatically below: New Yield Point •••••••••••.•••••••• ~/

..

.. .. ..

tr: tr: Il)

b

Failure point

•• ••• .. . . . . .. . . .•

'"

CIl

Elastic strain

Plastic Strain

When the temperature is returned to ambient temperatures, the yield point returns to practically the same position as at the start of the heat treatment.

6)

Pre-heating:

We can preheat metals and alloys when welding for a number of reasons. Primarily we use most pre-heats to achieve one or more of the following: I) 2) 3)

To control the structure of the weld metal and HAZ on cooling. To improve the diffusion of gas molecules through an atomic structure. To control the effects of expansion and contraction.

We can control the formation of un-desirable microstructures that are produced from rapid cooling of certain types of steel. Martensite is produced by the entrapment of carbon in solution at temperatures below 300°C. The function of a pre-heat with susceptible steels is thus 2 fold, the first being the suppression of martensite formation by delaying the cooling rate, and secondly allowing the trapped hydrogen gas to diffuse out of the HAZ, or weld metal area back to the atmosphere. We may also control the effect of expansion and contraction in welds.

Summary: We use heat treatments to change, or control the final properties of welded joints and fabrications. All heat treatments are cycles of 3 elements, heating, holding and cooling. The welding inspector should carefully monitor the heat treatment procedure, its method of application, and measuring system. All documents and graphs relating to heat treatments should be submitted to the Senior Inspector in the Q/C department to be logged in the fabrication quality document files.

Senior Welding Inspection - Heat Treatment of Steels Copyright © 2002 TW£ Ltd

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Summary of Heat Treatments of Steels: Treatment

lVlethod

I

·····.. ·---·----lThe steel is heated abo~e its upper critical temperature UlIU

Annealing

Normalising

s

Hardening

Tempering

Stress

Relieving

Pre-Heating

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L

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L

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Uses

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The furnace is then turned off and the steel remains in

the furnace to cool.

This produces a large or course grain structure that is

soft and ductile but has very low toughness.

The steel is heated above its upper critical temperature

as in annealing and soaked for 1 hour for every 25mm of thickness. Once the soaking time has elapsed the steel is removed from the furnace to cool in still air. Produces a small, or fine grain structure that has high toughness and strength, though ductility is lower than annealed steel.

Used to make steels tougher and stronger

The steel is heated above its upper critical temperature as in annealing and soaked for 1 hour for every 25mm of thickness. Once the soaking time has elapsed the steel is removed from the furnace to quench in a cooling medium. Produces a fine grain martensitic structure that has very high hardness and strength, though ductility is almost zero, with very low toughness. The steel is re-heated after hardening, and the balance of hardness to toughness is adjusted as the temperature is increased from 220° - 723°C At 723 °C all martensite has been tempered removing brittleness, and returning the ductility. The fine structure is retained giving high strength and further improving the toughness.

Used to make medium or high plain carbon and most low alloy steels

harder.

The steel is heated to a temperature dependant on the

type of steel being heat-treated.

Used after welding to relieve the trapped

elastic stresses caused by expansion/contraction.

Plastic flow of stresses increases as the temperature rises relieving the locked in elastic stresses. The steel is heated to a temperature dependant on the type of steel being heat treated, but normally less than 350°C This suppresses the formation of Martensite and allows time/temperature for diffusion of'H,

(

Used to rebalance the properties of thermally hardened steels.

(

Used to control the

formation of H 2 cracks. Also used to control the effects of expansion and contractional stresses.

I


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Questions Heat Treatments

QU1.

How can the levels of hardness be controlled in the HAZ?

QU2.

What is the maximum recommended heat treatment temperature for steel weldments? State which heat treatment may be considered when maximum toughness is required?

QU3.

What are the four main considerations for determining pre-heat temperatures, and as a welding inspector, which factors require inspection when applying pre-heat to carbon steel joint to be welded

QU4.

What factors need to be checked/controlled during a heat treatment process?

QU5.

Which heat treatment process is required when maximum' ductility is required. for example for cold working operations or extensive machining?

l)

\ 1

Senior Welding Inspection - QU Heat Treatments Sec 18 Copyright © 2003 TWI Ltd

~unlnJ pUB ~n!PlaM SBD

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Oxy Fuel Gas Welding and Cutting: The oxy fuel gas heating method has been used for many decades as a portable means of applying heat for many operations directly linked to welding, some of which are given below: 1) 3) 5) 7)

Pre-heating. Cutting. Brazing. Fusion welding.

2) 4) 6) 8)

PWHT. Soldering. Bronze welding. Straightening.

The equipment generally consists of 2 cylinders, 1 containing acetylene and 1 containing oxygen. Acetylene gas is very unstable and will self detonate at very low pressure, hence it becomes a very dangerous gas to store in a cylinder under pressure. To enable storage to be achieved acetylene is dissolved in liquid acetone, which can absorb around 25 times its own volume of acetylene gas. The acetone is then absorbed in a charcoal and kapok mass, this makes the gas much more stable to store.

\

For this reason the cylinder should always be used in the vertical position, as liquid acetone will be expelled from the blowpipe if it is not used vertically. This will have a similar effect to a flame-thrower, and is a very dangerous situation. If transported, or stored horizontally the cylinder should be placed vertically and not used for a minimum of 1 hour to avoid this effect. Oxygen may be supplied at pressures of up to 3,500 PSI and must therefore be treated with the greatest respect. Should the valve seat of an oxygen cylinder become fractured by sudden impact the results would be horrific, with a high possibility of death for anyone in the vicinity.

(

Key safety factors that must be observed: Cylinders must be secured in vertical position

Only correct fittings must be used for connections*

Oil and grease must not be used on connections**

Left-handed threads must be used for fuel gasses

Colour coding of hoses must be adhered to

Flash back arrestors must be used on oxygen and fuel gas supplies

One way valves must be used on each hose/torch connection

The correct start up and shutdown procedure must be followed

All equipment must be thoroughly leak tested

*Use of non-propriety grades of brass may contain a high % of Cu which may form

explosive compounds on contact with pressurised acetylene.

**Oxygen will readily spontaneously combust when in contact with oil and grease.

Senior Welding Inspection - Oxy - Fuel Gas Welding /Cuttit1!9.1 Copyright © 2002 TWI Ltd

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A typical set of oxy-acetylene welding equipment is shown below:

-.-: Outlet

pressure gaug e

Cylind.,r contents gauge

\",

l""/'

AcotlylillrW

hose

••

">. r.y!inder

A.cetv1eno

IMaroonl

/' Safety cradle cvlinder stands

Oxy - Acetylene Fusion Welding: \

"

The flame temperature of Acetylene combusted in air is 2,300 DC, whilst the flame temperature combusted with oxygen is 3,200 DC, which is the highest temperature achievable from the normal combustion of industrial gases. This is higher than all the metals with the exception of tungsten, which has a melting point of over 3,410 DC. During the welding of metals and alloys it is required that the surface oxide needs to be removed from the molten pool. In the arc welding processes the heat of the arc is generally high enough to melt the surface oxides of the metal with the exception of the TIG welding of aluminium as the surface oxide called alumina (aluminium oxide) has a melting point of over 2000 DC For this reason we often need to use a flux when gas welding many ferrous and non ferrous alloys, such as the fusion welding of stainless steels and aluminium alloys. When welding plain carbon steels we do not need a nux as the melting point of iron oxide is below that of the alloy.

Senior Welding Inspection - Oxy - Fuel Gas Welding ICuttilll9 ,2 Copyright © 2002 TWI Ltd

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Uses

Oxy - Acetylene Flame Types

A neutral flame used for the fusion welding of most metals and alloys, including all types of steels Also used for cutting (nozzle difference)

An oxidising flame used mainly for bronze welding.

A carburising flame used mainly for hard facing, and the fusion welding and brazing of aluminium and its alloys.

Oxy - Fuel Gas Brazing and Bronze Welding: Oxy fuel gas welding may be used very successfully as a heat source for brazing and bronze welding, the difference between the terms being that the term brazing involves a capillary action of some kind within the joint, and bronze welding is simply a shape of weld, which is generally a fillet or butt weld, made of a bronze, or brass alloy. Cast irons are very often brazed as the heat input is far less than fusion welding, and therefore the chances of cracking due to expansion forces is also less. 9% Nickel bronze filler wires are mostly used for brazing of cast irons. (Nickel bronze has a tensile strength double that of low carbon steels) Aluminium and aluminium alloys may be brazed using an Oxy-Acetylene flame heat source, with an aluminium braze filler metal containing>15% silicon. In the correct application, a brazed, or bronze welded joint may be stronger than a fusion welded joint, as the surface area of bonding is much higher, as shown below; Area of fusion welds

Area of braze weld .' .·.Z··~·.::·~·.::·~'.:.~·~:::5·:·~·:·:·_tr;< .

Fusion welded T joint

Senior Welding Inspection - Oxy - Fuel Gas Welding /CuttiI1l:9.3 Copyright © 2002 TWI Ltd

Brazed T joint

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Oxy Fuel Gas Cutting: lu oxy-fuel gas cutting we do not need to melt the steel, but simply heat it until il reaches its ignition temperature. (Appears bright cherry red) At this temperature the iron will react with pure oxygen to produce an exothermic chemical reaction, the product being FE3 0 4 or magnetic oxide of iron. A jet of pure oxygen is sent from an orifice in the centre of the nozzle that reacts with the iron at its ignition temperature. The velocity of the oxygen jet removes the magnetic iron oxide from the cut face (The kerf),

"

\-/)

As we do not require to reach the high temperatures needed for fusion welding, we do not need to use acetylene gas. Therefore propane, butane and other cheaper gases may be used for oxy-fuel gas cutting. Temperature reached during the chemical exothermic reaction of oxygen with iron is sufficient to melt most metals, though a restriction of oxy-fuel gas cutting is that it cannot be used successfully in its conventional form to cut metals with high melting point oxides (i.e. Stainless Steels). By the addition of an iron powder injection system, the iron-oxygen reaction can be produced ahead of the materials surface by the exothermic reaction of the heated iron powder within the oxygen jet. The thickness of steel that may be cut using the Oxy-Fuel gas cutting method is solely dependant on the nozzle size and gas pressure available. The oxy-fuel gas cutting system may be simply mechanised and used to cut plates (Photograph 1) and preparations on pipe to be welded. (Photographs 2.3. & 4). It must be recognised that the cut face may be hardened up to a depth of 3mm, therefore dressing is normally required to remove this hardened region as well as removing oxide. The main inspection points of conventional oxy fuel gas cutting will include: SAFETY POINTS +

\,

1) 3) S) 7)

Cutting nozzle type, and size. Cutting oxygen pressure. Angle of cut. Pre-heat, if specified.

Nozzle distance from work. Speed of travel of the cutting head. Fuel gas type and flame setting. The condition of the kerf.

2) 4) 6) 8)

If all the above parameters are set correctly then the cut face or kerf should appear as in photograph 4 below• •,.~.:

-;t.. ~'::~:--:..

":", ,,,"X',,,_ '".

' I

Main oxygen~ cutting jet

,:{f. :'<'.:~

:f!~ ';i

Senior Welding Inspection - Oxy - Fuel Gas Welding /Cuttirt9.4 Copyright © 2002 TW[ Ltd

Fuel gas & oxygen

Fe304 Jet

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Questions

Oxy Fuel Gas Welding and Cutting QU1.

What is the principal limitation of oxy/fuel gas cutting?

QU2.

Give three flame types and their respective applications

QU3.

What is the flame temperature of acetylene in Oxygen?

QU5.

Why is preheat some times required prior to oxy-gas cutting.

QU6.

Give any major limitations of oxy-acetylene welding

lJ

\

Senior Welding Inspection - QU Oxy Fuel Gas Welding & Cutting Sec 19 Copyright © 2003 TWI Ltd

.

)

~U!llnJ BWSBld pUB ~JV

OZ

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Arc and Plasma Cutting Processes: All thermal cutting processes that we use in fabrication must satisfy 2 major functions to be successfully used as a cutting/gouging process.

1)A high temperature. (Capable of melting the materials being cut) 2) A high Velocity. (Capable of removing the molten materials in the cut) In oxy-fuel gas cutting described in the previous section the temperature is achieved by the exothermic reaction of iron at its ignition temperature and pure oxygen. The product of iron oxide is removed from the cut edge, or kerf by the velocity of the oxygen gas jet.

~- )

Plasma Cutting: Plasma cutting utilises the temperatures reached from the production of the plasmas from certain types of gases. Nitrogen gas plasma can reach a temperature of over 20,000°C but temperature of air plasma is much lower. Air however is freely available and therefore cheaper and can be compressed by a compressor in the equipment, but is restricted in the depth of cut attainable. The velocity for plasma cutting is produced by the expansion of the plasma in the torch chamber, which is then forced through a constricting orifice at the torch head, producing the velocity required. There are 2 different types of the plasma cutting process, which are: 1) 2)

Transferred arc. (Used for cutting conductive materials) Non-transferred arc. (Used for cutting non-conductive materials)

Air Plasma Cutting Equipment

----, Power source

-

.. -.-. ~

Shielding gas

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Arc Cutting & Gouging: We can use the temperature attained by an electric arc in cutting processes to reach the temperatures required to melt the metal or alloy to be cut. There are 3 types of process that are generally used, the main differences being in the consumables and the gas used in producing the velocity required.

(,J

1)

Conventional cutting/gouging electrodes.

2)

Oxy-Arc cutting/gouging.

3)

Arc-Air cutting/gouging.

Conventional cutting/gouging electrodes: In conventional arc gouging there is no requirement for any additional equipment other than that required for MMNSMAW welding. The consumables consist of a light alloy central core wire, which is mainly to give rigidity, and a heavy flux coating, which provides elements that produce arc energy. The arc is struck in a conventional way to MMA welding, however the arc melts the base material, which is then pushed away by using a pushing action with the electrode. The process generates a great volume of welding fume and is not very effective, but is suitable for the occasional need to remove old welds, or gouge grooves in base metal.

Oxy-Arc cutting/gouging: In oxy-arc cutting we require a special type of electrode holder. The consumables are tubular in section and are coated with a very light flux coating. The electrode is located in the special electrode holder to which is attached a power cable and gas hose. The power cable is attached to the power source and the gas hose is attached to a source of compressed oxygen. The arc is struck and the compressed oxygen may be activated at the torch head. The heat of the electric arc will melt the base metal or alloy and the velocity to remove it is provided by the compressed oxygen. When cutting ferritic alloys, a similar effect can be produced to the exothermic reaction found when using conventional oxy-fuel gas cutting. This process is generally used for decommissioning/scrapping plant as the cut surface is generally not consistent.

Arc-Air cutting/gouging: Arc-air cutting is the most commonly used method of arc cutting/gouging and is used extensively for gouging old welds and removing materials. The consumable is a copper coated carbon electrode. The gas used is of course compressed air. The' process is basically a "melt and blow process" in that no exothermic reaction is involved The main disadvantages include the high level of high-pitched noise produced and the volume of fumes generated. The cut face will require dressing due to potential carbon pick up and the rapid heating/ cooling cycle involved. A major safety inspection point in the use of all arc processes is that correct ear protection is in use and also that an efficient fully isolated breathing supply system is also being used.


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Oxy-Arc Gouging.

1)

Light flux coating

Gouged metal

Cross Section

~

\J

Tubular steel core wire containing compressed oxygen

".l~:-:-

_l'''''':.:L''£''_'.~~ ••".{'..!~

2)

Arc-Air Gouging.

Jet of compressed air supplied from holes in the electrode holder ----. ~gedmetal

~ ~

~

0

Copper covered carbon electrode

.'.' ... ~.;.;.~. ;., ~::;,.,


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Questions

Arc and Plasma Cutting

QU1.

What are the two types of the plasma cutting process? State what each cutting process is used for.

QU2.

Name three types of arc cutting and gouging processes.

QU3.

What is the main application area for arc gouging, with regards to welding related activities?

QU4.

At what temperature is reached during Nitrogen gas plasma cutting?

QU5.

State at least one advantage of plasma arc cutting over conventional thermal cutting (oxy-fuel gas). .

Senior Welding Inspection - QU Arc and Plasma cutting Sec 20 Copyright © 2003 TWI Ltd

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Welding Safety: As a respected officer, it is a duty of a welding inspector to ensure that safe working practices are strictly followed. Safety in welding can be divided into several areas, some of which are as follows:

1)

Welding/cutting process safety.

2)

Electrical safety.

3)

Welding fumes & gases. (Use & storage of gases.)

4)

Safe use of lifting equipment.

5)

Safe use of hand tools and grinding machines.

6)

General welding safety awareness.

1)

\Velding/cutting process safety:

( )

Consideration should be given to safety when using gas, or arc cutting systems by: a)

Removing any combustible materials from the area.

b)

Checking all containers to be cut or welded are fume free. (Permits to work etc.)

c)

Providing ventilation and extraction where required.

d)

Ensuring good gas safety is being practised.

e)

Keeping oil and grease away from oxygen.

f)

Appropriate PPE is worn at all times

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Electrical Safety:

Safe working with electrical power is essential. Ensure that insulation is used where

required and that cables and connections are in good condition. Be especially vigilant in

wet or damp conditions.

Low voltage supply (110 v) must be used where appropriate for all power tools etc.

All electrical equipment must be regularly tested and identified as such accordingly.

3)

Gases & Fume Safety:

The danger of exposure to dangerous fumes and gases in welding cannot be over emphasised. Exposure to these welding fumes and gases may come from electrodes, plating, base metals and gases used in and produced during the welding process.

~)

Dangerous gases that may be produced during the welding process include ozone, nitrous oxides, and phosgene (caused by the breakdown of Trichloroethlylene based degreasing agents in arc light); all of which are extremely poisonous and will result in death when over-exposure occurs. Other gases used in welding can also cause problems by displacing air, or reducing the oxygen content. Most gases are stored under high pressure, and therefore the greatest care should be exercised in the storage and use of such gases. All gases should be treated with respect and are considered a major hazard area in welding safety.

(-

\

Cadmium, chromium, and other metallic fumes are extremely toxic and again will result in death if over-exposure results. Know the effects of a coating fume and always use correct extraction or breathing systems, which are essential items in safe welding practice. If in doubt stop the work! Until a health and safety officer takes full responsibility.

4)

Lifting Equipment:

It is essential that correct lifting practices are used for slinging and that strops of the correct load rating are used for lifts. All lifting equipment is subject to regular inspection according to national regulations in the country concerned. In the UK this is governed by the HSE under the LOLER requirements, which are mandatory for all operations within the UK. Cutting comers is an extremely dangerous practice when lifting and often leads to fatalities. (Never stand beneath a load)


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5)

Hand tools and grinding machines:

Hand tools should always be in a sate and serviceable condition (grinding machines should have wheels changed by an approved person) and should always be used in a safe and correct manner. Use cutting discs for cutting, and grinding discs for grinding only. 6)

General:

Accidents do not just happen, but are usually attributable to someone's neglect, or ignorance of a hazard. Be aware of the hazards in any welding job, and always minimise the risk. Always refer to your safety advisor if any doubt exists.

~


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Exercise:

Complete the table below, by inserting any specific safety issues that will need to be

considered:

Material

Process

Other Information

Stainless Steel

MAG

Vessel contained explosive & toxic compounds

Stainless Steel

Silver braze

Cd braze alloy

Steel

Gas Welding

Galvanized

Steel

MMA

Cadmium plated

Steel

TIG

Degreased with Trichloroethylene, but still damp

Steel

Arc Air Gouging

Confined space

Steel

Overhead Lift

500 tonnes

Steel

MMA

Site work Wet conditions

Stainless Steel

TIG

Confined space

Issues to be considered

l)

~

I

. Steel

Oxy- Fuel cutting

In an area containing combustibles

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Questions Welding Safety

QU1.

How can the welder protect himself against UVA light:

QU2.

Occasional accidental exposure to the eye can produce an extremely painful condition known as:

QU3.

To reduce the possibility of electric shock, a correctly wired welding circuit should contain three leads these leads are:

cJ

a).

b). c).

QU4.

Arc welding produce fumes and dust particles, state the precautions a welder must take to protect against fumes and dust particles:

QU5

When welding on items, which have been degreased particular precautions, must be made, why?

(

Senior Welding Inspection - QU Arc Welding Safety Sec 21

Copyright © 2003 TWI Ltd

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slaalS JO AnnquPla M. aql.

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The Weldabilitv of Steels: 0/

In general, the term weldability of materials can be defined as: "The ability of a material to be welded by most of the common welding processes, and retain the properties for which it has been designed" The weldability of steels can involve many factors depending on the type of steel, the process and the mechanical properties required. Welding engineers involved only with the welding of C/Mn structural steel could probably define weldability as carbon equivalent, however this is a narrow application of the term. Poor weldability generally results in the occurrence of some sort of cracking problem, though most steels have a degree of weldability. When considering any type of weld cracking mechanism, three elements must be present for it's occurrence: 1) 2) 3)

Stress.

Restraint.

Susceptible microstructure.

1. Residual stress is always present in weldments, through local expansion & contraction. 2. Restraint may be a local restriction, or through plates being welded to others. 3. The microstructure is often made susceptible to cracking by the process of welding.

The types of cracking mechanism prevalent in steels in which the CSWIP 3.1 Welding Inspector should have some knowledge are:

1.

Hydrogen induced HAZ cracking. (elMn steels)

2.

Hydrogen induced weld metal cracking. (HSLA steels)

3.

Solidification cracking. (All steels)

4.

Lamellar tearing. (All steels)

5.

Inter-crystalline corrosion. (Stainless steels)

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Definitions:

To compliment this section it is important to understand the following terms.

Solubility:

To be able to dissolve one substance in another, like sugar in tea.

Maximum Solubility:

The maximum % of a substance that can be dissolved in another.

Steel:

An alloy of the iron with the non-metal carbon. (0.01 - 1.4% C)

Plain Carbon Steels:

Steels that contain only iron & carbon as main alloying elements. Traces ofMn, Si, A, P & S may be also present from refining.

Low Carbon Steel:

Plain carbon steels containing between 0.0 I - 0.3% C

lVIedium Carbon Steel:

Plain carbon steels containing between 0.3 - 0.6% C

High Carbon Steels:

Plain carbon steels containing between 0.6 - 1.4 % C

Low Alloy Steels:

High

Alloy Steels:

Ferrite:

Steel containing iron and carbon, and other allying elements i.e. lVIn, Cr, Ni, lVIo < 7% Total

Steel containing iron and carbon, and other alloying elements i.e. lVIn, Cr, Ni, Mo > 7% Total . A low temperature structure of iron & dissolved carbon, the maximum solubility of carbon occurring in this structure is 0.02 %

Austenite:

A high temperature structure of iron & dissolved carbon, the maximum solubility of carbon occurring in this structure is 2.06%

Martensite:

A hard structure produced in some steels by the rapid ,cooling from high temperature austenite, generally to temperatures below 300°C

Diffusion:

The movement of solute atoms, or molecules through a crystalline structure. This can generally be accelerated with increasing levels of heat energy in the material.

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Effect of alloying elements: Elements may be added to steels to produce the properties required to make it useful for

an application. Most elements can have many effects on the properties 0 t' steels.

Below is a list of most common elements alloyed to steel, with some of their effects.

Aluminium:

Alloyed to steels mainly as a grain refiner, and is also used as a de oxidising agent in triple de-oxidised steel and welding consumables.

Carbon:

A prime and essential element in steel alloys. An increase in Carbon content will increase hardness and strength, but reduces the ductility.

Chromium:

Alloyed in additions > 12 % to produce stainless steels, but is 0 ften used in low alloy steels < 5% to increase hardness strength and greatly increase the resistance to oxidation at higher temperatures. Chromium stabilises carbide formation, but promotes grain growth if added in isolation. It is thus often alloyed together with Ni or Mo

Manganese:

Alloyed to structural steels < 1.6% to increase the toughness and strength. It is also used to control solidification cracking in ferritic steels. Alloyed up to 14% in wearlimpact resistant Hadfield steel.

Molybdenum:

Alloyed to low alloy steels to control the effects of creep. It is also used as a stabilising element in stainless steels, and will a limit the effects of grain growth. Alloyed in Cr/Ni/Mo low alloy steels to control an effect called temper embrittlement.

Nickel:

Nickel is alloyed to produce austenitic stainless steels. It may also be added < 9% in the low temperature nickel steels. It promotes graphitisation, but is good grain refiner, and is often used to offset some effects of Chromium. Nickel is very expensive, but improves the strength, toughness, ductility and corrosion resistance of steels.

Niobium:

Carbide former used to stabilise stainless, also in HSLA < .05%

Silicon:

Is alloyed in small amounts < 0.8% as a de-oxidant in ferritic steels. It is alloyed to valve and spring steels, and can also increase fluidity.

Titanium:

Used mainly to stabilise stainless steel, and < .05% in HSLA steels.

Tungsten:

Mainly alloyed to high alloy High Speed Tool steels. This increases the high temperature hardness required of such steels, due to the tempering effect of frictional heat on other steels during cutting.

Vanadium:

Used as a de-oxidant, or as a binary alloy as in HSLA steels < .05%

It should be remembered that most alloying additions increases the ability of a steel to harden by the thermal hardening process. This property is termed "hardenability" Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Crack type:

Hydrogen cracking (cold cracking)

Location:

a. HAZ. Longitudinal b. Weld metal. Transverse or longitudinal

Steel types:

a. All hardenable steels b. HSLA steels & QT Steels Martensite.

Susceptible microstructure:

Causes:

(~)

Hydrogen cracking may occur in the HAZ or the weld metal, depending on the type of steel being welded. Hydrogen may be absorbed into the arc from water on the plates, moisture in the air, paint or oil on the plates or the breakdown of gas shielding etc. An E60 I0 cellulosic electrode uses hydrogen as a shielding gas. Hydrogen will easily dissolve in the molten weld metal, and remain in solution on solidification to austenite. The weld will cool down and transform to ferrite, where the hydrogen has less solubility and will want to diffuse to the HAZ, which will still be austenitic. This occurs rapidly as diffusion is increased with high temperatures. If the HAZ is un hardenable it will itself transform to ferrite and the hydrogen, which has some solubility in ferrite, will eventually diffuse out of the weldment. If the HAZ has some hardenability, then the transformation of the HAZ will be from austenite to martensite, which has no solubility for hydrogen. This will result in great internal stress, occurring in a microstructure, which is very brittle. Cracks may occur at areas of high stress concentration, such as the toes of a weld, and move through the hardened HAZ and in extreme cases, the weld metal.

The four minimum critical factors and their values, where hydrogen cracking is likely to occur, are considered to be: a.

Hydrogen content: > 15 ml/l00 gm of deposited weld metal.

b.

Hardness: > 350 VPN.

c.

Stresses: > 0.5 of the yield stress.

d.

Temperature: < 300°C.

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Hydrogen may be absorbed into the arc zone and liquid weld metal from:

Rust, oil, grease, or paint etc. on the plate.

E 6010 electrodes produce

Hz as a shielding gas. "

A long, or an unstable arc .

.:U~

':'~"''''.Fo:.~ i~~l~~~~~5;Jjj:

:m~~,~.::.~,~i:

1111~~~~5~~~m:

\ ;I~~~~~~~~i

•

.

se

y

~

Austenite in HAZ

Weld metal changes phase to

a

ferrite and

Hz diffuses into HAZ H 2 diffusion to HAZ

martensite at 300°C trapping Hz and forcing it out of solution.

Martensitic HAZ

Hz HAZ Cracking

Austenite in HAZ changes to

(

Stress concentrations a. Butt joints.

Stress concentrations

Hz HAZ Cracking lVIartensitic HAZ

b. T joints.


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Prevention of hydrogen HAZ cracking: To control hydrogen cracking in the HAZ it may be necessary to pre-heat the weldment. Pre-heating retards the rate of cooling and suppresses the formation of martensite and other hard structures, which is formed on rapid cooling. It will also allow some of the trapped hydrogen to diffuse back to the atmosphere.

Elements that are to be considered when calculating pre-heat are: a. Hardenability of the joint. (i.e, Ceq) c. Arc energy input.

I, - ')

'--/

b. Thickness of metal and joint type. d. Hydrogen scale, or achievable limit.

Hydrogen induced weld metal cracking is found when welding HSLA (High strength low alloy) steels which are alloyed with micro amounts of titanium, vanadium and/or niobium. (Typically 0.05%) In order to match the weld strength to plate strength, weld metal with increased carbon content is used, as carbon content increases tensile strength. A graph showing the effect of carbon on the properties of plain carbon steels is given below. This results in a hardenable steel weld deposit, in which the austenite of the weld transforms directly to martensite, causing the same conditions as found in the HAZ previously and cracking may now occur within the weld metal.

.,

Prevention of H 2 for these steels is as per H2 HAZ cracking, by the preheating of the weld area, but this is principally to allow any trapped hydrogen the time at temperature to diffuse from the weld & HAZ area back to the atmosphere.

. (

Both HAZ and weld metal H2 cracks are considered as cold cracks « 300°C) and final inspection is often delayed for up to 72 hours as these cracks may appear within this time.

Tensile Strength

.o

Ductility ~

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 % Carbon


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It can be clearly seen from the graph that additions of carbon (up to O.83%C) will increase the tens i le strength 0 f plain carbon steel dramaticall y. \Vhilst this wi II serve the purpose of cheaply matching the weld metal strength to the base metal, it will also give the weld metal much higher hardenability. This may now result in H2 cracking in the weld metal, as the weld will transform from austenite - martensite trapping the hydrogen in weld, before it is able to diffuse to the HAZ. It can also be seen from the graph that higher carbon steels have very little ductility, which further complicates the problem. Cracks tend to be transverse, as the main residual stresses are generally in the longitudinal direction, though they may occasionally be longitudinal, or even at 45° to the weld metal.

High strength low ductility weld metal.

Hydrogen induced weld metal cracks.

Prevention of hydrogen cracking in the weld metal of HSLA, or Micro-alloyed steels is very much the same as for hydrogen cracking in the HAZ of other low alloy steels. Summary of prevention methods: a. b. c. d. e. f. g. h. i.

Use a low hydrogen process and/or hydrogen controlled consumables. Maximise arc energy (taking HAZ and weld toughness into consideration). Use correctly treated H2 controlled consumables Minimise restraint. Ensure plate is dry and free from rust, oil, paint or other coatings. Use a constant and correct arc length. Ensure pre-heat is applied and maintained before any arc is struck. Control interpass temperature Ensure welding is carried out under controlled environmental conditions

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Crack type:

Solidification cracking (Hot cracking)

Location: Steel types: Susceptible microstructure:

Weld centre. (longitudinal) All Columnar grains. (In the direction of solidification)

Causes: Solidification cracking, is a hot cracking mechanism that occurs during solidification of welds in steels, having high sulphur content or contaminated with sulphur.

(

--)

Another potential cause is the depth/width ratio of the weld, which in normal welding situations refers to deep narrow welds (cladding applications may produce shallow wide welds, which are also prone to this problem).

~

Therefore if we have a combination of deep narrow welds with a high incidence of sulphur we are great! y increasing the likelihood of hot cracking. As with all cracking mechanisms stress plays a major role in susceptibility. During welding, sulphur in or on the plate may be re-melted and will join with the iron to form iron sulphides. Iron sulphides are low melting point impurities, which will seek the last point of solidification of the weld, which is the weld centreline.

It is here that they form liquid films around the hot solidifying grains, which are themselves now under great stress due to the actions of contractional forces. The bonding between the grains may now be insufficient to maintain cohesion and a crack will result running the length of the weld on its centreline.

(

Prevention of solidification cracking in ferritic steels: To prevent the occurrence of solidification cracking in ferritic steels that contain high levels of sulphur (these steels are said to suffer from Hot Shortness), manganese is added to the weld via the consumable. Sulphur related:

Scrutiny of Mill sheets is essential to assess the materials Sulphur content. A typical maximum level allowed in a low carbon steel specification is 0.05%. Even this seemingly low figure may be excessive for certain high stress/higher carbon applications, or if the depth/width ratio is excessive. Another potential source of Sulphur is paint, oil and grease. This is why temperature Crayons always carry the statement "sulphur free".


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This is a prime reason for thorough cleaning, which becomes of even greater importance when dealing with Austenitic Stainless Steels if material availability dictates the necessity of welding high sulphur steels consumables with a relatively high Manganese content are specified. An example of steel with very high sulphur levels would be a free machining steel. Some of the free machining steels could be considered not weldable in normal circumstances as sulphur levels are so high.

Manganese has the effect of forming preferential manganese sulphides with the sulphur. Mn/S are spherical, solidify at a higher temperature than iron sulphides and therefore are distributed more evenly throughout the weld. The cohesion between the grains is thus maintained and the crack will not occur.

('--")

Careful consideration must be given to the Mn/S ratio, which should be in the region of about 40: 1. Increased carbon content can rapidly increase the required ratio exponentially; thus carbon must be reduced as low as possible, with low plate dilution and low carbon, high manganese filler wires. A summary of prevention methods: a. Use low dilution processes c. Maintain a low carbon content e. Specify low sulphur content of plate g. Thorough cleaning of preparation

b. Use high manganese consumables d. Minimise restraint/stress f. Remove laminations h. Minimise dilution

.Solidification cracking (Sulphur related)

sut~h;de<

Direction of grain solidification Weld centre line with liqnid Iron aronnd the solidifying grains -


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Effect of Manganese Sulphides formation

Direction of grain solidification

~~

Spheroidal Mn sulphides form between the solidifying grains, maintaining inter-granular strength.

(J

Depth/width ratio related The shape of the weld will also contribute to the possibility of cracking. This may be totally independent from the sulphur aspect but is usually in combination. Processes such as SAW and MAG (using spray transfer) may readily provide these deep/narrow susceptible welds.

\

However it is not the weld volume that is the prime factor but the weld shape as referred to previously. Therefore root runs and tack welds may readily provide the susceptible profile. As root runs are also areas of high dilution (therefore greater sulphur pick up) and more likely to be highly stressed these must always be inspected with solidification cracking in mind.

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Solidification cracking in Austenitic Stainless steels Austenitic stainless steel is particularly prone to solidification cracking.

This is due to:

A comparatively large grain size, which gives rise to a reduction of grain boundary area.

High coefficient of thermal expansion, with resultant high stress.

An atomic structure that is very intolerant of contaminants, such as sulphur,

phosphorous and additional elements such as boron.

The cause and avoidance may be regarded as the same as that of plain carbon steel but

with extra emphasis on thorough cleaning requirements prior to welding.

The welding procedure will have been written to control the balance of austenite and

ferrite in the weld metal. This balance will directly effect the structures tolerance of

contaminants and the resultant grain boundary area. This is why the filler material

specified often does not appear to match the parent material.

Careful monitoring of parameters is required to control dilution to ensure this balance is

maintained.


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Crack type:

Lamellar tearing.

Location: Steel types: Susceptible microstructure:

Parent material

Any steel type

Low through thickness ductility

Causes:

When welding of joints where high contractional stresses are passed in the through

thickness direction of one of the plates in the joint.

This short transverse direction is lacking in ductility in cold rolled plates, but ductility

is required to accommodate the plastic strain caused by contraction.

(,.

')

A stepped like crack may initiate in the affected plate, just below the HAZ, in a horizontal plane. Micro inclusions of impurities such as sulphides and silicates, which occur during steel manufacture, cause this poor through thickness ductility. When subjected to high short transverse stress this may lead to lamellar tearing

Lamellar tearing. (Ferritic steels)

b. Butt joints.

--.:.

~

'r.~~.

Through thickness contractional strain. =

c. T joints.


~

d. Lap joints.

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Methods of controlling the occurrence of lamellar tearing:

1) Change of weld design

[;

High ductility weld metal

2) Use weld metal buttering layers

3) Minimise restraint

I

Aluminium wire

A pre formed T piece

4)

Use pre formed T piece for critical joints


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Summary of Weldahility of Steels: Key words: Hydrogen induced HAZ or weld metal cracks. Cause' R~ HAZ cracks Process Consumables Paint, Rust, Grease Delayed inspection. Solubility HAZ o concentrations Diffusion Martensite Critical factors = Transformation Hardness> 350VPN Hydrogen>15ml o > 0.5 yield stress. Temp < 300°C HSLA weld cracks Weld contraction

()

(

Prevention' Pre-heat Minimise restraint Arc energy

High strength metal Transverse crack

High carbon weld Micro alloy Nb T V

Low ductility Longitudinal (J

Hydrogen control Remove coatings Use low Ceq plate

Bake consumable Stable arc length Use hot pass ASAP

Use low H Process y SIS Weld metal Use low H 2 Cons'

2

Solidification cracking in C/Mn steels. Cause' Sulphur. Fe/Sulphides Low melting point film Contraction forces

Weld centreline Loss of cohesion

Contraction Hot shortness

Prevention: High manganese % Control heat input

Control carbon % Change Preparation

Use low dilution Cleaning

Keywords:

Use low restraint Control sulphur %

Lamellar tearing in C/Mn steels. Cause: Poor ductility Plastic strain Contraction Short transverse

Key words: Micro inclusions Segregation

\

Prevention' NDT for laminations Re-design joint

I Through '1' tensile I Buttering layers I Forged T piece

I Chemical analysis

Contraction gap Control heat input

Inter - crystalline corrosion in stainless steels. Key words: Cause: Chromium depletion Temp gradient I Cr Carbide Sensitisation Parallel to weld I In HAZ I Loss of resistance Stabilised

T

Prevention: Low Carbon .03% .Low heat inout

Stabilising elements I Niobium Titanium I Solution anneal


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Questions Weldability of Steels

QU1.

Briefly discuss the four essential factors for hydrogen cracking to occur

QU2.

State four precautions to reduce hydrogen cracking

QU3.

In which steel type is weld decay experienced? and state how it can be prevented.

QU4.

State the precautions to reduce the chance ofthe occurrence of solidification cracking

QU5.

State four essential factors for lamellar tearing to occur

(~

~

)

Senior Welding Inspection - QU Weldabilityof Steels Sec 22 Copyright © 2003 TWI Ltd

smourssessv a.lnl~8.1JI £'Z

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Fracture Assessments: You are required to:

• Record the sample number • Sketch the fracture surface. • Indicate the fracture initiation points (if known) (

• Show any defects present on the fracture surface • Identify the primary mode of failure. • Identify the secondary mode of failure (if present) • State the location of failure e.g parent material, weld metal or both (ifknown) • Write a conclusion to summarise your findings, providing reasons for the

fracture occurance and evidence.

• Sign and date your report


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Fracture Assessments: Example Report

Sample Number 12.

D

N,

T.

".'

.. "I

:

C)

A. Crackslforging bursts

C

.

) P-,

B. Fatiguefracture surface C. Ductilefracture surface D. Brittlefracture surface

A

E rj!"t~f ~ ,

'.0

B

E. Initiation point

A

Primary and final mode of failure: Fatigue fracture

Secondary mode of failure: Brittle fracture.

Third mode of failure: Brittle fracture

( .Conclusion: The threaded barfa iledfrom afatigue crack, which initiated at the base 'of the thread (E). The primary mode offailure is a fatigue fracture (B) this is evident by the smooth fracture surface, which initiatedfrom the base ofthe thread (E). The secondary mode offailure is a ductile fracture (C) this is evident by the fibrous appearance ofthe fracture surface with evidence of plastic deformation. The final mode offailure is brittle (D) this is evident by the bright crystalline fracture surface. Name: Mark Roqers

Date: 13/06/03.


23.2

Signature: M.S Roqers

Rev 09-09-02

SW13.2

Fracture Surfaces Introduction: • Fatigue and brittle fractures are the two most

important forms of service failure in welded

structures

e

Fatigue fractures account for more than 90% of all "'I

service failures

C-.--/

- Brittle fractures although rare in occurrence are usually catastrophic in economic terms and may cause loss in life Copyright © 2003 Nil Ltd

M.

s , Rog9rs

SW13.2

Fatigue Fracture Surfaces Features of Fatigue fractures:

(

-Service failure -Occurs under cyclic/fluctuating stress -Smooth appearance -Initiates at some form of stress concentration. These stress points may be weld defects, poor profiles, notches etc -In certain cases evidence of beach markings -Fracture occurs perpendicular to the applied stress Copyright © 2003 TWI ltd M. S.Rogers.

Fatigue Fracture Surfaces

SW13.2

()

Copyright e 2003 TWI Ltd

:-i• .3. Rog·~o:s

Fatigue. Fracture Surfaces

SW13.2

c


M. S. Rogen

SW13.2

Ductile Fracture Features of ductile fractures:

-Rouqh fibrous appearance

-Dull grey in colour

·In certain cases evidence of shear lips

LJ

-ln most cases a reduction in area

-Occurs as a secondary mode of failure


K.

Brittle Fracture

S.Rog~r9

SW13.2

Features of brittle fractures: (

·Usually occurs without visible or audible warning

-ln certain cases bright crystalline appearance

-ln certain cases a chevron pattern appearance, the

chevron pattern points back to the point of

initiation

-Little if no reduction in area

-Little if no evidence off shear lips

-May be a straight brittle fracture or secondary

mode of failure,


l-:.S.ltogers

I .

!

SW13.2

Fracture Sample 1 Ductile Fracture

(J

Initiation point Initiation point Initiation point Initiation point Initiation point F. Initiation point G. Initiation point

H. Weld crater/crater pipe I. Cap undercut J. Ductile fracture K. Ductile fracture L. Fatigue fracture M. Shear lips


!of.

Fracture Sample 2

S.Rog~rs

SW13.2

(

,( ~-

A-A. Initiation point B. Stepping C. Stepping D. Ductile fracture E. Inclusions F. Inclusions G. Fatigue fracture Copyright © 2003 TWI Ltd

Ductile Fracture

M. S. Rogen

SW13.2

Fracture Sample 3 Ductile

Fracture

A.

Slag inclusion

B.

Slag inclusion

C.

Slag inclusion

D.

Weld Defect

( \

E. Slag inclusion F. Shear lip G. Fatigue fracture H. Ductile fracture Note: Reduction in area Copyright © 2003 TWI Ltd

\---)

M. S.R.ogers

Fracture Sample 4

SWl3.2

)

Ductile

Fracture

A.

Gas porelinitiation point

B. Beach mark


C.

Ductile fracture

D.

Fatigue fracture

E.

Shear lip

F.

Shear lip

G.

Shear lip M. S. Rogers

SW13.2

Fracture Sample 5

Brittle Fracture

..J _ \ '.)

A. Weld defect possible toe crack initiation point B. Small shear lip C. Shear lip D. Shear lip Note: Patterned fracture surface - Brittle fracture. Copyright @ 2003 TWI Ltd

M. S.Rogers

Fracture Sample 6

SW13,2

/_:"'1

~/

Brittle Fracture. Note: Patterned/chevron fracture surface - Brittle fracture. Note: Small shear lips along both plate surfaces. Copyright @ 2003 TWI Ltd

M. S.Rogers

Fracture Sample 7

SW13.2

CTOD Brittle Fracture Machined notch initiation point B.

Fatigue fracture surface

C.

Brittle fracture

Note: Very little reduction in area

.(~)

and no evidence of shear lips

Copyright © 2003 1W1 Ltd

M. G.Roger:J

Fracture Sample 8

SW13.2

,.,

~

CTOD Ductile Fracture A.

Machined notch initiation point

B.

Fatigue fracture surface

C.

Ductile fracture surface

Note: The reduction in area and the large shear lips

'Copyright © 2003 1W1 Ltd

· - . .,

C )

~

H. S. Rogers

....../

Senior Welding Inspector Guide Book

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