The Welding Procedure and its Qualification
I. Welding procedure specifications A. Is to define and document the details that are to be carried out in welding specific materials B. Contents sufficiently, detailed to ensure that the welding will meet all requirements of the applicable code, standard, C. Base Metals and applicable specifications 1- Give the chemical composition. 2- Indicate condition of base metal before welding (Normalized, annealed, quenched and tempered, solution (Normalized, treated) .
3.The fabricator must know the identity of all materials Full plates or sections can be “ID” by the mill numbers. small portions cut from plates marked with the same numbers. The rolling direction of plate should be identify.
D. Welding process (partial listing) 1. Oxyacetylene “OAW” 2. Brazing 3. “SMAW” 4. “GMAW” 5. “FCAW” 6.“GTAW” 7. “SAW” 8. “ESW” 9. “SW”
E. Type, classification, composition of filler metal 1. Composition, classification designation of the filler metal mu st be included 2. Also included in specifications a. Size of electrode or filler metal For varying ( positions, metal thick ness) ness) b. Storage requirements Low hydrogen “electrodes require a dry (120oC)
F. Type of current and current rang AC or DC (DCRP or DCSP). ¾ Current range should be listed for each of the welding variables (position, thickness, electrode size). G. Welder qualification requirements welding operator qualification. ¾
Make reference to applicable welder qualification specifications
H. Joint designs and tolerances. Indicate joint design details as well as welding sequence. Use crops sectional sketches that show the thickness of material and details. of the joint or refer to standard drawings or specifications. Give tolerances for all dimensions. Joint preparation and cleaning of surfaces for welding (Before or after welding or cutting ). Joint welding details, give details for (i.e. amps, electrode size, sequence of passes, weave limitations, etc.).
I. Preheat and inter pass temperatures
measured by touching the work piece close to the weld joint with . J. Peening If peening is to be used, give details of its application And verify the results during qualification test welding Peening the middle layer of a weld distributes and balances distortion. K. Heat input heat-treated alloy steels, must not heat above the final tempering temperature used by the steel mill. Specify the preheat and inter in ter pass temperature range “maximum”. . Arc voltage range “maximum”. . Welding current range “maximum”. . Travel speed “minimum”.
L. Root preparation prior to welding from second side Describe how (Chipping, grinding, air carbon arc gouging, oxyacetylene gouging, or whatever). M. Removal of weld section for repair May be the same procedure used for preparing the root from the second side . N. Repair Welding Give details of any repair welding methods and procedures . O. Examination Type of examination for each joint will receive (i.e. radiography, magnetic particle, etc.). Visual inspection of every weld is routinely required .
P. Post heat treatment Give a full description or reference drawing, or document. heat-treated alloy steels should not exceed the final tempering temp that was given the base metal. If a full reheat treatment is intended, do the wel ding with the metal in the annealed condition. Q. Marking Require that welder identification marks be made on or near each weld. . Maintaining a record of welds made by the welders. “I.D.” marking made with low stress steel die stamps. R. Records Indicate detailed records of the welding joints.
II. Welding procedure qualification
A. There are four steps in the qualification of a welding procedure (all or none). 1. Preparation and welding of suitable samples. 2. Testing of representative specimens. 3. Evaluation of overall preparation, welding, testing, and end results. 4. Approval (if the results are favorable ). B. Preparation of Procedure Qualification sample joints 1.The size, type, and thickness are related to the type and thickness of material to be welded in production and the number, type and size of specimens to be removed for testing.
C. Testing of procedure qualification welds 1.The type and number of specimens to be removed for destructive tests will depend upon the requirements specification (. Usually include tensile strength , ductility, soundness, and NDT). 2 Be sure that your records show how the procedure qualification test welds were made and tested. D. Evaluation of test results 1. These results will be analyzed by the responsible parties to determine whether the test details and results meet the requirements specifications.
E. Approval of qualification tests and procedure specifications 1. Qualification is accomplished when the required tests have been completed and approval has been obtained. 2. Documentary evidence must be available to show that the results were indeed satisfactory. 3 .You should witness the welding and testing of all specimens; because you will gain knowledge will help in inspection. .
III. Code qualification requirements A. AWS structural welding code D1.1
1. Paragraph 5.5 sets forth the requirements for qualifying those welding procedures, which do not meet the pre -qualified status of paragraph 5.1 of that code 2. The type and number of specimens that must be tested to
quality a welding procedure are given in paragraph 5.10 a test results required are in 5.12 B. ASME boiler and pressure vessel code 1. Section IX is the basic document “Welding and brazing qualifications” 2. All sections of the ASME code required welding procedures to be qualified “in accordance with section IX” 3. Section III on nuclear components for power plants Section VIII division I on pressure vessels
IV. Changes in a qualified procedure Re-qualification is necessary when any one of the essential variables listed in the governing standard or code is changed V. Welding inspector responsibilitie A. Welding procedure qualification 1. It is your duty to verify that welding procedures have been established they will 2- You You should witness the welding and testing of the qualification weld specimens 3- You You must have available authentic documentary evidence that joints were satisfactory
B. Welding Inspection 1. Passing of a qualification test does not ensure proper applica tion of the procedure. 2. Verify how the qualified procedure is being applied. 3.Checklist for Yourself for each procedure specification to guid e you . 4. It is your duty to obtain a good job, properly fabricated a-not to impose your preferences on the fabricator. Until your experience as an inspector covers many shops. b. Inspect as promptly and quickly as possible. c. Interfere as little as possible with production. 5. Make sure that weldments needing repair are correctly and adequately marked. a. Everyone should have a clear understanding about the marking system you will use to indicate any repairs. b- You You must approve the repair procedure and inspect the repaired weld.
C. Welding inspection progress
1. Inspection should progress in sequence with manufacturing operations. a. Interference between inspection and production is kept to a minimum. b. Inspection operations frequently are required at a certain stage of fabrication. Completion of the next manufacturing step may make inspection of the receding step impossible. D. Procedure of inspection (may vary with code company) 1. Prior to welding a. Chemical analysis b. Mechanical properties c. Base metal discontinuities 1. Laminations and cracks 2. Surface irregularities 3. Flatness
d. Joint fit-up 1. Edge preparation (including root face and beveling) 2. Dimensions 3. Cleanliness 4. Root opening 5. Tacking 6. Backing (where required) C. Special setups used for assembly and fabrication (to see that uniform practices are used) 1. Jigging and bracing 2. Pre-stressing or pre -cambering
2. Inspection during welding a. Preheat and interpass temperature b. Root pass c. Root preparation prior to welding second side d. Cleaning between passes e. Appearance of passes (sometimes in comparison with workmanship standard) f. Variations from approved welding procedure (materials, electrodes, currents, etc.)
3. Inspection after welding a. Post heat treatment b. Surface finishing of welds 4. Preparation of inspection reports and related correspondence E. Acceptance inspection 1. Method of cleaning for inspection 2. Nondestructive testing a. Visual inspection b. Surface appearance of welds c. Conformity of welds with drawings d. Liquid penetrate tests e. Magnetic particle tests f. Radiography g. Ultrasonic tests h. Proof testing i. Other suitable methods
3. Destructive testing a. Chemical b. Mechanical c. Metallographic 4. Repairs a. Marking for acceptance or refection b. Inspection of preparations for repair c. Inspection after repair 5. Inspection of loading prior to shipment 6. Preparation of inspection reports and related correspondence
How to formulate a welding procedure - a guide to best practice Requirements, considerations & essential steps to success Introduction this guide is based around carbon steels, much of the information it contains can be related to other materials,. many welding procedures fail to meet their objectives due to communication problems. Welders, inspectors and supervisors need procedures, which give essential information clearly and in enough detail The layout of a welding procedure can be just as important as the content itself: information should be presented in a manner, which is visually clear and easy to follow. make sure that you either use the latest revision of a Code or Standard, or, what the contract specifies regarding welding procedures.
Step1 Establish the class of work WP can be applied to a variety of different products. Each product have different requirement from quality for example, a garden gate. not required wps Conversely, if a product is regarded as 'safety critical', the welding procedure (or procedures) will have to contain more information and require approval testing to ensure that it will work in practice and that certain mechanical, metallurgical and physical properties can be achieved. many of the details will be established at the design stage in conjunction with company quality assurance/quality control requirements. It is also essential to establish. technical details of production: for example, facilities available, i.e. welding equipment (power sources, manipulators or positioners) because have an influence on the WP requirements.
Step 2 Determine if the product is to be manufactured to a Code of Practice In general terms, the code will include : 1- Design requirements. 2- Materials for construction 3- Workmanship requirements. 4-Inspection and Testing 5- Acceptance levels Typical codes of practice, which could be specified, are: BS5500 : Unfired fusion welded pressure vessels ASMEVIII: American boiler and pressure vessel code BS 2633 :Class 1 arc welding of pipe for carrying fluids BS4515: Process of welding steel pipelines on land and offshore AWS D1.1 : Structural welding code codes of practice very different requirements for welding proce dures. For example, BS5500 specifies that WP must be in accordance with BSEN 288. This compares with AWS D1.1, which allows the use of 'standard WP'. details are established before proceeding: failure to recognize specific
Step 3 Establish customer or contract requirements Details stipulated within contracts are varied. It is difficult to be specific about details of this nature but for guidance the following examples are provided Example A In BSEN 288 Part 3, details the requirements for wp approvals, for all positional approval that a pipe test piece wi ll be required to be welded (pipe axis at 45 degrees during the test). Welders find this welding position easier compared with a test with the pipe in the fixed pipe axis horizontal and fixed pipe axis vertical., therefore, important to first satisfy the welding procedure requirements, rather than the welder approval. It may be the customer would insist on two test pieces for each welding procedure approval and this will obviously increase costs.
Example B As mentioned in Step 2, BS5500 specifies that welding procedures are required to be approved to BSEN288. The code of practice also insists on further requirements in addition to BSEN288, including the need for further mechanical testing. For this reason it is essential that as many facts relating to specific contractual and code requirements are established beforehand to minimize future problems.
Step 4 Rationalize approval testing of the welding procedure(s) Because many welding procedures are required to undergo approval testing, it is important that the welding procedure meets the standard specified. It is also possible in many instances, to approve welding procedures to different standards simultaneously, e.g. to BSEN288 and ASME IX. It should, however, be recognized that both standards must be met in relation to technical requirements. The project leader should investigate the possibility of joint approval as this approach could satisfy further projects and save costs associated with future approvals.
Step 5 Check for concise communication Many WP fail due to communication problems. it is too easy for the originator of the WP to include information, The blame for quality problems during manufacture is often attributed to welders who are required to read and understand the technical details.. Conversely, over communication may lead to confusion and in the worst case the welder simply ignores all or most of the instructions. Some standards, such as BSEN288 Part 2, dictate specific additional items (e.g. baking or drying of consumables for MMA, pulse welding parameters for TIG or MIG) to be included in the document or weld procedure. Guidance on the layout or format of the WP is often provided in the appropriate standard. In addition, the information in a WP needs to be presented in a manner which is visually clear and easy to follow. To help fabricators manage their welding information more efficiently,
Step 6 Investigate range of approval The term 'range of approval' initially relates to the production details of the project or product. Production details often relate to the following items: ¾ Welding process to be used . Material types used in the project . Different thickness of material used. Pipe or plate applications (or both) . Weld joint type . Welding positions encountered . For the above items, wp (and welder approval) standards often provide a working tolerance for each individual factor in production. These are known as the range of approval,
for example: A fabrication of high strength steel, using the MMAW process, in a thickness range of (5 - 25mm). The fabrication requires use of pipe in a range of diameters from (100 to 300mm), and plate materials. The welding will involve all welding positions except vertical down, and the joint types are butt joints made from one or two sides, and fillet welded joints. To prepare WP for each detail,, would be extremely time consuming and costly. Therefore, approval standards often apply a range of to approval ,increase the working range of individual welding procedures. For the above example fabrication, the following is provided as general guidance (for approval, details must be obtained by referring to the appropriate standard or standards):
Welding process The welding process plays a major role in the quality and performance of the welded joint, Material Because the material is a high strength steel, the range of approval could include all materials with similar weldability and/or mechanical properties. So, it may be that one material will approve the other types used. Thickness of components The range of approval may be from half to twice the mean thickness. 0.5 - 2t., if a joint was 10mm, the range of approval will be from 5 to 20mm. For pipes, the diameter will be based on half to twice the diameter. If a pipe in 200mm diameter will satisfy diameters ranging from 100 to 300mm. also approve plate welds Joint type joint welded from one side is much more difficult than a joint welded from both sides, This single-sided joint, welded from one side, will therefore approve most other
Step 7 Consider essential variables varies from code to code (or standard to standard). However, the definition largely has the same implication. In BSEN 288, the term is defined as 'a variable which will influence or change the mechanical or metallurgical properties of the welded joint'. Other codes/standards use the definition 'changes that affect approval'. Essential variables may include: Material grade or group (material thickness range, form (pipe or plate), joint type ,details ). Welding process (AC, DC), polarity,A , V, speed, number of weld runs and sequence. Consumable details (manufacturer's name, size, shielding gases, flow rates). Other essential variables are based around these three essential variables.
Step 8 Select the method of approval involves welding test pieces, which to production requirements. correct method is established before proper formulation of the welding procedure is carried out this may have an impact on most of the previous steps. BSEN 288 Part 3 to Part 8
Step 9 Formulate the welding procedure the most difficult task. depend on the outcome of each of the pr evious eight steps. Unless you are a welding expert you will probably have to involve expertise from other sources which may include: A qualified welding consultant Use of reference books from welding consumable or welding equipment manufacturers Dedicated welding procedure information Codes and standards Pre-approved weld procedures Historical records of previously approved welding procedures
Example one-a general purpose fabrication the contract requires only the welders to be approved to BS4872 Part One: 'Approval Testing of Welders when Welding Procedure Approva l is not Required'. Assumptions for this example
Material type: Low carbon steel Material thickness: 10mm Material form: Plate Welding process: Manual metal arc Consumable details: to be confirmed by consumable manufacturer Current type: Alternating current Welding position: Vertical up Joint type: Fillet weld only Within the standard there is not a requirement for amperage, vol tage or travel speed. Nor is there a requirement for preheat or post wel d heat treatment, or specific techniques regarding the number of weld p asses or sequence of weld passes.
Example two - a safety-critical piping system The relevant code of practice in this example is BS2633 'Class 1 arc welding of pipe for carrying fluids'. The following provides an example of how a welding procedure would be formulated.
Assessment of materials
Mechanical/physical properties of the parent material (strength, toughness, hardness, corrosion resistance, weldability) Chemical analysis of the material - percentages of carbon, manganese, etc for ferritic steels and in addition chromium, nickel, molybdenum, etc for stainless steels. This may be established from the materials certification provided by the materials supplier or manufacturer and should relate to the materials used for testing or fabrication Material thickness, length, width, diameter for pipes, etc Joint design, butt joints, fillet welded joints, etc economics is also necessary so effective production methods can be decided. This will require appropriate joint details angle, root gap and root face. edge preparation tolerances .
Assessment of weldability the carbon equivalent value (CEV) in this case is 0.48% which means that the material could be susceptible to hydrogen induced cold cracking (H.I.C.C.). Appropriate precautions must be taken which may include requirements for preheat/heat input control and post weld heat treatment (PWHT). Preheat & weld hydrogen The amount of preheat required is based on other factors such as the expected hydrogen level of the welding process. the objective is to bring the hydrogen potential down as low as possible. based on the weld metal having less than 15ml of hydrogen in 100g of weld metal. Selection of consumables Because the material is regarded as 'crack sensitive' it is important to select a welding consumable which exhibits low hydrogen potential. the consumable type is dependent on the process choice. , some arc welding processes having a low hydrogen potential, e.g. TIG and MIG. But flux-based processes, such as (MMA) and (SAW), require correct selection of the consumable flux and appropriate controls to ensure hydrogen is at an acceptable level.
Size of consumable In order to establish the correct consumable size, several point s must be taken into consideration : Productivity requirements. Welding positions encountered . Joint designs encountered . Welder competence . Acceptance levels or quality requirements a small diameter electrode will be preferred so that the welder has greater control over the weld pool. For all welding position a 2.5mm diameter electrode could be used for the root pass and a 3.25mm could be used for the fill and and capping capping passes. passes. If the material was relatively thin (less than 8 - 10mm), it may be necessary to use a 2.5mm electrode throughout. It may also be necessary to contemplate using TIG welding for the root pass and completing the remainder of the weld with MMA , If TIG was chosen, a suitable shielding gas and filler wire size and type will also need to be included in the welding procedure, alo ng with other details that relate to the TIG process. .
Welding parameters The main welding parameters associated with arc welding processes are: Amperage ( 1 mm = 40 amps ) in MMA Voltage Travel speed the final run to be made with a 2.5mm diameter electrod e to avoid problems with undercut at the weld toe. In the MMA, arc voltages are dependent on the consumabl es being used. For MMA with a basic electrode, 20 to 24V. For rutile cove rings, 18 - 22V, and for cellulosic coverings, typically 28 - 32V. For TIG welding using argon, arc voltage will typicall y be 10 - 12V. Arc voltage is much more difficult to establish when sp ecifying continuous wire-fed processes such as MIG/MAG or SAW. The consumable manufacturer information may be availabl e from the shop floor. the travel speed is left to the welder's experience. Inter pass temperature & post-weld heat treatment control For some types of material, the inter pass temperature and post -weld heat treatment must be specified in order to achieve certain weldment properties. temperature measurement, heating/cooling rates,
Requirements for specific processes Different welding processes require certain additional features to be specified. Reference to BSEN288 Part 2 will provide specific details for each welding process. TIG welding, for example, it will be necessary to specify the tungsten electrode designation and diameter. In addition, the nozzle diameter and gas flow rate are also required. For other welding processes, Step 10 Evaluate information gathered The information which has been acquired for (pWPS) should be evaluated before any approval test is carried out. by the same welders who will be carrying out the approval testing become familiar with the WPS and provides feedback to validate recorded information
Step 11 Approve the welding procedure A suitably competent person should carry out approval of the welding procedure (and welder). It may also be necessary to have the test witnessed by a third party inspectorate, such as an insurance company representative. In addition, subsequent visual inspection, non-destructive testing and destructive testing will require, in most cases, personnel to have appropriate qualifications such as CSWIP (Certification Scheme for Welding and Inspection Personnel), To reduce costs, it is possible to carry out multi -standard approval from one test. approval to BSEN, ASME
Step 12 Establish documentation requirements For many people, this is the most important part of the process of formulating and approving welding procedures. Definitions to BSEN288/287 Pwps - Preliminary Welding Procedure Specification WPS - Welding Procedure Specification (welders, inspectors, supervisors, etc). WPAR - Welding Procedure Approval Record (by the company's quality con trol department ) WATR - Welder Approval Test Record
All of the above records - which will in addition include inspection reports, NDT reports and destructive testing reports - are kept as part of a quality control system. It will also be necessary for a responsible person to sign off t he welder approval test records/certificates on a regular basis otherwise the approval may lose validity and re -approval of welders may be required.
Step 13 Monitor production welds . It is important to ensure that the correct welding procedures are available for specific production welding details and that appropriately qualified personnel monitor the welding. Step 14 Consider cost implications The costs involved with successfully addressing all the issues, implications and requirements connected with each of the previous 13 steps could range from a few hundred pounds for a relatively simple welding procedure to many thousands of pounds for a large number of approved welding procedures. High quality training plus appropriate qualifications and the right practical experience are essential for successful formulation of welding procedures.
QUESTIONS TO START ??
What is "to manage welding procedure"? Explain it concretely according to the four-step circle method of 'Doming Circle' PDCA proposed by W. E. Deming to explain statistical quality control activities. (Answer) P : Planning the welding procedure specifications D : Preparation and manage of welding procedure following the welding plan C : Check and evaluation of welding procedure A : Go / Stop or correction of the welding procedure by check step's evaluation
Mention three items composing welding quality management activities (comprehensive quality management). (Answer) Three major factors that constitute quality management activities are 1) Quality assurance 2) Quality control (quality control in the narrow sen se such as SQC statistic quality control) 3) Quality improvement
The tasks and responsibilities required for the Welding Coordination are specified in ISO14731. What activities are specified in this standard for Welding Engineer(s)? Give five items.
(Answer) Select five items among the followings : (1) Contact review (2) Design review (3) Materials and Weldability (Traceability) (4) Welding consumables (Suitability, Requirements) (5) Subcontractor (Profitability) (6) Fabrication plan (7) Equipments and facilities (8) Preparation works (9) Welding procedures (10) Measuring and visual examination (11) Destructive and Non-destructive testing (12) Acceptance of welds (Repair) (13) Documentation (including document control)
Part 2 to 4 of ISO 3834 corresponds to ISO 14731 "Welding coordination - Tasks and responsibilities" and relates to ISO 9000s series standards- Mention concisely the title and contents of the ISO 3834 standard. (Answer) 1)
The title of the standard : Quality requirements for welding Fusion welding of metallic materials
2) Outlines of the standard : This standard consists of Part 2 through Part 4 corresponding to ISO 9001 through 9003. These are "Comprehensive quality requirements", "Standard quality requirements", "Elementary quality requirements" respectively, in which welding-related quality requirements regarding various activities from contract, delivery, through after-sale service are covered.
In order to assure welding quality, it is important to establish WPS (Welding Procedure Specification). To make WPS, to conduct welding and related jobs in accordance with WPS and to maintain WPS shall be a responsibility of Welding Engineer. What items shall be given and specified in WPS. Give at least five items. (Answer) Select five items among the followings: (1) Classification of base material (2) Classification and size of welding consumables (3) Welding process (4) Preheating and interpass temperature (5) Groove geometry and tolerance (6) Polarity, Number of electrodes and flow rate of shielding gas (7) Number of layer and deposition sequences (8) Welding position (9) Welding parameters (10) Qualification of welder (11) PWHT and its conditions
( Answer) (1)e. 15 (UW-52-b] (2)d.2/3T (UW-52-c(2) ] (3) c. 1.5m [UW-40-a(2)3 (4)b. 1.0m [UW-37-f(l)] (5) a. 13 mm [ UW-32 ] Note : No prescription in ASME-2000
The following sentences are relating to the fabrication by welding in ASME Code Sec. VIII, Div.l. Choose the correct number in the parenthesis and mark 0 its letter. Further put the number or letter of the chapter and section which is specified in the Code. (Example [UW-31-a]). (1) When spot radiographic examination is carried out, the sampling rate is one shot per every (a. 10, b.20, c.30, d. 40, e. 50 ) feet of weld length. [ ] (2) The maximum allowable reinforcement height of circumferential welding joint whose thickness is 26mm, is ( a. 3S2, b. 1/8, c. 3/16, d. 1/4, e. 5/16) inch, [ ] (3) In the butt welded joint of Category "B" of 2 inches plate thickness, the maximum allowable "misalignment", that is "offset", is ( a. 1/4, b.1/8, c. 3/16, d. 1/16, e. 3/4 ) inch. [
(4) It is recommended that at low temperature, for example at 20 °F, the surface of all areas within 3 inches of the point where a weld is to be be started started should be heated to a temperature at least (a. 36, b. 50, c. 60, d. 70, e. 80 ) °F before welding is started. [ (5) Each welder and welding operator shall stamp the identifying number, letter or symbol assigned the Manufacturer, on or adjacent to and at intervals of not more than ( a. 1, b - 3,c. 5, d. 7, e. 10 ) feet or less along the welds which he makes in steel plates 25 mm in thickness. (Answer) (1)e.50 [UW52-b] (2)d.l/4 [UW-35-d] (3) a. I/4 [UW-38-a] (4) c. 60 [ UW-30 ]
Preheating is sometimes required on welding procedure. Describe the objectives at least 3 items and their detail explanations on each. (Answer) (1) Prevent of cold cracks in the weld metal and HAZ (2) Improvement of the ductility and notch toughness of weld metal and HAZ (3) To avoid lack of fusion and poor penetration at weld root pass in welding heavy plate or in welding metals having higher thermal conductivity 1. Preheating effects welding cooling rate down, so that it induces to make softened HAZ and weld metal. 2. The above slower welding cooling rate will reduce the diffusible hydrogen content in weld metal. The above 1. and 2. effect will be avoid probable welding cold cracking. Softened HAZ and weld metal due to preheating may improve their notch toughness and ductility,
