R Reevviissiioonn Q Quueessttiioonnss ffoorr IInnssppeeccttiioonn EExxaam mss Although similar to those used in CSWIP exams, we must emphasise that these will not necessarily be the questions that will form part of your CSWIP exam We have included the answers these questions, although we recommend you make an attempt to answer Note, The printing option for these questions has been disabled, to safe guard indiscriminate copying and distribution.
We would like to take this opportunity to thank Phill Plevey for submitting the following inspection related questions
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CONTENTS PAPER “B” - SECTION 1 - MPI .................................................... 4 Question 1 .............................................................................. 4 Question 2 .............................................................................. 5 Question 3 .............................................................................. 7 PAPER “B” - SECTION 2 - UT ..................................................... 9 Question 1 .............................................................................. 9 Question 2 ............................................................................ 10 Question 3 ............................................................................ 12 PAPER “B” - SECTION 3 - CP .................................................... 13 Question Question Question Question Question
1 ............................................................................ 2 ............................................................................ 3 ............................................................................ 4 ............................................................................ 5 ............................................................................
13 14 15 16 17
PAPER “B” - SECTION 4 – Visual Inspection ................................ 18 Question Question Question Question Question Question
1 ............................................................................ 2 ............................................................................ 3 ............................................................................ 4 ............................................................................ 5 ............................................................................ 5 ............................................................................
18 19 20 21 23 24
PAPER “B” - SECTION 5 – General NDT..................................... 25 Question Question Question Question Question Question
1 ............................................................................ 2 ............................................................................ 3 ............................................................................ 4 ............................................................................ 5 ............................................................................ 6 ............................................................................
25 26 27 28 30 33
PAPER “C” - SECTION 6 – ROV Applied Systems ........................ 34 Question 1 ............................................................................ 34 Question 2 ............................................................................ 35 Question 3 ............................................................................ 36
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PAPER “C” - SECTION 7 – Recording and Processing .................... 38 Question Question Question Question Question Question Question Question Question Question
1 ............................................................................ 38 2 ............................................................................ 39 3 ............................................................................ 40 4 ............................................................................ 41 5 ............................................................................ 42 6 ............................................................................ 43 7 ............................................................................ 45 8 ............................................................................ 45 9 ............................................................................ 46 10 .......................................................................... 47
PAPER “C” - SECTION 8 - QA .................................................. 49 Question 1 ............................................................................ 49 Question 2 ............................................................................ 49 Question 3 ............................................................................ 50 PAPER “C” - SECTION 9 - Planning ............................................ 53 Question 1 ............................................................................ 53 Question 2 ............................................................................ 54 PAPER “C” - SECTION 10 – Capabilities and Limitations of Divers... 56 Question 1 ............................................................................ 56 Question 2 ............................................................................ 57 PAPER “C” - SECTION 11 – Capabilities and Limitations of ROVs... 59 Question 1 ............................................................................ 59 PAPER “C” - SECTION 12 – Care of Equipment ........................... 62 Question Question Question Question
1 ............................................................................ 2 ............................................................................ 3 ............................................................................ 4 ............................................................................
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62 62 63 64
PPAPER APER ““B” B” -- SSECTION ECTION 11 -- M PI MPI 1.
A node weld is to be inspected using magnetic particle inspection (MPI), however, it is not possible to use an encircling coil technique. Outline an alternative procedure for the MPI of such a weld.
Q Quueessttiioonn 11
1- ELECTROMAGNETIC YOKE TECHNIQUE Surface Checks 1. 2. 3. 4. 5. 6. 7. 8. 9.
Test all earth leakage circuit breakers (ELCB’s) for correct operation. Check all electrical cables for kinks and breaks in the insulation. Check rigging and buoyancy arrangements. Ensure the ultra violet light is functioning properly to BS 4489, ensure the woods filter is in good condition and undamaged. Ensure the detecting media is mixed to BS 4969 (carry out the settlement test), and that the ink delivery system is functioning properly, depress the trigger for 15 seconds to flush out all air from the system. Work out the expected amperage needed for the inspection with the electromagnet. Select the AC pole connectors on the subsea unit, function test the magnetizing apparatus ensuring correct current supply and adequate amperage. Ensure that the electromagnet can lift 4.5kg with pole spacing of up to 300mm, as per BS 6072. Check there is an undamaged flux indicator attached to the ultra violet lamp.
Subsea Operation / Inspection 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Clean the inspection site to SA 2½ at least 75mm either side of the weld. Establish a datum, usually 12 o’clock, and mark up the weld in 100mm increments, clockwise from datum, recording total weld length. Carry out a CVI of the weld looking for defects and sharp changes of contour, which could cause irrelevant indications during MPI. Rig the transformer in a safe position close to the inspection site. Switch on the ultra violet lamp and allow 15 minutes for warming up. Check access for electromagnetic yoke around full weld circumference. Ensure ambient light less than 10 Lux. Check for residual magnetism, demagnetise if required. Ensure the ink is being agitated constantly. Place the flux indicator on the centre of the weld between the electromagnet poles in the correct orientation for the defects sought. Energise the electromagnet and report current used. Apply the detecting media to the flux indicator.
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13.
20.
Inspect the flux indicator for proper indications to ensure 0.72 Tesla flux density. This should be done at the cardinal points of the weld i.e. 12, 3, 6 & 9 o’clock, possibly more often on a large weld. Provided that the flux density is sufficient then the inspection of the weld can commence. Ensure an adequate recording method is in place ready for use. Place the electromagnet across the weld at 45º and press the trigger to apply the magnetising amperage. Apply the ink to the weld surface and heat affected zone. Switch off the electromagnet, reverse the electromagnetic and repeat steps 16 & 17. If an indication is found, switch off the electromagnet and remove from weld. Clean off the particles and repeat steps 16 & 17. If an indication is still evident record and report the following:
a) b) c) d) e) f)
Location (distance from datum in millimetres) Length Orientation and position relative to the weld (HAZ, weld cap, etc.) Continuous or intermittent Branching or not (note location and orientation of branches) Weak or strong indication
21. 22. 23. 24.
Carry out remedial grinding as required by the client. Carry out re-test after grinding to assess the condition of the indication. Once the weld has been fully inspected, demagnetise if required. Remove all equipment and return to surface. 25. Wash all equipment with fresh water and flush the ink delivery system with fresh water. Report all findings correctly and concisely to the client.
14. 15. 16. 17. 18. 19.
26.
2.
A 6 element brace node is to be tested using MPI, describe the method you would use to carry out this inspection, the divers you would use and all quality control procedures normally adopted with this method.
Q Quueessttiioonn 22 Method of Inspection 1.
2.
Inspection would be carried out using the encircling coil method with florescent ink and ultra violet light, whereby each of the six members would be inspected separately after having applied the magnetising coils to the brace side of the weld under inspection and having checked the field strength on the chord side of the weld in the HAZ position at a minimum of 4 locations i.e. 12, 3, 6 & 9 o’clock. Ambient light levels will be checked to ensure lux level is less than 10.
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3.
Defect indication remedial grinding will be carried out to the client’s requirements, generally grinding would take place in increments of 0.5mm to a maximum depth of 2.0mm with re-inspection using MP after each 0.5mm increment.
Diver Qualifications As there are 6 welds to inspect on this brace it will be necessary to employ both CSWIP 3.1u and CSWIP 3.2u divers as follows: CSWIP 3.1u Workscope. 1. Initial General Visual Inspection (GVI) of the welds for gross damage, marine growth cleaning assessment and debris at site. 2. CP of welds prior to cleaning at cardinal clock positions. 3. LP air grit entrained cleaning of welds and parent metal to 100mm either side of the weld cap to SA 2.5. 4. Weld marking and datum positioning, Close Visual Inspection (CVI) of all welds. Following on from CSWIP 3.2u workscope carry out the following: 5. 6.
Photographic and video survey of welds. Post inspection CP inspection at cardinal clock positions.
CSWIP 3.2u Workscope. 1. 2.
MPI of all welds. Remedial grinding of any indications if required.
Quality Control Procedures 1. 2. 3. 4. 5. 6. 7. 8.
3.
Test all earth leakage circuit breakers (ELCB’s) for correct operation. Check all electrical cables for kinks and breaks in the insulation. Check rigging and buoyancy arrangements. Ensure the ultra violet light is functioning properly to BS 4489, ensure the woods filter is in good condition and undamaged. Ensure the detecting media is mixed to BS 4969 (carry out the settlement test), and that the ink delivery system is functioning properly, depress the trigger for 15 seconds to flush out all air from the system. Work out the expected amperage needed for the inspection. Select the AC pole connectors on the subsea unit, function test the magnetising apparatus ensuring correct current supply and adequate amperage. Check there is an undamaged flux indicator attached to the ultra violet lamp.
Describe how you would inspect a gusset weld with an articulated magnet and give the reasons why this method may have been chosen. 6 of 65
List any associated checks and QC measures you would employ. During the inspection crack like indications were found, describe what typical remedial measures would/could be employed. Q Quueessttiioonn 33 Subsea Operation / Inspection 1.
18.
Clean the inspection site to SA 2½ at least 75mm either side of the gusset weld. Establish a suitable datum point and mark up the weld in 100mm increments, in a clockwise direction from datum if possible, recording total weld length. Carry out a CVI of the weld looking for defects and sharp changes of contour, which could cause irrelevant indications during MPI. Rig the transformer in a safe position close to the inspection site. Switch on the ultra violet lamp and allow 15 minutes for warming up. Check access for the articulated magnet along the full length of the gusset weld. Ensure ambient light less than 10 Lux. Ensure the ink is being agitated constantly. Place the flux indicator on the centre of the weld between the articulated magnet’s poles in the correct orientation for the defects sought. Apply the detecting media to the flux indicator. Inspect the flux indicator for proper indications to ensure 0.72 Tesla flux density. This should be done at selected locations around the gusset and especially at geometry changes. Provided that the flux density is sufficient then the inspection of the gusset weld can commence. Ensure an adequate recording method is in place ready for use. Place the articulated magnet across the weld at 90º. Apply the ink to the weld surface and heat affected zone. Repeat steps 14 & 15 with the articulated magnet at 45º to the weld, and continue around the full length of the gusset weld alternating between 45º and 90º allowing 40% overlap at each position. If an indication is found, remove the articulated magnet from the weld area weld. Clean off the particles and repeat steps 14 & 15. If an indication is still evident record and report the following:
a) b) c) d) e) f)
Location (distance from datum in millimetres) Length Orientation and position relative to the weld (HAZ, weld cap, etc.) Continuous or intermittent Branching or not (note location and orientation of branches) Weak or strong indication
19. 20. 21.
Carry out remedial grinding as required by the client. Carry out re-test after grinding to assess the condition of the indication. Remove all equipment and return to surface.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
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Reason for Inspection Being Carried Out With Articulated Magnet The primary reason why gusset welds are inspected using an articulated magnet is that it is not normally possible to use the en-circulating coil or kettle element methods for introducing magnetism into the weld. This is usually due to the geometry of the weld site. Checks and QA Measures Surface Checks 1. 2. 3. 4. 5. 6. 7.
Test all earth leakage circuit breakers (ELCB’s) for correct operation. Check all electrical cables for kinks and breaks in the insulation. Check rigging and buoyancy arrangements. Ensure the ultra violet light is functioning properly to BS 4489, ensure the woods filter is in good condition and undamaged. Ensure the detecting media is mixed to BS 4969 (carry out the settlement test), and that the ink delivery system is functioning properly, depress the trigger for 15 seconds to flush out all air from the system. Ensure that the articulated magnet can lift 18kg with pole spacing of between 75mm and 150mm, as per BS 6072. Check there is an undamaged flux indicator attached to the ultra violet lamp.
Subsurface Checks 1.
Using a flux indicator check the weld to ensure 0.72 Tesla flux density. This should be done at selected locations around the gusset and especially at geometry changes.
Remedial Measures The method for confirmation and/or removal of crack like indications will be specified by the client. This normally consists of the following: 1. 2. 3. 4. 5.
Using a 6mm spherical burr in a peanut grinder, remove 0.5mm of material along the length of the crack like indication. After each 0.5mm has been removed reapply the magnetising media and reinspect the site and report on the changes, if any, to the crack like indication. If the indication remains continue removing 0.5mm at a time until it is removed or until a maximum of 2mm of material has been removed. Acting on instructions from the client, dress the area with a suitable burr to remove any sharp edges profiling the area as necessary. On completion of grinding work, accurately record and measure the area referenced to the datum point, and take photographs to include suitable identifications and scale.
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PPAPER APER ““B” B” -- SSECTION ECTION 22 -- U T UT 1.
With the aid of sketches detail how to calibrate an ultrasonic A-Scan CRT to measure the wall of a steel pipe approximately 30mm in thickness.
Q Quueessttiioonn 11 The following is a typical calibration procedure for a ‘V1’ block calibrating the time base to 50mm of steel using a twin crystal compression probe: 1. 2. 3. 4. a) b) c) d) e) f) g)
Select a twin crystal compression probe and connect to both probe connection points. Once this is done set the probe select switch on the unit to DP. Switch on the unit and allow to warm up for approximately 15 minutes. After the warm up period check the battery condition. Calibrate the time base as follows: Ensure reject is switched off. Set the coarse range control to suit the block - this will set the pulse repetition frequency, ensure the fine range and delay controls are in the centre of their travel, making calibration possible. Set the coarse and fine grain to 20 decibels. Using the delay control locate the initial pulse and place on the left hand side of the screen. Apply couplant to the 25mm side of the ‘V1’ block. Apply the probe to the 25mm side of the calibration block. Find the second echo (first back wall echo, 1st BWE) and bring it to full screen height by adjusting the gain controls.
NB: Initially we need to calibrate the unit for 100mm of steel to check the unit for linearity. This is done as follows: h) i)
j)
Using the fine range bring in three more back wall echoes. Using the fine range and delay controls so the left hand of the 4 peaks cuts the time base at the 2.5 for the 1st BWE, 5 for the 2nd BWE, 7.5 for the 3rd BWE and 10 for the 4th BWE. (Note: The ‘0’ position is the surface of the test piece), if this cannot be done then the time base my not be linear and the set cannot be used. There will now be no initial pulse on the screen, as the calibration procedure will have pushed this off to the left hand side.
The time base is now linear and calibrated for 100mm of steel. Prior to setting the unit up for 50mm of steel, carry out a resolution check as follows: k)
Set the probe opposite the notch on the ‘V1’ block, maximise the signal using the gain control, three peaks should appear - one at 8.5 (85mm) one at 9.1 9 of 65
(91mm) and one at 10 (100mm) on the time base scale, this proves that the set can differentiate between small defects at extreme range and thus has good resolution. The time base may now be calibrated to measure up to 50mm of steel as follows: l)
Using the fine range and delay controls reduce the peaks on the screen to two, with the 1st BWE at the 5 and the 2nd BWE at the 10.
The time base is now linear and calibrated for 50mm of steel. 5. 6. 7. a) b) c) d)
To check the calibration place the probe on the Perspex insert, a peak should appear at the 10 on the time base scale. Place the probe on the calibration block (25mm), a peak should come up at the 5 on the time base scale. Amplifier linearity check: Set the probe opposite the 1.5mm diameter drilled hole in the ‘V1’ block. Attenuate the 1st BWE to 80% full screen height (FSH). Increase gain by 2 db, the peak should now be at FSH. Attenuate the signal using the fine gain control by 6 db, the signal should now be at 50% FSH.
If all of this checks out then the amplifier is working as it should and the set is calibrated for 50mm of steel and is ready for use. When the probe is placed on the 30mm test piece the 1st back wall echo will show at 6 on the CRT screen time base scale if no
defects are noted or no thinning of material has occurred.
2.
List the controls on an underwater ultrasonic set (A-Scan) and describe their functions. Which type of probe would typically be used for measuring wall thickness?
Q Quueessttiioonn 22 Controls Typical system controls: 1. Reject or Suppression This control is used to suppress incoming signals and so clean up the base line on the cathode ray tube (CRT). This control should be in the off position for underwater inspection work. 2.
Range Controls a)
Coarse Range
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This alters the pulse repetition frequency (PRF), in order to ensure the incoming signal is not affected by the transmission of a pulse; the coarse range control should be set to the thickness of the metal under test. b)
Fine Range
This alters the spread of the peaks on the screen so that the operator can spread them further apart or bring them closer together in order to calibrate the set. This control ensures that the graduations on the X-axis can be made to represent almost any value the operator chooses. 3.
Pulse Delay Control This control will move the whole display sideways across the X-axis without changing the spread of the peaks. It is used in conjunction with the Fine Control for calibration of the set.
4.
Gain Control
There will be either two or three depending on the type of set being used. They control the impute gain and so the peak height on the CRT. a)
Fine Gain Controls the input gain by 0 to 2 db.
b)
Medium Gain Controls the input gain in steps of 2 db.
c)
Coarse Gain Controls the input gain in steps of 20 db.
Using the three gain controls (some sets will not have the fine gain) it is possible to place the top of the peak at any point on the screen, imperative in the accurate location and sizing of defects. 5.
Battery Indicator There will be some indicator as to the condition of the battery as the set will not perform properly if the battery is not adequately charged.
6.
Probe Select Switch This must be set to the correct position in order for the set to interpret the information from the probe, the set will behave differently according to whether a single or twin crystal probe has been used, this control may also be the on/off switch for the set.
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7.
Probe Connections There will be two of these and they will normally be marked TX for transmit crystal and RX for receive crystal, if using a single crystal probe it must be connected to the TX connection.
8.
Charging Connection This will be a connection, which should be blanked while the set is in use. Due to problems associate with hydrogen gas being produced while charging there may also be a connection for ventilating the housing while charging.
Probe for Measuring Wall Thickness For wall thickness measurements a twin crystal probe would be used. This would have a high frequency and small diameter crystal.
3.
Describe how to calibrate an A-Scan unit and name the types of calibration blocks typically used for this task.
Q Quueessttiioonn 33 Calibration See above. Question No. 1. Calibration Blocks 1. 2. 3. 4.
The IIW ‘V1’ Block. Primary calibration block. The IIW ‘V2’ Block. On-site calibration and checks. The IIW Beam angle Profile Block, (Normally used for assessing the probes and not calibrating the A-Scan system). Step Wedges. On-site calibration and checks.
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PPAPER APER ““B” B” -- SSECTION ECTION 33 -- C P CP 1. Describe the reasons for and the function of sacrificial anodes. Give details of any major disadvantages of this type of corrosion protection system. Q Quueessttiioonn 11 Reasons The reasons for the use of sacrificial anodes is to protect the structure from corrosion attack and therefore to the deterioration of the structural components. Function The function of the sacrificial anode is to sacrifice (corrode) itself to protect the structure. This is accomplished by attaching a quantity of less noble metal such as zinc to the structure which is steel, and more Nobel than zinc, the structure will become the cathode so being protected, the zinc being a less noble metal will become the anode so sacrificing itself. Major Disadvantages 1.
The amount of anode material necessary to protect a structure in vast and adds a considerable weight to the structural members and components. 2. To replace exhausted anodes is costly and involves a considerable amount of work in attaching retrofit anodes. 3. There is no way of controlling the actual level of protection afforded by these anodes. 4. Anode output decreases with age. 5. The anodes snag diver and ROV umbilical.
2.
Describe with the aid of suitable sketches the calibration of: a) b)
Contact half-cell Remote half-cell (proximity)
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uestion 22 Q Question Calibration of Ag/AgCL Diver Held Contact Meter – Contact Half-Cell
Voltmeter. Reading –4mV (+/- 5mV) Calomel Electrode 4 (L) Pin
- + Fresh Seawater in Plastic Bucket
Diver Hand Held CP meter
1. Ensure the calomel electrodes have been properly calibrated. 2. Immerse the CP Meter in a plastic bucket of clean fresh seawater with a “1L 4M” in-line connector fixed, ensure electrolyte (seawater) level does not cover shorting plug connection in handle. 3. Make contact with pin 4(L), (connect Ag/AgCL reference electrode) to negative terminal of digital voltmeter. 4. Immerse the saturated calomel electrode in clean fresh seawater and connect to positive terminal of digital voltmeter. 5. Allow the electrode to reach a stable potential (10 - 15 minutes). 6. The voltage difference between the saturated calomel and Ag/AgCL reference electrode can be read off the digital voltmeter and should be -4mV +/-5mV. Calibration of Ag/AgCL Remote Half Cell (Proximity)
Voltmeter. Reading between 0 – 10mV -1000mV to –1050mV on Zinc Block Remote Half Cell
Calomel Electrode - +
Zinc Block
Fresh Seawater in Plastic Bucket
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1. 2. 3. 4. 5. 6. 7.
3.
Ensure the calomel electrodes have been properly calibrated. Soak the Ag/AgCL half-cell in a plastic bucket of clean fresh seawater in for 30 minutes. Connect the negative terminal of the voltmeter to the Ag/AgCL measuring electrode (half-cell). Connect the positive terminal of the voltmeter to the calomel electrode and immerse the electrode tip in the seawater. Record the reading from the voltmeter; it should be between 0 to -10mV. Repeat this procedure if the readings are outside this range. Using the procedure above measure the potential of a Zinc Reference block with the proximity cell. The reading should be in the region of -1000mV to 1050mV.
Compare and contrast the reason and functions of sacrificial anodes and impressed current systems.
Q Quueessttiioonn 33 Sacrificial Anodes Advantages 1. 2. 3. 4. 5. 6. 7. 8. 9.
No external power supply needed. Anodes start to work as soon as structure is submerged. Over protection is not possible. The system can easily be monitored. No electrical danger to divers. Installation relatively simple. Danger of cathodic protection interaction is minimised. No running costs. High reliability.
Disadvantages 1. 2. 3. 4. 5.
The number of anodes required to protect a structure add considerable weight to the platform. Replacement is costly. The anodes snag diver and ROV umbilical. There is no control of the protection levels afforded. Anode output decreases with age.
Impressed Current Systems Advantages 1. 2.
System is lightweight. Very few anodes are required.
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3. Level of protection can be monitored and controlled. 4. Replacement of anodes is relatively easy. 5. The platform is free of obstructions. 6. System output can be varied to compensate for changes in amount of structure to be protected, loss of coating, etc. Disadvantages 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
System and cables are easily damaged, particularly in bad weather in splash zone area. System has to be switched off when diving work is required, high voltages and currents (in order of 25 volts and 1000 amps). Platform is unprotected at launch until platform is commissioned. System can be set up in reverse polarity and the structure damaged. The system cans ‘over cook’ the platform by being turned up too high. Possibility of over protection causing hydrogen associated problems. Shadowing, areas where protection is not offered, can occur. Possible interaction effects on other structures. Subject to availability of suitable power supply. Regular electrical maintenance checks and inspection required. Complete failure if power supply lost. Running costs high for un-coated structures.
4. Show with the aid of diagrams one method of corrosion protection, which can be effectively applied below the waterline of a steel structure. uestion 44 Q Question The Impressed Current Anode System
- ve terminal, connected to the Structure
- ve
DC power source
+ ve
+ ve terminal, connected to Auxiliary Node
Sea Level
Electrons emitted to satisfy Reduction reaction in the Electrolyte
Impressed current node Made of Noble material
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5. Discuss the methods currently available for effective monitoring of an impressed current protection system employed on an offshore structure. Q Quueessttiioonn 55 High Purity Zinc Electrodes These are pieces of zinc, which are placed at specific locations around the structure. These locations may be areas where the stress is high or where protection is thought to be marginal, they are generally used with impressed current systems as they can be left in situ on the jacket and will give constant readout of the structures potential at that location. The readout will normally be displayed in the Control Room on the surface. Monitored Anode System The Impressed current system can be observed by the use of a Monitored Anode, this is simply a sacrificial anode, which is only in electrical contact with the structure via an ammeter. If the impressed current fails for any reason, leaving the structure unprotected, then the Monitored Anode will exhibit a current flow shown on the surface readout thus raising the alarm of a failure in the impressed current system.
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PPAPER APER ““B” B” -- SSECTION ECTION 44 –– V isual IInspection nspection Visual 1.
Discuss the effects of marine growth on a steel structure. Give details of which type of growth is most detrimental to the integrity of the structure.
Q Quueessttiioonn 11 Effects The main problem from an engineering point of view is that the structural members involved will be increased in size; it will also loose its smooth finish so becoming rougher. Both of these will increase the drag forces on the structure and so the loads that need to be dealt with will also increase. The following outline the major effects marine growth will have on a structure: 1. 2.
3. 4. 5. 6. 7.
It will cause an increase in the mass of the structure without adding stiffness and so cause a decrease in the natural frequency of the structure. It will increase the drag coefficients of the structure, especially in the splash zone where the maximum water force is present. This will also be the furthest point from the anchor point of the leg - the seabed and so the bending movement will be increased. Obscures the structures features such as valve handles and structural markings. Hides all but obvious major defects. Makes close visual inspection (CVI) of components impossible without removal of the marine growth. Reduces the effective area of intakes and outfalls. Certain types of hard marine growth cause corrosion of the structure and prevents effective operation of cathodic protection systems. Increases the scour at the base of the structure due to increased fluid velocity around the base of the structure.
Most Detrimental Hard marine growth has the most detrimental effect on structures as follows: 1. 2.
It adds both weight and bulk to the structural members as it has a specific gravity of 1.4. It produces biological corrosion, a) Production of Corrosive Substances - The most significant chemicals produced are ammonia from the excreta of the organisms and hydrogen sulphide formed when the organisms die. b) Anaerobic Corrosion (Corrosion Without Oxygen) - Certain sulphate reducing organisms are able to take the place of oxygen in the corrosion circuit. They occur under clams and other hard marine growth, when they are
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present there will be an increase in corrosion usually under marine growth or just below the mud line. c) Concentration Cell - Because the growth will exclude the water from the structure it will not allow a renewable supply of oxygen, so the area beneath the animal will become the anode and the ring around the edge will become the cathode.
2.
List the six categories of visual defects listed by the International Institute of Welding in BS 499 and give two examples of each.
Q Quueessttiioonn 22 The Six Categories 1. 2. 3. 4. 5. 6.
Cracks. Cavities. Solid Inclusions. Lack of fusion and penetration. Imperfect shape. Miscellaneous.
Examples of Two of Each 1.
Cracks A linear discontinuity produced by a fracture. Cracks may be longitudinal, transverse, edge, crater, centreline, fusion zone, weld metal or parent metal.
2.
Cavities Blowholes – A cavity generally of less than 1.5mm in diameter formed by entrapped gas during solidification of molten metal. Porosity – A group of gas pores can be located in a variety of locations.
3.
Solid Inclusions Inclusion – Slag or other foreign matter entrapped during welding. The defect is more irregular in shape than a gas pore. Oxide Inclusion – Metallic oxide entrapped during welding.
4.
Lack of Fusion and Penetration Lack of Fusion – Lack of union in a weld, this can be either: Between weld metal and weld metal.
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Between parent metal and weld metal. Incomplete Root Penetration – Failure of weld metal to extend into the root of a joint. 5.
Imperfect Shape Undercut – An irregular groove at the toe of a run in the parent metal or in previously deposited weld metal, due to welding. Overlap – An imperfection at the toe or root of a weld caused by excess weld metal flowing on to the surface of the parent plate without fusing to it.
6.
Miscellaneous Grinding mark – Grooves in the surface of the parent metal or of a weld made by a grinding wheel or a surfacing tool. Spatter – Globules of metal expelled during welding on to the surface of parent metal or of a weld.
3.
List the defects that you would expect to find in an underwater visual inspection of a concrete structure. Describe methods, features or aids you would use to assist your visual inspection of a damaged area of concrete.
Q Quueessttiioonn 33 Defects in Concrete - Category ‘A’ 1. 2. 3. 4. 5. 6. 7. 8.
Cracks. Delaminations Pop out. Impact damage. Tearing. Exposed reinforcement. Faulty repair. Variable cover.
Visual Inspection of Damaged Area The Grid System When the grid system is employed it will involve marking the structure with a series of numbered boxes. The diver or ROV would then be directed to box No. ***. This is a good method certainly in the structures early years, although in later life some of the markings may well be at the very least difficult
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to find. All defects noted will be referenced to its unique box number and sized accordingly. The Shot Line and Tape Method This method is taken from the archaeological method of laying a graduated line straight across or down and area and running a marked (measured) line off at 90º. Offshore the straight line would be a graduated shot line from the surface placed at the correct vertical location. From this the diver would take a tape measure and run it out horizontally across to the point of interest, thus fixing it in two dimensions. Established Structural Fixtures Where known datum have been established i.e. Embedment plates, riser clamps, towing points, etc. these can be used as datum fixes and used to reference areas of interest or damage to. This method is particularly useful to ROV surveys where lines and tape measures cannot be used.
4.
What methods are available for the removal of marine growth from an offshore structure? Discuss the advantages and disadvantages of each method you have listed.
Q Quueessttiioonn 44 Hand Cleaning (Scraper, Wire Brush) Advantages Inexpensive (small area) Easy to deploy No training necessary Pneumatic Tools Advantages More efficient than hand tools Less diver fatigue Easy to deploy
Hydraulic Tools Advantages Same as pneumatic No depth restriction
Disadvantages Diver fatigue over long periods Slow Will not remove Tube Worm casts
Disadvantages Depth limitations Exhaust air impedes visibility High maintenance cost Can be a hazard to diver Slow
Disadvantages Expensive Choice of tools is limited Heavy, bulky hose Diver fatigue
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Can be a hazard to diver Slow High Pressure Water Jet Advantages Fast and effective Good for intensive cleaning Least detrimental to structure
Disadvantages Heavy hose High noise level for diver / Supervisor Hazardous for diver Diver fatigue over long periods Will not remove Tube Worm casts
High Pressure Water Jet with Grit Entrainment Advantages Disadvantages Fast and effective Expensive Good for intensive cleaning Heavy, bulky hose Removes all marine growth Diver fatigue High noise level for diver / Supervisor Hazardous for diver Will remove protective coatings Large amount of spread equipment Grit gets into diving equipment, wear. Low Pressure Air Grit Entrainment Advantages Fast and effective Good for intensive cleaning Removes all marine growth Easy to use Low noise Possible ROV deployment Inexpensive (shallow depths) Little diver fatigue Cavitation Jets Advantages Effective for hard growth removal Possible ROV deployment Relatively safe No grit required Marine Growth Inhibitors Advantages No diver intervention Inexpensive once installed
Disadvantages Will remove protective coatings Limited depth capability without large compressors Some hazard to diver Grit gets into diving equipment, wear.
Disadvantages Will not remove soft growth Expensive
Disadvantages Will only remove soft growth Only good in Splash Zones
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Little or no maintenance
4.
Liable to damage in storm conditions Requires divers/RAT to install Jacket members must be free attachments
of
List the Category “A” (Defects) associated with concrete structures. Describe three of those you have listed.
Q Quueessttiioonn 55 Defects in Concrete - Category ‘A’ 1. 2. 3. 4. 5. 6. 7. 8.
Cracks. Delaminations Pop out. Impact damage. Tearing. Exposed reinforcement. Faulty repair. Variable cover.
Cracks Cracks can be divided into three categories: Fine Cracks – a fracture of the concrete not more than 1mm wide. Medium Cracks – fracture is between 1mm and 2mm wide Wide Cracks – fracture is more than 2mm wide. The edges of the fracture will normally be sharp and aggregate may also be fractured. The normal cause is structural movement. Although all concrete structures have some cracks in them they will not become significant until they are measurable, this will usually only occur in service. Pop out A pop out can be described as a small conical depression in the concrete surface, usually with a piece of corroding reinforcement at the bottom of the pit. It is caused by the expansion of isolated particles in the concrete (or the corrosion of the ends of reinforcing bars). This causes the surface of the concrete to be put under tension and will so produce local failure in the form of a conical piece of the concrete popping out from the structure. The edges will usually be sharp and well defined. Pop outs are an in service defect.
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Exposed Reinforcement The steel reinforcement bars become visible on the surface of the surface of the concrete accompanied by rust staining. There are two ways in which this can occur either by displacement of the steelwork during construction or by removal of the outside covering of concrete during the in service life of the structure (impact damage).
5. Describe the types of ‘In Service’ defects that could affect the life of an offshore structure. Q Quueessttiioonn 55 Fatigue due to hydrodynamic forces (wind and wave action) and vibration of the structure from drilling operations, etc. Overloading, due to changes in the production technique. It is likely that the structure will have to carry a larger payload than was originally foreseen and this can cause problems which could lead to ductile failure, especially if there is any significant corrosion to compound the problem. Corrosion of the steel causing a reduction of the wall thickness and an uneven surface. This could lead to stress concentration so reducing the safety factor. Fouling, both marine growth and debris can be detrimental to the structure. Accidental damage. As the structures are designed to high specifications if they become damaged then they will not be able to perform properly and so could fail. Scour and unstable foundations will under mine the structure and may cause instability of the structure, especial on concrete gravity structures. Internal metal and welding defects.
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PPAPER APER ““B” B” -- SSECTION ECTION 55 –– G eneral N DT General NDT 1.
Discuss the advantages and limitations of radiography and ultrasonics as underwater inspection methods.
Q Quueessttiioonn 11 Radiography - Advantages 1. 2. 3. 4. 5.
Permanent record is produced. Can be viewed by many. It is a proven method. Necessary cleaning standard is low (SA 1). Resolution of volumetric defects is good.
Radiography - Disadvantages 1. 2. 3. 4. 5. 6. 7. 8. 9.
Safety hazards are high. Storage and transportation of source are a problem. Needs Home Office approval. Must have badged personnel. Highly qualified divers required. Cost is extremely high. Access to both sides of the weld is necessary. Interpretation is difficult. Resolution of planar defects is poor.
Ultrasonics - Advantages 1. 2. 3. 4.
It is a proven method. Can be applied from one side of the weld / material. Will locate both planar and volumetric defects in weld body. Equipment is easily transportable and inexpensive.
Ultrasonics - Disadvantages 1. 2. 3. 4. 5. 6. 7.
Highly qualified divers required for weld examination (Shear wave inspection). No permanent record. Inspection results are very subjective. Time consuming operation. High level of cleaning required (SA 2.5 to 3). Weld geometry can cause problems with probe access. Near surface defect detection and resolution is poor.
2.
What are the differences between volumetric and planar defects? Give two examples of each and describe which method of NDT would be best for finding these defects. 25 of 65
Q Quueessttiioonn 22 Differences 1.
Planar Defects. This type of defect has a large surface area but low volume, they are essentially a two dimensional defect.
2.
Volumetric Defects. These defects will have a comparatively small surface area but a large volume.
Examples of Planar and Volumetric Defects 1.
Planar Defects. a) Laminations. b) Cracks.
2.
Volumetric Defects. a) Cavities. b) Porosity.
NDT Methods 1.
Planar Defects. To locate planar defects in the weld material or in plate, ultrasonic NDT would be used, either A-Scan or Digital Wall Thickness meters. The A-Scan system has the ability to use probes of varying angles so that the angle of a planar defect can be found and sized.
2.
Volumetric Defects. The method most easily used to detect volumetric defects is Radiography, either X-ray or Gamma Ray. This method of NDT will show the defects on a film as a shadowgraph. Ultrasonic inspection will also locate volumetric defects, however, due to their irregular shape the ultrasound beams will be deflected and a clear picture is not always given. Radiography gives a permanent record of the defect where U/T does not.
3.
Describe with the aid of sketches the inspection of a horizontal member using FMD. List the three types of FMD. What further inspection might be carried out on a member and where if the member was found to be flooded?
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estion 33 Q Quuestion Inspection of Horizontal Member Receiver
12
12
Ultra Sound Waves 12
3
9 6
Heat Radiation
Radioactive source
Radiographic FMD Types of FMD 1. 2. 3.
Thermal pad
Ultrasonic probe
Ultrasonic FMD
Thermal FMD
Ultrasonic FMD Radiographic FMD Thermal FMD
Additional Inspection The most obvious reason for a member to be flooded is that there has been a breach in the integrity of the member; this can be attributed to a number of reasons: 1. The welded joints at the end of the member where it joins the node may have cracked. 2. Circumferential and/or longitudinal welds along the length of the member may have cracked. 3. The member may have appurtenances welded to it i.e. anodes, riser clamps, etc. there may be a crack at the joining point of the member and the appurtenance. 4. The member may have corroded through. 5. There may be a puncture in the member due to a piece of debris having fallen. 6. An appurtenance may have been torn off and a hole has now been left in the member. 7. Inspection access ports/hatches used during the fabrication process may have cracked. The courses are many and at each site listed above an inspection must be made to find the reason why the member has flooded. Sometimes no obvious or visible cause can be found and it may be necessary to drill a hole in the member and force a coloured dye into the member and look for where it appears to locate the flooding point. NDT is
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another method of inspection where cracks can be found which are invisible to the naked eye.
4.
Briefly describe the operation of the ACPD and ACFM inspection techniques giving their capabilities for the detection and sizing of crack defects. Where appropriate sketched may be uses.
uestion 44 Q Question ACPD – Alternating Current Potential Difference ACPD is the method by which the depth that a surface-breaking defect has penetrated can be assessed. This method of NDT is not suited for front line inspection for the location of surface breaking defects only for defect depth sizing once located by other NDT techniques. Once a defect has been located, by MPI for instance, ACPD can be applied and can be used to build up a picture of the defect profile (depth) by taking readings at intervals along the crack length. The metal has to be cleaned to SA 2½ - 3 so as to obtain good electrical contact. The ACPD technique requires two connections between the instrument and the specimen under inspection – namely the current output or field connection, and the voltage input from a manually deployed single probe. The field connection is used to inject a current into the specimen by direct contact, being placed either side of the crack location, equidistance, reasonable far apart, with the crack lying perpendicular to the line between the contacts. The single probe, which has a double tip, is placed on the parent metal away from the crack and a reading taken (Vr). At this time the topside unit measures the potential drop experienced between the two contacts. The single probe is then placed so as the tips straddle the crack and a reading taken (Vc) the topside unit again measures the potential drop. This measurement will be greater than the first as the distance the electricity will have to travel to go around and under the crack. Measurements are continued along the line of the crack at 10mm spacing so as to draw a profile of the crack depth though out its length, alternating between parent metal and crack. The topside unit calculates the difference between the 1st and 2nd readings in each case and this in turn is converted into a crack depth measurement. The following equation demonstrates the technique: d¹ = U Vc - 1 2 Vr For example, for a probe spacing of 10mm, a cross-crack voltage of 800 and a reference voltage of 400 indicates a crack depth of 5mm.
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Refer to the following drawing for detail of single probe locations to obtain crack depth measurements. Field Lead – Electrical Contacts
~
Reference Reading
Crack Depth Reading
Surface breaking d f
Measuring Contacts
AC path through
Alternating Current Potential Difference Testing ACFM – Alternating Current Field Measurement ACFM is an NDT method which can locate surface breaking cracks and size them for length and depth, this through various non-conducting coatings. Cleaning to SA 2½ is not necessary, also marine growth fouling need only be removed so as not to impede probe movement, however, for underwater inspection it is simpler to use LP Dry Grit cleaning methods for speed which automatically cleans to SA 2½. The ACPD method of inspection uses PC based hardware and software to gather the data and analyse it and therefore there is a permanent record of the inspection. The ACPD method requires two people, the diver and the topside technician. The diver need only understand the basics of the method and probe manipulation as the topside technician interprets all data. Various probe are available for differing geometries and can be changed at the dive site with underwater mateable connectors by the diver. Inspection consists of the diver (probe pusher) running the probe around the weld toes calling out the clock markers as the probe passes them. If the weld cap is wider than 20mm then a cap scan will be carried out in the same manner as the toe scans. If a crack is located the diver will rescan the area locating the crack stop/start positions as instructed by the topside technician and mark these with magnetic arrows. Having located the stop/starts, the diver will once again scan the crack location this time calling out the arrow positions as well as the clock positions as the probe passes them. These points will be recorded on the scan trace by the topside technician.
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All scans will be overlapped by at least 50mm so no defects are missed. Having acquired the scans the topside operator will calculate the cracks length and depth using the ACFM’s software. All data will be backed up to hard drive and floppy disc.
5.
A node weld with suspected surface breaking cracks requires to be inspected. Describe an NDT method(s) to complete this work that will include sizing of any cracks located. List any associated checks and QC measures you would employ.
Q Quueessttiioonn 55 ACFM – Alternating Current Field Measurement Technique Equipment Requirements ACFM Model U21 or U31 Underwater Crack Microgauge with Topside Unit and Power / Comms Umbilical. Isolating transformer 240V to 110V or 110V to 110V with centre tapped output. Laptop computer with Serial Port (COM1) for connection to topside unit. Bus mouse or Serial mouse on dedicated port (or COM2). Optional parallel port for printer. Machine must be suitable for 110V operation. RS 232 Ribbon and 9-25 Way Adaptor. WAMI Software disc and manual. Underwater ACFM Probes – Standard Type 45, 84 or 137, Tight Access Type 46, 80 or 138, Pencil Type 20 or 22, and (optional) Edge Effect Type 94. Flat Plate Weld Ops Check Block with spark eroded slots (cracks). 3.5” floppy discs for data back up. Report Sheets. Magnetic arrows and tape measure. System Set Up and Surface Checks Ensure all mains switches are OFF. Make connections between subsea unit and topside unit. Connect Probe to subsea unit. Make all connections between computer, printer and Topside Unit. Connect Topside Unit to isolating transformer. Connect isolating transformer to 240V supply. Switch on 240V supply. Switch on Switch 1. Switch on Switch 2. Switch on Switch 3. If the 350m umbilical is connected, switch on Switch 5. Push TEST button on main RCD device (2). The device should trip and the neon ON Switch 3 should go out. If this does not function - SUSPEND ALL OPERATIONS AND TURN OFF 240V SUPPLY. DISCONNECT ISOLATING TRANSFORMER.
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If TEST button trips the device, repeat 8 and 9. Push TEST button on the 350m umbilical RCD (5). The device should trip and the neon ON Switch 3 should go out. If this does not function - SUSPEND ALL OPERATIONS AND TURN OFF 240V SUPPLY. DISCONNECT ISOLATING TRANSFORMER. If TEST button trips the device, repeat 10. Switch on Switch 4. The unit is now ready for subsea deployment. If During Operation the RCD trips SUSPEND ALL OPERATIONS AND TURN OFF 240V SUPPLY. Pre-Dive System Set Up Check all connections – Umbilical and probe to both subsea and topside units, including laptop. Switch on laptop. Switch on mains power to topside unit. Open WAMI file (ACFM Program) and check screen display. Select ‘Open’ and select probe file to match probe being used. Select ‘New’ and create a file for the Pre-Dive check on the probe. Scan the Weld Ops Check Block with the probe, if all satisfactory, save file. Select ‘New’ and create a file for the weld to be inspected. The Pre-Dive System checks and set up are now complete. Deploy the subsea unit to the diver. Subsea Operation / Inspection 1. 2. 3. 4. 5. 6. 7. 8. 9.
Clean the inspection site as necessary to allow uninterrupted probe scans, should be at least 75mm either side of the weld and the weld itself. Establish a datum, usually 12 o’clock, and mark up the weld in 100mm increments, clockwise from datum, recording total weld length and width of weld cap at widest point. Carry out a CVI of the weld looking for defects and sharp changes of contour, which could cause irrelevant indications during scanning and also restrict scanning operations. Also for probe access. Rig the subsea unit in a safe position close to the inspection site. Check access for probe around full weld circumference. Ensure topside system is switched on and no safety trips have dropped out. Enter clock notation stop / start and scan direction and note probe direction on laptop. Carry out Ops Check at the 12 o’clock position on both sides of the weld to check for 360° circumferential weld toe cracking. Select either chord toe or brace toe and start scanning around the weld toe in a clockwise direction starting 50m before 12 o’clock with the diver calling out the 100mm increment marks as the centre line of the probe passes them. When scan is complete tell the diver to relax while topside operator reviews the data. Continue around the weld toe until the 12 o’clock position is reached. All
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10. 11. 11.
12.
13. 14. 15. 16. 17.
scan stop / start positions will be overlapped by 50mm to 75mm. Scan speed will be monitored by the topside operator and the diver advised accordingly. Complete both toe scans and cap scan if weld cap is wider than 20mm until all weld has been successfully scanned and data recorded to laptop. The topside operator will record the details of each scan on an ACFM report log. If a crack indication is found, the topside operator will instruct the diver to locate the start and end locations with selected probe scans. Once the start and end locations have been identified the diver will mark them with magnetic arrows. The topside operator will then instruct the dive to rescan the area starting 100mm before the 1st arrow and continue 100mm past the 2nd arrow. The diver will call out the 100mm increment markers and the arrow positions as the centre line of the probe passes them for the topside operator to input them on the acquired scan data. Some readjustment of arrow locations may be necessary to pinpoint the exact crack stop / start location. Once this is done and a satisfactory rescan is acquired, the diver will measure the distance between the arrows and the distance from datum to 1st arrow and the topside operator will record these measurements on the ACFM report log. Crack sizing will be carried out off line by the topside operator, so as to save dive time, using the WAMI software program. Once the weld has been fully inspected, remove all equipment and return to surface. Wash all equipment with fresh water. Carryout Post-Dive checks on probe by scanning the Weld Ops Check Block, if all satisfactory, save file and back up all scans to hard drive and floppy disc. Report all findings correctly and concisely to the client.
Off-Line Crack Sizing Open weld inspection data file and move to scan with crack defect. Enter ‘Data’. Select ‘Peak Marking’. This allows the cursor to be moved around the screen using Shift + Arrows keys. Locate the maximum Bx then select ‘Max/Min’ from dropdown menu. Enter Background Bx and save. Locate the minimum Bx then select ‘Max/Min’ from dropdown menu. Enter Minimum Bx and save. Select ‘Calculate Depth’ from dropdown menu and enter measured length of crack given by the diver and enter ‘OK’. The WAMI program will then calculate the crack length and depth and display on the acquired scan data display. Re-save the file and report results to Client’s Representative. Record the details on the ACFM report log. Back up all scans to hard drive and floppy disc.
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6.
With the aid of a sketch show a typical Butt Weld and Fillet Weld identifying all sections and areas.
uestion 66 Q Question Included angle Prepared angle Prepared face Root Face Root gap
Plate Edge Preparation – Single “V” Weld zone Cap of the Weld
Excess weld metal
Throat thickness Toe of the weld
Filler beads, Weld beads making up the Bulk of the weld
Heat Affected Zone HAZ
Effective throat thickness
Root bead or Penetration bead
Butt Weld Terminology
Toe of the weld
Leg length
Included angle
Cap or face of the weld Effective throat thickness
Throat thickness
Toe of the weld
Root
Fillet Weld Terminology
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Leg length
PPAPER APER ““C” C” -- SSECTION ECTION 66 –– RROV OV A pplied SSystems ystems Applied 1.
List the types of camera most suitable and any technical requirements when using an ROV for the following:
Q Quueessttiioonn 11 a) b) c) d)
Use in turbid water, Inspection of a concrete structure, Inspection of a riser, To test for flooded members.
Use in Turbid Water For turbid water the use of a Silicon Intensified Target (SIT) camera would be recommended. This type of camera gives a black and white image and uses the ambient light available on site to illuminate the picture; therefore there is no need to use a dedicated light source, which would cause backscatter from the suspended particles in the water. For night / black water work a small light may be used to give a very low level of ambient light. The use of sonar in conjunction with the SIT camera would also be recommended. Inspection of a Concrete Structure For concrete inspection the inspection would be carried out in two phases, initial inspection would be conducted using the Silicon Intensified Target (SIT) camera which would allow a more overall view of the concrete surface in the stand off mode, allowing areas of interest / anomalies to be picked out and referenced to a suitable datum or reference point. Having located these areas, the pilot/observer would switch to a colour CCD camera for close up work, i.e. Osprey 1364 camera or the CVI camera Osprey 1368 for very detailed recording work. Inspection of a Riser As with concrete inspection the initial survey of a riser would be carried out using the Silicon Intensified Target (SIT) camera, which would show an overall view of the riser and its associated components. Having established the overall view, switch to a colour CCD camera and carry out the riser inspection in this mode, either in single or double pass as required by the client. To Test for Flooded Members As this inspection is carried out using dedicated FMD equipment the video requirement is only necessary to aid the ROV pilot/observer in locating the FMD inspection sites and for him/her to fly the ROV around the structure. Therefore camera requirement will be either a Silicon Intensified Target (SIT) camera, which would allow a more general
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overall view, or colour camera, which would allow a more detailed view to aid placement of the specific FMD equipment.
2.
What methods could be used by an ROV to monitor CP readings on a steel structure? List any factors, which could influence the accuracy and the ability to obtain readings. The diving spread is located on an accommodation vessel 30m from the structure.
Q Quueessttiioonn 22 Methods 1.
Ag/AgCL Half Cell - Proximity
This method does not require any contact below the water line. All the ROV has is a small probe in its manipulator or on its frame and a wire in its umbilical, which goes back to the surface where it is connected to the positive terminal of a voltmeter. The negative terminal of the voltmeter is connected to the structure. Using this method the ROV flies around the structure and holds the probe close but not in contact with the structure. A reading is then taken on the surface and over laid on the video monitor and recorded on tape. 2.
Ag/AgCL Half Cell - Contact
This method requires the steel tip of the probe, which is held in the ROV's manipulator or attached to its frame, to make contact with the steel of the structure. The ROV will move into the structure and force the steel probe in to penetrate the marine growth and any coating or corrosion layers and read the cathodic potential, which is relayed by a high resistance voltmeter on the ROV, at the surface. This reading is over laid on the video monitor and recorded on tape. Factors Influencing Accuracy As the ROV dive station is 30 metres from the platform it will be difficult to have an electrical wire strung between the ROV control room and the platform, thereby making the use of the Proximity method of obtaining CP data difficult. Proximity readings in their nature are general readings of the structure that do not give detailed spot readings as with the Contact method, however, they do give a continual read out of the CP data as the ROV flies around the platform. Furthermore, it is essential to have a good contact on the structure for the electrical connection so as to obtain good data, clean metal-to-metal contact. Any part of the structure or its components, which are electrically isolated from the contact point, will not register reading during the Proximity survey. Risers are normally isolated from the structure by neoprene inserts in their clamps, to obtain Proximity data from risers each in turn has to be inspected with the electrical connection attached to the relevant riser. This can be
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difficult and incorrect connections are sometimes made or the wrong riser is surveyed sub sea by mistake. The use of the Contact method elevates the problems of topside electrical connection, however, to get a good metal-to-metal contact on the structure subsea is often difficult, especially with a lightweight ROV. In attempting to ‘ram’ the structure to get the steel probe to penetrate the marine growth and coatings, the ROV may cause itself and/or the structural components damage. With the Contact method there is no continual read out and only spot inspections can be carried out.
3.
Show with the aid of diagrams how the utilisation of a tether management system could improve the efficiency of a pipeline inspection.
uestion 33 Q Question The TMS as an Aid to Pipeline Inspection Sea Level
DP DSV on off set from ROV
Off set distance
ROV’s TMS
ROV on Pipeline with Transponder
Umbilical / Tether
Pipeline
Elevation View TMS DP DSV on off set from ROV
ROV on Pipeline with Transponder
Umbilical / Tether
Pipeline
Plan View distance 36Off ofset 65
As can be seen from the above diagrams, the use of a TMS allows the ROV to be deployed from the mother vessel to the working depth vertically. The TMS deployment and recovery wire is both the main lift wire and the ROV's main umbilical, which supplies all services to the vehicle. As this is vertical to the mother vessel there is no way that the lift wire/umbilical can become entangled or severed by the vessel’s thrusters/propellers. Having reached the working depth the TMS deploys the ROV using its onboard tether, normally up to 300 metres long. This allows the ROV to excerpt horizontally across the seabed to the pipeline. Having taken up a fixed position on the pipeline, the mother vessel can stand-off at any position from the ROV to allow for wind, tide, proposed direction of travel, etc. and hold station on the ROV using the ROV's transponder as a reference system. This fixing the vessel’s DP system on the ROV will enable the vessel to go into the ‘Follow Sub’ mode and as the ROV tracks down the pipeline so the mother vessel will follow it maintaining the fixed stand-off. When the ROV moves the vessel moves, when the ROV stops the vessel stops.
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PPAPER APER ““C” C” -- SSECTION ECTION 77 –– RRecording ecording aand nd PProces rocesssiing ng 1.
What methods are available for recording the results of an offshore marine growth survey carried out by divers? Discuss the advantages and disadvantages of each method you have listed.
Q Quueessttiioonn 11 Available Methods 1. 2. 3. 4.
Scratch boards. Photography. Close Circuit Television (CCTV), video recording. Sampling
All the above methods would entail the use of tape measures, graduated probes, scrapers and possibly a circumferential webbing strap for compression measurements. Scratchboard - Advantages 1.
No need for communication to and from the diver.
Scratchboard - Disadvantages 1. 2. 3. 4.
Report will be subjective. No permanent record. Time consuming and difficult for diver to carry out. This method not often used.
Photography - Advantages 1. 2.
Permanent record. Verbal report and measurements to accompany photograph.
Photography - Disadvantages 1. 2. 3. 4. 5.
2 dimensional image only. Have to wait for results of film development. No real time image. Report can be subjective. Photo image is localised and may not be representative of the whole area.
Close Circuit Television (CCTV), video recording - Advantages 1. 2. 3.
Permanent record. Real time inspection. Commentary from diver.
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4. 5. 6.
Scale and depth can be incorporated on video. Large area can be covered to give both general and selective assessments. Instant results can be acted on.
Close Circuit Television (CCTV), video recording - Disadvantages 1. 2.
2 dimensional image only. Stand off; long-range views are in B&W only.
Sampling - Advantages 1.
Marine biologists have samples of marine growth from site.
Sampling - Disadvantages 1. 2. 3. 4. 5. 6.
2.
Very time consuming to collect samples. Logistically the need to get sample to laboratory in good time is not practical. Storage of samples is not practical. May not be representative of site; some samples from measured area may have been lost/dropped by diver during the collection phase. Only good for localised reporting. Needs other reporting methods to accompany/clarify sample.
Why is it necessary to have a good QA system for the recording and reporting of data?
Q Quueessttiioonn 22 The QA System 1. 2. 3. 4. 5. 6. 7.
Ensures proper and proven procedures are in place and are followed correctly. Personnel used for the work are correctly qualified. Using the 'Acceptance Criteria' anomalies will be flagged. Ensures that all equipment used is 'In Date' and certified as tested. All consumables are tested properly and logged as such. Ensures that all equipment calibration is detailed and recorded as being carried out to the required specifications and is satisfactory. Briefings of all personnel can be carried out properly such that all personnel understand what is required of them.
The QC System 1.
The QC system will police the system ensuring that all data is logged in the correct fashion, using the correct format and that any follow up inspection is carried out according to the procedures. This ensures that the company's verification plan can be satisfied properly.
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3.
List the items of data usually recorded on a typical riser data sheet and a video log sheet.
Q Quueessttiioonn 33 Riser Data Sheet 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Report Sheet No. Client. Location. Report No. General Subject. Date. Sheet…of…. Data Sheet No. Video Log No. Photo Log No. Inspection Engineer Name. Anomaly No’s. CP Calibration, pre/post dive. Clamp No’s. Anode No’s. Coating Data. Drawing Box. Company Name.
Video Log Sheet 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Company Name. Structure Identification. Client Name. Video No. Date. Dive No. Task Group No. Location. Dive/ROV spread diver/pilot name. Task List Code. Time, to/from. Comments.
4.
Discuss the methods that an Inspection Controller can use to familiarise himself with a job site and the tasks to be performed, and describe why this is most important.
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Q Quueessttiioonn 44 Familiarisation Methods 1.
Technical Specifications This is the document which will contain all design / fabrication drawings (asbuilds), it will also contain the procedures for inspection and any other tasks such as remedial grinding, in short the specifications is the place where the Inspection Controller should look for the Technical information regarding the structures i.e. wall thickness, etc.
2.
Scope of Work Designed to precisely identify where the work is to be done during the next inspection, this can be simply presented as a complete task code listing, as a written statement or in a tick box format, the exact format will depend on the client. It may change from year to year thus it needs to be flexible.
3.
Workbook This is the most important document to the Inspection Controller, all operators have their own approach to the Workbook (Work Pack) and subsequently a large variety of forms exist, it should contain all the documentation necessary to carry out the inspection offshore, it will contain: a) The inspection programme allowing the Inspection Controller to schedule the inspection activities. b) Platform drawings indicating areas to be inspected. c) Inspection procedures to be used, detailing how to inspect with what equipment and using which technique. d) Data sheets for the recording of inspection data normally tailored to suit the particular inspection being undertaken and general non specific data sheets, video loge, photo logs, etc.
4.
Procedures The procedures for inspection will dictate the exact method by which a particular inspection is carried out and with what equipment, it should be follow exactly, it may also indicate method of reporting or further action regarding an anomaly.
Importance of having a Detailed Approach
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The inspection Controller is responsible for the production of the final report at the end of the inspection programme. Therefore it is essential that all data gathered is accurate and nothing in the Work Scope is over looked. It is also the Inspection Controllers responsibility to schedule the work to be carried out in the most efficient, orderly and timely manner and for him/her to accomplish this he/she needs to be totally familiar with the task requirements of the inspection programme so that, if necessary, he/she can react immediately to changes caused by outside forces, equipment failures and additional work requirements, etc. The success of the whole inspection programme depends on the Inspection Controller being able to ‘Control’ the work; therefore he/she must be total familiar with the client’s requirements and be able to act on them accordingly.
5.
Show what must be included in an end of contract inspection report stating the headings, and what should be included under each.
Q Quueessttiioonn 55 Typical Final Report Format 1.
Title Page. This should be as short and as descriptive as possible, it is usually presented as a frontispiece with the title, author, project and the date.
2.
Signing Off Sheet. Signatures of those involved.
3.
Table of Content. Should show the pattern of the report at a glance, should be on a separate p age.
4.
Introduction. Gives brief details as to the purpose of the report and background, it may efine the terms of reference for the report.
5.
Summary. Should be a highly condensed précis of the report to enable the engineer to skip reports, which do not need his attention. It should include the following: The extent of the report The findings of the writer If appropriate, proposed action.
6.
Results. The main body of the report should be concise but clear and include all photographs, etc.
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7.
Conclusions. May not be required, if required they should follow from the facts logically, opinions can be included but you must make sure that they are just opinions.
8.
Recommendations. Again not always needed but if required they will be derived from the conclusions, they should be practical and within the confines of the report.
9.
References. Should list all material relevant to the report, which has been drawn on to provide additional background data or support.
10.
Glossary. A list of technical or special word or definitions used in the report.
11.
Appendices. Copy of the Workscope Raw data sheets Sketches Calculations Printouts Video logs Photo logs
6.
Describe the differences between an anomaly based and full reporting system, and give the advantages and limitations of both.
Q Quueessttiioonn 66 Anomaly Based Reporting System The anomaly reporting system is set up around the client’s ‘Criteria of Noncompliance’ or ‘Out with acceptance’. This method or reporting only reports on those items inspected which are not within the acceptable compliance as specified by the client and does not include within the body of the Final Report all other items inspected which do comply with the client’s specification or ‘Criteria of Compliance’. The advantages of this system is that the client’s engineers only receive the information of what is actually wrong with the structure and allows them to immediately react to these ‘Anomalies’. This saves the engineer time in not having to read a full report of all activities and inspections carried out on the structure only to find there is nothing wrong. The client can act on this while the inspection facility, DSV, is still on site if he wishes. This method also instructs the Inspection Controller as to what is and what is not anomalous and what action to take on finding anomalous items.
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The disadvantages of this system is that items which may soon be classified as anomalies i.e. low CP readings, U/T wall thickness reading, which are at present just within the level of acceptance will not be ‘Flagged’ to the client and he will not be forewarned of possible future problems until they actually become anomalous. Full Reporting System This method of reporting produces a detailed record of all inspection carried out for the client and normally requires the client’s engineer to review the report in detail to ascertain if there is anything wrong with the structure. The disadvantages of this system is that no decisions or assessments as to the condition of the structure can be taken until the final report is issued and then examined by the engineer, by which time the inspection facility, DSV, has usually left station. Furthermore, the Inspection Controller had no definitive listing as to anomalous items and may be reporting in much detail an item, which he may consider an anomaly but the client’s engineer may not or may already know about. The advantage of this system of reporting is that trend analysis may be carried out on data such as CP levels, U/T wall thickness data, also it will bring to the attention of the client’s engineer any possible future problem areas.
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7.
Describe with the aid of diagrams a complete recording procedure for a photographic survey to be carried out on a circumferential weld in the centre of a tubular brace.
uestion 77 Q Question
A Circumferential Weld 12
9
6
A
12
13 14/2
3
4 Photo Sequence starting at Datum Clock Idents Weld Tape Measure
1 & 15
Each photo in the mosaic is over lapped by 40% to ensure
Weld Identification View at A-A 8.
Discuss the advantages and limitations of photography as method to record inspection data.
uestion 88 Q Question Advantages Permanent record. High resolution (compared to CCTV).
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Scale and information can be included; very accurate measurements and assessments can be made employing stereo photogrammetry. Cheap. (Photogrammetry is expensive). Readily available. Adaptable. Proven technique. Easy to deploy and equipment is readily available. Magnification is possible. Time-lapse photography is possible. Disadvantages There will be time needed for development of the film, this will mean that the diver or ROV and may be even the ship carrying them may have left the job site before the results are known. Complex lighting and camera settings may be needed in order to gain the correct exposure. Trained personnel and a fair amount of equipment will be needed to carryout the developing processes. Photography is the recording of reflected light onto a photosensitive surface, it is always dependant on the amount of light available. Cannot record movement, freeze frame only.
9.
List the three Laws of Light encountered during underwater photography and describe the affects that each has when using a camera underwater.
Q Quueessttiioonn 99 The three Laws of Light are: Reflection The angle of incidence equals the angle of reflection. This will occur at the air water interface and also when suspended particles in the water (plant and animal as well as sediment). It will also reduce the intensity of light and produces bright spots on the picture termed backscatter when it occurs. Refraction The bending of light at an interface, occurs as the light passes from one medium to another such as air to water. Light is bent as it passes from water to glass/Perspex camera housings. Refraction causes the image to appear closer and larger.
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Absorption Different wavelengths of light will penetrate further through water so colours disappear at different depths. The colours will tend to disappear according to wavelength as they appear in a rainbow: 0 Metres
Red
Orange Yellow Green Blue
Indigo
Violet
5 Metres 10 Metres 15 metres 20 metres 25 metres 30 metres 35 metres Absorption Rates of Light in Seawater
10.
Discuss the advantages and limitations of Closed Circuit Television (CCTV) as method to record inspection data.
0 uestion 110 Q Question Advantages CCTV will give real time pictures. Will also be a permanent record when applied using video recording techniques. Plenty of additional information can be included in frame, this can include CP readings, Depth, Time and so on, can also have written information with the employment of a video typewriter. Instant playback (no time needed for developing). Safety – if there is a camera on site then the diver will be monitored more easily and so will be safer. Can include an on the spot commentary, if the camera is carried by a diver then he will be able to comment on the item under inspection with the benefit of actually being on the spot, thus being able to back up his assessment of the situation using his other senses and brain. Can record movement. ROV operable and always available. Disadvantages Cannot freeze fast movement.
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Poor resolution compared to photography. Gives a two-dimensional image only. Can cause dive fatigue.
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PPAPER APER ““C” C” -- SSECTION ECTION 88 -- Q A QA 1.
In line with the current requirements of document No. CSWIP-DIV-791 outlines the job responsibilities of a Pilot/Observer Grade 3.3u.
Q Quueessttiioonn 11 Job Responsibilities The objective of the 3.3u qualification is to demonstrate an inspector’s ability to carry out an inspection by means of ROV or manned submersible using visual and selected NDT techniques, to a standard approximately equivalent to that of a 3.1u Underwater Inspector, as detailed in the Job Responsibilities following: 1.
The inspector will be responsible for recording and processing data and the use of communications systems.
2.
The inspector must have a knowledge of the inspection and testing methods included in the 3.1u syllabus; the capabilities of other relevant non-destructive testing methods in current use; the modes of failure, cracking and deterioration in steel and concrete structures (including the relevance of various inspection methods); and protection systems. He/she will have knowledge of QA relevant to underwater inspection and an appreciation of the abilities and limitations of remotely applied inspection systems, ROV's and submersibles.
3.
A 3.3u ROV Inspector will nominally be expected to monitor, or conduct ROV or manned submersible inspection and testing operations, record and report the relevant information and be able to use standard communication systems, and, if relevant, those specific to manned submersibles.
Proficient In: 1. 2. 3. 4. 5. 6.
Close Circuit Television (CCTV). Photography. Cathodic potential measurements. Ultrasonic thickness measurements using the ROV probe technique. Date management and handling. Capabilities and limitations of vehicles.
2.
In line with the current requirements of CSWIP outline the job responsibilities of an Underwater Inspection Controller.
Q Quueessttiioonn 22 Job Responsibilities
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1.
The Underwater Inspection Controller must have knowledge of all aspects of the ROV inspector (3.3u) grade, and of the inspection and testing methods included in the 3.2u examination. The Controller will also have knowledge of the capabilities and limitations of diving, ROV's and submersibles, and an understanding of inspection planning and briefing. He/she must have an appreciation of the roles and responsibilities of other personnel and organisations, including the Offshore Installation Manager, Master, Diving and ROV Supervisors, client’s Representatives Certifying Authorities and Government Departments.
Proficient In: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Visual inspection. Close Circuit Television (CCTV). Photography. Digital thickness meter. Cathodic potential measurements. Magnetic particle inspection. Ultrasonic inspection using A-Scan. Advanced methods of NDT. Date management and handling. Capabilities and limitations of divers and vehicles. Work scheduling and planning. Quality assurance and control.
3.
Write an inspection procedure including checklists for the inspection of a node using MPI.
Q Quueessttiioonn 33 Method of Inspection 1.
2. 3.
Inspection would be carried out using the encircling coil method with florescent ink and ultra violet light, which will include applying the magnetising coils to the brace side of the weld under inspection and checking the field strength on the chord side of the weld in the HAZ position at a minimum of 4 locations i.e. 12, 3, 6 & 9 o’clock. Ambient light levels will be checked to ensure lux level is less than 10. Defect indication remedial grinding will be carried out to the client’s requirements, but will normally allow grinding to take place in increments of 0.5mm to a maximum depth of 2.0mm with re-inspection with MPI after each 0.5mm increment.
Diver Qualifications The inspection will be carried out using a CSWIP 3.1u & 3.2u diver as follows:
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Workscope. 1. 2. 3. 4. 5. 6. 7. 8.
Initial General Visual Inspection (GVI) of the weld for gross damage, marine growth cleaning assessment and debris at site. CP of weld prior to cleaning. LP air grit entrained cleaning of weld and parent metal to 100mm either side of the weld cap to SA 2.5. Weld marking and datum positioning, Close Visual Inspection (CVI) of weld. MPI of all weld. (3.2u only). Remedial grinding of any indications if required. (3.2u only). Photographic and video survey of weld. Post inspection CP inspection.
Quality Control Procedure 1. 2. 3. 4. 5. 6. 7. 8.
Test all earth leakage circuit breakers (ELCB’s) for correct operation. Check all electrical cables for kinks and breaks in the insulation. Check rigging and buoyancy arrangements. Ensure the ultra violet light is functioning properly to BS 4489, ensure the woods filter is in good condition and undamaged. Ensure the detecting media is mixed to BS 4969 (carry out the settlement test), and that the ink delivery system is functioning properly, depress the trigger for 15 seconds to flush out all air from the system. Work out the expected amperage needed for the inspection. Select the AC pole connectors on the subsea unit, function test the magnetising apparatus ensuring correct current supply and adequate amperage. Check there is an undamaged flux indicator attached to the ultra violet lamp.
Inspection Procedure - MPI 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Take CP readings at cardinal clock positions on weld prior to marine growth removal. Clean the inspection site to SA 2½ at least 75mm either side of the weld. Establish a datum, usually 12 o’clock, and mark up the weld in 100mm increments, clockwise from datum, recording total weld length. Carry out a CVI of the weld looking for defects and sharp changes of contour, which could cause irrelevant indications during MPI. Rig the transformer in a safe position close to the inspection site. Switch on the ultra violet lamp and allow 15 minutes for warming up. Position encircling coils, 3 turns, around the brace member adjacent to weld. Ensure ambient light less than 10 Lux. Check for residual magnetism, demagnetise if required. Ensure the ink is being agitated constantly. Place the flux indicator on the chord side parent metal adjacent to the weld in the correct orientation for the defects sought. Energise the coils and report current used. Apply the detecting media to the flux indicator.
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14.
19.
Inspect the flux indicator for proper indications to ensure 0.72 Tesla flux density. This should be done at the cardinal points of the weld i.e. 12, 3, 6 & 9 o’clock, possibly more often on a large weld. Provided that the flux density is sufficient then the inspection of the weld can commence. Ensure an adequate recording method is in place ready for use. Start the weld inspection at 12 o’clock, datum, and proceed around the weld in a clockwise direction once the coils have been energized applying the ink to the weld surface and heat affected zone under inspection. If an indication is found, de-energize the coils, clean off the ink particles and repeat step 17. If an indication is still evident record and report the following:
a) b) c) d) e) f)
Location (distance from datum in millimetres) Length Orientation and position relative to the weld (HAZ, weld cap, etc.) Continuous or intermittent Branching or not (note location and orientation of branches) Weak or strong indication
20. 21. 22. 23. 24.
Carry out remedial grinding as required by the client. Carry out re-test after grinding to assess the condition of the indication. Once the weld has been fully inspected, demagnetise if required. Remove all equipment and return to surface. Wash all equipment with fresh water and flush the ink delivery system with fresh water. Report all findings correctly and concisely to the client.
15. 16. 17. 18.
25.
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PPAPER APER ““C” C” -- SSECTION ECTION 99 -- PPlanning lanning 1.
You are the Inspection Controller responsible for a saturation and air diving inspection contract on a steel structure. List the personnel and equipment resources you would require to carry out the contract. Write your justification of your requirements to the client.
Q Quueessttiioonn 11 Scope of Work The personnel and equipment resources listed below are based on the requirements to conduct simultaneous saturation and air diving on a twenty four hour basis to fulfil an inspection programme from a DSV which includes MPI (max. depth 10mts), selected anode inspection, marine growth inspection, cathodic potential inspection, seabed debris survey, scour survey, riser inspection, riser J-tube U/T wall thickness checks, video survey and photography. Personnel Requirements 1 3 3 3 5 3 8 8 4 1 3 2 2
Superintendent Inspection Controllers, CSWIP 3.4u Bell Supervisors Gas Divers, CSWIP 3.2u Gas Divers, CSWIP 3.1u Air Supervisors Air Divers, CSWIP 3.2u Air Divers, CSWIP 3.1u Life Support Technicians Rigging Foreman Riggers Saturation System Electricians Saturation System Mechanics
Inspection Equipment Requirements 2 1 3 3 3 1 6 5
MPI systems and all associated equipment, inks and spares. LP air grit entrained cleaning system. Roxby CP meters c/w spares. Cygnus U/T wall thickness meters c/w spares. Olympus OM1/2 cameras c/w strobes, close up and stand off lens and Scoones housings with close up kit and all necessary spares. Negative film to include 100, 200 & 400 ASA. Dark room for developing and printing of film to C41 process. Hat mounted CCTV colour video cameras, c/w lights. Colour monitors, video decks, editing suite and video cassettes (SVHS and VHS) of 120 and 180-minute duration.
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Selection Tape measures, pit gauges, markers, magnetic idents, Dymo tape and Dymo gun, wire brushes, hand scrapers, peanut grinder and a selection of burrs Justification Based on the personnel listed above the saturation team will be made up to give three two man diving teams allowing for three eight hour bell runs per each 24 hour period with each team being made up of a CSWIP 3.1u and 3.2u. The two remaining Gas Diver, CSWIP 3.1u, will be held as emergency divers working along side the Bell Supervisors in case of the need to jump a surface gas diver. The aid diving teams will be split to ensure equally qualified CSWIP personnel in each 12-hour shift. MPI is to be carried out as and when necessary using high ambient light ink. Rigging crews will be split into 12-hour shifts work on deck to deploy equipment to the divers as and when required. There will be two Inspection Controllers working a 12-hour shift system with one Senior Inspection Controller on 24-hour call supervising the work programme. This will allow coverage for both saturation and air diving teams The equipment load out has been calculated to include redundancy and spares to cover breakdowns and dual operation as necessary. 2. Describe how you would monitor the progress of a 14-day ROV inspection programme on a steel structure in 200m of water. There are strong tides in this area, how would you organise diving to allow the maximum amount of work to be achieved?
Q Quueessttiioonn 22 Work Monitoring 1. 2.
3.
Ensure the Inspection Controller has a detailed knowledge and understanding of the Workscope and Structure layout. Make up a working data base of all items to be inspected and what inspection is required on each item, this may be in the form of a wall chart which can be updated as and when work is completed and also added to if further work, i.e. anomalies, are noted. It should also include a date column for entry of the date when inspection was completed. Personnel should receive good briefings, this is to include Shift Data recorders as to what is required of them during shift and at hand over (Toolbox Talk). The Inspection Controller will work a split shift routine so that he covers all hand overs of the normal running shifts.
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4.
The Inspection Controller must maintain good liaison with the Party Chief, Client's Representative, Captain, the ship's crew and if necessary the OIM, to allow uninterrupted work as far as is possible.
Strong Tide Diving 1. 2.
The utilisation of a Tether Management System (TMS) would be beneficial to allow the ROV to work from its garage / cage below the tides which are usually strongest at / or near the surface. Carry out all shallow Workscope during the slack tide periods, also carry out all work that requires long tether excursions during slack tide periods.
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PPA PER ““C” C” -- SSECTION ECTION 110 0 –– C apabilities aand nd LLimitations imitations ooff D iv e r s APER Capabilities Divers 1.
With the aid of sketches, detail the equipment layout of a high pressure jetting system. Discuss the precautions required to ensure the divers’ safety during the operation of such equipment.
uestion 11 Q Question Equipment Layout
ssseell V Vees
HP W SSeeaa To diver
Seawater suction for pump
HP Jetting gun with retro gua HP Jetting hose
Precautions 1. 2. 3. 4. 5. 6. 7. 8. 9.
All diving personnel are to be given instruction in the use of high pressure jetting equipment. Instruction is to include safety aspects of the system and detail of typical injuries that my result from the misuse of the system. All connections are to have anti-whip restraints fitted. All jetting guns are to have equally balanced jets and retro jets. All jetting guns are to be fitted with diffusers over the retro jets. All triggers are to be checked for automatic release “Dead Man Handles”. No triggers are to be fitted with any mechanisms that will allow the trigger to be held open. No jetting operations are to take place if diver/supervisor communications fail, or communications are of poor quality. Topside pumps will not be made “Hot” until requested by the Dive Supervisor acting on instructions from the Diver. Jetting gun will be deployed to site on a down line with tie back lines to the jetting hose.
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10. 11. 12.
2.
All recovery winch/drums are to be of a large diameter so as not to put strain on the hose. No sharp bends. Recovery or deployment of the gun and hose is not to take place with the hose line under pressure. The diver is to keep all parts of his body and diving equipment clear of the high-pressure jet nozzle.
List the deployment methods currently used for the deployment of surface and bell divers. How does diving from a DP vessel affect these deployment systems?
Q Quueessttiioonn 22 Surface Diver 1.
JUMPING. This method primarily requires the diver to jump into the water while his umbilical is tended from the surface at the 'Jump' site. This method is not usually used in the UK waters, as it does not comply with the HSE requirements. It is however, used quite frequently in the Middle and Far East. This method would not be used from a DP vessel as the possibility of the diver or his umbilical being sucked into the thrusters is very high.
2.
LADDER. This method of entry into the water goes hand in hand with the 'Jump' method, as having ‘Jumped’ into the water the diver requires a ladder to allow him to exit the water. As with the 'Jump' method the ladder entry is not employed in the UK for the same reasons concerning the thrusters.
3.
BASKET. This is the preferred method of deploying surface air divers. The basket is deployed using a clump weight system to guide the basket to the working depth and also to prevent it from twisting and being affected by the tide / currents. The diver or divers, as the baskets are designed to accommodate 3 divers, 2 working divers and an emergency stand-by diver should he be deployed to render assistance, have a predetermined length of umbilical fed to them from the surface, via a stopper through the basket. This length of umbilical will not allow the diver to approach the nearest thruster any closer than 5 metres, therefore the basket method is used for diving from a DP vessel as well as a moored vessel.
4.
WET BELL. The wet bell is deployed in a similar fashion to the basket, however, the divers are able to reach their working depth with their breathing apparatus off as the bell affords them a safe haven and dry environment. The working diver enters the water through the bottom of the bell and is tendered from within the bell by the second diver (stand-by). As with the basket method, the umbilical length is limited by the distance to the nearest thruster less 5 metres.
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All the above methods of deployment require the divers to undergo decompression for each dive and this is usually carried out on the surface using the Sur D 02, (Surface Decompression using Oxygen) table. 5.
CLOSED BELL. This method of deployment can be used for both air and saturation diving and is much the preferred method of deployment. In the air diving mode the divers are sealed in the bell at atmospheric pressure and deployed to the working depth, when the diver is ready to enter the water the bell is pressured to the working depth and the bell's doors are opened. As can be seen by using this method of entry to the water the divers are only exposed to pressure for the duration of the work. Recovery is achieved by sealing the bell at depth and bringing it back to the surface under internal pressure and 'locking' the divers through to a surface chamber where decompression can take place in comfort and without submitting the divers to a surface interval. When using the closed bell in the saturation diving mode using a helium / oxygen or nitrogen / oxygen breathing mixture, the divers are only exposed to decompression at the end of the saturation programme, normally 24 days, thereby making this a very safe method of diving and allowing the divers to have maximum bottom time without the worry of decompression. The rules for umbilical lengths using the closed bell are the same as all other methods in that the divers umbilical is secured so that he cannot approach the nearest thruster any closer than 5 metres.
When surface diving from a DP vessel, the use of the Moonpool is not allowed if the working depth is between the ship's draft +10 metres and the surface. This is to prevent the possibility of the diver being sucked into the thrusters. For working at these depths a wet or closed bell must be used. Stand-by diver’s umbilical is always 1 metre longer than the divers to ensure he can reach the diver in an emergency.
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PPAPER APER ““C” C” -- SSECTION ECTION 1111 –– C apabilities aand nd LLimitations imitations ooff RROVs OVs Capabilities 1.
Give details of the various means of launching ROV's from a diving support vessel. Of those you have detailed, which would be the most suitable when carrying out a pipeline inspection survey.
Q Quueessttiioonn 11 Launch Methods There are generally four methods of launching vehicles they are as follows: 1. 2. 3. 4.
Articulated HIAB type crane. A-Frame. Fixed deployment cursor / guide wire system. Line and quick release hook.
Articulated HIAB Type Crane With the HIAB crane a docking mechanism is fitted which will allow a reasonably smooth launch / recovery of the vehicle. A-Frame The A-Frame method is similar to the HIAB Crane in that there can also be a docking mechanism. The A-Frame should have a reasonable reach over the stern or side of the vessel. The A-Frame system can also be situated over a moonpool to give added launch / recovery stability. Fixed Deployment Cursor / Guide Wire System Fixed deployment cursor / guide wire systems are usually utilised with a moonpool, this will extend the weather window and allow the deployment of the vehicle in poorer weather conditions than the two previously mentioned methods. However, a ‘Dead Vehicle’ recovery may cause problems as if the vehicle is deployed buoyant it may surface out board of the vessel and have to be recovered by an inflatable craft and then pulled to the side of the vessel for recovery. The tether or umbilical would then have to be disconnected from the vehicle and recovered back through the moonpool. Line and Quick Release Hook This method of launch is the leased used as it relies on the vehicle being lifted over the side of the vessel by means of a crane or some winch and cable other than the umbilical, when the vehicle is in the water the lifting hook would be released using a trip line. Recovery of the vehicle is difficult, especially if the sea conditions have increased during the time since the vehicle was launched, and necessitates the hook from the winch / crane attached to a pole to hook the lifting wire into the lifting eye on the vehicle.
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Suitability for Pipeline Inspection Of the four launch methods described above the Articulated HIAB type crane, the AFrame and Fixed deployment cursor / guide wire methods would be most suited to pipeline inspection work. However, it should be noted that these three methods would require the use of an umbilical / tether management system (TMS). There are basically three types that could be used: a) b) c)
Top Hat System Side Entry Garage Front Entry Garage
Of these the Top Hat System is probably the best where the recovery of a ‘Dead Vehicle’ is concerned as the other two can sometimes cause problems. 1.
For pipeline inspection from a DP DSV a free-swimming vehicle should never be used.
2.
Compare and contrast the use of a workclass ROV and a 1 Atmosphere diving suit for the inspection of a subsea Christmas tree. Describe how you envisage launching and retrieving both applications.
Launch and Recovery Systems Workclass ROV Deployment of the Workclass ROV would utilize a Tether Management System (TMS) whereby the ROV would be lowered to 20 metres above the work site and then would disengage itself from the TMS and fly over to the Christmas Tree paying out its tether as it goes. The recovery would be the reverse of the deployment. 1 Atmosphere Diving Suit – JIM Deployment of JIM would be via a winch with a lift wire attached to the JIM Suit. To allow JIM to descend to the work site it would be necessary for a guide wire, shot line to be established. Jim would then hook onto the guide wire using one manipulator and be lowered to the work site by the winch. Recovery would be the reverse of the deployment. Advantages and Disadvantages of Each System Workclass ROV Advantages Unlimited water time, continuous operations.
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Greater tooling package. No guide wires necessary for deployment. Small control room and deployment station. Small operating crew. Greater operating range and flexibility. No human involvement in the water. Has the use of video cameras; colour, SIT. Also still camera and sonar. No modifications required to Christmas Tree Not greatly affected by tidal conditions Disadvantages All operations are remote. 2 dimensional imagery only. ROV size restricts access. 1 Atmosphere Diving Suit – JIM Advantages Can see in three dimensions. Can use other senses to back up visual. Can give on the spot interpretation (commentary). Access good with prior preparation. Able to focus from a few inches to infinity. Disadvantages Limited duration dives (7 hours). Prone to fatigue. Human in water. Limited torque power. Large topside team and deployment system. Second JIM system required for emergency rescue. Affected by tidal conditions. Christmas Tree needs to be modified / adapted for JIM use. Small operating radius. Limited video and recording system. Requires guide wire for deployment. Poor mid-water operating ability. Affected by water clarity – visibility.
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PPAPER APER ““C” C” -- SSECTION ECTION 112 2 –– C are ooff EEquipment quipment Care 1.
List the inspection requirements needed to support the underwater inspection of a node weld with suspected surface cracking. The inspection is to be carried out by a diver. What equipment checks would the diver require to carry out before commencing the dive?
Q Quueessttiioonn 11 Inspection Requirements 1. 2. 3. 4.
Cleaning system / equipment to remove hard marine growth from weld and parent metal to 50mm either side of weld, sufficient to allow unrestricted movement of probe manipulation. Tape measure, suitable underwater marker, magnetic arrows and hand held wire brush. Hat mounted CCTV video camera and white light. Lizard EMA DiveScan system c/w LP100, LP300 and LP600 probes.
Equipment Checks 1. 2. 3. 4. 5. 6. 7.
2.
Connect up system and test earth leakage circuit breaker (ELCB) for correct operation. Apply wear protection tape to faces of all probes. Switch on Lizard EMA system and create inspection file for weld. Connect each probe in turn to the DDPU and take scans using each face on the standard reference block, LK100, saving each scan to disc. Once all QA scans have been performed, connect the LP100 probe to port 1 on the DDPU and the LP600 probe to port 2 on the DDPU. Attach the LP300 probe to the side of the DDPU ensuring it will not get damaged during deployment. Instruct the CSWIP 3.1u or CSWIP 3.2u diver on the use of the probes and the method of scanning and inspection required to carry out the weld inspection.
List the common video standards and discuss how the quality differs with each. Briefly comment on video printers. Describe what type of video camera you would use for a location, which had heavy suspension in the water and how you would set the equipment up for best results?
Q Quueessttiioonn 22 Common Video Standards 1. 2.
NTSC. This system uses 510 lines PAL/Secam. This system uses 625 lines
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Recording Methods 1. 2.
VHS. This method uses 200 lines. S-VHS. This method uses 400 lines.
The more lines the better the picture quality. Video Printer Video printers at the moment will not give a very high definition print when put alongside a photograph, however, they are always available when installed and so can give a quicker and easier shot, they also give exactly what is seen on screen. The quality of the produced image is also affected by the quality of the printer; a high pixel printer will give a much better picture than a low pixel printer. Video Camera Requirement for Heavy Suspension in the Water Heavy suspension will require the use of a SIT (Silicone Intensified Target) camera, this is a low light camera which is monochrome and relatively low resolution but will not need lights so will not suffer from backscatter as much. Any lighting must be arranged to allow for backscatter if a colour camera is to be used and there must be correct labelling and referencing for the videotape etc.
3.
Write a detailed procedure for calibration of a silver/silver chloride cathodic potential proximity probe using calomel electrodes.
Q Quueessttiioonn 33 Calibration Procedure Using Calomel Electrode Equipment Needed 3 Calomel Electrodes High Impedance Voltmeter (10 Mega ohm) Zinc Block with Clamp and Lead (Zinc should be 99.99% pure) 1. 2. 3. 4. 5.
Visually inspect the electrodes, ensure they are filled with Potassium Chloride (KCL) solution. Free crystals should be visible and there should be no air bubbles evident. Label the electrodes 1, 2 & 3. Connect electrode 1 to the negative terminal of the voltmeter and electrode 2 to the positive terminal. Immerse the tip of the electrodes in a plastic bucket of clean fresh seawater and record the reading from the voltmeter. Rinse the electrodes in fresh water.
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6. 7.
Repeat the test with each of the possible permutations of electrode, 1 & 2, 1 & 3, 2 & 3. The following procedure will dictate which electrode should be used for the calibration of the meters. Acceptable readings between a pair of electrodes is -2mv to +2mv, if all the readings are within this range then any electrode may be used, if one reading is out of this range then the electrode not in that pair is the one to use. If one reading is in range then either of the electrodes in that pair can be used. If all of the readings are out then the pair giving the least reading may be used assuming client's approval.
Calibration of Ag/AgCL Remote Half Cell (Proximity) 1. 2. 3. 4. 5. 6. 7.
Ensure the calomel electrodes have been properly calibrated. Soak the Ag/AgCL half-cell in clean fresh seawater in a plastic bucket for 30 minutes. Connect the negative terminal of the voltmeter to the Ag/AgCL measuring electrode. Connect the positive terminal of the voltmeter to the calomel electrode and immerse the electrode tip in the seawater. Record the reading from the voltmeter; it should be between 0 to -10mv. Repeat this procedure if the readings are outside this range. Using the procedure above measure the potential of a Zinc Reference block with the proximity cell. The reading should be in the region of -1000mv to 1050mv.
Note: See also Section 3, Question No. 2 for drawing.
4. Detail the pre and post dive checks and procedures, which should be carried out, on a 35mm camera system to ensure reliability and proper performance. Q Quueessttiioonn 44 Introduction The camera and housing being used in this example is the Olympus OM1N and the Schoones Housing. Pre-Dive Checks Check OM1N camera has new batteries installed. Fit motor wind and install new batteries. Load suitable film for the scope of work. Install lens, 50mm for close up and 23mm / 28mm for stand off work.
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Set shutter speed, focus and aperture as necessary. 1/60 – 1/90, Infinity, F11 for close up and 0.45 to 1m, F8 for stand off. Fix camera in Schoones Housing making sure its secure and all electrical connections are made. Remove the seal from the Schoones Housing, clean, regrease and replace in housing. Close housing and check to see it’s fully screwed tight closed. Install new batteries or ensure strobe lights are fully charged and attach to Schoones Housing, silicone grease the connection and connecting up electrical lead. Test fire the camera system and ensure all units are working. Fit close up prods if required. Make up idents boards with sufficient spares for the task in hand. Ensure lanyard and carabina hook are in good condition and securely attached to the camera. 14. Prepare photo-log. Post Dive Checks Wash the Schoones Housing and strobe in fresh water and dry. Check Housing, strobe, lanyard and carabina for damage. Open Schoones housing and remove camera. Check shots used against photo-log. Rewind film and remove. Remove all batteries from camera and motor wind. If the strobe uses batteries, remove or put strobe on charger. Log when camera was used, log time strobe put on charge. Clean housing ‘O’ ring and regrease. Process the film, reconfirm shots taken against photo-log.
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