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Document Title: Leak investigation of circumferencial weld seam failure of V-3369 Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10 Report date: May 3, 2012 Page 1 of 12 Leak Investigation of Circumferencial Weld Seam failure of V-3369 RSV team visited the Tangri facility for the inspection of subjected leak dated 03-05-2012 and following are the observations: 1) Location: Tangri Facility 2) Date of Inspection: 03-05-2012 3) Equipment /Pipe Description: Equipment V-3369 4) Vicinity Reference: Inside fence 5) Fluid inside /Service: Lean Amine 6) Coating Type: Paint 7) Operating Temp. / Pressure: 190 0 F / 3~4 Psi (positive pressure) 8) Location of Leak: Shell to head circumferencial weld seam 9) Morphology of point of failure: Transverse crack 10) Leaked equipment connected to system / Isolated: Connected 11) Type of Welding: Submerged Arc Welding 12) RT level: 1 13) Stress Relieving: No Photographs of Equipment and Point of Failure

Crack Investigation of 3369 (Crack Report)

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Page 1: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 1 of 8

Leak Investigation of Circumferencial Weld Seam failure of V-3369

RSV team visited the Tangri facility for the inspection of subjected leak dated 03-05-2012 and following are the observations:

1) Location: Tangri Facility2) Date of Inspection: 03-05-20123) Equipment /Pipe Description: Equipment V-33694) Vicinity Reference: Inside fence5) Fluid inside /Service: Lean Amine6) Coating Type: Paint7) Operating Temp. / Pressure: 190 0F / 3~4 Psi (positive pressure)8) Location of Leak: Shell to head circumferencial weld seam9) Morphology of point of failure: Transverse crack10) Leaked equipment connected to system / Isolated: Connected11) Type of Welding: Submerged Arc Welding12) RT level: 113) Stress Relieving: No

Photographs of Equipment and Point of Failure

Leaked Weld Seam

Page 2: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 2 of 8

Point of failure

Point of failure after scrubbing Paint

Drop wise leakage

Morphology of point of failure after 12 hours

Morphology of point of failure after 30 hours

Morphology of point of failure after 30 hours

Page 3: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 3 of 8

Surface breaking transverse Crack

Page 4: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 4 of 8

Proposed NDE Techniques:

Surface breaking cracks can be investigated and sized using combination of following non destructive examination;

1. DPT2. MPI3. UFD4. RT

Limitations of DPT and MPI:

Temperature limitation restricted the use of MPI and DPT techniques on examination surface. The recommended temperature of manufacturer of all consumables present on site was 55C while of examination surface was 86C.

Limitation of RT:

As equipment was connected to system limiting the possibility of panoramic technique, the only possible way to carry out RT was DWSI technique. The exposure time calculated with max.10 Ci for single exposure using even D7 film was about 7 hours.Moreover potential health and safety hazards of gamma rays do not permit radiography as a better choice for crack investigation.

Execution and Limitations of UT:

The only non destructive examination technique which could prove helpful in failure investigation was Ultrasonic flaw detection with following draw backs affecting the reliability and accuracy of the test as far as available resources are concerned.

1. UFD is always recommended above wall thickness of 13mm of examination surfaces for reliable and precise results. Special purpose miniature probes with higher frequency and mock up blocks for calibration can be helpful for better detection of discontinuities as far as thickness ranges below 13mm are concerned.

2. Examination surface temperature above 65C impacts the test accuracy as mentioned in API 510 and ASME V. Special procedures are to be qualified for carrying out such sort of research work including calibrating the equipment on hot mock up blocks and establishing the temperature correction factor.

3. Skip distance requirements while using the narrowest available 70 degree shear wave probe were not met as far as low thickness of test object is concerned. Flushing the weld capping equal to base metal could serve the purpose but equipment was in-service and no hot work was permitted.

Page 5: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 5 of 8

However ultrasonic flaw detection with longitudinal and shear wave examination was carried out by calibrating the equipment on the hot test object and following are the main findings:

The defect was characterized as transverse crack and only prevailed the capping of weld. Crack has not still propagated into HAZ.

Normal beam scanning over weld capping did not reveal any other objectionable discontinuity in the vicinity of point of failure as marked in snap below. Sharp echoes in conjunction with back wall were received at the thickness of 8mm and 5mm near the point of failure.

Shear wave examination over weld capping also counter proved the results of normal beam scanning. There are chances of metal deterioration deep below 8mm of weld.

No objectionable indication was noticed in HAZ No objectionable indication was noticed in scanning area of 1ft above and 1ft

below the point of failure.

Length of Crack =25 mm as measured by UFD.

Page 6: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 6 of 8

Root Cause of Failure:

Amine stress corrosion cracking is most likely to occur in lean MEA, DEA services and associated with residual stresses from welding, cold working or fabrication, that not have been removed through an effective stress relieving treatment. Same is the case with subject equipment. Submerged Arc Welding process with higher heat input has been applied for joining of base metal and head and no heat treatment is given to remove residual stresses. Consequence is the origination of transverse crack after equipment is in service.

Based on the age of equipment (almost 10 years) and findings up to now, one can guess that transverse cark is the result of propagation of residual weld defect omitted at the time of fabrication. The defect propagated with time under stress conditions due to service and resulted into surface breaking crack. Although the defect remains in an acceptable limit at the time of fabrication, as equipment is RT-1, but absence of PWHT assist the above hypothesis. According to API 945 publication, PWHT of all amine circuits is essential to avoid any catastrophic failures in welding and heat affected zones.

Above pasted snaps show that first a single point of failure appeared on weld seam. After some hours couple of more pin holes type indications was vivid on weld seam. After 30 hours of service after leakage, points got connected themselves and transformed into surface breaking transverse crack.

Proposed Temporary Repair by UEP:

As vessel is not heat treated and propagation of crack is towards base metal, patch with larger dimension in the direction of major axis of crack propagation is recommended. Schematic layout for cold patch work is given below.

One of the greatest disadvantages of patch working is that the propagation of crack cannot be monitored on periodic basis as there will be no provision for scanning area for UT.

Proposed Cold Patch-Work on Weld Seam Leakage of V-3369

Page 7: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 7 of 8

1ft 1ft

1 ft

V-3369

Please note that; about 2-ft area of all circumferential weld seam at liquid to vapor interface location was UFD scanned (with straight beam); indication were observed in shell to dish welding seam as marked in above sketch.

Notes:

Surface should be properly cleaned of both patched plate and vessel plate area which suppose to be patched.Proper mixing and application of belzona 1311 chemical.Proper intact of patched plate with vessel plate

Proposed repair by belzona cold patch work (see below detail)

Detail dimension and magnified view of patch work by belzona

Failure/leak area

A A‘View given below’

View A’-A’

Weld seem

MS plate

Indication found on both weld seam of front and back side of V-3369

Indication found on back side weld seam of V-3369

CW-1 CW-2 CW-3 CW-4

Page 8: Crack Investigation of 3369 (Crack Report)

Document Title: Leak investigation of circumferencial weld seam failure of V-3369Client: United Energie Pakistan Limited. RSV Job No: Contract No: CON-PK-073-10Report date: May 3, 2012 Page 8 of 8

Proposed Permanent Repair:

Permanent repair involves grinding the defect (crack) until it is completely removed from the base and weld metal and then weld build up, preferably using GTAW.WPS by strictly controlling the welding parameters. Following steps should be followed while permanent repair is made;

Offline the equipment. Weld metal and adjacent base metal should be ground / gouged until crack is

completely removed. Drilling the holes on both ends of crack and then grinding it may eliminate the aspect of further propagation of crack during grinding.

UT, RT, MT, PT or combination of these techniques should be utilized to assure that no more defects are present in the vicinity of ground area. Radiography of all welding seams of equipment must be carried out to assure the sound health of other remaining welds as failure has occurred on the welding seam rather than base metal or HAZ.

Once the adequate certainty level is achieved that affected area is free of crack and any other discontinuity, next step is weld build up.

GTAW.WPS with low heat input is preferable in the situations like that. Qualified experienced welder should be chosen to accomplish the welding process by strictly following all the welding parameters.

According to API 945 publication, PWHT of all Amine piping circuits and equipments is essential at the time of fabrication as well as after any repair, alteration or rerating of equipment. PWHT of the equipment should be the next step to be followed after weld build up.

As the equipment is offline, Radiography of all welding seams before and after PWHT must be carried out to ensure the integrity of the equipment for continued safe operation. As leak has occurred on welding seam. It is important to know about the health of other welding seams to avoid any potential of failure.

Hydro testing is graded as prime tool to ensure the integrity of any fabrication or repair work but can this step can be alternated with RT/UT on the sole discretion of end user (owner/user) in consultation with API 510 Inspector, Engineer and corrosion specialist.

Painting the equipment after mandatory surface preparation will be the final step to be followed according to standard UEP approved procedures.