PETRONAS Management Training Sdn Bhd © 2006.All right reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or means (electronic, mechanical,

photocopying, recording or otherwise) without the permission of the copyright owner.

REPAIR

© PMTSB 2006

Repair

Observe the following rules

• Definition – work necessary to restore vessel to a condition suitable for safe operation at design condition

• Use only repair procedure which has been qualified by pressure vessel engineer

• Employ only qualified welding procedures & welders to do the job

• No welding if carbon content exceeds 0.35%

© PMTSB 2006

Repair

Common repair types

1. Crack repair

2. Patch repair using fillet welds

3. Full encirclement lap band repair

© PMTSB 2006

Repair

Common repair types

1. Crack repair

2. Patch repair using fillet welds

3. Full encirclement lap band repair

© PMTSB 2006

Repair

Crack repair

• Important!!! Consult your pressure vessel engineer before repairing any crack

• General steps:

1. Remove crack

2. Build up area by welding

3. Ensure repaired area is free from defect

4. Perform PWHT, if required

5. Perform pressure test if required

© PMTSB 2006

Repair

Crack repair

Step 1 – Remove crack

• Remove completely by making U or V shaped groove

• Perform NDE to ensure area is free from defect

© PMTSB 2006

Repair

Crack repair

Step 2 – Build up area by welding

• Ensure filler metal is as strong as base metal

• Preheat base metal temperature to a minimum of 150oC

• Preheat area should cover 4” of material or 4 times thickness, whichever is greater, on both sides of weld

• Ensure interpass temperature is maintained between layers

• If required, ensure post heat is immediately applied after welding

© PMTSB 2006

Repair

Crack repair

Step 3 – Ensure repaired area is free from defect

• Perform NDE on repaired area – either PT or MT, as required

• For vessels made of P-3, P-4, or P-5 materials, which are operated in hydrogen service, they should be inspected for delayed cracking using ultrasonic examination after 24 hours

© PMTSB 2006

Repair

Crack repair

Step 4 – Perform PWHT, if required

• Normally required for thick ferrous vessels over 1½”

• Normally required for vessels made of P-4, or P-5 materials, regardless of thickness

• PWHT area should cover at least 2 times thickness on both sides of welded area

• PWHT should be monitored by at least 2 thermocouples

© PMTSB 2006

Repair

Crack repair

Step 5 – Perform pressure test, if required

• Where possible, use water and pressurize to 130% of MAWP

• After holding for a certain amount of time, reduce pressure to 90% of test pressure and perform close visual inspection

• If pressure test using water is not possible, pneumatic test at 110% MAWP is possible

• Similarly, after holding for a certain amount of time, reduce pressure to 90% of test pressure and perform close visual inspection

© PMTSB 2006

Repair

Common repair types

1. Crack repair

2. Patch repair using fillet welds

3. Full encirclement lap band repair

© PMTSB 2006

Repair

Patch repair using fillet welds

• Usually for temporary repairs of thinning area

• Important!!! Consult your pressure vessel engineer before attempting this method

• The engineer must ensure by calculations that;

Fillet patches provide design safety equivalent to reinforced openings

They effectively absorb all membrane stress in shell

They don’t create local stress at the fillets that exceed allowable stresses

• Steps shall be performed in the same sequence as crack repair

• Fillet patches shall have rounded corners

© PMTSB 2006

Repair

Common repair types

1. Crack repair

2. Patch repair using fillet welds

3. Full encirclement lap band repair

© PMTSB 2006

Repair

Full encirclement lap band repair

• Important!!! Consult your pressure vessel engineer before attempting this method

• Can be considered long term repair if;

Not used for crack repair on pressure vessel

Can take full design pressure

Use full penetration butt welds

Fillet welds can carry full longitudinal load, using joint efficiency of 0.45

Not subject to fatigue

PETRONAS Management Training Sdn Bhd © 2006.All right reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or means (electronic, mechanical,

photocopying, recording or otherwise) without the permission of the copyright owner.

End of REPAIR