GAP BETWEEN REINFORCEMENT PAD AND PIPE WALL

[PMCap]

WE ARE ADDING A REINFORCEMENT PAD AT A PIPE BRANCH CONNECTION. THE RUN PIPE IS DISTORTED (SUCKED IN AND SOMEWHAT FLATTENED) THE REINFORCEMENT PAD WILL BE WELDED ON WITH THE PIPE IN SERVICE AND UNDER PRESSURE AND ROUNDING UP OF THE PIPE IS NOT BEING ALLOWED BY THE CUSTOMER.

QUESTIONS
1. DO ANY OF THE ASME CODES HAVE A CRITERIA ON THE ALLOWED GAP BETWEEN THE REINFORCEMENT PLATE AND THE PIPE WALL AT THE OUTER EDGE LOCATION OF THE FILLET WELD?

2. SEPARATELY IS THERE ANY GAP CRITERIA AND THE INNER FULL PENETRATION WELD LOCATION?


3. WE ARE CONSIDERING 2 PIECE REINFORCEMENT PAD WITH PARTIAL DEPTH SLOTTING SO THAT THE PAD BECOMES MORE FLEXIBLE AND CAN BE CLAMPED DOWN ONTO THE PIPE WITH MINIMAL FORCE. THEN THE INNER FULL PENETRATION AND OUTER FILLET WELDS WILL BE MADE. THEN THE PARTIAL DEPTH SLOTS WILL BE WELDED UP. ANY COMMENTS OR OTHER SUGGESTIONS WOULD BE APPRECIATED?

THANKS

 

[metengr]

Off the top of my head, I don't know of any minimum requirement other than good engineering practice would require an intimate fit between the repad and pipe OD surface so the repad can function to provide added strength in this section of the pipe.
If I understand your post correctly, I would be very concerned that installation of a repad with a known gap due to out of round pipe will result in no structural reinforcement because the fillet welds would be carrying the entire load with no support from the repad. Also, excessive opening at the root of the fillet weld would result in local stress concentration and possible crack propagation in cyclic service. Not a very good design.

 

[rakuday]

Refer ASME sec8 d1, part UG37 for repad calculations. Though the standard does not say about the fit between the repad and pipe, its better to have a tight fit, else there is always a possibility that the weld can fail due to lack of penetration between the pipe and repad.

 

[stanweld]

Are you applying a full circumference wedding band type repair or local reinforcement. If so, API 1104 Appendix B has recommended repair practices and qualification requirements.

 

[PMCap]

Thanks for the responses. much appreciated.

 

[4Pipes]

I am with metengr. There are serious questions on the design. The stress and stress concentration at the back of the fillet welds could be anybodies guess. The only reason a normal repad is permitted is because it has stood the test of time with reasonable (but not total) success. A proper analytical calculation of a real repad is virtually impossible. Temperature makes it very much worse. Big gaps will increase thermal stresses. What is in the pipe, pressure temperature etc? What is the purpose of the pad and why add it now? Is it because the nozzle is too flexible / weak and has been subject to excessive external loads. My only guess and it is a guess would be to look at some form of ribbing / gussets to add strength. At least you could get a good fit up and welds you could profile and NDT on both sides. If the ribs are properly attached, then it would be possible to 3d scan and do an FE calc of the actual deformed shape. How you judge the actual affect of the load distribution given that the pad is stress free when welded onto a stressed pipe on for either pad or gussets will be interesting. Any design would have to locally yield at some time when the pipe is depressurised and cooled.

 

[PMCap]

The piping system is being re-rated for operation at a higher temperature and pressure. The reinforcement pad is being added to reduce the S.I.F. at the branch connection location. The installed reinforcement pad will be snug fit to the pipe by special tooling that minimizes load on the pipe and maintains pipe current configuration. Laser Scan data of the pipe branch connection surfaces was used to determine configuration of reinforcement pad and and best location of partial depth pad grooving / slotting so that that pad can be clamped down to the pipe surface with minimum load. Following fit up the inner full penetration weld and the outer fillet welds will be made. Lastly the partial depth grooves will be welded up.