Flange modifications due to rerating

[metaal]

Due to the rerating girth flanges are overstressed. The shell can't be removed due to complicated piping routing.
What actions can be taken to keep the existing girth flanges (reinforcement,stiffening ribs, weld deposit,....)

 

[metengr]

What type of vessel? How did you determine the flanges are overstresses? Is the overstress situation based on flange wall thickness or contour or what?

I would suggest you discuss your specific problem with an experienced pressure vessel design engineer. Any type of rerating is an alteration, and this should have been evaluated at the time you had re-rated this vessel.

 

[metaal]

Shell side floating head heat exchanger.
ASME VIII-Div. 1 flange calculation.
Flange thichness is not enough for the increased design pressure.

 

[metengr]

metaal;
Words of advice - I would strongly suggest you seek the guidance of a registered or licensed, Professional Engineer that is experienced in pressure vessel design. This is something that you do NOT want to fool with.

 

[waskillywabbit]

How was the vessel re-rated if the flanges couldn't take the new rating? Sounds like a big SNAFU on someone's part.

Seek "professional" help.

Brian

 

[jte]

metaal-

I agree with the others on seeking help and wondering how this rerate could have been completed without evaluating the flanges.

As for approaches I'd explore if I were in your shoes: First, your flanges are presumably failing in the operating calc which uses the M factor, not the gasket seating calc which uses Y. The first step for me would be to find a gasket with a lower M factor. Try a GMGC (kammprofile) or CMGC (eg. Graphonic).

The second, more involved (i.e. expensive) option would be to weld buildup the flange thickness. If you can do this on the backside of the flange, great. Don't forget to check for PWHT issues and you'll have to machine the flange face to bring it back from the warpage you'll cause. Otherwise, build up the flange face side, PWHT and machine as req'd. Lots of companies can offer the onsite machining. This approach, however, will likely cause you to rework the piping or nozzles on the channel.

jt