Bending P91 small bore pipe

[douglasaudfroid]

I am presently on a project in Mexico and the HRSG supplier has supplied straight run pipe (small bore), P11, P22 and P91. I have read some of your forums and have been in the industry for 30 years as an OEM rep, but have never used or have done any bending in the field. I guess I would like some guidance, procedures and people that are available to do this and are good at it. I know Shaw Group does some, but there must be others? We have some 2"sch 160 which is pretty tricky, so please forward me some info if you have the time.

Best Regards
Douglas

 

[metengr]

You don't mention the degree of bend required. For Sch 160 pipe of P91 material, the bending should be performed hot and subsequently re-heat treated in accordance with SA 335 material specification requirements. Hot bending is an operation that should be conducted under controlled conditions by professionals in a qualified shop with heat treatment capabilities especially for Cr-Mo alloys and grade P91 material. I would not recommend hot bending in the field, especially for grade P91 material.

I know of one additional pipe bending shop located in Duluth MN called BendTec. They are excellent at handling induction bending of heavy wall (large or small bore) pipe material, including P91. This material must be treated with extreme care otherwise you will have premature failure in service. BendTec can also handle P11 and P22 material with no problems.

 

[davefitz]

To add to Meteng's advise, any hot bending of P91 pipe will require that the entire pipe length that was attached to the bend at the time of hot bending be normalized and tempered N+T.

We found that there are many small Mom + Pop pipe bending shops that do not realize this is a requirement for P91 piping. The reason for this requirement is that if you inductively heat only the zone that is being bent to 1900 F, there are adjoining zones that will be heated to only 1400 F- 1600F, and those zones will be overtempered and have much lower creep life than assumed by ASME code. To elimiante this issue, the entire pipe length that might have been overtempered will need a N+T.

When I say "requirement", I do not mean that ASME currently requires this directly, although itis being considered to be added as a code requirement. It is an implied requirement based on a liberal reading of the ASTM SA335 specification - any fabrication operation on a sa335 pipe should leave the fabricated component wit the same properties as the supplied sa335 pipe.

 

[douglasaudfroid]

Thanks, I appreciate your input and they validate my concerns. I will be in contact with BenTech or try and convince the end user to buy some fittings.

Regards
Douglas

 

[douglasaudfroid]

I guess I forgot to mention that these are drain and vent pipes off the HRSG. The drains obviously are rarely opened during operations unless of course it is the initial in service runs where you want to purge the sludge and crap out of the headers at low pressure. Also the only vents that will be left opened are the drum vents to 25psig and then the last to close off would be the final supeheater vents once on line.

Regards
Douglas

 

[douglasaudfroid]

Just thought I should add the minimum bends are 4" radius.

Sorry!

 

[rmw]

You are inquiring about pipe, but boiler tubing benders who have had experience with T-91 have some horror stories to tell about their early experiences.

If you have any contacts there, check with them, although the question has already been adequately answered in this thread. I recommend this just for reinforcement, if you need it to justify the costs of doing it right.

rmw