is N+T req'd for P91 induction bend?
is N+T req'd for P91 induction bend?
(OP)
When I read the Mannesman guidebook for fabricating components of P91, it states that all hot formig operations must be followed by a full normalized + tempering N+T treatment of the entire piece. This is to ensure that any sections that may have austenized or become overtempered by exposure to a temperature range 1500-1800F have their crystal structure repaired.
I have just been advised that there are many recent combined cycle sites which had their P91 HP main steam line bends fabricated using an induction heating bending machine, and these bent pieces did not later undergo a N+T . Does this mean we can expect a rash of premature P91 failures in the near future? And why doen't ASME code require the N+T?
I have just been advised that there are many recent combined cycle sites which had their P91 HP main steam line bends fabricated using an induction heating bending machine, and these bent pieces did not later undergo a N+T . Does this mean we can expect a rash of premature P91 failures in the near future? And why doen't ASME code require the N+T?





RE: is N+T req'd for P91 induction bend?
RE: is N+T req'd for P91 induction bend?
In this business, the customer must beware and understand material limitations. I believe the reason the Code is silent on this issue is it hasn't been a concern. The Code deals with design, material selection and joining to result in a safe component. Bending is one of those detailed fabrication steps that until serious problems develop or enough users complain about it, nothing will be said or done about it.
As far as a rash of P91 failures, the only way we will know will be operating experience. My feeling is that P91 used on Power Boilers is probably not going to be a problem because moist utilities have the in-house technical expertise or use experienced suppliers to avoid mishandling of P91 piping. I would believe that smaller IPP's are probably left exposed and unless they have someone like stanweld, you or myself on staff - they will be in a world of hurt.
RE: is N+T req'd for P91 induction bend?
RE: is N+T req'd for P91 induction bend?
RE: is N+T req'd for P91 induction bend?
Just because a particular job is turnkey doesn't mean less involvement. EPC (engineer/procure and construct) is a new way of doing business by our procurement folks. We still insist on hold points during fabrication and construction of boiler components - new or retrofits. It would be foolish to let this fall into the hands of others that have no special interest from the customers perspective. Our company will hire outside help, if need be, to assure compliance with our tight fabrication specifications - especially when it comes to P or T91 components.
Second item is weld repair of P91 or T91 tube material. This material can be properly weld repaired provided very strict controls are followed. This requires the correct selection of welding electrodes, maintaining of preheat, interpass temperatures and a very specific post weld heat treatment procedure (time and temperature). These are items that can be reviewed and monitored as hold points. So, I do NOT agree with your gloom and doom assessment regarding repair of P91 material.
We have performed weld repairs on T91 material in the boiler due to sootblower erosion damage with no adverse affects.
RE: is N+T req'd for P91 induction bend?
The potential problem is not as minor as a boiler tube leak- it is instead a concern related to a 14" OD main steam transfer pipe in the work space. And it is not just our site; the pipe vendor said he and all other fly- by- night shops do it the same way. This means that once they start to fail, no P91 transfer pipe will be considered safe. It will be like the Mohave P11 failure all over again.
What I am finding is that the EPC vendors ( big players , at that) and pipe shops do not have metallurgists on staff and their designers have no significant understanding of P91 metallurgy. Time for all shops to conveniently lose their recrds.
RE: is N+T req'd for P91 induction bend?
It's not only on 14" lines. I've seen hot bends on 24" hot reheat lines 18" main steam lines and on down to 8" lines.
This brings on another observation. A burst in the bend of a superheater crossover line recently occurred at a Power plant that we did not construct. Elbow was supposed to have been P91 but was found to be P5 - finding a tad late! We have discovered many such mixes but PMI has almost never been required by owners or engineers. It's as if the lessons learned decades ago regarding mixed steels were never learned.