Straigthening P91 headers by cold pressing

[lgracio]

thread330-381311

Hi everybody.
In our factory we are able to make a proof process qualification report for cold pressing of P91 headers after welding nozzles to header pipe, without a subsequent heat treatment PWHT.

We know that all grade 91 components that have been welded shall not be subjected to any forces to align, adjust or straighten before an interim post weld heat treatment (730-760ºC for 1 hour per inch of thickness but in no case less than 30 minutes) has been completed.

There is an exception in our spec, that enable us to do cold pressing straightening operations if the bow is small, i.e. at mid-span is measured a minor deflection of 5mm (for a span of 1040mm), so that proof qualification test is giving results by mechanical tests that strain is within limits for the correspondent material OD and Thk (thinnest and thickest).

So as far as the strain is within limits the creep strength is not compromised.

Anyone knows how to calculate the limit strain for a P91 header pipe length span of 1040mm, which is loaded in 3 point bending?





LPSG-Engineering Solutions
Mechanical Engineer
Portugal-Setubal

 

[metengr]

The maximum strain limit for P91 is in ASME BPV I. You need to adhere to this strain limit to avoid premature creep failure.