BASE MATERIAL FOR A P1-P1 PQR

[juancito]

Dear all,
We subcontracted the fabrication of a 2in thick pressure vessel (in SA 516 Gr70 N). To back-up the WPS´s the fabricator is showing us a PQR which was done using SA36 as base material, whose tensile strength is 58ksi (minimun).
Surprisingly the two tensile tests broke just above 70ksi which seems to be fine.
My questions are:
a)Is it reasonable that a SA36 base material has a much higer tensile strenght than specified (as it didn´t break @70ksi)?
b)Does the code requiere that PQR qualifications must be done in base material of same mech. properties as the one to be used in production or just to have the same P number?
Thanks in advance

 

[pipewelder1999]

# 2

The same P Number is usually the only requierement unless supplementary essential variables are required. In that case the group number is also an essential variable.

However that does not mean you throw out good engineering practice.

Have a nice day.
Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[GRoberts]

It is certainly common for A36 to be above its 58ksi minimum. Most certs I have on hand are between 65-70ksi UTS, but they are well below the 80 ksi maximum. So there is a good sized range for the tensile of the steel to fall into, but this should be taken into account be people who design with this material.

I also agree with Mr. Austin, and have also heard it from a member of the ASME B&PV Section IX code committee member that as long as it is the same P#, it is permissable to qualify to weld a base metal with a weld that did not even meet the tensile strength of that metal as long as it met the tensile strength of the metal it was tested with. I do not know anyone recommending this approach though. However it is not uncommon to have lower specified strength metals meet the tensile strength of higher specified strength metals, and haven't ever heard of anyone that has an issue with that.