Hello,
I have a joint on a pressure vessel (2" wall thickness) that an engineer came to me with the concern of cracking during or after PWHT. Since the material is 516 Gr. 70 I don't think Reheat cracking could be an issue, but am not sure. I know that austenitic SS have this problem and some Chrome Mollys but is it something I should be watching for on other materials? If so what would they be?
Any help on this issue would be gratefully accepted,
Thanks, Charles
By 3.1 Inspector
Date 08-20-2008 19:14
Uncle,
It usually wont happen on P1 materials, but I have read somewhere that even P1 material above 50mm wall thickness(almost 2 inch) could be susceptible to reheat cracking.
Watch out for it on Cr - Mo - V steels.....P5, P11, P22, P91, etc....
Thats the reason that NDT have to be performed after PWHT
With a 2" wall thickness I would think you aren't using PWHT with long enough soak times to get into PWHT cracking regimes with almost all materials since its diffusion related.
By 3.1 Inspector
Date 08-20-2008 20:53
You are most likely right.
I don't think you will have a problem, since carbon steel does not harden by precipitation mechanisms as is required for reheat-cracking. If there is still concern, one way to avoid re-heat cracking is to use low heat input during your welding so as to reduce the grain size and the overall size of the coarse-grain HAZ where re-heat cracking takes place.
If concern the cracking, Maybe you can do the stress relief by vibration
To reduce & redistribute the welding stress, avoid its cracking & distortion
My Email:sunnn@semboo.com Alice
Sorry, but as far as I know vibratory stress relief is not permitted by any pressure vessel code that I am aware of. Perhaps you should approach ASME with sufficient technical data to support a Code Case allowing it as an alternative to stress relief by heat treatment.
We have one of those so called magic bubble machines here and they finally realized that cooper heat was worth investing in, so bye bye metlax and hello cooper heat!
It didn't crack, everything went fine. Thanks for all the great responces.
Charles
