Stress Relieving 2

[thwilli2]

This procedure calls out for a complete X-ray of the welds during inspection. After the X-ray inspection, we plan on stress relieving all the welds. Is it necessary to do a follow up X-ray? I say no b/c stress relieving should not introduce any additional stresses.

 

[NickE]

I dont think (but am not sure) that X-Ray is used for stress analysis of welds. I thought that X-Ray is used for weld integrity checking.

That said I wouldn't expect that the stress relieve cycle will change the integrity of the welds.

Can you do the X-Ray last anyway?

Nick
I love materials science!

 

[stanweld]

It depends on the Code or the Owner's/Engineer's specifications; e.g. per ASME VIII, Div.1, ASME Section I and ASME B31.1 the weld would not require re-examination after PWHT.

 

[metengr]

I concur with stanweld.

If you don't have any Code requirements and are just looking for a tip;

if the material is carbon steel - no need for radiographic testing (RT - aka x-ray) after PWHT. If the materials are higher alloy, air hardening, Yes, I would require RT after PWHT.

 

[gr2vessels]

thwilli2,
This subject was debated several times, with opinions pro and contra. It appears that the debate is between the owners and the fabricator. The code is not helpfull either, sitting pretty on the fence, without specifying when to perform the major NDT's.
As a fabricator you would prefer to perform the NDTs before the expensive PWHT, to give yourself a chance to repair all the defects BEFORE the PWHT (the code generally prevents the welding repairs after PWHT). On the other hand, as an owner read the code which says that the NDT should be performed after welding and that PWHT is part of the welding process. This implies NDT after the PWHT. Also, the fabricator cannot hide any defect evident on NDTs after the PWHT.
For carbon steel I typically agree with RT before PWHT, provided that UT or/and surface testing will also be performed after PWHT, to detect any cracks. For high alloys, NDT only after PWHT, as required. All the above posters are also right. Clear now? I thought so..
cheers,
gr2vessels

 

[PAN]

In case of low alloy steels, you may refer to API RP 934. UT and MT/PT are requirement after final PWHT.

 

[jsokal]

Having had a lot of experience in welding,NDT and heat treatment,here is my two cents on the matter.
Generally speaking,performing an x-ray before and after PWHT is a huge waste of time. The sensitivity of x-rays are such that you will not necessarily see any cracks if they are too fine or even not oriented properly in relation to the x-ray beam. X-ray if required is useful after welding to check the internal weld quality, ie. penetration, fusion,..the internal defects not necessarily visible to the naked eye. Following the PWHT the better NDT to perform would be an FPI which will look at the weld and HAZ surfaces for cracking,and which by the way is MUCH more sensitive to crack detection than X-rays alone. The idea of doing the FPI after PWHT, is that if there are microcracks present, often they are too small even for FPI to detect, but following a PWHT, microcracks often "open up" and render themselves detectable to the penetrant.

John