NDT 3

[Eck75]

Can you advise if you can get away with just x-ray of butt after PWHT,Rather than X-ray before the PWHT wait 48hrs and x-ray again?

 

[Mr168]

If code permits, sure. The problem however, is that if the weld doesn't shoot, you're looking at making the repair and re-postweld heat treating, which isn't always a feasible option.

 

[metengr]

If there is a 48 hour mandate for NDT you better check with the client because they want to ensure no delayed cracking from hydrogen after PWHT (above and beyond code requirements). This requirement applies to certain steels that are prone to delayed cracking because of their chemical composition.

So, I would not be too quick to recommend delete this practice unless you exercised caution using adequate preheat and low hydrogen welding consumables.

 

[stanweld]

From an ecomnomic standpoint, RT after PWHT only is based on your reject rate. If your reject rate is very low, repairing and re-PWHT will prove cheaper than RT before and after PWHT. When Exxon first required final RT after PWHT over 30 years ago, they expected to get two shots (before and after PWHT) for the price of one. And they got what they wanted until pipe fabricators realized that their rejection rates were so small that they could perform RT only after PWHT and make the few repairs, RT them and re-PWHT after the repair at considerably less cost.