Radiography of weldings before or after PWHT? 3

[ChriChri81]

Hi, i need to know what You think about radiography of weldings. These radiographies must be done after or before PWHT? if i've a perfect radiography before PWHT, could i find some defects after PWHT? Why?
Are there differences between low alloy & Carbon Steel weldings?

 

[stanweld]

Radiography of hardenable steel alloys performed prior to PWHT may not reveal delayed cracking when PWHT is performed well after RT. Both ASME B31.1 and B31.3 require final RT after PWHT for low alloy steels in P Nos 3, 4 and 5.

In highly restrained joints in carbon steel, we have seen delayed cracking up to 72 hours after weld completion.

 

[ChriChri81]

Hi Stanweld,
thank you for your quick reply. It's clear your answer about low alloy steels.
Regarding C.S. materials please can you explain better your experience? if i do the radiography after (for example) 72 hours, i'll be sure that PWHT won't cause defects in welding (only for c.s.)?

 

[stanweld]

Most Codes do not require RT of low carbon steels after PWHT. I have never seen delayed cracking in low carbon steels, including those microalloyed with Nb and V, after 72 hours from weld completion.

 

[metengr]

One always has the option to specify beyond code requirements for RT after PWHT for P-No 1 base materials. If anything, I would at least perform a surface examination using wet fluorescent MT if you elect to have RT before PWHT.

 

[robsalv]

Our corporate standard is to recommend NDE before and after PWHT - but definitely after PWHT for CS and low alloy steels.


I've always considered it a prudent conservative practice and have never really questioned it.

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