DHT for CrMo P4 welds

[Villabrille]

Does anybody have a good information (probably a link) about the convenience or real effects in the use of Dehydrogenation Heat Treatment (DHT) after welding for welds in P4 and P5 materials?

 

[metengr]

What do you need to know exactly? For piping and pressure vessels, hydrogen back-out or a post weld bake is normally performed, immediately after welding is completed, at 500 deg F minimum for 1 hour per inch of nominal weld deposit thickness. This technique is not necessary IF low hydrogen electrodes were used in fabrication/repair.

 

[Villabrille]

Thanks first of all. We are a pressure vessels manufacturer and we have welded for many years reactors and others made of Cr-Mo materials, mainly P4. The way we apply the DHT treatment often depends on the client`s requirements but we do not have any clear criteria to propose in the case that no requirements exist. Also, there is no too much information about this issue, I mean, about the real effects ( difussible hydrogen decreasing, toughness improvement, etc..) of applying different DHT's. It would be great to find any good information ( probably some complete technical article) as a basis to define the need for DHT for different thicknesses, welding conditions ( for example high restrained welds) based in knowing the real effect of the DHT.

Thanks in advance

 

[metengr]

Ok. I believe what you refer to as your DHT is actually post weld heat treatment (PWHT) in accordance with Code requirements, is this correct?

If so, when you respond back, I can provide some guidance on this matter for these materials.