Re: [MW:10498] Socket weld

Dear Hasin

I would like to try to answer your question from the best of my knowledge.

First of all, let's discuss about background of PWHT. a crack mostly happen when hydrogen diffusing from a solidified weld meets with a hard microstructure which is under specified range or its parent metal. Hydrogen cracking normally occurs in the HAZ area where we can find an undesired microstructure. we also fully aware that the other benefit of PWHT is to avoid residual stress and distortion.

Why an inconel 625 is more advisable in use for welding - i assume weld for dissimilar metal - and why we not go with other electrode?
We should take a carefully when we welding for dissimilar metal. The consideration is to avoid formation of martensite. The using of enconel 625 is main factor which is contributing to avoid a crack, due to containing of 22% Cr will keep the weldment in austenite range and avoid it from martensite formation. You can check nickel equivalent and Cr equivalent in your case.

It can say that the using of enconel 625 will help you improve hard microstructure which may be happen in your case. One of your PWHT's purpose (reducing the hardness of the weld heat affected zone) now has been answered. But, let's go back to the background of PWHT. One of the other PWHT purpose is to avoid residual stress and distortion. This purpose can not be answered by using of enconel. Weld shrinkage can not be avoided. Residual stress and distortion still happen, eventhough an enconel is used.

That is why, if your PWHT purpose is to avoid residual stress, basically, the enconel is not really doing anything to the heat affected zone. Inconel can be used for dissimilar metal, corrosion resistance overlay and to help reduce residual stress. They may be useful to reduce residual stress, but it has a little effect.

if a PWHT is requested by the technical document or considered as a significant, please keep doing PWHT.

Once again, this is from the best of my knowledge and experience. Therefore, other comments are welcomed. If any, I am thanking to you.

 

Rgds

2011/3/21 hasin shaikh <hasin.shaikh@gmail.com>

Dear sir

 

we have socket weld for plug joint after hydrotest with P5b to P5B material ,can we useTo weld the joint Inconel ER 625 to avoid PWHT?

 

With Regards

Hasin.Shaikh

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