N2 purge during PWHT 2

[gmorin]

I have a carbon steel pipe component (B31.3) that I need to PWHT because of a sour service requirement. All of our past projects have not had the PWHT requirement.

This component has a critical interior surface finish, so I need to limit corrosion as much as I can, such that any rust that had accumulated during welding can be removed relatively easily without blasting or chemicals that could affect surface finish.

Anyway, we ran a test PWHT (local resistance - not in an oven) open to air and we got a tough rust that the only approved cleaning product couldn't remove.

The solution we've been thinking of trying is to put a nitrogen purge on the pipe (we'd maintain a flow to keep pressure or vacuum from building up) Anyway, our (conservative) metallurgist recommended that we use argon instead of nitrogen, citing concerns about unintentional nitriding of the material. It's regular carbon steel - not much Cr or Al to speak of and the PWHT temperature is only 1050. I'm thinking that N2 will remain inert at that temperature.

I'd prefer not to do argon, as I need to do 150 of these components and it could get pricy

Does anyone have experience with N2 purges during PWHT?

Thanks

Greg

 

[metengr]

Yes, the use of a nitrogen purge provides no adverse effects during PWHT.