PWHT of reinforcement

[nlgcode]

We are going to construct an above ground storage tank per API 650.
Regarding the PWHT requirements:
1) Do we must PWHT whole the thickened insert plate together with the welded reinforcement pad and the welded nozzle? OR Can we only PWHT for the welded re-pad together with the welded nozzle?

2) Can perform PWHT by local electrical resistant with insulation OR must put the prefabricated assembly in a furnace?

3) How can maintain the radius of plates (shell and re-pad were formed to desired radius) during PWHT?
Because I think during performing PWHT these plates will be returned back to the straight shape or maybe some part of radius to be changed. Is that right?

Thanks all in advance!

 

[JStephen]

For a shell nozzle, it would be the section of shell/insert plate plus the reinforcement plus the neck.
The stress relief is to be done prior to welding the plate into the tank. I don't think the electrical-resistance-with-insulation is prohibited as such, but it can't be done after the plate is installed in the tank. There have been one or more official interpretations to this effect.
I think you can brace pieces with a piece of angle running from end to end to help hold the curvature. They won't go from rolled to completely flat, but could distort some.

 

[nlgcode]

Thanks JStephen,
Yes, we will do it before welding to the tank.

 

[IFRs]

API 650 is silent on the method used to heat up the assembly being PWHT, other than you can't do it in the field after the assembly is welded into the tank. Maintaining curvature of the assembly is always a concern but welding cross braces sounds like the way to go.

 

[nlgcode]

Thanks IFRs,
I learned much from you, JStephen and others.

Have a nice day!