NDE of Dish Head Seam Welds

[sree60]

Hello Members

The specification for manufacture of coded pressure vessels
stipulates that if the dish head (SA 516 Gr 70 2:1 semi ellipsoidal)is made of more than one plate, the seam joint shall be 100% radiographed prior to forming.In a previous project the requirement of 100% NDE requirement was after forming.Is there any reference in ASME sec VIII as to when NDE is to be carried out?

On analysing both options I can conclude,

1) If RT is specified to be done before forming we are ensuring that the weld is accepted before forming and we are minimising repairs after cold working on the dish heads. If some visible defects develop during forming they only need to be repaired and there is less potential for hot works on formed surface.

Demerits:
1)We may not capture the defects which have developed internally due to forming

2 If RT is specified after forming ,the defects if any which have developed internally due to forming are also captured during RT along with the original seam welds

Demerits: there is potential for more hot works during repairs on cold formed dish head surface

Would like to have some inputs

Thanks in advance

Sree

 

[metengr]

The RT should be done after forming. You can always perform addition RT before forming, this is up to you.

Codes and Standards do not provide detailed process steps both for forming or NDT sequence of events. Only that NDT, if specified, is normally after fabrication process steps are completed.

 

[sree60]

Thanks metengr
I think we can consider this forming similar to heat treatment operation. Most codes and specifications stipulate NDE after heat treatment whereas fabricators carry out internal NDE before heat treatment to be on the safer side.

sree