ASME Sect. 1 sequence of RT and PWHT completion 3

[InspectorJim]

Customer has a client that insists the radiography of ASME Sect. 1 header be performed after PWHT. I found nothing in Sect. 1 that states the order these processes must be performed. Logically, we want all welding to be completed prior to performing the PWHT, so RT's are shot and any repairs made prior to PWHT. After PWHT, MT and hydro testing are completed, but not a second RT. Is there a mandatory order (sequence) for completing these processes?

 

[hakkik]

There is nothing about the squence in ASME BPVC. It is very common that asking RT after PWHT. if problem found on RT, repairing PWHT weld probably requires another PWHT. So i prefer double (before and after PWHT) RT
If it is written in eng. specs or any other document between you and your customer than you have to RT after PWHT. If it is not than it is up to you to decide.

 

[DG72]

I agree. Unless the customer specifies otherwise, our standarad practice is to perform RT prior to PWHT. Of course, many require us to RT after, in which case, we perform RT before and after.

 

[racookpe1978]

PWHT is a stress relieving action involving low rates of heat rise and low rates of cooling down while the weld itself is not under pressure or excess strain from the process fluid and pressures.

So cracking because of PWHT itself is not expected and should never occur.

However, cracks present before PWHT will never go away or become less significant under the motion and stress of heat treatment. Cracks already present will never "fix themselves" or magically re-weld themves during PWHT.

Cracks found by X-Ray or Mag particle exam (or UT or PT) before PWHT will always require reheat, grinding out the indication, re-welding, and a repeat of the PWHT.

So given that, why would you ever go to PWHT without completing NDE?

 

[InspectorJim]

Thanks for the great info.

 

[REGRUMBLE]

My question is that ifracookpe1978 is correct and cracking because of PWHT never occurs why do so many engineers insist that testing is done after PWHT? The cost to do the testing twice is tremendous. We do vessels that are 12' dia and 1 1/2" plate and to RT both before and after PWHT is a huge expense.

 

[stanweld]

Delayed cracking after RT but prior to PWHT may occur. RT after PWHT will provide greater assurance of its discovery. We have experienced two such incidents in the past 15 years.

 

[DVWE]

The only place in Section VIII that I have found a mandatory sequence for RT is Appendix 7 (Steel Castings). Many customers that I deal with are quite familiar with App 7 and have adopted the RT after PWHT for fabricated parts.

 

[DVWE]

Scratch the last post, I was getting that confused with PT/MT.