In-Service Caustic Service CS Piping PWHT

[sahsanb]

We have a 2" - 80 Sch CS piping being used on 47% caustic service. Recently we observed failure on a spool on this line and hence had to replace it. Our plant procedure requires all welded joints of CS piping on Caustic service to be subjected to PWHT. Due to plant emergancy we could not perform the PWHT on replaced spool. We are planning to replace the spool with new one in upcoming plant outage. PWHT is generally recommended in CS piping under 20 mm thickness to guard against Caustic Stress Corrosion Cracking, however based on your experience please share if I can carry out PWHT of the spool that has been in service for approxmiately 3 months now or I need to replace the spool and then carry out PWHT.

Regards

 

[metengr]

Unless you can perform NDT of the ID surface to ensure no cracks in service without PWHT for the replacement spool, I would replace the spool, and perform PWHT.

 

[sahsanb]

Thanks.