TIME INTERVAL BETWEEN DHT AND PWHT

[ianmontes]

Dear Sirs,

We welded a 15E Pipe material (16 inch - 87mm thickness).
Our procedure will be preheated with 205 deg centigrade then welding and will be
( hydrogen ) bakeout 310 deg Centigrade and perform PAUT, If accepted in PAUT, immediately followed
by PWHT and will perform MT.
Process is B31.1

The joint has been accepted by PAUT, my query is, how long should be acceptable if there is a delay in performing PWHT?
Right now it is almost 1 week that the welded joint is not yet PWHT. What will be your DECISION here?

Need your advise.

 

[metengr]

The decision is based on environment. If there is excessive humidity or chance of water exposure to the region where PWHT will be applied, PWHT should be performed as soon as possible. If the environment is dry or low humidity, it can be long as necessary for scheduling or staging purposes.

Either case, if there is a delay in PWHT, I would perform a surface NDT (wet fluorescent MT) before PWHT.