Can Post Heating 300 deg C will help

[661660]

Hello Expert,
I am having a situation , where i need to do repair welding (including root, in few segment) of 40 mm thick & 400 dia (no inside access) SA 333 Grade 6 seamless pipe.

I am in opinion that repair shall be conducted in following steps,
1. Remove complete defects by grinding,
2. Make V groove
3. Put the insert in required segment and leave small peep hole for root visual inspection.
4. Complete the welding by GTAW +SMAW process.
5. Immediately after completing the welding do post heating for 1 hour at 300 deg C.
6. Do relevant NDE as required in Spec.
7. Do PWHT.

My Question are following
1. IS new WPS/PQR required for this ?
2. Is Post heating at 300 Deg C for one hour will help ?
3. Please suggest if any points need to add.
Any precautions need to take , please suggest ?

The line having 126 mpa pressure and approx 326 degree C temperature as design.

 

[metengr]

Why are you performing a post weld bake? Why not use low hydrogen electrodes H4 with the SMAW process? I see no reason for the 300 deg C bake for this material.

Everything else looks fine.

 

[weldstan]

While the dehydrogenation heat treatment will not be detrimental and may prove helpful, as per metengr, it is not warranted and is more costly. A new PQR with the dehy treatment is not required.