Welding after PWHT for API 650 tanks

Date 02-22-2012 06:30

API 650 tank shell plates welded with nozzles & re pads require Stress relieving. After SR, fixtures removed and the shell plates were minor touch up welding carried out on fixture removal areas. Plate material is ASTM A573 Gr 70, medium is gas oil/fuel oil; no service requirement for PWHT or Impact requirement for shell plates. Is it acceptable welding after PWHT?

By dbigkahunna (****)

Date 02-22-2012 13:36

If the repairs are to be done on the shell plates which were not stress relieved, then minor welding would be acceptable. With visual and MT/PT on the repaired area.
If it is on a stress relieved component or the entire shell plate was stress relieved: API 650 5.7.4
The material being Group IV refer 5.7.4.3
No allowance for welding after stress relieving.

This would be allowed on stress reieved components for Group I, II, III and IIIA 5.7.4.2.a with 5.7.4
Looks to me the contractor should have not put themselves in the position with this material where they had to do touch up welding on fixture removal areas. There are ways to remove these fixtures where it does NOT require touch up welding. It looks like your contractor did not elect to do this and they will have to do additional stress relieving.
Depending on how deep the gouges are, you may want to see if you could grind and feather with a flapper disk instead of welding. If they have already been welded, looks like the contracto will have to be doing some field stress relieving.

By Solluz

Date 02-24-2012 14:51

Suggest talking with the Purchaser's Inspector on this issue. Performing a local stress relief on a tank will likely cause more damage than good (and trying to stress the entire tank or a complete band around the tank usually isn't practical). API requires stress relief of these sub-assemblies before insertion. I suspect the code intent is to relieve the bulk of the stresses of the complex subcomponent - not require stress relief of minor pickups after fabrication is complete. Suggest discussing this with the Inspector.

By JWJUNG Date 11-05-2018 01:25

Hello

To minimize the mis-understanding, I would like to ask your opinion about below cases, please leave it as 'No.- (o) or (x)'.

As per para 5.7.4.3 of API 650
1. All opening connection located in shell plate have to be PWHT, when there is no reinforce pad and shell plate is thinner than 13mm (o) or (x)
2. All opening connection located in shell plate have to be PWHT, when there is no reinforce pad and shel plate is 15mm (o) or (x)
3. All opening connection located in shell plate have to be PWHT, when there is a reinforce pad and shel plate is thinner than 13mm (o) or (x)
4. All opening connection located in shell plate have to be PWHT, when there is a reinforce pad and shel plate is 15mm (o) or (x)

Thank you