PWHT Welding on DA Tank

[HightyHo]

I have a DA Tank onsite that is PWHT (As Built) that is in need of some repair. I was always under the impression with PWHT you are required to stress relieve after repairs are completed. The tank was never required to be PWHT but we are stuck with it now. Am I required to conduct PWHT after repairs or can it be bypassed since it was not ever really required?

 

[chandljm]

I am assuming by DA Tank, this is a dearator storage tank. If you are performing weld repairs on the DA Tank, plan on performing a PWHT (local) on the repair area. Weldments in DA Tanks are subject to cracking. There was quite a bit of study/inspection on the cracking mechanism a few (?) years ago. But performing a PWHT will reduce the probability of occurence. I once inspected a DA Storage Tank that was previously repaired using weld metal build-up around a nozzle penetration on the inside surface (corroded area) without performing a PWHT. WFMP inspection of this repair area after ~5 years of service revealed extensive cracking. The area was repaired, locally PWHT, and placed back into service. Future WFMP inspections revealed no cracking in the repair region.

 

[metengr]

It is recommended to perform PWHT on DA storage tanks because of residual tensile stresses from local weld repairs or from original fabrication. It is well documented that the on-set of stress corrosion cracking or even corrosion fatigue in regions adjacent to fabrication or repair welds is from exposure to tensile stresses and environment. For either damage mechanism, if you can effectively reduce the tensile stress (decrese residual tensile stress) the damage mechanism will stop.

 

[HightyHo]

Thank you both very much for the information! We have people here onsite that believe PWHT is not needed for repairs. I always thought with PWHT at construction you would be required to conduct PWHT after repairs also.....This just confirmed my thoughts.

Thanks again!

 

[insult2injury]

If you check any current design standard for deaerators, PWHT will be a requirement whether new or repair.

I2I

 

[MJCronin]

Ho....

Ask questions to the masters of deaeration....

Kansas City Deaerator

http://www.deaertor.com:

Ho...Please complete this tread by letting us all know what you find out and what you finally decide

Regards...

-MJC