SS Lining on a PWHT Vessel

[TanEng]

I have a CS vessel in operation that was POST WELD HEAT TREATED because of the sour service. Can we install SS Internal linnig on the vessel shell and bottom head to avoid any errosion that is only becuase of catalyst loading/unloading?

Normally welding after PWHT is not allowed but i believe since this linning will isolate CS shell and bottom head from sour gas therefore It may be ok to intall SS linning on post weld treated vessel. PWHT after linnig installation would not be possible.

 

[SJones]

From your statement, and assuming ASME VIII Div 1, UW-2 appears to have been invoked which means that UCS-56 (e) applies. Maybe you could confirm?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[PAN]

TanEng,

In my understanding, PWHT is required after lining...

 

[TanEng]

Thank You SJones and PAN.

Yes the vessel was designed per ASME VIII Div.1 but PWHT was not a code requirement(Thk. 5/8") rather it was a NACE Requirement (Sour Service).

One thing that I missed to mention is the vessel see full Vacuum frequently and I beleive lining would not be a good idea...what you guys think??

 

[gr2vessels]

TanEng,
It seems to me that there is a bit of confusion, perhaps it's only me. However, I do differentiate the lining from cladding, in the way that the linig is not necessarily fully welded / attached to the shell, on the other hand the cladding is fused to the shell by weld deposit or other bonding method (explosive, etc.. ) in case of new cladded plate.
The lining as defined above will not whitstand the Full Vacuum you mentioned, which in turn will not affect the cladding as defined above. Also, the "loose" linig is not acceptable protection of the vessel for sour service in accordance with NACR MR 0175, but it may provide some mechanical protection agains erosion. Poor choice however, for erosion protection.
Also, the welding after PWHT would normally require another PWHT in accordance with NACE MR 0175, but if you intend to install an internal "sleeve" only with a few tackwelds, that's a different story, perhaps another post.
OK, before I complicate it even further, can you clarify what you intend to install? Cladd, lining, extensive welding, tackwelds, what?
Cheers,
gr2vessels

 

[vesselfab]

Now....full vacuum....will the vessel really ever see full vacuum or is it rated like that for steam out only. you never really say whether you intend on putting in weld over lay lining or laying in strip lining. Either way...that welding on the existing vessel will most likely require pwht since it was for service (nace) and not strictly per code. Stainless steel does not help at all for isolation of carbon steel for sour service.

 

[SJones]

PWHT is not a 'NACE requirement' for H2S containing service: it is an option, it is not mandatory. My original question has still not been clarified: does UW-2 apply to this vessel? I ask because if the vessel has been designated as being in lethal service then PWHT is unavoidable. In addition, the gentleman is seeking a solution for erosion not, apparently, for corrosion - a thermal spray coating perhaps?



Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[2468jjcr]

See table UCS-56, Note: 2(c)(5)

 

[TanEng]

I really appreciate every ones response. I hope the below lines would answer most of your questions.

1- Vessel Material is SA516-70N
2- The vessel is in Sour Service not in Lethal Service (UW.2 doesn’t apply)
3- We were thinking about SS strip lining, not weld overlay.
4- The vessel does see a full vacuum.

The vessel was PWHT to meet NACE requirements for sour service.
For some reasons corrosion rate is much faster than we expected that’s why we though to install SS strip lining but it seems NACE prohibit lining for sour service. The vessel very is huge so weld overlay would be very expensive.

 

[gr2vessels]

NACE does not prohibit the lining of the vessel, on contrary it recommends the CRA lining of the wetted areas exposed to H2S. However, where did the erosion vanish? Remember that the Austenitic CRA lining is not realy suitable for erosion in combination with strong corrosive environment, the metal loss rate will increase considerably due to constant removal of the protective chromiun oxide layer.
There are other problems for to consider;- please read the non-mandatory Appendix F ASME VIII-1. The vacuum condition is a factor to consider when calculating / selecting the thickness and width of the strip, in order to get the minimum required thickness. Then you have to consider the lining of the nozzles internal surface, flange facing and the joint of nozzle lining with the shell lining.
A positive aspect is that once the lining installed, the carbon steel vessel will stop corroding, thus service life may be extended indefinitely. However, the monitoring of the lining thickness will become an issue, to not mention any breach / crack of the weld will result in rapid and irreparable damage to the linig, ie you'll have to start all over again.
Perhaps you should evaluate the long term benefit of the weld overlay, agains the insecurity of the strip lining and the risks involved with the failure of this lining.
Cheers,
gr2vessels

 

[stanweld]

Is the repair done per API 510 or NBIC or other? It is assumed that the original vessel was post weld heat treated for service and the Owner (and I assume that you represent the Owner) must determine if PWHT is not to be performed and the use of alternatives to PWHT be used. You do not provide adequate info regarding operating conditions (temp, pressure, stream makeup)to make a recommendation. If you choose to strip line, be sure to perform hardness testing of the SA-516 HAZ to assure acceptable hardness. Do not forget the catastrophic failure at the UNOCAL refinery near Chicago.

 

[TomEun]

[Given Data]

- Materials : CS post weld heat treated in wet sour service.
- SS lining/weld overlay is required on the shell and bottom head because the erosion on CS surface is expected during catalyst loading/unloading.
- Thickness of CS : 5/8”
- Full vacuum condition

[Review Summary]

1. Erosion resistance against catalyst
Normally the severe erosion of SS during catalyst loading and unloading is not expected.

2. SS layer bonding type in full vacuum condition
The only weld overlay is recommended. Sleeve/Lining is not permitted.

3. PWHT requirement after weld overlay
The PWHT of base metal welds in wet sour service is not a mandatory requirement in NACE MR0103, however, the PWHT (regardless of thickness of CS/LAS) is normally required in company specifications.
Even though the PWHT (as a requirement per base metal thickness) for weld overlaid CS is not a mandatory requirement in ASME Section VIII, Table UCS-56, Note: 2(c)(5) and the PWHT in wet sour service may be exempt from the requirement of companies when we apply the entire clad or weld overlay, the PWHT requirement may greatly depend on the hardness values of base metal when you apply the partial weld overlay. Provided the hardness values on welds are above 200 BHN, the pressure vessel should be PWHT’d.

Thomas Eun