Welding on PV after Stamped

[Xianglu]

I have an SA-516-70 vessel 42” dia x 7/8” thick shell c/w 1” thick lifting lug which covers the seam of head and shell. This vessel has been PWHT’ed due to amine service, and has been hydroed, inspected and stamped. Subsequent to these an attachment weld was made to the lifting lug cross the vessel seam weld and close to the side weld of the lifting lug.
My concern is that the residue stress due to welding may cause amine craking in the future. However schedule has been critical to the project and many people insist that there is no issue since the weld is on lifting lug.
Please advise your recommendations on my questions: 1. Is there any code compliance issue? 2. Is this just an application issue? 3. What correction are required, hydro, localized PWHT, local NED?
Your comments are greatly appreciated.
Thanks,
Henry

 

[code1]

Can you explain what you mean by 'attachment weld' and by the 'side weld'?

Was a re-pad provided in between the lifting lug and the vessel?

It seems to be an akward position for the lifting lug, to have it straddling the weld seam of the head and shell. Perhaps it could have been beter positioned?

 

[stanweld]

If the weld is to the head/shell (pressure part), it should be treated as a repair in accordance with NBIC or API 570 or other jurisdictional requirement since the vessel has been hydro-tested and stamped. NBIC has provision for local bulls-eye heat treatment.

Generally speaking, vessels that are PWHT'd for process reasons have requirements prohibiting welding to the pressure parts after PWHT.

 

[vesselguy]

Xianglu,

This sentense is not clear to me.

"to these an attachment weld was made to the lifting lug cross the vessel seam weld and close to the side weld of the lifting lug."

However, it appears from what you described, a lifting lug was "directly" welded to the shell after completion of fabrication as an after thought. The word "directly" welded is usually used to imply there is no repad between the shell and the lifting lug. If this is indeed the situation, then you must PWHT the welds/shell area, and rehydrotest according to the Code. People who told you the weld only affect the lug don't know what they're talking about.

 

[Xianglu]

I am sorry for any confusions. Let me make some clearifications.
1. This is a 42" vertical vessel, with WT 7/8". the vessel is for the service which requires PWHT. the vassel has two lifting lugs with WT of 1", welded at the top of the cylinder, ie the area of the seam of cylinder to the top head.
2. The vessel has been finished after PWHT, hydro, inspection and "U" stamped.
3. After the vessel was installed in place, the electrical guy welded a vertical 2" angle structure attachement to the vessel to support the cable tray. the angle is not welded directly to the vessel shell or head, insted, it is welded to the lifting lug.
4. Because the angle welds is quite close to the lifting lug welds, - 1", my concern is if this could raise rasidual stress in the pressure containing part and cause craking in the future.
5. Another concern is that there is Code conpliance issue.

Thanks again.

 

[vesselguy]

Ok, now the picture is clear. You are welding a cable tray support clip to the lifting lugs rather than to the vessel pressure membrane. As long as you're not welding to the pressure membrane, there is no code issue. The code is very clear on this.

As for heat input is close to the lifting lug weld, do you think the heat input from a fillet weld is sufficient to do any microstructural changes to the lug welds? You can do a conductive heat transfer calculation to support it to satisfy yourself. The answer is no. Just my 2 cents.

 

[doct9960]

Xianglu,

Was there grinding (to remove weld spatters, if any) done on the vessel itself?

 

[weldtek]

I agree with vesselguy, however, the biggest concern I would have is that someone is welding on a vessel at all. Maybe this was planned and the proper people were consulted ahead of time, but, if not, you need to change the procedure. My opinion.

 

[unclesyd]

Your case isn't governed by code requirements, it is as you state a process consideration. It will be up to you to determine if the weld might have imposed stresses on the vessel proper that would be detrimental in service. We make a number of different amines as part of our process as well as MEA. With the lighter molecular weight amines we PWHT/Stress Relive all components. We have had a number incidental welds being made on previously PWHT components and I recall no problems.

The sage advice give above about having control over any welding is an absolute necessity to prevent some very expensive problems.

 

[doct9960]

Xianglu,

It could be a Code or process issue if:
1. cosmetic grinding was done on the vessel base material which might have affected the required vessel material thickness [UG-99(a)(1)]
2. there were intentional or accidental arc strikes done on the vessel.

If the "electrical guy" have done any of the above, repairs should be done as mentioned by stanweld. I suggest you also read API RP 945 (Avoiding Environmental Cracking in Amine Units). This practice provide guidelines for the fabrication, inspection & repair of carbon steel material in amine service.