Procedure for WeldOverlay

[AravindSujay]

Hi All,

In my current project for Amine vessel, a carbon shell(SA 516 70N) has to be Weld overlayed with one layer of SS309L and a second layer of SS317L with 5/32" Thk. It has to be welded with SS316L cleats. PWHT is necessary.

My idea is to weld a Poison pad to the shell, then weldoverlay and Heat treat it, after which a small portion of the PP is to be grinded and atlast to be welded with SS316L cleats at the grinded portion.

Am I right with my point or do you guys have a better idea?

Need all your expertise on this.

Thanks in advance,
Aravind Sujay

 

[doct9960]

Aravind,

Where is the SS316 cleat welded? Is it welded on the outside of the vessel or the inside of the vessel? Is the inside of the vessel weld overlaid or cladded?

 

[AravindSujay]

The SS316 cleat is to be welded inside the vessel. The Vessel is also weld overlayed inside.

 

[gr2vessels]

Aravind,
I assume the overlay is internal, hence the cleats are internal also. I also assume that in the Amine service, you would prefer to minimise the number of internal welds. You should be able to weld the cleats directly to the carbon steel shell(including the NDT's), without problem, then re-weld the exposed area with 317L per the approved WPS/PQR and test again;- or depending on the required strength of the weld, you could weld the cleats on the overlay without the need for a poison plate (obviously, NDT's). Remember, if you weld the SS cleats directly on the Carbon Steel substrate with suitable consumables and then re-weld the overlay in top of the mixed weldment, you got no corrosion issues.
Cheers,
gr2vessels

 

[AravindSujay]

gr2vessels,
Ya, what you have given is right. But there is PWHT. At what point should it be done? -can it be done after welding of SS cleats & overlay or overlay then heat treat and finally weld SS cleats? In general, what is the procedure?
Hope HT affects the chemical properties of SS

 

[doct9960]

I agree with gr2vessels that cleats can either be welded on the base metal or on the weld overlay.

Lightly loaded cleats or supports (e.g. tray supports) may be welded directly to the weld overlay. For heavily loaded cleats or supports (e.g. packed bed supports), you should determine if they should be welded directly to the base metal. For determining what is "lightly loaded", you can use the definition of "lightly loaded" in ASME VIII-2 AD-912(a) footnote 4 which says, "Weld stress due to mechanical loads on attached member not over 25% of allowable stress for fillet welds."

I can't say much about PWHT (i am not a welding or material engineer). All I know is that all welding should be completed before final PWHT. But I believe there's an exception on welding of attachments to the weld overlay. You could probably weld the attachments after PWHT as long as you can prove that this does not produce HAZ in the base metal. Maybe the welding/materials expert of this forum can shed light to this.

 

[gr2vessels]

Aravind,

The heat treatment requirements are described in the Clause 6.2 of ASME SA 264 or ASTM A 264 and accordingly, you can select the weld of the cleats to the base metal or to the SS overlay. The heat treatment is required anyway after the final weld overlay, either way.
Cheers,
gr2vessels

 

[AravindSujay]

Hi all,

Finally it was decided to do
1.Weld overlay head & shell separately(without cutting holes for nozzles )
2.Cut holes & fabricate the nozzles and all seams
3.Weld overlay the seams
4.fabricate the SS cleats inside of the vessel
5.PWHT

Thanks for all your valuable comments.

Regards,
Aravind Sujay