Wet Flue Gas Desuplurization ( WFGD ) - Shell repair

[JIPMKWA]

I did not know where to post this as I do not know what original code of construction these are built to. I am assuming ASME Sec. 8 Div. 1.

We want to repair erosion on the floor ( 2205 Duplex S.S) using 1/4" plate of the same material - welding with NiCrMo-3 as per the customer. My question is , if we do a full sheet 4' x 8' , does it need reinforcing plug welds. I have searched through Sec. 8 and cannot find anything pertaining to patches.


Thank you in advance and I am sorry if this thread is in the wrong category.

 

[metengr]

I would probably use equally spaced plug welds to reinforce the floor plate repair in addition to fillet welds.

 

[weldstan]

These items are generally not designed, constructed per ASME VIII, Div.1.
Welding procedures are generally required to be qualified per ASME IX. Whereas the repairs are most likely considered weld build up to restore thickness the procedure should be qualified as a groove weld with tensile tests and bends.

There are problems with this type of repair. While the NiCrMo-3 will resist the corrosion, the HAZ of the 2205 may well not due to the galvanic mismatch and un-removed heat tint on the 2205 duplex. There has also been some concern that corrosion is MIC related and the weld repair zone may be ideal for microbial colonization. What one ends up with is a continuous weld repair cycle. And trust me, this indeed is what is happening to a number of wet scrubbers fabricated from 2205 that I am highly familiar with. Blend grinding the deposited weld metal coupled with glass bead blasting or pickling (pickle paste) to remove the heat tint is advised.

 

[weldstan]

Sorry, I misread your post. Fillet weld and plug weld per metengr. My last paragraph still applies.

 

[metengr]

Information I have seen over the years from EPRI, MIC or underdeposit corrosion has been an issue with WFGD vessels. However, I believe rough grinding that was used during fabrication, plays a more significant role. Local grinding can introduce remnant cold work and subsequent increased risk of corrosion. Be careful with any surface conditioning methods, like grinding, to avoid harmful cold work and increased risk of corrosion.

 

[JIPMKWA]

Thank you for the replies.

We were planning on seal welding it to the floor with approx. a 3/16" seal weld. But with the flex in the floor and the plate itself, I didn't know if there was somewhere that said you had to put a plug weld every X amount of feet. I didn't even know what the original code of construction let alone repair.

 

[metengr]

Plug weld on 24" centers across the sheet.

 

[weldstan]

Are you lining the entire bottom or just the bottom plates that are corroded/eroded? If the entire bottom surface, you may wish to rethink liner metallurgy. If the current 2205 bottom plates are rapidly corroding, the same is likely for the new 2205 liner plate.

 

[JIPMKWA]

We are just overlaying some patches onto the floor over top of the bad areas