USING FCAW PROCESS FOR SS OVERLAY IN A CLAD VESSEL 1

[OLUBAJI]

Good day Gents,


I am building two clad vessels one LP NAG INLET SEPARATOR applicable code ASME Div. VIII(I.D-3200 TTL-6700 thickness-90mm; plate mat'l A537 Cl 1 ) & one COMPRESSION SUCTION SCRUBBER applicable code PD5500 (I.D-1500 TTL-3500 THK-47mm; plate mat'l A516 Gr. 70) with 3mm SS weld overlay which will undergo PWHT, the plates for the shell of the vessels are produced with 3mm SS clad. Our fabrication process involves back grinding the SS overlay away from the edge of the plate so that we can weld with normal carbon steel consumables after which comes rolling and welding the long seam (LS) & the circ. seam (CS).We usually make use of SMAW process in welding the back grinded overlay using E309LMo-17 (2 runs) then E316LMo-17. However, this process is quite slow given the size of the LP NAG which has an ID of 3200mm. Is it acceptable to use FCAW process with appropriate consumable to carry out the welding considering the vessel will be PWHT. If the FCAW proceess can be used what should i watch out for when qualifying the welding procedure. For the ASME code are the tests stated on QW-453 IN ASME IX sufficient when qualifying the procedure, for the PD5500 please advice applicable test to be carried out when qualifying the procedure. Many thanks in anticipation to your responses.





Best regards,
Olubaji

 

[metengr]

I don't see a problem with using the FCAW process to restore the weld overlay for ASME Code application - I won't address the PED. Yes, you would need to qualify the FCAW as a weld overlay using QW-255.1 and QW-453.

 

[stanweld]

Cladding restoration with the FCAW process is often done. ASME Boiler Code does not prohibit its use.

 

[Guest102023]

I found a small but very large problem buried in your question: 3mm (a.k.a. 1/8") SS weld cladding.

Designers specify it without pondering whether fabricators can actually achieve it. Fabricators can NOT achieve 'stainless'* with any conventional, commercially viable process within that window, although most will unblinkingly proceed to weld. Even the AI doesn't ask questions, but I can show you many back-clad 316L steel shell courses with a nice straight red strip on the inside after having been stored out in the weather (if I still had the photos).

I won't go into the details that any competent WE should understand, but suffice to say it is nigh on impossible to deposit a layer of FCAW less than 3mm thick.

* Exactly what 'stainless' means is not usually defined in the spec or on the fab drawing.

 

[Deccocwb]

Hi all, I agree with brimstoner, you can weld with FCAW to restore of clad, but you need to keep in mind that restoration must aquire the same corrosion resistance of the clad plate. That means your FCAW deposit must result the same composition of clad plate in 3mm depth. To do this you need to deposit plus that 3mm. Also it´s better to qualify the procedure also using the ASTM 262 Practice A or E when using PWHT.

 

[moseley]

One other thing that must be kept in mind when PWHT of any Austenitic stainless is performed..... ferrite content as to limit the effects for Sigma Phase formation. It's best to also perform a Ferrite inspection of the surface prior to PWHT to ensure that the ferrite content is between 3FN - 6FN. I have seen many times, PWHT of stainless which destroys the materials corrosion resistance. As for the use of the FCAW process; I agree with brimstoner and Deccocwb above.. you must keep in mind that depositing a 3mm layer is next to impossible with this method. If you are meaning that the 3mm depth is the depth at which complete chemistry (316L) is required then by depositing the layer of 309LMo is going to have to be machined/ ground down prior to depositing the 316L layer in order to help achieve chemistry at that depth. Hope this helps shed some light on your situation/ problem.

 

[MikeMet]

I agree with others that getting a proper chemistry at 3mm with E316L filler may be a challenge. To overcome this we have at times used an over alloyed filler metal, such as ERNiCrMo-4 or -10, just for restoring the cladding at the seam welds. Typically in the as welded condition, even in thin layers with moderate dilution you will have corrosion resistance better than if you used E316. Of course you have to assure yourself that the higher alloy is still suitable for the process conditions.

 

[stanweld]

Beware of too much over alloying. I have seen a number of cases where rapid, knife edge (fusion line) corrosion occurred between E/ERNiCrMo-4 and E/ERNiCrMo-10 weld deposits between 316 base metals and clading.