Hello fireminime3, you mention that this is a critical weld, are you working for an employer or is this a job that you have taken on yourself? If you are working for an employer he/she needs to provide you with the necessary procedure, this will take the monkey off of your back should anything go south on this repair. You mentioned A36 forged plate, is this possibly a forged lip or some other sort of part that is being welded onto a bucket or some other sort of earth moving attachment or equipment? In many cases the manufacturer of this forging will have instructions or other available procedures that will detail the welding for this item to avoid any problems and match their engineering criteria for the part. To partly answer your question, I do believe that some form of a preheat regimen might be called for, additionally, I also believe that welding and back gouging or back grinding to ensure complete joint continuity is likely also called for. Run-on tabs and run-off tabs might also be a good idea in this case along with removal and proper grinding once the tabs are removed upon completion of the welding. When welding a double beveled joint such as the one that you are describing alternating from one side to the other during the progression of the welding will likely aid in balancing the internal stresses from weld bead shrinkage and additionally help with any possible cracking issues that could arise. The real bottom line here is to avoid taking advice from an online forum and seek verification of the welding procedure for this "critical" weld from an engineer of record to keep yourself out of the liability bite. I am sorry for being so vague, but your initial question sort of leads to additional information or, as I have tried to stress here, going through the proper channels to keep yourself from being liable in case there are issues with this welding challenge. Best regards, Allan

I agree with Allan...get more info before stiking an arc. Preheat is partially determined by the thickness...and with 2", I'd almost bet that there is some degree of preheating involved to avoid quenching your first few passes until some heat gets built up from welding.

A 36 "forged plate"?

Depending on the Code, preheat would be required. AWS D1.1 with FCAW would require a 150°F preheat. But like the others said, make the customer tell you.

You work for an artist?  Awesome; I was a sculpture major in college...  Anyway, you probably don't answer to an engineer, ISO, have weld maps, a tolerance chart, etc...  Fit it like you would for 1".  That's pretty heavy for non-industry. For 2" A-36, I would "sweat it", i.e: heat it with an oxy or mapp torch until you see moisture form on its surface and subsequently disappear. About an 1/8" gap is good for a full bevel.  Brace it, if you can, but it'll still move some.  Like you're chasing it back into itself over and over so you end up closest to where you started.  Maybe, 27V/375+/- wfs with A/C-25 gas @ 40ish psig.  Play with the parameters on some scrap in the position you'll ultimately be in, I guess.  Its no different from 1", just more heat to consider, and A-36 is "mild steel", as in compliant.  Get your mill scale off, though.  Are you at liberty to say who is the artist and where do you show?