I was involved in some of the comments, and I'll still stand by that in power stations, with 3,000psi, 1000F, I have only ever seen very limiteg MIG (or variant), as they are too easy for people to make great looking stuff without it having the structural integrity required.
Can it be done, yes, and most certainly.
And every weld, by code, must have a qualified weld procedure that must be followed (applicable base materials and thicknesses, weld location (flat, vertical), welding direction, amp range, pre-heat, consumable type/brand/size, bead pattern, interpass temperature, PWHT where necessary, and cooling conditions)...
all of those must be controlled, so that fusion, mixing, alloying/de-alloying, grain size/refinement are predictable and controlled.
Then the weld undergoes visual inspection, MPI, and X-Ray where possible.
It's the latter two processes that can be "tricked" by wire feed, when the procedure isn't followed, to the letter, by the guy who puts it in his back pocket.
Like I said, wire feed can do the job, but it's generally not used where life/safety is concerned in my industry...unless in a shop, where all of the variables are automatically controlled, like a sub-arc, or repetetive things like gas bottles (and steam mains) are involved.
I've been involved in on site repairs of aged 1/2-1/2-1/4 CrMoV, and subsequently joining that to new F22 forgings, and in spite of MIG's ability to fill the gaps, a tight critical path, and irate management, temper bead with a stick was the only way forward.
Similarly, boiler tubes and TIG, and rebuilding turbine blades for re-revetting with a TIG are the norms.
