Thomas Eagar (prof @ mit) has a good youtube channel with all kinds of shit, including welding engineering. Whole courses. Here's one on welding engineering:
https://www.youtube.com/watch?v=TCmd_zoXkK8&list=PLCgPBt05jaJ5GMZ2imX7ABClhg6qMMZK1
Other ideas:
Do you have access to any ASME boiler &...
There's a few things that come to mind, but the biggest one is welder skill.
First off, I hate FCAW for root passes, even if you have a backing plate. That alone raises some eyebrows.
Have you gone and audited the welding? Like actually looked at them doing their work? You mentioned problems...
You're going to have a hell of a time welding anything to that cast iron.
It would require pre-heat, peening, or special filler metal. Even then, you're liable to encounter cracking issues.
I'd avoid this unless it's 100% necessary. It's possible, but not simple.
