Well, the welders will require separate qualification when changing from solid wire to flux-cored, the flux "may" have high halogen content which can cause stress corrosion cracking in austenitic stainless steels, and ,as you noted, the slag on the inside may be a concern for plugging instrumentation or affect purity of the process fluid. A test sample could be welded and the slag analyzed for halogen content to determine if it is acceptable to the client. Similar concerns with Solar Flux on the halogen content. Making a sound GTAW root with flux-core is different enough that some welder training will be required to get used to it.
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