Deve I agree in regards to clean... but what criteria is used to determine what "clean" is?
I spent the last decade of my career in the oil and gas industry engineering repairs to pressure vessels. For these vessels the only way to get them "clean" is to steam clean them. The petrochemicals can't be wiped or ground or sandblasted away... steam cleaning is the only proven means to clean the metal in preparation for repair welding.
In the real world the bottom line is different methods must be employed to produce a clean surface, based on what contaminents are present. If the surface isn't clinically clean, a welding process must be used that has suitable flux that provides an acceptable end result. And that process, for welding on a surface with some contaminents, is not MIG welding using solid wire with a shielding gas.
