Kraig,
Most All of the high pressure steam piping in power plants contains a percentage of Chromium, which is used because of its natural resistance to cracking and fracture in the Higher temperature ranges,,, Pre Heat is required to weld chrome piping and Also a pre determined temperature during the entire welding Process,,, then a Post Heat or "Bake" is Required after weld is completed to relieve any stress in the material caused from the welding,,, the argon is just an inert gas to displace oxygen inside the pipe during the first or "root" pass,,, unlike regular carbon steel,,, pipe which contains Chromium will "sugar" or crystallize (similar to stainless) when molten. The argon "purge" prevents this and allows the tig root pass to be contaminant free on the inside of the pipe during welding,,,
This NEW Induction Pre and Post Heat is the Blue Cables which is a New Process similar to Electro Magnatism that excites the molecules in the metal causing the temperature to increase, Almost but not "Really" like a microwave,,,,
Before Induction Heatiing Ceramic tiles were used with heating elements and they literally HEATED the Pipe and the Entire surrounding area!!!!!
The Temperatures are Very Closely Monitored and Every Single Step in the welding process is Inspected by an Independent Quality Control Contractor!!!!
That Kraig is a Very Crude Brief Summary!!!