Installing power plant boiler tubes - GIF

[tachetailleur]

Yes, TIG isn't great for the reason you say but it's the most controllable for a good full penetration joint often with difficult access. SCH 160 isn't unusual on high pressure boilers. The material is probably a tube specification (as opposed to pipe), most heat transfer surface is tube (in boilers think pipe for fluid transport and tube for heat transfer, but this is not always true and the difference is subtle). Materials typically range from carbon steels up to the more expensive low alloys (9% Cr, just short of stainless) for high temperature components (superheaters and reheaters). Steels start to lose their mechanical properties at higher temperatures (creep) so you have to increase their resistance (eg add chrome) or make them thicker. All the materials in boiler pressure parts will (should!) have full traceability and have been manufactured to a particular standard, so yes, as you say, they are relatively expensive. Boilers are interesting bits of kit, though. Especially when you get a leak on one of those tubes right in the middle of a bundle...