jeff216410 wrote:The stainless pipe rusting issues seem to be a poor grade or mislabeled stainless. Any seam welds of pipe coule be an issue as well (weldors don't often use the right welding rod on stainless pipe). I've got 304 pipe and there no single mark of rust staining anywhere inside or out. If I wipe the inside of the pipe with a rag it is shiny new. I think it's time to find a new stainless vendor.
Jeff, time, moisture, and coal differences change luck with stainless dramatically. Stainless, be it 304 or 316 won't last long with coal and moisture doesn't help, if your pipe isn't pinholed yet, wait a few years, perhaps a few more if you're in a dry location.
There are four things that lead to rapid deterioration of stainless. Iron pitting corrosion from iron particles in coal flyash leading to a compromised passivation layer, low oxygen levels in coal exhaust leading to an inability to replenish the passivation layer, chlorine (HCL and other chemicals) attack, and acid attack from the sulfur in the coal. These four things combine to form a very aggressive corrosion against stainless steel. Yes, moisture does need to be present to allow stainless to deteriorate, however, the moisture in the air is often enough to initiate the corrosion and once it starts it's only a matter of time.