That depends on concentration and temperature. At some conditions there is only a little difference. At the other end, under some conditions, alloy 20 will be 20-100 times as durable as 316.
Scrubbers are strange, and almost every know alloy from carbon steel to the exotics has been used for one section of another at various times.
What is there now? How did it fail? How long did it last? How much will you be changing operating conditions (fuel source)?
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
Concentration: the stagnant puddle in the anular space is 25-30% acid (probably sulfuric). This estimate is based on a tritration of a sample of the stagnant puddle.
Temperatures: ambient or slightly warmer at the bottom of the stack.
What is there now: half of a carbon steel pipe. I say "half" because it's no longer a pipe but an inverted gutter at this point. The pipe runs horizontal at the ground level and the bottom half of the pipe's circumference is gone. Dissolved to nothingness.
How long did it last: unknown. May be original (1975).
How much will you be changing operating conditions (fuel source): Will continue to run unit on daily cyclic operation, continue to burn #6 bunker oil, all the bad things that keep operating condition prediction completely unknowable.
SMF1964,
The 25-30% acid could be handled in CPVC plastic piping, or in fiberglass piping. If temperatures are limited to less than 190 deg F then there is not concern for hot stack gases destroying the plastic pipe. More pipe supports (shorter spacing) will be needed for the flexible CPVC compared to steel pipe. If CPVC plastic or fiberglass pipe are not acceptable, then a polypropylene lined steel piping system will tolerate the wide range of acid concentrations from the stack drain while withstanding almost the same temperature range. Cost of polypropylene lined steel pipe could be slightly more than cost of stainless steel pipe for the smaller sizes.
