corrosion of mild steel tanks 1

[stonerabroad]

we've got CO and CO2 concentrations accounting for about 65% of our gas stream and the remainder H2, in a 100% RH environment. operating temperatures are 30 to 40 degrees C and the pressures around 130PSIG.

we've got mild steel vessels and everything that i find implies we may have a carbonic acid forming that could assist in corrosion of the mild steel vessels.

stainless steel piping and cadmium plated mild steel are used throughout the rest of the machine.

we haven't been able to look at the machines in operation to determine if these vessels are corroding (since the unit in question is in japan) but accumulations of iron oxide on valve surfaces imply there may be an issue. i'm suggesting replacement of the mild steel vessels with 316SS instead of a plating or powder coating option.

Question#1 is there a problem with mild steel corroding in the environment listed above?
Question#2 would 316SS be an economical replacement? considering coating mild steel vessels for corrosion resistance could be a daunting task...nickel plate, powdercoat, cadmium or zinc plating...

 

[mcguire]

Your observation of rust seems to answer question #1 and this seems logical. The answer to question #2 is that any stainless would stand up to this environment. You needn't go all the way to 316. any austenitic or stabilized ferritic would do. 201, 301, 304, 439; even 409 would suffice at about half the cost of 316.

 

I ran into a problem like this once. Is your gas stream filtered of ALL contaminants(ie: do you know 100% if purity is being maintained) before contacting the mild steel portion?