Estimating the Lifetime of Electropolished Stainless Steel (EPSS) Tubing in Corrosive Gas Services

Abstract

Tubing lifetime in HCI service, defined as the time to begin particle shedding due to corrosion, can be estimated by the method described in this paper. This could provide an additional selection criterion for materials used in corrosive applications. In this method, particle shedding by a length of electropolished stainless steel (EPSS) tubing is measured before and after its controlled exposure to 100 percent HCl. The shedding is measured in dry nitrogen at several different flow rates. The experimental variables are moisture concentration, exposure duration, and shedding flow rates. A dosage-response model is used to correlate the particle data with a combined dosage parameter of moisture concentration and exposure duration. The time for the tube to begin to act as a particle source under HCl exposure is then estimated as follows. For a given allowable particle level C, at a specified flow rate, the dosage parameter X can be determined from C = exp (a+bX) where a and b are constants obtainable from the experimental correlation. Once the dosage parameter X is obtained, the lifetime of the EPSS tubing in HCl service can be estimated from {H2O in ppm} x {Lifetime in days} = X For EPSS tubing exposed to 100 percent HCl with I ppm moisture concentration, this method estimates 2.3 yr for this tubing to shed particles greater than 10 particles/scf at a 3.531 scfm (100 slm) flow rate. This estimate is in line with field experience.