Chloride Stress Corrosion Cracking
Austenitic stainless steels may be susceptible to chloride stress corrosion cracking (CSCC). The standard 304/304L and 316/316L grades are most susceptible. Increasing nickel content above 18 to 20% or the use of duplex, or ferritic stainless steels improves resistance to CSCC. High residual or applied stresses, temperatures above 65-71C (150-160F) and chlorides increase the likelihood of CSCC. Crevices and wet/dry locations such as liquid vapor interfaces and wet insulation are particularly likely to initiate CSCC in susceptible alloys. Initiation may occur in several weeks, in 1-2 years or after 7-10 years in service.
Methods of minimizing chloride stress corrosion cracking:
- Improve design.
Examples: Fill or seal crevices, paint under insulation, keep tensile stresses below the yield strength, shot peen, provide galvanic or cathodic protection.
- Select a higher nickel content austenitic alloy.
Examples: Alloy 330, 904L.
- Select a ferritic stainless steel if the lower corrosion resistance is acceptable.
Examples: 439, 26Cr 1Mo, 18Cr 2Mo
- Select a duplex stainless steel.
Examples: 329, 2205.
- Evaluate stress relief.
Note! Stress relief treatments above 425C (800F) may sensitize stainless steel to intergranular