Evaluation of Stress Corrosion Cracking Susceptibility for Austenitic Alloys in Salt Production Environments

Abstract

Constant strain SCC tests have been performed on five kinds of austenitic alloys, SUS316L, YUS270, NAS254N, NAS354N, and C-22, in simulated salt production environments. From the results of the SCC tests, susceptible conditions to SCC for each alloy. were clarified SUS316L and YUS270 were susceptible to SCC, but NAS254N, NAS354N, and C-22 were not susceptible in the salt production environments. Cold rolling increased SCC susceptibility for SUS316L and YUS270. And there was no potent influence on SCC resistance by a change in atmosphere, judging from the SCC test results under conditions of bubbling O₂ and N₂ gas only in bittern.
The material selection guideline for salt production plants has been determined based on both the test results and reported SCC experiences in actual plants. The material selection guideline for the salt production environmentsis as follows;
· It is possible to apply SUS316L to the condensation process.
· It is reasonable to apply super stainless steel of over 40 in PRE to low density crystallization process.
· If it is necessary to avoid all local corrosion in high density crystallization processes and later, super stainless steel of over 50 in PRE or Ni-base alloys should be applied.
(Pitting Resistance Equivalent: PRE = Cr + 3.3Mo + 20N)