EXPERIMENTAL STUDY OF CHLORIDE-INDUCED STRESS CORROSION CRACKING (CISCC) FOR AUSTENITIC SUS 304L UNDER THERMAL INSULATION

Abstract

Chloride-Induced Stress Corrosion Cracking (CISCC) has been frequently reported in the petrochemical industries where it usually causes failure to the austenitic stainless steel structures encased with thermal insulation in a chloride-containing environment. This study aims to analyze and evaluate the risk of chloride concentration and different types of insulation materials on CISCC of Austenitic SUS 304L. The experimental study was carried out for 14 days using U-bend specimens through the Drip Test apparatus, as per ASTM G30 and ASTM C692. U-Bend specimens were installed onto the test rig and shielded with different insulation materials. Sodium chloride (NaCl) salt solutions were periodically dripped onto the specimens, to simulate the wet and dry cycle. Insulation materials used were rockwool, calcium silicate and perlite, whereas the concentrations of NaCl solutions were set at 0.1, 1.0 and 3.5 wt.%. The specimens were inspected usingdye penetration tests (DPT), stereo microscope and optical microscope throughout the study to determine the CISCC susceptibility. Results showed that cracking was observed on the specimen with rockwool insulation at 3.5 wt% NaCl and 90°C. Rockwool has a high water absorption capacity at which saltwater will evaporate when in contact with a hot metal surface, resulting in the build-up of salt deposits of high concentration over time. SCC was not observed on other specimens with different conditions, but salt deposits, general corrosion and pitting corrosion were found. From the study, the thermal insulation of rockwool was found to have the highest tendency to cause SCC, followed by calcium silicate and perlite.Keywords: SUS304L, chloride-induced stress corrosion cracking, insulation materials, U-Bend specimen, drip test