Effect of Halogens and Inhibitors on the External Stress Corrosion Cracking of Type 304 Austenitic Stainless Steel

Abstract

The methodology of the drip procedure of the Standard Test Method for Evaluating the Influence of Thermal Insulation on External Stress Corrosion Cracking Tendency of Austenitic Stainless Steel (ASTM C 692-95a) was used to research the effect of halogens and inhibitors on the external stress corrosion cracking (ESCC) of Type 304 stainless steel as applies to the insulation industry. Simulated insulation extraction solutions were made with pure chemical reagents for the halogens and inhibitors. The results indicated that sodium silicate compounds that were higher in sodium were more effective for preventing chloride-induced ESCC in type 304 austenitic stainless steel. Potassium silicate was not as effective as sodium silicate. Fluoride, bromide, and iodide may cause ESCC but they were much less active than chloride and could be effectively inhibited by sodium silicate compound. The addition of fluoride ions to the chloride / sodium silicate systems, at the threshold of ESCC, appeared to have no synergistic effect. The ratio of sodium + silicate (mg/kg) to chloride (mg/kg) at the lower end of the RG 1.36 Acceptability Curve was not adequate to prevent ESCC using the methods of this research.