Low-Temperature Stress Corrosion Cracking of Stainless Steels in the Atmosphere in the Presence of Chloride Deposits

Several cases of ceiling collapses and other failed elements have been reported in indoor swimming pool halls in the last two decades. The collapses were caused by stress corrosion cracking (SCC) of stainless steel fastening elements covered with chloride deposits at temperatures as low as room temperature. The goal of this study was to assess the application limits of different austenitic and austenitic-ferritic (duplex) stainless steels subject to tensile stress and contaminated with chloride deposits in atmospheric non-washing conditions as a function of temperature (20°C to 50°C), relative humidity (15% to 70% RH), and deposit composition. Austenitic stainless steels Type 304 (UNS S30400) and Type 316L (UNS S31603) were susceptible to SCC in the presence of magnesium and calcium chlorides at temperatures of 30°C and higher and at low relative humidity. The tendency to SCC increased with increasing temperature and decreasing relative humidity. The corrosivity of chloride deposits under given exposure conditions decreased in the following order: calcium chloride (CaCl₂) > magnesium chloride (MgCl₂) > sodium chloride (NaCl). It was governed by the equilibrium chloride concentration in the surface electrolyte formed as a result of interaction of a given salt with water vapor in the air. Threshold values of the minimum chloride concentration and relative humidity intervals leading to SCC were established for Type 304 and Type 316L. Duplex stainless steels S32101 (UNS S32101), 2304 (UNS S32304), 2205 (UNS S32205), and 2507 (UNS S32750) were resistant to SCC but corroded selectively with the maximum depth of 200 µm. Austenitic stainless steels Type 904L (UNS N08904) and Type S31254 (UNS S31254) showed no tendency to SCC.