Atmospheric Stress Corrosion Cracking of Stainless Steel Rock Climbing Anchors, Part 1

Abstract

Austenitic stainless steels Cr-Ni (Types 304, 304L, 321, and similar) and Cr-Ni-Mo (Types 316, 316L, 316 Ti, and similar) are susceptible to atmospherically-induced stress corrosion cracking (AISCC) at ambient temperatures if hygroscopic salts such as MgCl2or CaCl2are present on the surface and the air relative humidity (RH) is in a critical range. This phenomenon has been responsible for incidents of rock climbing anchors breaking under minimal load in seaside areas, putting climbers lives at stake. A systematic failure analysis of anchors collected from various seaside locations throughout the world, namely from Portugal, Azores, Hong Kong, Taiwan, South Africa, and Australia, has been performed. Transgranular AISCC was proven the reason for failures in the majority of investigated anchors made of Type 304L stainless steel. Intergranular cracking due to sensitization by improper welding or heat treatment was also identified as a critical safety issue for both Types 304 and 316 stainless steel types. Comparison of literature data and climatic data from the failure locations suggests that limited washing of deposits in confined zones together with elevated temperature and low RH generated locally by direct sunshine are the key factors of AISCC initiation and ultimately of anchor failure.