Atmospheric Stress Corrosion Cracking of Stainless Steel Rock Climbing Anchors, Part 2: Laboratory Experiments

Abstract

Atmospherically-induced stress corrosion cracking (AISCC) in the presence of chloride deposits has been responsible for considerable incidents of rock climbing anchors breaking under minimal loads in seaside locations, putting climbers lives at stake. However, to date, failures due to AISCC have only been documented in anchors made of Type 304/304L and similar, and no rigorously documented failures have been shown to occur to Type 316/316L anchors. In order to support preparation of a new standard classifying anchors according to their corrosion resistance, the influence of environmental parameters such as periodic washing of chloride deposits, electrolyte pH, and type of rock on AISCC initiation and crack growth rate was studied in laboratory conditions by exposing U-bent specimens of stainless steel Types 321, 304, and 316L with MgCl2 deposits in air at 40°C to 50°C and at 35% to 45% relative humidity. The type of rock and electrolyte pH were not critical parameters for AISCC. Alkaline conditions only slightly prolonged stable crack initiation period and decreased the crack growth rate. Periodic washing in sufficiently short intervals was capable of significantly retarding or even arresting AISCC. The crack growth rate in Type 316L stainless steel was 2- to 3-fold slower than in the molybdenum-free Types 304 and 321. These last two effects are quite likely responsible for the lack of failures observed in Type 316/316L. In view of the lifetime expectancy of rock climbing anchors and other safety-relevant members, the crack growth rate was unacceptably high in all studied materials and their installation should be avoided in vulnerable seaside regions.