Stress corrosion cracking of rock bolts

This paper outlines the mechanism of Stress Corrosion Cracking (SCC) and how it can cause premature failure of rock bolts. SCC occurs due to the progressive development and growth of cracks in the surface of a metal, and it is caused by the combined effects of stress and a corrosive environment affecting susceptible metals and alloys. It can occur in most metals including stainless steel. It is not a new phenomenon, but its effect on rock bolts has only been recognised recently. Rock bolt failures caused by SCC appear to be brittle failures which occur at less than the ultimate tensile strength of the bolt. In the mining industry , SCC failures of rock bolts can occur a few months, or after many years of exposure to stress and a corrosive environment. If SCC of rock bolts is suspected, then thl~ rock bolts should be examined by a metallurgist, and steps should be taken to reduce the problem. Considerable research in the past has shown that SCC is a complex phenomenon and no one mechanism can explain all cases of SCC failures. I1 is therefore unrealistic to expect research to find a complete solution to SCC failures of rock bolts. but simple measures can be taken immediately to reduce or minimise the SCC problem. These measures include: . to ensure that rock bolts are fully encapsulated with resin; and, . to use rock bolts that are less susceptible to SCC.