This presentation addresses the results of the examination of stress corrosion cracking (SCC) of both smooth surface and ribbed wires used in cable bolts. The cable bolts had been utilised as roof supports in a number of Australian coal mines. Both forms of wire were subject to SCC although the ribbed wires tended to exhibit a greater number of cracks primarily associated with the deformed ribs, similarly encountered on the solid steel roof bolts traditionally employed in coal mines. Without the stress raising influence of the deformed ribs, the smooth wires exhibited colonies of cracks likely associated with a localised environment, such as deformation resulting from strata movement or an increase in concentration of a corrosive species. Fracture of the wires was heavily influenced by the hard drawn microstructure giving rise to a stepped appearance, unlike roof bolts which exhibit transverse fracture with minimal microstructural influence. Ribs are typically used to increase the pull-out resistance of fully grouted roof bolts, however the distance between ribs tends to have only a minor effect on the pull-out resistance when fully encapsulated in concrete. This suggests that an increase in resistance to SCC can be found in a balance between the beneficial. Corrosion protection, in the form of wire coating, would also contribute to an increase in resistance to SCC. Galvanising has been shown to produce an increase in resistance, however the contribution to SCC by MIC can reduce its effectiveness.
Presenter
Judy Turnbull (Bureau Veritas)
Judy Turnbull is a consultant Metallurgist with Bureau Veritas, undertaking component failure investigations. She has held this role since 2013. Judy has more than 30 years of experience in the engineering field, having worked in heavy engineering, hard rock mining, concrete, oil & gas and pipeline inspection as well as information technology.