The catastrophic corrosion failures of rockbolts and cable bolts in underground coal mines have been reported from several mines in the past few decades. Many of the failed bolts have been in service for a short period. The preliminary studies have found that the failures occur by hydrogen-induced stress corrosion cracking (HISCC) and microbial-induced corrosion (MIC). In these types of failures, the local environment where the bolt was installed is the key to initiating and accelerating the corrosion process. This study investigates the capabilities of polymer coating and galvanising technologies for preventing bolt corrosion failures. We use our previously developed HISCC and MIC reproduction method to reproduce the corrosive environment in the lab. The laboratory study shows the benefit of polymer barrier coating compared to galvanising in an extreme environment, and it also has good resistance to MIC.
Cable bolts and rockbolts are used as primary and secondary anchoring systems in many underground mines, particularly in the Australian underground coal mines. In the past two decades, there has been a rise in reports concerning the early failure of cable bolts and rockbolts in underground coal mines due to stress corrosion cracking (SCC). Previous studies have established that the SCC in both rockbolts and cable bolts occur due to hydrogen diffusion into the material, known as hydrogen-induced stress corrosion cracking, HISCC (Craig et al., 2016; Wu et al., 2018).
SCC is a type of corrosion failure that only occurs when a material is under stress (tensile and/or shear) in a corrosive environment. SCC failure normally does not occur when the stress on the material is below its critical value. However, in most cases, this critical value is much lower than the material's yield point. It can vary by the changes in the environment (Toribio & Ovejero, 2005), which makes SCC failure difficult to predict, i.e. it can not be identified until the final fracture occurs. There are several ways that SCC can initiate on the metal surface; two most common initiation methods for SCC are 1) hydrogen diffusion (HISCC) (Wu, et al., 2018) and 2) formation of pitting corrosion (McCafferty, 2010).
