Development and Evaluation of PyFlexU2™ Coating for Expandable Rock Bolt Against Highly-Corrosive Ground Conditions

Expandable rock bolt, as an efficient ground control product, is widely used in underground mines. However, its capacity and service life are significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the US, highly corrosive ground conditions exist and the bolts corrode within a few months after installation. To provide mining industry a corrosion resistant expandable bolt, Keystone Mining Services, LLC (KMS) analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new Python M3^TM rock bolt that is protected with an innovative PyFlexU2^TM coating. The Python M3^TM bolt features improved steel chemistry for reliable performance and modified profile for better inflation, surface preparation, and coating application. With a flexible, adhesive, and highly corrosion-resistant undercoat, and a very hard sacrificial topcoat, the PyFlexU2^TM coating system provides the Python M3^TM a superior protection against chemical corrosion and physical scratch damage. The product has been tested in the most challenging conditions including extreme laboratory corrosion tests and field borehole scratch insertion tests. With demonstrated performance, the product has been embraced by hard rock mines in the US. This paper identifies the root causes of the bolt corrosion, briefs analysis process, and details laboratory and underground test results on the Python M3^TM rock bolt coated with PyFlexU2^TM.