Development and evaluation of corrosion resistant coating for expandable rock bolt against highly corrosive ground conditions

Expandable rock bolts are widely used in hard rock mines as an efficient ground control product. However, capacity and service life can be significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the U.S., highly corrosive ground conditions exist, and it has been reported that inflatable rock bolts have corroded within a few months after installation. To provide mining industry a cost-effective inflatable bolt and combat the corrosion issues, Jennmar Corporation, Inc., and its subsidiary Keystone Mining Services, LLC (KMS), analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new inflatable rock bolt, Python M3™, that is protected with an innovative PyFlexU2™ coating. The new generation Python M3™ features improved steel chemistry for reliable performance, modified profile for better inflation, and surface preparation and coating application. The PyFlexU2™ is impervious to liquid and air, durable, and UV resistant. With a flexible, adhesive, and highly corrosion-resistant undercoating, and a very hard sacrificial surface coating, the PyFlexU2™ coating system provides the Python M3™ superior protection against chemical corrosion and physical scratch damage. The under-coating has exceptional flexibility and adhesion to prevent coating micro-cracks or fractures after bolt inflation and possesses excellent corrosion resistance to acids (pH < 3), alkalis (pH > 11), fuels, and salt solvents. The corrosion and scratch resistant PyFlexU2™ coating offers very effective bolt protection for extra longevity in highly corrosive environments. The Python M3™ coated with PyFlexU2™ has been tested in the most challenging conditions, including laboratory corrosion tests in extreme acidic and basic solvents, rock slurry, and borehole scratch insertion tests. With demonstrated corrosion and scratch resistance, the product has been greatly welcomed by hard rock mines in the West and is currently installed in large scale. This paper identifies the root causes of the bolt corrosion, discusses the analysis process, and details laboratory and underground tests carried out on the Python M3™ coated with PyFlexU2™. The Python M3™ and PyFlexU2™ are subjects covered by pending U.S. Patent Applications assigned to FCI Holdings Delaware, LLC.