Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Drill Rod Casing Is special steel tubing screwed or welded together and lowered into a bore hole to prevent collapse of the hole or to prevent loss of circulation liquid coming up from the drill rod into surrounding ground. Drill rods are matched with rod casings. It is easy to visualise that the cooling and cleaning drilling fluid travels down the hollow drill rod and then comes back up from the bottom of the hole in the gap between the drill rod and casing. Thus the grease that is applied to the outer surface of the rod must be able to provide a sufficient level of lubrication, and a balance of adhesion and cohesion to resist being washed off by the fast upward flowing drilling fluid.
Drill Rod Grease Properties As with most lubricants, drill rod grease serves several purposes. Beyond being lubricants they are secondarily designed to coat and protect the rod from corrosion while in storage. Lack of lubrication would result in high twisting forces (torque), scuffing, pitting, wear, and reduced longevity.
Drill rod greases are often formulated from products that are known to have high resistance to water washout. The components of the grease include base fluids, thickener, and performance enhancing additives. The base oil for manufacturing grease is selected based on the intended end use. For drill rod greases requiring a bodied structure, high viscosity base oils are used. Traditionally, base oils have been
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petroleum based. Being of the highest concentration ingredient in the product formula, the base oil requires particular attention. There is an increasing emphasis on environment friendlier base oils derived from vegetable and synthetic oils. High viscosity fluids, such as synthetic polybutenes and PAOs are also employed.
Additives or performance enhancing chemicals are added to the lubricants to enhance desired performance properties. Common lubricant properties include friction modifying chemicals (Anti-Wear and Extreme Pressure additives), corrosion prevention, oxidation resistance, and tackiness enhancers. In addition to being a lubricating substance, the drill rod grease must resist water washout and protect the rod from rust and corrosion. Anti rust additives are designed to provide resistance to oxidation or interaction of the metal with oxygen. Anti-corrosion additives are designed to prevent interaction of chemically corrosive materials with the metal. While oxygen comes from air or process fluids, corrosive materials are often formed due to chemical reactions between various components of the grease and the metal surfaces.
Many lubricant applications are pumped to the moving parts. But, for most drill rod grease applications they are applied manually or by some mechanical means. So, the method of application is taken into consideration in formulation of the grease. Figure 3 shows grease applied to drill rod.
Figure 3. Grease manually applied to drill rod as the rod is lowered into the drilled hole. LUBE MAGAZINE NO.133 JUNE 2016 27
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