When there is relative motion between two contacting bodies, frictional forces that resist motion always come into play. Frictional resistance to rotation of the drill string is called torque, and is especially enhanced when drilling a deviated hole. Many different materials, such as graphite, fine mica, and diesel or crude oil, have been used as mud additives to improve lubricity.
Since evaluation of the various materials cannot realistically be done on the drilling rig, a lubricity test was designed to simulate the speed of rotation of the drill pipe and the pressure with which the pipe bears against the wall of the hole. The newly-redesigned EP and Lubricity tester from OFITE is a high-quality instrument used to measure the lubricating quality of drilling fluids, provide data to evaluate the type and quantity of lubricating additives that may be required, and predict wear rates of mechanical parts in known fluid systems.
The test consists of measuring the torque of a steel block while being pressed against a rotating steel ring. The torque limit is 600 inch-pounds. Test rings and blocks for both tests are available from OFITE.
EP (Extreme Pressure) Test:
This test produces an indication of the film strength of the fluid being tested by applying a measured force to a torque-sensitive bearing cup with the torque arm. The EP test is typically run at a high shear rate, 1,000 RPM, with fluid pressures ranging from 5,000 to 100,000 PSI between the steel surfaces.
Lubricity (Surface to Surface Drag) Test:
The more common lubricity test measures fluid resistance of various lubricating additives. For the standard lubricity coefficient test, 150 in-pounds of force (the equivalent of 5,000 to 10,000 PSI pressure on the intermediate fluid) is applied between two hardened steel surfaces, a block, and a ring rotating at 60 RPM.
Digital Control – The digital control board provides more accurate data than older, analog methods.
User-Friendly Interface – The simple, intuitive interface makes testing quick and easy. Functions include pre-set speeds (60, 200, 600, and 1000 RPM), manual speed control, and torque zeroing.
Maximum Speed – 1,000 RPM
Maximum Torque – 600 inch-pounds