Testing high temperature lubricity of waterbased and synthetic hydraulic fluids

Abstract

Two water-glycol- and two synthetic (polyalphaolefin) hydraulic fluids have been tested to determine the influence of 150°C temperature on the wear- and lubrication properties. The aim was to assure reliable operation of dynamic piston seals in “surface controlled subsurface safety valves” in petroleum production wells. To simulate the operating conditions of the piston seals, a new test equipment was developed, using a pin-on-disc arrangement in a closed pressure- and temperature chamber. The lubrication properties were studied at 150°C and room temperature, using new fluids and fluids exposed to four months of degradation at 150°C. For the interacting parts, two material combinations relevant for the piston seals were used: two nickel alloys, and a nickel alloy against PTFE. For the synthetic fluids, the metal wear increased significantly when increasing the temperature from room temperature to 150°C. For the waterbased fluids, the temperature had no significant influence on metal wear. One waterbased fluid showed poorer metal wear performance than the three other fluids, and one synthetic fluid showed higher PTFE wear rate at 150°C than the other fluids. Four months of degradation at 150°C seemed to have little or no effect on the lubrication performance. The repeatability of the test system was not yet satisfactorily, and some modifications are desirable.