THE EFFECT OF PRESSURIZED GASES ON THE VISCOSITY OF POLYALKYLENE GLYCOLS

Experiments have been conducted into the effect of pressurised hydroca rbons on the viscosity of a polyalkylene glycol. This lubricant is int ended to be used in a sub-sea compressor/pump unit and the risk of dil uting the lubricant by the surrounding natural gas, thus reducing the lubricant's viscosity, was to be investigated. Dilution can cause insu fficient lubrication of the compressor's moving parts. A pressurised H oppler type viscometer was used for the tests which were conducted at 50 degrees C with a methane based hydrocarbon mixture and with pure ni trogen. The viscosity of the lubricant was reduced to 24% after 24 h e xposure at 100 bar with the hydrocarbon mixture. A gas analysis was pe rformed which indicates that the heavier hydrocarbons used are relativ ely soluble in the lubricant even at relatively low pressures. Nitroge n was found to have a very limited effect on the viscosity even if som e was dissolved in the oil. A long duration test of 11 days was also m ade with nitrogen. This test did not show any significant reduction of the viscosity. (C) 1997 Elsevier Science S.A.