The development of a new test method for the evaluation of galling in OCTG connections
Blackstone, William Robert
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Galling is a form of lubricant-related adhesive wear which occurs in threaded connections used in oil wells. The research reported herein involved the design of a test apparatus providing testing conditions and specimens closely simulating field conditions and the development of a new test method employing fundamental principles of statistical design of experiments. The tester comprised a hydraulic drive motor for providing torque and a modified universal tension/compression testing machine for providing axial load. The specimen comprised a pair of cylinders with conical contacting surfaces 1.05 in^ in area. Two sets of specimens were machined from 2-7/8 in. OD tubing of American Petroleum Institute steel grade L80 and a third set was made from grade N80 tubing. All sets were lubricated with the industry standard thread compound. The well known "up-and-down" test method was employed to gather data on the three specimen sets. The results indicated that the difference in galling sensitivity (the interfercncc level at which galling initiates) between L80 and N80, if one existed, was relatively small. On the other hand, analysis of galling severity (a semiquantitative measure of the level of severity reached) showed N80 to be better than L80. The severity ratings were commensurate with field observations for these materials, while the sensitivity ratings were not. From these results, it was concluded that combined sensitivity and severity tests would be required in future work.