Article ID: 20-00009
Metal-to-metal seals in premium threaded joints (PJ) for Oil Country Tubular Goods need to have high-pressure gas tightness. The gas tightness of such seals is affected by sliding of contact surfaces during integration, the kind of applied greases, temperature and pressure. In this study, a new fundamental testing method is proposed that enables quantitative evaluation of the impact of these factors on the gas tightness. In the proposal method, specific greases as well as helical sliding are employed in order to simulate the sliding conditions in practical PJ. In addition, the seal portions are baked at 180°C to simulate the high temperature condition of oil or gas wells. The gas pressure was applied until leakage was occurred. The proposed method provides more realistic contact conditions of PJ than those of conventional method in which seal surfaces are subject to rotary sliding before gas tightness tests. It is found that the gas tightness of the grease specified by American Petroleum Institute standards is about 2.8 times higher than that of the environmentally friendly grease.
