The Impact of Test Gases on American Petroleum Institute High-Pressure Testing

Abstract This study investigated the effects of different test gases, including CO2, CH4, and N2, on American Petroleum Institute (API) high-pressure testing, focusing on the fixture test and PR2 test as defined by API Specification 6A, Annex F. The high solubility and diffusivity of CO2 in elastomers under extreme pressures and elevated temperatures lead to significant challenges for the API Specification 6A fixture test when CO2 is the primary pressurization medium. Notably, the ratio of fixture volume to seal volume in fixture tests was found to play a critical role in achieving pressure stabilization when CO2 is used as the pressurization gas. Similarly, the high solubility of CH4 in hydrocarbons greatly influences the outcomes of API tests when hydrocarbon test media are used as the liquid phase. The study also revealed that the pressure dependence of the glass transition temperature (Tg) of elastomers in N2 may not follow a straightforward trend as reported in the literature. Unexpectedly, Tg can decrease with increasing pressure or increase at a significantly slower rate than previously documented. This behavior has important implications for API tests using N2, including the PR2 test outlined in API Specification 6A. The findings contribute valuable insights for designing advanced elastomer seals, refining API test standards, and addressing the demands of both traditional oil and gas applications and emerging energy technologies.