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The article presents the latest developments in the study on the effects of casing imperfections and nonuniform loading conditions to the collapse resistance of well casing used in the oil and gas industry. It cites the new equations that were developed by the China-based Southwest Petroleum Institute to estimate the collapse resistance pressure for casing under variable loading conditions. The equations were partly based on the theory of elasticity and plasticity.

The article reports on the pressure equations developed by the Southwest Petroleum Institute of China that can be used to calculate collapse-resistance values for special casing that undergoes external deformation, and for non-American Petroleum Institute (API) standard pipes. Data illustrates the reliability and universality of the equations. An equation for estimating the collapse resistance for an ideal round tube has been obtained and modified using the theory of elasticity and plasticity.