Influence of shaft load-corrosion coupling on the service life of carbon steel casing pipe

Considering the corrosion media such as CO₂, H₂S and the complex load (e.g., pulling, pressing, etc.)suffered by carbon steel casing pipe in high temperature & pressure super-deep wells, as well as the influence of thermal stress on casing corrosion rate, an analytical model was built based on stress-corrosion medium synergy principle and mechanochemical effect, and an analytical formula was presented for calculating the influence of stress on the attenuated lifetime of tubular column so as to study the service life of carbon steel oil well pipe. Moreover, this paper studied the influence of internal pressure, corrosion rate actually measured during coupon test and wall thickness on the serve life of carbon steel casing pipe. The result from analytical model was accord well with that from experimental research on the influence of stress on corrosion rate (reported in literatures). Under the influence of shaft load and corrosion, increasing wall thickness cannot significantly prolong the service life of casing pipe compared with reducing internal pressure inside casing pipe. Furthermore, initial corrosion rate exhibits great impact on the service life of casing pipe; the larger the stress on pipe column is, the quicker the actual lifetime of pipe column will be attenuated.