Study on internal pressure strength prediction for casing and tubing

For wells with high pressure, high temperature, and high H2S, once the tubing or casing burst into failure, the gas may cross between tubing and casing, even the sulfur-containing gas may blow out to the ground, so the harm is self-evident. Therefore, an accurate prediction of the internal pressure strength is essential in tubing and casing design process. For high H2S gas wells, the API Bulletin 5C3 formular cannot satisfy with the design criteria, and the burst model for capped-end conditions has been provided in ISO10400, but some predictions by ISO burst model exceeds the actual burst strength. According to the significant influence of yield-to-tensile strength ratio Y/T on failure behavior of tubing or casing, a new internal pressure strength model is presented for casing and tubing with high calculation accuracy. The comparison work show that the results calculated by the new model essentially coincide with test burst data, which provides a powerful reference for optimizing strength design for casing and tubing.