Interpretation on API Standards of Casing Capability Resisting to Internal Pressure

The API standards of casing hydrostatic testing pressure, casing internal yield pressure and resisting inner pressure performance were analyzed, and it was considered that the purpose of hydrostatic pressure test specified by API was mainly to inspect whether or not the casing pipe body leaked, but not to inspect the connection seal performance. Through the analysis on the internal pressure-to-failure test results, it was found that the internal yield pressure of the casings was much higher than that specified by API TR 5C3-2008 as long as the various parameters of the casings were in accordance with API specification. Thus the casings should be designed in accordance with casing internal yield pressure specified by API TR 5C3-2008, instead of the hydrostatic pressure. Through the analysis on the calculation formula of casing internal yield pressure and the investigation on the casing coupling accidents, it was deduced that casing couplings of deep well and ultra deep well could be prevented from failure by the machining on the casing coupling outside surface. It is suggested that the thread compounds, hydrostatic test pressure and hold time, and casing internal yield pressure etc. should be required strictly by users.