An Investigation of Coiled Tubing Mechanical Properties for Effective Well Control

Within each string design, the strength of nominal grade coiled tubing (CT) strings varies within an expected range. String lengths routinely reach 30,000 feet (9+ kilometers), and as expected in all steel structures, the variation in strength makes intuitive sense. But what strength values should be used for shearing calculations to ensure wells can be effectively controlled should pressure control equipment (PCE) be required to control the well? The yield strength values for coiled tubing strings are presented by manufacturers as material test reports (MTRs), frequently called weld location records (WLRs), which show the location of strip joining (bias) welds required to manufacture coiled tubing. Specification minimums for the grades are typically given in the name of the grade itself as a minimum yield strength value in kilopond per square inch (ksi).