Expanding the coiled-tubing collapse ratings envelope

Recommended practices for determining the collapse strength of coiled tubing (CT) predict conservative ratings and do not include the effects of plastic fatigue cycling and elevated temperatures. The full-length paper summarizes the major findings of an extensive experimental and theoretical research program on CT collapse. The research studied effects of temperature and changes in tensile properties induced by low-cycle bending fatigue. A better understanding of the collapse failure mechanism enabled a new formula to be derived for plastic collapse of CT with an outside-diameter/wall-thickness ratio (D/t) less than 14.