Tube-to-tube joints in coiled tubing can be achieved by either fusion bonding or mechanical connections. A critical performance requirement of such joints is their ability to sustain plastic bending cycles that ideally, equal in number to that of the coiled tubing itself. Orbital girth welds in coiled tubing butt joints can typically achieve a low cycle bend fatigue (LCF) life in the range of 50% to 60% of the coiled tubing. Mechanical connectors of existing design and construction, have shown a considerably poorer LCF performance that is reflected by their infrequent use in coiled tubing operations.

A new spool-able mechanical connection with flush outer diameters for coiled tubing strings has been developed with comparable bend fatigue performance to that exhibited by orbital TIG girth joints. Current designs, that are based on strategic material selection and mechanical design details, range in size from 1-1/2″ to 2-7/8″. In addition to comparable or superior LCF lives, these connections overcome many of the disadvantages of welded butt joints. This paper describes the research and development, various mechanical and materials testing results and recent offshore well servicing applications undertaken with these new mechanical CT connectors.

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