Abstract
Coiled Tubing is extensively used for well intervention and completion operations and the use of high strength tubing is rapidly increasing. Limitations on fatigue performance in high strength coiled tubing introduced by the conventional manufacturing process, particularly in welded areas provided the motivation to introduce a new manufacturing route using metallurgical principles. The objective was to generate microstructural improvements and additionally to extend coiled tubing to even higher strengths. A sour environment implies an integrity risk to carbon and low alloy steels; this risk increases for higher strength grades. The use of inhibition in sour environments is common and recommended but an acceptable inherent resistance to different types of cracking is desired to limit the risks in the case of a temporary non proper inhibition. This paper summarizes results of a sour performance evaluation program involving several grades of coiled tubing (from 80 ksi to 125 ksi yield strength). The study included distinct chemistries, microstructures and heat treatments of base material and welds. Different tests were carried out including C-ring, low-cycle fatigue after sour exposure, and Hydrogen Induced Cracking. The severity of the environment was varied by using different H2S partial pressures in high chloride aqueous solution and acidic pH.
