HEAVY WALL BENDS FOR SOUR AND ARCTIC-ALIKE ENVIRONMENT

摘要

During last decade, customers' requirements of Line Pipes and accessories became more and more stringent. This process is led by the exploitation of fields with more severe conditions of pressure, environment and temperature. For this reason, heavy wall products (both straight pipes and bends) need to be developed. A development program was carried out in order to satisfy more stringent requirements and higher wall thickness. The metallurgical approach to steel design aimed to improve the combination of strength and toughness and increase the control of hardness after quenching and tempering, preserving adequate weldability. Industrial trials were performed to manufacture 60 mm thick hot induction bends in grade X65. Characterization was carried out after various post bending heat treatments (quenching, tempering and post welding). The new low-C steel showed promising results. The full characterization of off-line Q&T bends at various locations (tangent length, transition zone, and bend body) confirmed the achievement of X65 grade, with hardness HV_(10) ＜ 240, Charpy V-notch transition temperature ＜ - 60 °C, Crack Tip Opening Displacement ＞ 0.7 mm at - 45 °C, and very good HIC and SSC resistance.