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Development of Large Diameter Heavy Wall Seamless Tee Fitting of WPHY-80 Grade for Low Temperature Pipeline Station Application

This paper describes the development of large diameter heavy wall seamless tee fitting of WPHY-80 grade for low temperature pipeline station application. Steel tees with thicker wall generally tend to have low fracture toughness either in pipe body or in weld joint and low weldability. Therefore, improvement of fracture toughness and weldability are particularly important with respect to development of higher strength and thicker wall seamless tee fittings.
 For the requirement of the China-Russia Eastern Gas Pipeline Project, WPHY-80 large diameter, seamless heavy wall reducing outlet tees were developed, with DN1400 × DN1200 and 57mm wall thickness. The billet steel production process was electroslag remelting (ESR), and the tee fitting production process used a forging and hot extrusion combination. Finally, quenching and tempering were carried out.
 In this paper, the mechanical properties and microstructure of WPHY-80 seamless tee were studied. The results of mechanical testing showed that the tensile yield strength of the tee body was more than 590 MPa and also provided excellent low temperature toughness (CVN > 200 J at −45°C), which met the requirements of the specification for fittings applied in the China-Russia Eastern Gas Pipeline Project. In addition, the results of welding procedure qualification showed that the welding performance of the WPHY-80 seamless tee was excellent.