Development of X80 Grade Induction Bend Pipe

API X80 grade induction bend pipe was developed using longitudinally submerged arc welded pipe as a mother pipe and applying subsequent quenching after induction heating and tempering in the full length portion. As a preliminary study for optimizing manufacturing process, the effect of heating process in induction bending had been investigated, and full length quenching and tempering process was recommended in order to obtain satisfying strength as X80 grade and superior toughness for the bend portion and tangent, as well. Based on the above examination, API X80 grade induction bend pipe with the pipe size of 761.0mmOD × 20.7mmWT, bending radius of three times the pipe diameter and bending angle of 90 degree, was manufactured by applying the full length quenching and tempering process, using a UOE pipe which has relatively lower chemistry with Ceq of 0.44%. It was proved that the trial X80 bend pipe has sufficient tensile properties for all portion in the transverse and longitudinal direction, measured by round bar tensile specimens. However, by using API standard full-thickness specimen, yield strength of all portion in the transverse direction and yield strength of the intrados in the longitudinal direction showed lower value than those obtained by round bar specimens because of the Bauschinger effect caused by flattening of the specimen. Owing to low chemistry of the mother pipe and optimized induction bending condition, the bend portion as well as the tangent showed quite low Charpy transition temperature and large absorbed energy even under −60 °C, and superior toughness was also achieved in the seam weldment.