Induction Hot Bending and Heat Treatment of 20” API 5L X80 Pipe

Abstract

The present work discusses the effect of the induction hot bending process on the microstructure and the mechanical properties of an API 5L X80, 20” pipe produced by the UOE process. The key characteristic of the pipe was the manufacturing process of the steel plate, involving thermomechanical controlled rolling without accelerated cooling. The pipe bending was carried out applying local induction heating followed by water quenching and a further temper heat treatment which was applied to the curved section. The methodology of analysis compared the curved section with the original body pipe (tangent end), taking into account dimensional analysis, microstructural evaluation and mechanical tests which included Charpy-V impact, tensile and microhardness. A significant microstructural change and decrease, not only in the transition temperature, but also in the yield strength, occurred after induction bending. This reduction resulted in a tensile strength below the standard requirements. The subsequent tempering heat treatment applied to the curved section produced an increase in the yield strength to achieve the API 5L requirements for this class of steel.