Fabrication of hot induction bends from LSAW large diameter pipes manufactured from TMCP plate

Induction bending is a largely automated, free forming process. The necessary heat for bending is induced in a narrow circumferential band by means of an induction coil, which advances continuously ing operation. In order to guarantee a homogenous microstructure, heating of the pipe to be bent must be above Ac3 transition temperature, consequently above end rolling temperature of the TMCP mother plate. As a result of this requirement, the composition of the plate has to be specially designed in order to maintain mechanical-technological properties of the base material grade after induction bending. Alloying and micro-alloying element contents must be optimized, ensuring sufficient hardenability, which is essential for induction bend fabrication, especially for higher material grades such as X65 through X80 and wall thickness above 20 mm. Nevertheless, applicable specification limits and requirements, such as chemical composition of line pipes with low Carbon Equivalents and good weldability for field welding, must be maintained. Induction bending is normally followed by a full body temper heat treatment or, dependent on dimensions and requirements, a full body quench & temper heat treatment. This paper presents details of hot induction bend manufacturing, including aspects of dimensional and chemical design of the mother plate (TMCP) and SAW material that must be considered during induction bend fabrication. (AU)