Effects of coiling temperature and pipe-forming strain on yield strength variation after ERW pipe forming of API X70 and X80 linepipe steels

Since pipes are undergone repeated tension and compression strains during pipe-forming, and flattening, flattened sheets often show too higher or lower yield strength than hot-rolled coils, which poses to difficulties in satisfying yield strength standards. In this study, effects of microstructure and pipe-forming strain (thickness/diameter (t/D)) on yield strength variation were investigated in X70 (483 MPa) and X80 (552 MPa) linepipe steels...