THE RESEARCHES ON TOUGHNESS INDEX OF REHEATED HIGH GRADE LINEPIPE BEND PIPES

摘要

In the development of high grade pipeline steels, the technologies on bend pipes are key points. Most reports are mainly on the cold bending techniques which allow a small deflection angle usually less than 10°. And induction heat is then introduced for higher deflection angle bend pipes. So it is very important to know the toughness index of reheated high grade linepipes. In current used standard in China for West-East Gas project, Charpy toughness is required to be ≥120J at -20°C, and corresponding shearing area is required to be ≥ 85%. Based on a large number of experimental data on high grade linepipes with heat treatment, it was found in the present study that the shearing area and Charpy toughness have a linear relationship and the slope coefficient is 0.34. As a result, the when shearing area is 85%, the corresponding Charpy toughness is 250J. and This is different from that of mother pipe. To find the reasons, the fractures and microstructure of these reheated linepipes are analysed and compared with that of mother pipes.