Yinglai Liu

The Toughness Index of X80 Mother Linepipe Steel and Its Optimum Microstructure

Large amount of experimental data indicated, that the index of CVN toughness and shearing area of mother pipe of X80 are (200J, 90%). And the results showed that when charpy toughness was closing to 200J, the shearing area would reach to 90%; when the charpy toughness increased continuously, the shearing area would not increase further more. So the selection of charpy toughness value as 200J for pipeline steels is reasonable, and also its corresponding shearing area. To gain thus component index, the optimum microstructure of X80 steel should be strip-like ferrite mastered, small amount of granular bainite contained-acicular ferrite type steel, and, in which the size of MA island should be less than 1μm. This kinds of optimum microstructure of X80 pipeline steel will exert its softening role in improving toughness and simultaneity not decrease its strength.Copyright

The Researches on Toughness Index of Reheated High Grade Linepipe Bend Pipes

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.Copyright