Analysis of Influence Factors on Impact Toughness of ERW Steel Pipe Welds

How to improve the impact toughness of ERW steel pipe welds is a major problem in the technology of pipe making. On the basis of mass production practices, various factors affecting the impact toughness of ERW straight seam resistance welded steel pipe welds were analyzed. It is pointed out that in order to further improve the impact toughness of welds and meet the high toughness requirements of long-distance pipelines for ERW steel pipes, it is necessary to start with the control of the quality of raw material coils, combined with the pipe-making process, and strengthen the quality control of forming, welding and on-line heat treatment after welding. 

1 ERW steel pipe weld joint toughness characteristics

The welding process of ERW steel pipe uses the principle of skin effect produced by high-frequency current to heat the edge of the hot rolled plate to the molten state, and then it is welded by the mechanical extrusion method. A white fusion line appears at the center of the weld seam of the steel pipe produced by this process, and the heat affected zone on both sides of the fusion line will generate a metal flow line extending from the middle to the inner and outer surfaces. As the ERW steel pipe uses the base metal as the welding material, the performance of the weld seam is greatly related to the performance of the base metal. In ordinary materials, there is little difference in the absorbed energy value of the Charpy impact test between the weld and the base metal. On the contrary, there is a big difference in high-toughness materials. The weld joints are significantly inferior to the parent metal in terms of impact toughness, but they are significantly better than those of common materials. It can be seen that the impact toughness of the center of the weld of the ERW steel pipe, even if the use of high toughness materials, although the toughness of the weld is improved, but can not completely improve the impact toughness of the weld center.

2 Influence factors of weld impact toughness

The main factors affecting the impact toughness of welds are: (1) Physical and chemical properties of raw materials (2) Grain size and non-metallic inclusions of raw materials (3) Heat treatment conditions of welds (4) Forming conditions (5) Welding conditions