Factors Affecting The Weld Resistance Of Longitudinal Welded Pipes

Longitudinally submerged arc welding pipe production process is simple, high production efficiency, low cost and rapid development. The strength of the ssaw steel pipe is usually higher than that of the straight welded pipe. It is possible to produce a welded pipe with a larger diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter with a blank of the same width. However, compared with straight pipe of the same length, the length of the weld is 30~100%, and the production speed is low.

Large diameter or thick welded pipes are usually made directly from steel billets, while small welded pipe thin-wall welded pipes need only be welded directly by steel strips. Then, by simply polishing, the wire can be drawn. Therefore, most of the smaller diameter welded pipes are straight seam welded, and the large diameter welded pipes are mostly spiral welded.

The factors affecting the weldability of straight welded pipe are complex, and can be summarized as follows:1. The chemical composition of the welded pipe;2. High frequency welding technology;3. Post-weld heat treatment.Simply manipulating these primary factors can greatly ensure the resistance of the straight seam welded pipe weld arrangement.

The shape of the weld heat affected zone can reflect whether the technical parameters of the straight seam welded pipe are suitable, and it is also an important basis for directly judging the weld joint resistance. If the welding temperature is too high, the welding speed is too small, the heat affected zone of the weld is widened, the color of the heat affected zone is white, and the weld resistance is low at this moment; the welding temperature is low or the welding speed is slow, and the heat affected zone is narrow at this moment, and the color is dark.

The weld placement resistance is generally low; when the welding temperature, welding speed and welding extrusion force are properly matched, the shape of the weld heat affected zone is normal and the color is bright, and the weld arrangement resistance can reach a good level at the moment.

The shape of the metal streamline is often used as the most important basis for judging the influence of the technical parameters of the straight seam welded pipe on the weld placement resistance. The metal flow line is a specially shaped crystal arrangement of a partially melted or semi-melted metal on the pipe under pressure. It is closely related to welding temperature, welding extrusion force and welding speed. When the welding technical parameters are not suitable, the angle of the metal streamline is too large, small or asymmetrical. At this moment, the weld is often accompanied by cold welding, the weld inclusions are too much, and the weld arrangement resistance is drastically reduced.

The post-weld heat treatment technique has a great influence on the weld placement resistance. Studies have shown that the mismatch between heating temperature and heating time in the heat treatment process will result in a decrease in the weld resistance of the straight seam welded pipe.

A worker from a steel pipe company, which is located in China.