Factors Affecting the Quality of ERW Pipes

With the development of ERW pipe technology, its application fields continue to expand. ERW steel pipe uses the skin effect and proximity effect of the current to heat the edge of the tube blank to the welding temperature for extrusion and welding. Compared with seamless pipe, it is obvious that ERW pipe has a weld seam, and its performance depends largely on the quality of the weld seam.

The factors affecting the quality of welds are more complicated. Including the chemical composition of raw materials, inclusions, banded structure, sickle bend, plate edge burrs, etc. will affect the quality of the weld, and the inclusions and banded structure have a great impact on the impact toughness and flattening performance of the weld. Excessive inclusions tend to accumulate in the heat-affected zone of the weld, and easily form crack sources to cause cracking. When the camber and edge burrs are serious, it will cause misalignment, arc strike, weld deviation, inclusions are difficult to discharge, etc., which will reduce the quality of the weld.

And its high-frequency welding process. The welding temperature, speed, extrusion amount and opening angle will all affect the quality of the weld. If the temperature is too high, the burr has no convex shape, the weld seam is flat, and the temperature is too low, the top of the outer burr is not smooth, and there is no intermittent convex shape on the burr line. Faster welding speed, easy to ensure the quality of welds. Under normal circumstances, the amount of extrusion should refer to the wall thickness, and it is better to control it at about 5.0mm. For thick-walled pipes such as those above 10mm, the amount of extrusion can be appropriately increased by 0.5-1mm. As the pipe diameter and thickness change, the opening angle should also be adjusted appropriately.

The stability of high-frequency welding is also the key to stable weld quality. Excessive impurities and burrs on the edge of the board will cause instantaneous short-circuit ignition during high-frequency welding, and local cold welding of the weld. To prevent such defects, it is necessary to check frequently whether the installation of the high-frequency coil is reliable, whether the coolant is filtered clean, whether the welding opening angle is proper, and whether the edge burrs of the coil are removed. Secondly, strengthen the inspection of water pressure and ultrasonic, and strictly control the quality of steel pipes.

The heat treatment process is also one of the influencing factors. The heat treatment generally adopts online intermediate frequency weld heat treatment, and the influence of the length of the air cooling section after intermediate frequency heating on the weld quality is easily overlooked. If the water inlet temperature is too high, the impact toughness of the weld will drop sharply. If the water inlet temperature is too low, the impact toughness will also drop. The length of the air cooling section must be determined by comprehensively considering the operating speed of the production line.

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