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The Influence of Extrusion Force on the Welding of High Frequency Welded Pipe

Date:2021-03-15    keywords:high frequency welded pipe, extrusion force
In the welding process of high-frequency straight seam welded pipe(ERW welded pipe), does the extrusion force have a decisive effect on the quality of the pipe? In simple terms, the force on the squeeze roller consists of two parts: one is the force required to squeeze the open tube until the two edges contact, and the other is the force required to deform the tube blank during edge welding.

The effect of extrusion force:

High-frequency straight seam welding is a kind of pressure welding. After the two edges of the tube blank are heated to the welding temperature, the two edges need to be pressed together under a certain external force to squeeze the oxide on the heating surface to form a common Metal particles realize welding. The certain external force here is the extrusion force in the production process of welded pipes, which is an important process parameter in the production process of welded pipes.

In fact, the larger the extrusion force, the better, and the appropriate extrusion force is the guarantee for obtaining high-quality welds.

When the extrusion force is insufficient, on the one hand, the oxide on the edge of the tube blank is difficult to be squeezed out, and non-metallic inclusions are formed in the weld, which damages the continuity of the weld and becomes the source of weld cracking during the flaring test. On the one hand, the smaller squeezing force makes the number of ordinary crystals formed in the weld be smaller, the microstructure is loose and not dense, and the weld is prone to cracking after being stressed.

When the extrusion force is too large, most of the high-temperature metal used for crystallization at the edge of the tube will be squeezed out of the weld, causing a small amount of high-temperature metal crystals to form a weld, but the metal that is far away from the edge of the tube and the lower temperature actually forms Weld crystals, resulting in lower bonding strength of the weld.


erw steel pipe


Matching of extrusion force and welding shape:

It is meaningless to discuss whether the extrusion force is appropriate or not without the welding temperature. Whether the extrusion force is appropriate depends on whether the welding temperature is appropriate and kept constant. Large extrusion force is suitable for solid solution welding, but it is too large if it matches with fusion welding. Matching is not enough.

Judgment method of extrusion force:

1. Average size method, that is to say, the horizontal "diameter" and vertical "diameter" of the tube blank out of the squeeze roll, and then compare them with the diameter of the squeeze roll pass. If the former is slightly larger than the latter, It is considered that the squeezing force is normal. If the former is less than the latter, the corresponding force reduction adjustment is required.

2. The reversing observation method is to rewind the tube 50~80mm from the squeeze roller, and observe whether there are obvious reduction "strikes" on the tube blank. If the "strikes" are obvious, the squeezing force is too large. The "strike" is slight, indicating that the squeezing force is appropriate, if there is no "strike", the squeezing force is insufficient.

3. Dynamometer, usually only as a reference.

4. Destructive test, through destructive tests such as bending, flaring, flattening, etc., to check the strength of the weld to determine the extrusion force. The test method is a more reliable, convincing, and authoritative test method among the judgment methods.

The above methods for judging the extrusion force all have deficiencies and application limitations. If there is any doubt about the extrusion force in actual production, a combination of multiple methods should be used for comprehensive judgment. In addition, even if the extrusion force and welding temperature are just within the specified range of the process If it is not matched with the welding speed properly, high-quality welds will still not be obtained. This needs attention.


Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces. ASTM A53 ERW steel pipe is a typical carbon steel pipe. It is largely used to convey fluids at low / medium pressures such as oil, gas, steam, water, air and also for mechanical applications.

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