What are the key points affecting the quality control of straight seam high frequency welded steel pipes

There are many factors that affect the straight seam high frequency welded steel pipe, and these factors interact. Only by mastering the quality control points of the straight seam high frequency welded steel pipe can we better adjust them.

High-Frequency

The high-frequency will affect the uniformity of the current distribution inside the steel plate. When selecting the frequency of high-frequency welding, it is necessary to consider not only the depth of heat penetration, but also the proximity effect. Generally, the current frequency can be appropriately increased, which not only saves electric energy but also improves the quality of the weld and reduces the size of the heat-affected zone of the weld. In terms of welding efficiency, use a higher frequency as much as possible. 100kHz high-frequency current can penetrate ferritic steel 0.1mm, 400kHz can only penetrate 0.04mm, that is, the current density distribution on the surface of the steel plate, the latter is nearly 2.5 times higher than the former.

In production practice, the frequency of 350~450kHz can generally be selected when welding ordinary carbon steel materials; when welding alloy steel materials, the frequency of 50~150kHz can be used for plate thicknesses above 10mm, because the chromium contained in alloy steel, The skin effect of zinc, copper, aluminum and other elements is somewhat different from that of steel.

Welding V-shaped angle

The size of the V-shaped angle has a direct impact on the welding quality. The proximity effect is significant when the V-shaped angle is small, which is beneficial to increase the welding speed, but the preheating section and melting section become longer, making the flashing process unstable, and it is easy to form deep pits and pinholes after the lintel blasting, making it difficult to press. When the V-shaped angle is too large, the melting section becomes shorter and the flash is stable, but the proximity effect is weakened, the welding efficiency is significantly reduced, and the power consumption is increased. At the same time, when forming thin-walled steel pipes, if the V-shaped angle is too large, the edge of the pipe will be elongated, resulting in wavy wrinkles. In actual production, the V-shaped angle is generally adjusted within 2°~6°, thin-walled pipes generally use a smaller meeting angle; thick-walled pipes have slower welding speeds, and larger meeting angles are required for extrusion molding.

Welding power

If the power is too small, the heating of the groove of the tube blank is insufficient, and the welding temperature cannot be reached, which will cause unwelded defects such as virtual welding, desoldering, and clamp welding; The temperature is much higher than the temperature required for welding, resulting in serious spattering, pinholes, slag inclusions and other defects, which are called overburning defects. The input power during high-frequency welding should be adjusted and determined according to the thickness of the pipe wall and the forming speed. Different forming methods, different unit equipment, and different material steel grades need to be optimized through practice.

In addition to the above factors, it also includes various factors such as welding speed, welding method, welding extrusion force and resistors used.