Analysis Of Factors Affecting Weld Quality Of ERW Steel Pipe

ERW steel pipes are manufactured by high frequency contact welding or high frequency induction welding. They are round pipes welded by longitudinal seams of steel plates, and are often used to transport gas and liquid objects such as oil and natural gas.

ERW welded pipe has great development potential and market competitiveness due to its high dimensional accuracy, uniform wall thickness, high production efficiency, good compression resistance and comprehensive mechanical properties, and no perforation cracks. Therefore, it is particularly important to ensure the welding quality of ERW welded pipes.

Analysis of Factors Affecting Weld Quality of ERW Steel Pipe:

1. Raw Material

The quality requirements of welded pipe raw materials mainly refer to whether the pipeline steel coils produced by steel mills through thermomechanical rolling technology meet the raw material control requirements of steel types specified in API standards. For the control indicators of steel coil quality, not only the manufacturer should do corresponding physical and chemical performance testing, and issue a quality assurance certificate for qualified products, but also after receiving the raw materials, the pipe manufacturer should also conduct a third-party supervision unit that meets the relevant API standards. . Under the supervision of the staff, the physical and chemical properties of the raw materials are tested. The raw materials can only be used after all the inspection items meet the relevant standards.

2. Frequency

The frequency of high-frequency welding has a great influence on welding, because the high-frequency frequency affects the distribution of current inside the steel plate. The influence of the selected frequency on welding is mainly the size of the heat-affected zone of the weld. From the perspective of welding efficiency, a higher frequency should be used as much as possible. 100KHz high-frequency current can penetrate 0.1mm of ferritic steel, 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 350KHz~450KHz can generally be selected when welding ordinary carbon steel materials; when welding alloy steel materials, when welding thick steel plates above 10mm, lower frequencies can be used, such as 50KHz~150KHz, because alloy steel contains chromium The skin effect of elements such as zinc, copper, and aluminum is different from that of steel. At present, most foreign high-frequency equipment manufacturers adopt solid-state high-frequency new technology. After setting the frequency range, it will automatically track and adjust the frequency according to the thickness of the material and the speed of the unit when welding.

3. Input Power

Input power control during high frequency welding is very important. 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; when the power is too high, the welding stability will be affected, and the groove surface of the tube blank will heat up. The temperature is much higher than the temperature required for welding, resulting in serious defects such as spatter, pinholes, and slag inclusions, 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 molding methods, different unit equipment, and steel types of different materials require us to summarize from the first production line and compile equipment suitable for our own unit. high frequency process.

4. Welding Speed

Welding speed affects welding quality. When the welding speed is increased, it is beneficial to shorten the heat-affected zone and extrude the oxide layer from the melting tank; on the contrary, when the welding speed is very low, the heat-affected zone becomes wider, resulting in larger welding burrs and thicker oxide layer. , Welding quality deteriorates. Of course, the welding speed is limited by the output power and cannot be increased too high.

5. Welding Pressure

Theoretical calculations suggest that the welding pressure should be 100~300MPa, but it is difficult to measure the pressure in this area in actual production. Generally, it is estimated based on experience and converted into the amount of extrusion at the edge of the pipe. Different wall thicknesses require different extrusion amounts. Usually, the extrusion amount below 2mm is 0.5t~t when it is 3~6mm; 0.5t when it is 6~10mm; and 0.3t~0.5t when it is more than 10mm.