Installation and length measurement of induction coil for straight seam steel pipes

The high-frequency induction coil of the straight seam steel pipe should be as close as possible to the position of the extrusion roller. The internal stress of the steel pipe is small and evenly distributed, which can effectively prevent stress corrosion cracking, high dimensional accuracy, and facilitate on-site welding construction. If the induction coil is far away from the extrusion roller, The effective heating time is longer, the heat-affected zone is wider, and the strength of the weld seam decreases; on the contrary, the edge of the weld seam is insufficiently heated, and when the heat input is insufficient after extrusion, the edge of the weld seam being heated cannot reach the welding temperature, and the metal structure remains. It remains solid and forms incomplete fusion or incomplete penetration; when the input heat is insufficient, the heated weld edge exceeds the welding temperature, resulting in overheating or molten droplets, causing the weld to form a molten hole. The impedance is one or a group of special magnetic rods for welded pipes. The cross-sectional area of the impedance should generally not be less than 70% of the inner diameter of the steel pipe. The proximity effect is generated, and the eddy current heat is concentrated near the edge of the weld of the tube blank, heating the edge of the tube blank to the welding temperature. The process of pre-welding and finishing welding is adopted, the welding process is stable and the welding seam is high. The impedance of the straight seam steel pipe is dragged in the tube blank by a steel wire, and its central position should be relatively fixed close to the center of the extrusion roller.

The burrs inside the steel pipe are generally not. After the two edges of the tube blank are heated to the welding temperature, the petroleum casing is squeezed by the extrusion roller to form common metal grains that penetrate and crystallize each other, and finally form a firm weld. The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the relevant formula, the high-frequency eddy current thermal power is mainly affected by the current frequency, and the eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is affected by the excitation voltage, The effect of current and capacitance and inductance. If the extrusion force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracks will occur after being stressed; the weld will produce weld scars after welding and extrusion. The method is to fix the tool on the frame and scrape the weld scars flat by the rapid movement of the welded pipe. The steel pipe has a longitudinal weld, and the inner and outer welds are welded by submerged arc welding.

How to measure the length of straight seam steel pipe:

1. Measuring length with a grating ruler.
The basic principle is: two fixed-length grating rulers are set on the outer sides of the two ends of the straight seam steel pipe, and the rodless cylinder is used to drive the grating ruler close to the two ends of the steel pipe, and the measurement of the length of the straight seam steel pipe is realized by using the interference phenomenon of light. It is characterized by high accuracy. But grating scales are expensive and difficult to maintain and are sensitive to dust and site vibration.

2. Camera length measurement.
Camera length measurement is to use image processing to measure the length of steel pipes. The principle is to install a series of photoelectric switches at equal distances on a certain section of the straight seam steel pipe conveying roller table and add a light source and a camera to the other section. When the steel pipe passes through this area, the length of the steel pipe can be determined according to the position on the screen of the image captured by a certain photoelectric switch through the camera. The feature is that online measurement can be realized, and the length data can be obtained when the steel pipe passes through the length measurement area without intervals. The disadvantage is: if the special light source is not used, the steel pipe will be disturbed by the external light, but after the special light source is used, the light reflection of the steel pipe is very high due to the high brightness of the pipe end after chamfering, which is easy to cause reading errors.

3. Encoder length measurement
The principle is to install an encoder at the oil cylinder, use the oil cylinder to push the steel pipe to move on the roller table and install a series of photoelectric switches equidistant on the other side. When the steel pipe is pushed by the oil cylinder and the end of the pipe touches the photoelectric switch, the recorded encoder reading, converts the stroke of the oil cylinder, so that the length of the steel pipe can be calculated. The characteristic is that the steel pipe needs to be raised when measuring the length. In addition, there are errors in the detection of photoelectric switches, which may need to be fully measured.

4. Improved encoder length measurement
This method is an indirect measurement method. By measuring the distance between the two end faces of the steel pipe and their respective reference points, the length of the steel pipe is indirectly measured. Set up a length-measuring trolley at both ends of the steel pipe, the initial position is zero, and the distance is L. Then move the length of the editor to the walking distance (L2, L3) of the respective steel pipe ends, L-L2-L3, which is the length of the steel pipe. This measurement method overcomes the difficulties of bulky steel pipe, complex production site environment, and the inability of the measuring mechanism to pass through the supporting platform under the steel pipe. This method is easy to operate, the measurement accuracy is within ±10mm, and the repeatability is less than or equal to 5mm.