Straightening and length measurement of LSAW pipes

Straightening and length measurement of LSAW pipes

Straightening processing of LSAW pipe

The straightening of straight seam steel pipes is an important process in the production of straight seam steel pipes. Especially for API standard oil casings, oil and gas pipes, and special pipes for mechanical equipment that have higher quality requirements. These steel pipes not only have strict requirements on steel grade and weld quality, but also have high requirements on the straightness of the steel pipes. Requirements, because the deviation of straightness is directly related to the processing and connection of pipe end threads and pipe hoops of oil casing and delivery pipes, as well as the distortion and deformation of pipelines during use. There are currently two processing forms of pipe end wire turning - pipe rotation and tool rotation. Most wire processing uses pipe rotation, which requires higher straightness of the steel pipe.

There are many reasons for the bending of steel pipes, such as the thermal impact of the welding seam, eccentricity during forming, compression force, imbalance of bending force, etc. But fundamentally speaking, bending is the result of internal stress in the steel pipe. Simply put, bending is stress imbalance. So, does a straight steel pipe have no internal stress? no. Straight steel pipes also have internal stress, but the internal stress of straight pipes is smaller.

What is internal stress? Temperature, an interaction force between molecules that causes deformation due to the influence of external forces. When steel pipes are formed and welded, they will also be affected by external forces such as welding temperature and forming bending, resulting in internal stress. The cross-section of the steel pipe is an annular shape, and two basic stresses will be generated in this annular area: a force parallel to the annular shape and a force perpendicular to the annular shape. Parallel stresses will cause the tube to become out of round; vertical stresses will cause the tube to bend. Therefore, there is a cold diameter expansion process in the production process of straight seam steel pipes. The purpose is to eliminate the internal stress of the steel pipe and increase the strength of the straight seam steel pipes.

The pipe that needs to be straightened is fed into the lower roller of the straightening machine from the feeding device at the left end (or right end) of the machine. The upper roller moves downward to press the pipe and stop after reaching the corresponding position. The upper and lower rollers are respectively inclined at a certain angle with the axis of the straightened pipe. The hyperbolic generatrix of the rollers matches the outer diameter of the pipe and forms an envelope.

The three upper rollers are pressed against the pipe under the action of their respective hydraulic cylinders, and the two lower rollers are driven to rotate by their respective hydraulic motors, driving the pipe to both rotate around the axis and move along the axial direction. Changing the rotation direction of the hydraulic motor can change the rotation direction and axial movement direction of the pipe to achieve reversible straightening. The straightened pipe is then sent to the material rack through the discharging device at the other end. For pipes with large local bending deformation, the punches at both ends can be used to perform partial straightening first, and then perform overall straightening.

Length measurement of LSAW pipe

1.Measure the length of the grating ruler

The basic principle is to install two fixed-length grating rulers on the outside of both ends of a straight-seam steel pipe. The grating ruler is driven by a rod near both ends of the steel pipe. The length of the straight-seam steel pipe is measured by the interference phenomenon of light. It has the characteristics of high precision. However, scales are expensive, difficult to maintain, and therefore sensitive to the effects of dust and on-site vibration.

2. Camera length measurement

Camera length measurement is achieved through image processing to measure the length of steel pipes. The principle is to install a series of equidistant photoelectric switches on one section of the straight-seam steel pipe conveyor roller, and add a light source and camera to another section. When the steel pipe passes through this area, the length of the steel pipe can be determined based on the photoelectric switch based on the position of the image captured by the camera on the screen. Its characteristic is that when the steel pipe passes through the measurement area without gaps, online measurement can be achieved and length data can be obtained.

3. Encoder length measurement

The principle is to install an encoder on the cylinder, use the cylinder to drive the steel pipe to move on the drum, and install a series of equidistant photoelectric switches on the other side. When the steel pipe is touched by the photoelectric switch at the end of the cylinder, the cylinder's stroke can be converted from the recorded encoder readings to calculate the length of the steel pipe. Its characteristic is that the steel pipe needs to be lifted when measuring the length. In addition, there are some errors in photoelectric switch detection, which may require adequate measurement.

4. Improved encoder length measurement

This method is an indirect measurement method. By measuring the distance between the two ends of the steel pipe and their respective reference points, the length of the steel pipe can be measured indirectly. Set up a length measuring vehicle at both ends of the steel pipe, with the initial position being zero and the distance being L. Then move the length of the editor to the walking distance (L2, L3) of one end of each steel pipe, which is the length of the steel pipe. This measurement method overcomes the difficulties of large steel pipe volume, complex production site environment, and the measurement mechanism cannot span the lower support of the steel pipe. It is easy to operate, has a measurement accuracy of less than ±10 mm, and a repeatability accuracy of ≤5mm.