The Study on Inspection Method Of Seamless Steel Tubes

According to the physical properties involved can be divided into several kinds, through the physical effects of radiation irradiation method known as ray detection (referred to as: RT); using elastic wave called ultrasonic testing (referred to as: UT) including acoustic holography; electromagnetic tests using the electromagnetic properties of steel include magnetic powder (MT), eddy current (ET), magnetic flux leakage (EMI), and penetration testing using metal surface properties (PT). At present, seamless steel pipe production process of automatic detection methods are ultrasonic, eddy current, magnetic leakage three methods.

Seamless steel pipes(short for smls pipe below) are generally made by smelting, pouring, blooming, rolling and drawing processes. The defects are in addition to the various metallurgical defects brought about by the slab in the forming process. Layer defects, in the production process at all stages will be due to improper processing technology, roll or drawing die design and other reasons in the steel pipe caused by cracks, folding, Alice, scratches or strain and other surface and internal defect. Four typical defects in smls pipe. According to the pipe production process, the main defects are generally in the rolling direction, that is, longitudinal injury (with the tube axis 0 degrees or a small fixed angle, such as 15 degrees). There is less chance of a cross injury (90 degrees) and an oblique injury (45 degrees). In order to ensure the quality of smls pipe, according to the relevant product technical standards, in the smls pipe production line to be surface and internal non-destructive testing.

Eddy current testing method is widely used in various fields of industrial non-destructive testing methods. It is based on electromagnetic induction theory,without any coupling agent on the specimen can be 100% of the rapid automatic detection. For the seamless shape of the steel pipe and a single specimen, it is a large number of rapid detection of powerful tools. Suitable for the quality inspection of the steel pipe automatic eddy current testing methods are mainly a little probe detection method and through the probe detection method two. The former uses the method of high speed rotation of the point probe to detect the longitudinal defects in the steel pipe. The detection speed is determined by the number of the probe and the speed of its rotation. Generally speaking, it is relatively slow, and the equipment is more complicated. While the latter is a through-type probe to detect transverse defects in the steel pipe, and the steel surface and near the surface of the common defects such as cracks, concave, scar and part of the outer fold and so have a higher detection sensitivity, so become a steel pipe inspection and because the eddy current testing method is particularly sensitive to the through-hole, the relevant standard stipulates that it is also one of the main methods to replace the steel pipe hydraulic pressure test. This method is usually used to detect tubing with a diameter less than 100 mm (maximum 180 mm) and a wall thickness of less than 6 mm. The advantages of this method are: simple equipment, fast detection, no consumables; drawback is: poor penetration. Sensitivity is related to the nature and geometrical position of the material, and the tube end is larger.

Magnetic flux leakage testing is a non-destructive testing technique based on magnetic properties of ferromagnetic materials. When the ferromagnetic material is magnetized,the presence of defects in the workpiece surface will produce leakage magnetic field, therefore, by magnetic flux leakage detection can be found in the material defects. The magnetic flux leakage testing technology of steel pipe is mainly divided into two kinds: magnetic particle detection method and magnetic field measurement method. The former is simple, but requires the naked eye to observe the magnetic marks, so it is difficult to achieve automation. Although the latter complex equipment, high cost and difficult to operate, but it is through the sensor to pick up the leakage magnetic field information, so easy to achieve automated testing, suitable for high-volume steel pipe automatic inspection. Therefore, in general, if there is no special note, the magnetic flux leakage detection of steel pipe usually refers to the magnetic field measurement method.Using the magnetic flux leakage method to detect the outer surface of the pipe and a certain wall thickness of the internal surface defect sensitivity. Usually used for diameters greater than 50mm, wall thickness less than 12.7mm of the pipe. Its advantages are: detection speed, no coupling agent. Sensitivity is moderate; shortcomings are: by the external magnetic field interference, uneven pipe material interference, the tube side of the blind area.

Ultrasonic flaw detection is mainly used to detect the steel pipe inside and outside the surface and its internal longitudinal defects, according to user needs can also detect lateral defects. The speed of longitudinal detection is usually about 20 μm / min, and the speed of lateral detection is usually about 10 μm / min.Ultrasonic testing of the internal and external surface and internal defects are very sensitive. Have a higher detection sensitivity, the cracks in the steel pipe, straight and other defects are more sensitive, but also to detect non-metallic inclusions and other volume-type defects. Therefore, it is suitable for testing high quality requirements of seamless steel tubes, such as high pressure boiler tubes and high pressure fertilizer pipes, etc., can also be used in accordance with user requirements instead of steel pipe hydraulic test. However, due to the slow detection speed, it is difficult to carry out rapid on-line inspection on the production line of steel pipe, so it is generally used as the off-line inspection method of high quality steel pipe, which is usually used for pipe with diameter greater than 50mm and wall thickness greater than 3mm. Disadvantages are: detection speed is slow, need to wet coupling agent, the system is complex. Such as increasing the detection speed, the system will be more complex. High cost, low cost of consumables required. Advantages are: high sensitivity, can detect the tube end, can be quantitative detection.