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Basic Knowledge of Flaw Detection Tech for Cold Drawn SMLS Pipes
Oct 24, 2021
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Here is the basic knowledge of internal and external flaw detection technology for cold drawn seamless steel pipes.
In the field of flaw detection technology, the cold-drawn seamless steel pipe refers to a steel pipe with an outer diameter greater than φ80mm. The cold drawn seamless steel pipe is an important material for petroleum, chemical, thermal, boiler, mechanical and hydraulic industries. With the development of the national economy, the demand for cold-drawn seamless steel pipes increased greatly during the "11th Five-Year plan" period. It showed the development trend of large diameter obviously. Especially for those pipes, such as corrosion resistant, extrusion resistant oil well tubes, large diameter high-pressure boiler tubes, high quality petroleum cracking tubes, petroleum and petrochemical transportation pipeline pipes, they will become a hot demand with the increase of national investment in energy infrastructure. Therefore, a new topic in method and technology is put forward for nondestructive testing to ensure the quality of products.
The flume ultrasonic testing is carried out by spiral steel pipes, and the ultrasonic probe is fixed. The thickness of the coupling layer is ensured by the characteristics of sufficient water coupling between the bottom of the water tank and the steel pipe. They are expected to be inspected. However, there are blind areas for surface and sub-surface defects mainly detected by ultrasonic. Moreover, the detection cannot be carried out. In addition, the use of spiral advance requires a space of 30m for steel pipes with the length of 12m. It has been affecting the selection and promotion of detection methods of steel pipes.
Therefore, the magnetic flux leakage method or water pressure test is generally used for flawed detection of cold-drawn seamless steel pipes at home and abroad. In China, there is no good performance for the magnetic leakage testing equipment of cold-drawn seamless steel pipes. Once used, it needs to be imported. Imported magnetic flux leakage testing equipment is expensive, which is difficult for most domestic enterprises to accept. However, the hydraulic test efficiency is low and labor intensity is heavy. When the operator's sense of responsibility is not high, hydraulic tests are useless. It can be seen that the realization of flaw detection of cold-drawn seamless steel pipes has become an urgent problem to be solved in the metallurgical steel pipe industry.
The characteristics of cold-drawn seamless steel pipes are its large diameter and relatively thick wall thickness. Therefore, according to this feature, the "no-blind zone" flaw detection can be realized by combining the characteristics of ultrasonic detection inside and eddy current detection surface and sub-surface. By adopting the "combination mode of steel pipes rotating in place and detection probe moving forward". Not only the detection problem is solved, but also the space occupied by the site reduced.
In sanitary stainless steel pipe automatic flaw detection, the most difficult problem is the effect of lifting effect and stable coupling layer on flaw detection. In automatic flaw detection, lifting effect and stable coupling layer are the main causes of missing detection and false positives. The reliability of detection will be affected by either missing detection or false alarm. For a long time, the problem of reliability decline caused by lift fluctuation or the thickness change of water coupling layer has always been the "bottleneck" which troubled the normal use of this technology in the practical application of automatic flaw detection.
Generally, the main methods to solve the lifting effect are probe:
1. The mechanical tracking method
2. The probe coil bridge connection method
3. The changing the capacitance value of LC loop detection coil and using multi-frequency detection technology
In addition to the mechanical tracking method, several other solutions can be achieved by improving the probe and instrument, but mechanical tracking can only improve the probe frame to prevent the change of lift clearance. In the practical industrial application, the probe mechanical tracking method is the most commonly used method to overcome the lift effect. There are two common probe mechanical tracking modes:
1. The combination of roller limit and cylinder or spring push. The detection probe and the surface of the work piece can maintain a constant distance. Although this method can play a good role in suppressing the lift effect, it will increase the vibration noise at the same time.
2. The probe mechanical tracking. It is to use the ranging probe in time to measure the fluctuation of the detection probe lift from the gap. It also uses the ranging signal to control and drive the stepping motor and other power devices to drive the detection probe action. In order to ensure that the gap between the probe and the inspected work piece is constant. This method is suitable for surface inspection of plates or billet. The disadvantage is that the reaction speed of mechanical action is slow and complicated.
The probe is loaded into a trolley. After that, a method of two-stage spring pushing is adopted to keep a certain distance between the probe and the surface of the inspected work piece. According to the experimental results, the probe has a strong follow-up, which guarantees the constant distance between the probe and the surface of the steel pipe. They need to be tested to ensure the inspection results are good. In general, the solution to the water-coupling layer mainly includes fixing the tank and stabilizing the water spray device. Due to the use of steel tube rotating probe forward, the length of cold-drawn seamless steel pipe is generally about 10m. Therefore, it is necessary to consider using a stable water spray device, such as increasing the diameter of the flow port and reducing the height of the flow port and the steel pipe to reduce the spray. At present, the conventional solution can only do so, but the effect of the solution is acceptable.
In the field of flaw detection technology, the cold-drawn seamless steel pipe refers to a steel pipe with an outer diameter greater than φ80mm. The cold drawn seamless steel pipe is an important material for petroleum, chemical, thermal, boiler, mechanical and hydraulic industries. With the development of the national economy, the demand for cold-drawn seamless steel pipes increased greatly during the "11th Five-Year plan" period. It showed the development trend of large diameter obviously. Especially for those pipes, such as corrosion resistant, extrusion resistant oil well tubes, large diameter high-pressure boiler tubes, high quality petroleum cracking tubes, petroleum and petrochemical transportation pipeline pipes, they will become a hot demand with the increase of national investment in energy infrastructure. Therefore, a new topic in method and technology is put forward for nondestructive testing to ensure the quality of products.
The flume ultrasonic testing is carried out by spiral steel pipes, and the ultrasonic probe is fixed. The thickness of the coupling layer is ensured by the characteristics of sufficient water coupling between the bottom of the water tank and the steel pipe. They are expected to be inspected. However, there are blind areas for surface and sub-surface defects mainly detected by ultrasonic. Moreover, the detection cannot be carried out. In addition, the use of spiral advance requires a space of 30m for steel pipes with the length of 12m. It has been affecting the selection and promotion of detection methods of steel pipes.
Therefore, the magnetic flux leakage method or water pressure test is generally used for flawed detection of cold-drawn seamless steel pipes at home and abroad. In China, there is no good performance for the magnetic leakage testing equipment of cold-drawn seamless steel pipes. Once used, it needs to be imported. Imported magnetic flux leakage testing equipment is expensive, which is difficult for most domestic enterprises to accept. However, the hydraulic test efficiency is low and labor intensity is heavy. When the operator's sense of responsibility is not high, hydraulic tests are useless. It can be seen that the realization of flaw detection of cold-drawn seamless steel pipes has become an urgent problem to be solved in the metallurgical steel pipe industry.
The characteristics of cold-drawn seamless steel pipes are its large diameter and relatively thick wall thickness. Therefore, according to this feature, the "no-blind zone" flaw detection can be realized by combining the characteristics of ultrasonic detection inside and eddy current detection surface and sub-surface. By adopting the "combination mode of steel pipes rotating in place and detection probe moving forward". Not only the detection problem is solved, but also the space occupied by the site reduced.
In sanitary stainless steel pipe automatic flaw detection, the most difficult problem is the effect of lifting effect and stable coupling layer on flaw detection. In automatic flaw detection, lifting effect and stable coupling layer are the main causes of missing detection and false positives. The reliability of detection will be affected by either missing detection or false alarm. For a long time, the problem of reliability decline caused by lift fluctuation or the thickness change of water coupling layer has always been the "bottleneck" which troubled the normal use of this technology in the practical application of automatic flaw detection.
Generally, the main methods to solve the lifting effect are probe:
1. The mechanical tracking method
2. The probe coil bridge connection method
3. The changing the capacitance value of LC loop detection coil and using multi-frequency detection technology
In addition to the mechanical tracking method, several other solutions can be achieved by improving the probe and instrument, but mechanical tracking can only improve the probe frame to prevent the change of lift clearance. In the practical industrial application, the probe mechanical tracking method is the most commonly used method to overcome the lift effect. There are two common probe mechanical tracking modes:
1. The combination of roller limit and cylinder or spring push. The detection probe and the surface of the work piece can maintain a constant distance. Although this method can play a good role in suppressing the lift effect, it will increase the vibration noise at the same time.
2. The probe mechanical tracking. It is to use the ranging probe in time to measure the fluctuation of the detection probe lift from the gap. It also uses the ranging signal to control and drive the stepping motor and other power devices to drive the detection probe action. In order to ensure that the gap between the probe and the inspected work piece is constant. This method is suitable for surface inspection of plates or billet. The disadvantage is that the reaction speed of mechanical action is slow and complicated.
The probe is loaded into a trolley. After that, a method of two-stage spring pushing is adopted to keep a certain distance between the probe and the surface of the inspected work piece. According to the experimental results, the probe has a strong follow-up, which guarantees the constant distance between the probe and the surface of the steel pipe. They need to be tested to ensure the inspection results are good. In general, the solution to the water-coupling layer mainly includes fixing the tank and stabilizing the water spray device. Due to the use of steel tube rotating probe forward, the length of cold-drawn seamless steel pipe is generally about 10m. Therefore, it is necessary to consider using a stable water spray device, such as increasing the diameter of the flow port and reducing the height of the flow port and the steel pipe to reduce the spray. At present, the conventional solution can only do so, but the effect of the solution is acceptable.
