Principle of flaw detection
1. Eddy current testing Eddy current testing is a non-destructive testing method based on electromagnetic induction. This method has obvious effects on point defects.It excites the probe coil with a sine wave current. When the probe approaches the surface of the seamless steel pipe, the alternating magnetic field around the coil generates an induced electromotive force on the surface of the steel pipe to generate an induced current, that is, an eddy current. The eddy current generates an inductive collision field that acts on the coil. Thereby changing the electrical parameters of the coil.The loss resistance of the eddy current channel, as well as the anti-collision generated by the eddy current, are reflected to the probe coil, changing the current size and phase of the coil, that is, changing the impedance of the coil.The probe moves relatively on the surface of the seamless steel pipe, and when a defect is encountered, the reaction of the eddy current magnetic field to the coil is different, causing the coil impedance to change, so as to measure the change to identify the surface defect of the seamless steel pipe.
2. The basic principle of magnetic flux leakage detection of seamless steel pipes is based on the high permeability of ferromagnetic materials. After the ferromagnetic seamless steel pipes are magnetized, the leakage magnetic field is formed due to defects on the inner and outer surfaces.By detecting the leakage magnetic field change signal, the existence of defects can be detected, and the magnetic permeability of the defect in the seamless steel pipe is much smaller than that of the steel pipe.When the seamless steel pipe enters the steel pipe detection line in a streamlined manner, it will be magnetized by the transverse and longitudinal magnetic fields generated by the DC coil when it quickly passes through the detection area.If the seamless steel pipe has no defects, most of the magnetic lines of force pass through the seamless steel pipe, and the word means that the magnetic lines of force are evenly distributed; if the seamless steel pipe is defective, the magnetic lines of force are bent, and some of the magnetic lines of force leak out of the surface of the seamless steel pipe.
1. Eddy current flaw detection
1) The mechanical transmission of the flaw detection equipment is relatively simple
2) As long as the seamless steel pipe is conductive, and the outer diameter and wall thickness meet the conditions, the eddy current method can be used for detection. It is widely used in the surface defect detection of seamless steel pipes such as carbon steel, alloy steel and stainless steel.
3) Generally, only single-sided surface defects (inner surface or outer surface) of seamless pipes can be detected
2. Magnetic flux leakage detection
1) The mechanical transmission device of the flaw detection equipment is relatively complex
2) It is only suitable for the detection of ferromagnetic seamless steel pipes. It can detect the inner surface defects and outer surface defects of seamless steel pipes, and is suitable for the detection of large-diameter thick-walled seamless pipes.
3) It can detect the inner and outer surface defects of the seamless pipe at the same time, and also has a certain sensitivity to the internal defects.