Common non-destructive testing methods for steel pipes include: radiographic testing, magnetic particle testing, penetrant testing, ultrasonic testing, and eddy current testing.
1. Radiographic testing (RT)
The earliest application of a non-destructive testing method has been widely used for internal defect inspection of metal and non-metal materials and products, with a history of at least 50 years. It has unparalleled unique advantages, that is, the correctness, reliability and intuitiveness of inspection defects, and the obtained radiographic film can be used for defect analysis and as a quality certificate for archiving. However, this method also has the disadvantages of more complex equipment and higher cost, and attention should be paid to radiation protection.
2. Magnetic particle testing (MT) or magnetic flux leakage testing (EMI)
The detection principle is based on the fact that after the ferromagnetic material is magnetized in the magnetic field, the discontinuity (defect) of the material or product generates a leakage magnetic field, adsorbs the magnet powder (or detects with the detection element) and is displayed (or displayed on the instrument) ). Therefore, this method can only be used for surface or near-surface defect inspection of ferromagnetic materials or products.
3. Penetration Testing (PT)
Including fluorescence and coloring. Because of its simple equipment and convenient operation, it is an effective method to make up for the lack of magnetic particle inspection. It is mainly used for surface defect inspection of non-magnetic materials.
The principle of fluorescence inspection is to immerse the inspected product in the fluorescent liquid. Due to the capillary phenomenon, the defect is filled with the fluorescent liquid and the surface liquid is removed. Due to the photo-induced effect, the fluorescent liquid emits visible light under ultraviolet radiation to show the defect.
The principle of color inspection is similar to that of fluorescence inspection. All of them do not need special equipment, just use the developing powder to suck the coloring liquid absorbed in the defect out of the surface of the part to show the defect.
4. Ultrasonic testing (UT)
This method uses ultrasonic vibration to find internal (or surface) defects in materials or parts. According to the different modulation methods of ultrasonic vibration, it can be divided into continuous wave and pulsating wave; according to different vibration and propagation modes, it can be divided into four forms: longitudinal wave, transverse wave, surface wave and Lamb wave, which propagate in the workpiece; according to the emission of sound wave Different from the acceptance conditions, it can be divided into single probe and multiple probe methods.
5. Eddy current testing (ET)
The principle of eddy current testing is that an alternating magnetic field generates eddy currents of the same frequency in a metal material, and the relationship between the size of this eddy current and the specific resistance of the metal material is used to detect defects. When there is a defect on the surface of a metal material (such as a crack), the specific resistance there will increase due to the existence of the defect, and the related eddy current will decrease accordingly, and the small change of the eddy current will be amplified and indicated by the meter. , The existence and size of defects can be revealed.
1. Radiographic testing (RT)
The earliest application of a non-destructive testing method has been widely used for internal defect inspection of metal and non-metal materials and products, with a history of at least 50 years. It has unparalleled unique advantages, that is, the correctness, reliability and intuitiveness of inspection defects, and the obtained radiographic film can be used for defect analysis and as a quality certificate for archiving. However, this method also has the disadvantages of more complex equipment and higher cost, and attention should be paid to radiation protection.
2. Magnetic particle testing (MT) or magnetic flux leakage testing (EMI)
The detection principle is based on the fact that after the ferromagnetic material is magnetized in the magnetic field, the discontinuity (defect) of the material or product generates a leakage magnetic field, adsorbs the magnet powder (or detects with the detection element) and is displayed (or displayed on the instrument) ). Therefore, this method can only be used for surface or near-surface defect inspection of ferromagnetic materials or products.
3. Penetration Testing (PT)
Including fluorescence and coloring. Because of its simple equipment and convenient operation, it is an effective method to make up for the lack of magnetic particle inspection. It is mainly used for surface defect inspection of non-magnetic materials.
The principle of fluorescence inspection is to immerse the inspected product in the fluorescent liquid. Due to the capillary phenomenon, the defect is filled with the fluorescent liquid and the surface liquid is removed. Due to the photo-induced effect, the fluorescent liquid emits visible light under ultraviolet radiation to show the defect.
The principle of color inspection is similar to that of fluorescence inspection. All of them do not need special equipment, just use the developing powder to suck the coloring liquid absorbed in the defect out of the surface of the part to show the defect.
4. Ultrasonic testing (UT)
This method uses ultrasonic vibration to find internal (or surface) defects in materials or parts. According to the different modulation methods of ultrasonic vibration, it can be divided into continuous wave and pulsating wave; according to different vibration and propagation modes, it can be divided into four forms: longitudinal wave, transverse wave, surface wave and Lamb wave, which propagate in the workpiece; according to the emission of sound wave Different from the acceptance conditions, it can be divided into single probe and multiple probe methods.
5. Eddy current testing (ET)
The principle of eddy current testing is that an alternating magnetic field generates eddy currents of the same frequency in a metal material, and the relationship between the size of this eddy current and the specific resistance of the metal material is used to detect defects. When there is a defect on the surface of a metal material (such as a crack), the specific resistance there will increase due to the existence of the defect, and the related eddy current will decrease accordingly, and the small change of the eddy current will be amplified and indicated by the meter. , The existence and size of defects can be revealed.
