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Frequently Used Nondestructive Testing Methods For Steel Tubes
- Mar 19, 2018 -

 Nondestructive testing methods for steel pipes include: radiographic testing, magnetic powder (or magnetic flux leakage) detection, penetrant testing, ultrasonic testing, eddy current testing.



1 x-ray detection (RT)

The application of the earliest Nondestructive testing method is widely used in the internal defect inspection of metal and non-metallic materials and products, at least more than 50 years of history. It has incomparable unique advantages, that is, the correctness, reliability and intuition of the test defects, and the resulting radiographic negatives can be used for the analysis of defects and archives of quality documents. But this method also has the shortcoming that the equipment is more complex, the cost is high, and should pay attention to the protection of Ray.


2 Magnetic particle detection (MT) or magnetic flux leakage detection (EMI)

The detection principle is based on ferromagnetic materials in the magnetic field after magnetization, the material or products in the discontinuity (defects) generated leakage magnetic field, adsorption magnet powder (or detected by detection components) and is displayed (or on the instrument display). Therefore, this method can only be used for the surface or near-surface defect inspection of ferromagnetic materials or products.


3 Penetrant Testing (PT)

It include fluorescence and coloring two kinds. Because of its simple equipment and convenient operation, it is an effective method to make up the defects of magnetic particle inspection. It is mainly used for surface defect inspection of non-magnetic materials.

The principle of fluorescence testing is to be seized products immersed in fluorescent liquid, due to capillary phenomenon, in the flaw filled with fluorescent liquid, remove the surface liquid, due to the light effect, fluorescent liquid in the ultraviolet radiation emitted visible light and show defects.

The principle of coloring test is similar to that of fluorescence test. are not required special equipment, but with the image of the powder will be adsorbed in the defect in the color liquid suction part of the surface and show defects.


4 Ultrasonic Testing (UT)

This method uses ultrasonic vibration to detect defects in a material or a workpiece (or surface). According to the different modulation methods of ultrasonic vibration, can be divided into continuous and pulsating waves, according to the different modes of vibration and propagation can be divided into longitudinal waves, shear waves, surface waves and lamb waves 4 forms in the workpiece transmission; According to the acoustic emission and acceptance conditions, can be divided into single probe and multiple probe method.


5 Eddy Current Testing (ET)

Eddy Current testing is the principle of alternating magnetic field in the metal material to produce the same frequency vortex currents, with the size of the vortex current and metal material of the relationship between the specific resistance to detect defects. When the metal surface defects (such as cracks), the specific resistance of the place is increased by the existence of defects, and its associated eddy current will be correspondingly reduced, the small changes in the eddy current after amplification by the instrument to indicate the existence and size of defects.