First of all, what is nondestructive testing?

Non destructive testing (NDT for short). To put it simply, it means conducting various tests on objects without damage. (In detail, on the premise of checking that the mechanical materials do not damage or affect the service performance of the object to be tested, and do not damage the internal organization of the object to be tested, take advantage of the changes in thermal, acoustic, optical, electrical, magnetic and other reactions caused by the abnormal internal structure of the material or the existence of defects, take physical or chemical methods as the means, with the help of modern technology, Electronic & Instrument Enclosures and equipment, the internal and surface structures, states, and types and numbers of defects of the test pieces The method for checking and testing the quantity, shape, nature, position, size, distribution and their changes.)

Now let's talk about the five common NDT methods:

Ultrasonic testing (UT)

Basic principle of ultrasonic flaw detection: it is a method to inspect part defects by using the characteristics of reflection at the interface edge when ultrasonic energy penetrates into the depth of metal materials and enters from one section to another. It is also the most common of the five conventional nondestructive testing Electromagnetic Induction.

So, how is ultrasonic flaw detection?

Answer: When the ultrasonic beam passes from the surface of the part to the inside of the metal from the probe, the reflected wave will occur when it encounters a defect and the bottom of the part, forming a pulse waveform on the fluorescent screen.

The position and size of defects can be judged according to these pulse waveforms. There are multiple waveforms when ultrasonic wave propagates in the medium. The most commonly used waves in inspection are longitudinal wave, transverse wave, surface wave and plate wave.

The longitudinal wave can be used to detect inclusions, cracks, shrinkage tubes, white spots, delaminations and other defects in metal ingots, billets, plates, large forgings and parts with simple shapes;

The transverse wave can be used to detect circumferential and axial cracks, scratches, pores, slag inclusions, cracks, incomplete penetration and other defects in the pipe;

The surface defects on castings with simple shape can be detected by surface wave;

Radiographic Testing (RT)

As we all know, X-ray and γ The ray has a strong penetrability. When it shines on an object, only a part of the energy will be absorbed by the object. Most of the energy can pass through the object. Using this feature (the difference in the amount of rays reaching the film), different black and white images will be formed.

Where the density is high, the ray is absorbed more and the photo shows white shadow. On the contrary, where the density is low, the ray is absorbed less, and the picture is dark.

Magnetic particle testing (MT)

Principle.

Eddy Current Testing (ET)

It refers to the nondestructive testing method that uses the electromagnetic induction principle to measure the change of induced eddy current in the tested workpiece to evaluate some properties of conductive materials and workpieces, or find defects. In industrial production, eddy current testing is one of the main means to control the quality of various metal materials, a small number of graphite, carbon fiber composites and other non-metallic conductive materials and their products, and plays an important role in the field of nondestructive testing technology.

1.Characteristics of nondestructive testing: on the premise of not damaging the service performance of the tested object, based on the theories of physics, chemistry, material science and engineering, effective inspection is conducted on various engineering materials, parts and products to evaluate their integrity, continuity, safety and reliability.

2.The five most commonly used nondestructive testing methods can be divided into: internal testing (ultrasonic testing, radiographic testing，Metal Box Printing), surface testing (magnetic particle testing, eddy current testing, penetrant testing).

3.Thank you for reading, and each test method will be introduced separately.