Detailed explanation of NDT technology

Date：2021-09-14 14:24:00Views：1018

Modern nondestructive testing technology can be simply divided into two categories: surface nondestructive testing and near surface nondestructive testing. Surface nondestructive testing technology is a technology used to detect product surface defects, such as fluorescent penetrant testing. It can effectively locate cracks or other types of defects on the surface. Near surface nondestructive testing technology is used to detect defects below the surface. Including ultrasonic testing, laser testing and radiographic testing. There are many kinds of nondestructive testing methods, most of which can be divided into two categories: surface and internal testing. Surface detection methods are used to detect defects and anomalies on or very close to the surface. The two most commonly used methods are penetration detection and laser shear imaging.

Internal inspection methods are used to identify defects below the surface. The two most commonly used methods are radiographic inspection and ultrasonic inspection. Some methods can be used for local detection, such as ultrasonic detection and electromagnetic detection; There is another type of method, such as acoustic resonance method, which can perform "whole body examination", which means that it can evaluate the overall structural integrity of the whole component.

Surface nondestructive testing method

Penetrant testing, referred to as Pt, also commonly known as fluorescent penetrant testing (FPI), is a kind of liquid penetrant testing. In this method, the components are coated with liquid dye by dipping, spraying or brushing, and then the parts stay for a certain time, and the liquid will penetrate the defects by capillary action. At the end of the residence time, the excess penetrant is removed from the surface, leaving only the dye penetrating into the defect. The penetrant remaining in the defect is then pulled back to the surface with a developer. After a certain period of time, any visible dye indication can be checked and evaluated under ultraviolet light and disposed of. The last step of the process is cleaning after thorough inspection. There are several cleaning methods, but the key is to remove all residual dyes. PT is a very effective method.

Laser shear imaging, also known as LS, is an optical detection method that uses laser to detect surface deformation.

Ls has many complex optical processes, but fundamentally speaking, it is based on the comparison of two deformation states in components or structures, and uses the surface displacement in response to load changes to identify defects. The light from the laser source is used to illuminate the target or area of interest. When the light is reflected from the surface, it is captured by the camera. The reflected light is divided into two parts and reflected into two separate images. One of the images is offset or cut relative to the other. The figures are then compared and the differences found are evaluated. Ls has excellent sensitivity and can be used to detect very small signs and abnormalities, so it is more and more used.

Internal NDT method

Radiographic testing, commonly known as RT, is a widely used nondestructive testing method. Radiographic testing involves the use of X-rays or γ X-ray to evaluate product defects or dimensional verification. After considering and implementing all safety protection measures, the X-ray will aim at the component or the area of interest in the component. When the X-ray passes through the target, some of them will be absorbed by the material area with high density; In areas with lower density, more X-rays will pass directly through the target. This amount of absorption and variation of X-rays passing through the target provides image contrast. There are many ways to capture X-rays. The most common are film, imaging board and digital detector. For most ordinary people, this is the nondestructive testing technology most closely related to life, because most people have done X-ray examination in the hospital.

Ultrasonic testing, called UT, is also a very reliable and commonly used nondestructive testing method. When the geometry of parts allows the normal transmission and reception of ultrasonic waves, ultrasonic testing technology can play a great role. UT is an acoustic method, which uses ultrasonic energy to detect defects and inconsistencies in materials. The sound wave is introduced through the transducer to convert the electric pulse into sound wave and propagate in the tested material. If there are defects, the sound wave will be reflected back to the transducer earlier than expected. This reflection is displayed on the digital screen for interpretation and evaluation. In many inspection occasions, UT is more popular than RT because it has few safety requirements.

To sum up, the commonly used nondestructive testing methods provide safety guarantee for various industrial fields every day. At present, nondestructive testing (NDT) technology is widely used. The structural integrity and safety of almost all components, especially the most critical components, need to be verified, in which nondestructive testing plays a very important role. NDT technology is required in almost all manufacturing, service, maintenance or overhaul inspection fields.