What is Non-Destructive Testing?
Non-destructive testing is an effective technique that allows inspectors to collect data without damaging the product. It is used to inspect for defects and degradation inside objects without disassembly or destruction of the product.
Non-destructive testing (NDT) and non-destructive inspection (NDI) are synonymous terms that refer to testing without causing damage to the object. In other words, NDT is used for non-destructive testing, while NDI is used for pass/fail inspection.
In some cases, non-destructive testing (NDT) and non-destructive inspection (NDI) can be used interchangeably, both referring to the testing of objects without causing damage. In other words, NDT is used for non-destructive testing, while NDI is used for pass/fail inspection. As this section also includes NDT methods under non-destructive inspection, it is advisable to differentiate between the two depending on your application and purpose.
The most two NDT purposes are:
Quality assessment: Checking issues in manufactured products and components. For example, used to inspect casting shrinkage, welding defects, etc.
Life assessment: Confirming the safe operation of the product. Can be used to check for abnormalities in the long-term use of structures and infrastructure.
Advantages of Non-destructive Testing
Non-destructive testing offers safe and effective ways of inspecting objects as follows.
High accuracy, easy to find defects that cannot be seen from the surface.
No damage to objects, available for all inspection.
Increasing product reliability
Identify timely repair or replacement
The reason why non-destructive testing is particularly accurate and effective is that it can identify internal defects of an object without damaging it. This method is similar to X-ray inspection, which can reveal the fracture site that is difficult to judge from the outside.
Non-destructive testing (NDT) can be used for product inspection prior to shipment, as this method does not contaminate or damage the product. This helps to ensure that all inspected products receive better inspections, which increases product reliability. However, in certain cases, multiple preparation steps may be required, which can be relatively expensive.
Methods of Common NDT Methods
There are several techniques used in non-destructive testing, and they have varying degrees depending on the defects or materials to be examined.
Radiographic Testing (RT)
Non-destructive testing (NDT) can be used for inspection prior to shipping of goods, as this method does not contaminate or damage the product. This helps ensure that all inspected products receive better inspections, thus increasing product reliability. However, in some cases, multiple preparation steps may be required, which can be relatively expensive. Radiographic testing (RT) uses X-rays and gamma rays to inspect objects. RT detects defects by using differences in image thickness at different angles. Computerized tomography (CT) is one of the industrial NDT imaging methods that provides cross-sectional and 3D images of objects during inspection. This feature allows for detailed analysis of internal defects or thickness. It is suitable for thickness measurement of steel plates and internal investigation of buildings. Before operating the system, certain considerations need to be taken into account: extreme caution needs to be exercised in the use of radiation. RT is used for internal analysis of lithium-ion batteries and electronic circuits boards. It can also be used to detect defects in pipes and welds installed in power plants, factories, and other buildings.
Ultrasonic Testing (UT)
Ultrasonic testing (UT) uses ultrasonic waves to detect objects. By measuring the reflection of sound waves on the surface of materials, UT can detect the internal condition of objects. UT is commonly used in many industries as a non-destructive testing method that does not damage materials. It is used to detect internal defects in products and defects in homogeneous materials such as rolled coils. UT systems are safe and easy to use, but they have limitations when it comes to irregularly shaped materials. They are used to detect internal defects in products and to inspect homogeneous materials such as rolled coils.
Eddy Current (Electromagnetic) Testing (ET)
In eddy current (EC) testing, a coil with alternating current is placed near the surface of an object. The current in the coil generates a rotating eddy current near the surface of the object, following the principle of electromagnetic induction. The surface defects, such as cracks, are then detected. EC testing is one of the most common non-destructive testing methods that requires no pre-processing or post-processing. It is very suitable for thickness measurement, building inspection, and other fields, and is often used in manufacturing plants. However, EC testing can only detect conductive materials.
Magnetic Particle Testing (MT)
Magnetic Particle Testing (MT) is used to detect defects just beneath the surface of materials in an inspection solution containing magnetic powder. An electric current is applied to the object to inspect it by changing the magnetic powder pattern on the object’s surface. When the current encounters defects there, it will create a flux leakage field where the defect is located.
It is used to detect shallow/fine cracks in a surface, and it is available for aircraft, automobile, and railroad parts.
Penetrant Testing (PT)
Penetrant testing (PT) refers to a method of filling the interior of a defect by applying penetrant to an object using capillary action. After processing, the surface penetrant is removed. Penetrant that has entered the interior of the defect cannot be washed away and is retained. By supplying a developer, the defect will be absorbed and become visible. PT is only suitable for surface defect inspection, requiring longer processing and more time, and is not suitable for internal inspection. It is used to inspect turbojet engine turbine blades and automotive parts.
Other methods
The hammer impact testing system is usually handled by operators who inspect the internal condition of an object by striking it and listening to the resulting sound. This method utilizes the same principle where a intact teacup produces a clear sound when struck, while a broken one produces a dull sound. This testing method is also used for inspecting loose bolts, railway axles, and external walls. Visual inspection is one of the simplest and most commonly used non-destructive testing methods where personnel visually inspects the object’s external appearance. Non-destructive testing provides advantages in quality control for castings, forgings, rolled products, pipelines, welding processes, etc., thereby improving the safety and reliability of industrial installations. It is also used to maintain transport infrastructure such as bridges, tunnels, railway wheels and axles, aircraft, ships, vehicles, as well as to inspect the turbines, pipes, and water tanks of power plants and other everyday life infrastructure. Furthermore, the application of NDT technology in non-industrial fields such as cultural relics, artworks, fruit classification, and thermal imaging testing is becoming increasingly important.
Post time: Jun-08-2023
