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What are the application categories of common NDT? What's the difference?

Date：2022-03-29 17:00:00Views：1000

Nondestructive testing is a testing technology to check the internal or surface defects of materials without damaging the tested materials, or to determine some physical quantities, properties and organizational states of materials. Nondestructive testing technology is needed in almost all areas of manufacturing, service, maintenance or overhaul inspection. At present, there are many kinds of nondestructive testing technologies in practical application. In addition to the five conventional nondestructive testing methods of ray, ultrasonic, magnetic particle, penetration and eddy current, there are also microwave, acoustic emission, laser, infrared and so on. The following introduces the classification and differences of several commonly used nondestructive testing applications.

classification	purpose	advantage	shortcoming
Ultrasonic testing	Detect the cracks, delaminations and inclusions of forgings, cracks, pores, slag inclusions, incomplete penetration, etc. in welds; Crack, delamination, inclusion and folding of profile; Shrinkage cavity, bubble, hot crack, cold crack and thickness measurement of castings.	It is very sensitive to plane defects, easy to carry and strong penetration.	Sound coupling shall be good, and the surface of the tested object shall be smooth; It is difficult to detect small cracks and pores; High requirements for testing personnel; It is not suitable for workpieces with complex shape and rough surface.
Radiographic testing	Detect the incomplete penetration, porosity and slag inclusion of the weld, shrinkage cavity, porosity and hot crack of the casting, and determine the location, size and type of defects.	Adjustable power, high photographic quality and permanent recording.	The equipment is expensive and difficult to carry; Radiation hazard; High requirements for the quality of testing personnel; It is difficult to find weld cracks and incomplete fusion defects; Not suitable for forgings and profiles.
Magnetic particle testing	Detect cracks, folds, interlayers, slag inclusions, etc. on the surface or near surface of ferromagnetic materials and workpieces, and determine the location, size and shape of defects.	Simple, easy to operate, fast speed and high sensitivity.	Ferromagnetic materials only; Clean the workpiece before flaw detection; In some cases, it is difficult to determine the defect depth.
Penetrant testing	Detect surface cracks, folds, looseness, pinholes and other defects of metal and non-metallic materials, and determine the location, size and shape of defects.	All materials are applicable; Simple equipment and low price; The flaw detection is simple and the results are easy to explain.	The workpiece must be cleaned before and after flaw detection; It is difficult to determine the depth of defects; Not suitable for loose porous materials; The holes on the pore surface are easy to cause false display.
Eddy current testing	Detect cracks, inclusions, folds, pits, looseness and other defects on the surface and near surface of conductive materials, and determine the location and relative size of defects.	Simple, economical, without coupling, and the probe does not need to contact the workpiece.	It is only limited to conductor materials, and the penetration is shallow. There should be reference standards, so it is difficult to judge the type of defects.
Optical fiber detection	Detect the defects on the inner surface of boiler, pump body, casting, barrel, pressure vessel and pipeline, as well as the quality and fatigue cracks of weldments and welds.	High sensitivity, good insulation, corrosion resistance and free from electromagnetic interference.	The price is high and the internal defects of the structure cannot be detected.
Acoustic emission detection	Detect the dynamic crack, crack initiation and crack growth rate of the component.	Real time continuous monitoring and detection, remote control and portable device.	The coupling between the sensor and the workpiece shall be good; The workpiece shall be in stress state; The ductile material produces low amplitude acoustic emission, and the noise cannot enter the detection system; Expensive equipment and high requirements for personnel quality.
Microwave detection	Detect composite materials, non-metallic products, tires, etc; It can measure physical parameters such as thickness, density and humidity.	Non contact detection, fast detection speed and automation.	It can not detect the internal defects of metal conductors. Generally, it is not suitable for detecting defects less than 1mm, and the spatial resolution is low.