Applicable scope and limitations of various NDT

Date：2022-06-17 15:52:41Views：868

Nondestructive testing is the general term of all technical means to use the characteristics of sound, light, magnetism and electricity to detect whether there are defects or nonuniformity in the inspected object, give the size, location, nature and quantity of defects, and then determine the technical status of the inspected object (such as qualified or not, residual life, etc.) without damaging or affecting the service performance of the inspected object.

1、 Brief description

1.1 each NDT method has its scope of application and limitations. The detection probability of defects by each method will not be 100% or the same. For example, radiographic inspection and ultrasonic inspection will not have the same inspection results for the same inspected workpiece.

1.2 in conventional NDT methods, radiographic testing and ultrasonic testing can be used to detect defects in the interior and surface of the inspected workpiece; Eddy current testing and magnetic particle testing are used to detect defects on the surface and near surface of the inspected workpiece; Penetrant testing is only used to detect the defect of the surface opening of the inspected workpiece.

1.3 radiographic testing is more suitable for detecting volumetric defects in the inspected workpiece, such as pores, slag inclusions, shrinkage cavities, looseness, etc; Ultrasonic testing is more suitable for detecting the area type defects in the inspected workpiece, such as cracks, white spots, delaminations and lack of fusion in the weld.

1.4 radiographic testing is often used to detect metal castings and welds, and ultrasonic testing is often used to detect metal forgings, profiles, welds and some metal castings. Ultrasonic testing is usually superior to radiographic testing in detecting defects in welds.

2、 Radiographic testing (RT)

2.1 scope of application:

a) It can detect defects such as lack of penetration, porosity and slag inclusion in the weld;

b) It can detect shrinkage cavity, slag inclusion, air hole, porosity, hot crack and other defects in castings;

c) It can detect defects that form local thickness difference or local density difference;

d) It can determine the position and size of the plane projection of the defect, as well as the type of defect.

Note: the radiographic thickness is mainly determined by the ray energy. For iron and steel materials, the transmission thickness of 400 kvx-ray can reach about 85 mm, the transmission thickness of cobalt 60 gamma ray can reach about 200 mm, and the transmission thickness of 9 MeV high-energy X-ray can reach about 400 mm.

2.2 limitations:

a) It is difficult to detect defects in forgings and profiles;

b) It is difficult to detect the small cracks and lack of fusion in the weld;

c) The defect of thin layer perpendicular to the radiation direction cannot be detected;

d) The depth of burial and vertical height of the deficiency cannot be determined.

3、 Ultrasonic testing (UT)

3.1 scope of application:

a) It can detect defects such as cracks, white spots, delaminations, large or dense inclusions in forgings;

Note: internal defects or defects parallel to the surface can be detected by direct beam technique. The defects which are not parallel to the surface or surface defects can be detected by oblique beam technique (including surface wave technique).

b) It can detect defects such as cracks, incomplete penetration, incomplete fusion, slag inclusion, air holes, etc. in the weld;

Note: the oblique shooting technique is usually used.

c) It can detect cracks, folds, delaminations, flake slag inclusions, etc. in profiles (including plates, pipes, bars and other profiles)

Deficiency;

Note: liquid immersion technology is usually used, and focused oblique beam technology is also used for pipe or bar.

d) It can detect hot cracks in castings (such as steel castings or nodular cast iron with simple shape, flat surface or after processing and renovation)

Defects such as cold crack, looseness, slag inclusion and shrinkage cavity;

e) It can measure the depth and height of the defect.

3.2 limitations:

a) It is difficult to detect defects in coarse-grained materials (such as castings and welds of austenitic steel);

b) It is difficult to detect defects in workpieces with complex shape or rough surface;

c) It is difficult to determine the nature of the deficiency.

4、 Eddy current testing (ET)

4.1 scope of application:

a) It can detect defects such as cracks, folds, pits, inclusions and looseness on the surface and / or near the surface of conductive materials (including ferromagnetic and non ferromagnetic metal materials, graphite, etc.);

b) It can measure the coordinate position and relative size of defects.

4.2 limitations:

a) Not applicable to non-conductive materials;

b) Can not detect the internal defects in the conductive material away from the detection surface;

c) It is difficult to detect defects on the surface or near surface of the workpiece with complex shape;

d) It is difficult to determine the nature of the deficiency.

5、 Magnetic particle testing (MT)

5.1 scope of application:

a) It can detect the surface and / or near surface of ferromagnetic materials (including forgings, castings, welds, profiles and other workpieces)

Cracks, folds, interlayers, inclusions, pores and other defects;

b) Be able to determine the position, size and shape of defects on the surface of the workpiece to be inspected.

5.2 limitations:

a) Not applicable to non ferromagnetic materials, such as austenitic steel, copper, aluminum and other materials;

b) Internal defects in ferromagnetic materials far away from the detection surface cannot be detected;

c) It is difficult to determine the depth of the deficiency.

6、 Penetrant testing (PT)

6.1 scope of application:

a) It can detect open cracks, folds, looseness, pinholes and other defects on the surface of metal materials and dense non-metallic materials;

b) Be able to determine the position, size and shape of defects on the surface of the workpiece to be inspected.

6.2 limitations:

a) Not suitable for loose porous materials;

b) It is unable to detect defects inside and / or near the surface of the material without opening on the surface;

c) It is difficult to determine the depth of the deficiency.

The above is the NDT related content compiled by the core testing team. I hope it can help you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.