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You are here: Home » News » Industry Knowledge » What is Eddy Current Testing?

What is Eddy Current Testing?

Views:2     Author:Site Editor     Publish Time: 2019-04-19      Origin:Site

What is Eddy Current Testing?

Eddy Current Testing

Seamless steel pipe NDT Test

is the most commonly used method, but is limited to non-ferromagnetic and slightly magnetic alloys.  The Eddy Current technique is based on the induction of an electromagnetic field in the component being examined and can detect various forms of internal and external damage.  The inspection consists of a full-length examination performed on the inside of the tube with equal inner and outer surface discontinuity detection and sizing.  The purpose of this application is to detect I.D. and O.D. degradation such as cracking, corrosion, erosion, pitting, fretting and gradual wall loss generally found in non-ferromagnetic tubing.

Magnetism, the underlying principle behind electric motors and generators, relays and stereo speakers, is also the force that enables an important category of NDT tools called eddy current instruments. Eddy current testing is widely used in the aerospace industry and in other manufacturing and service environments that require inspection of thin metal for potential safety-related or quality-related problems. In addition to crack detection in metal sheets and tubing, eddy current can be used for certain metal thickness measurements such as identifying corrosion under aircraft skin, to measure conductivity and monitor the effects of heat treatment, and to determine the thickness of nonconductive coatings over conductive substrates. Both field portable and fixed system instruments are available to meet a wide variety of test needs. 

Eddy current NDT can examine large areas very quickly, and it does not require use of coupling liquids. In addition to finding cracks, eddy current can also be used to check metal hardness and conductivity in applications where those properties are of interest, and to measure thin layers of nonconductive coatings like paint on metal parts. At the same time, eddy current testing is limited to materials that conduct electricity and thus cannot be used on plastics. In some cases, eddy current and ultrasonic testing are used together as complementary techniques, with eddy current having an advantage for quick surface testing and ultrasonics having better depth penetration.