EDDY CURRENT TESTING
In Eddy Current Testing (ET), a coil carrying an AC current is placed close to the specimen surface, or around the specimen. Flaws and material variations in the specimen affect the strength of the eddy currents. The presence of flaws, etc. is therefore measured by electrical changes in the exciting coil.
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.
Eddy current Instruments can be used in a wide variety of tests.
Some of the most common are
| Weld Inspection – Eddy current method to scan the surface for open surface cracks on weld caps and in heat affected zones. |
| Conductivity Testing – Eddy current testing’s ability to measure conductivity can be used to identify and sort ferrous and nonferrous alloys, and to verify heat treatment. |
| Surface Inspection – Surface cracks in machined parts and metal stock can be readily identified with eddy current. This includes inspection of the area around fasteners in aircraft and other critical applications. |
| Corrosion Detection – Eddy current instruments can be used to detect and quantify corrosion on the inside of thin metal such as aluminium aircraft skin. Low frequency probes can be used to locate corrosion on second and third layers of metal. |
| Tubing inspection – Both in-line inspection of tubing at the manufacturing stage and field inspection of tubing like heat exchangers are common eddy current applications. Both cracking and thickness variations can be detected. |