Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic 
testing methods used in non-destructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surface flaws in conductive materials. The Eddy Current method is the most versatile and cost effective method for testing metallic tubes. Eddy Current technology can be operated over the widest speed range. This is the preferred method to detect small, short, incomplete welds, and some subsurface and Inside Diameter conditions in carbon steel or stainless or nonferrous tube.
ddy current instruments can be used in a wide variety of tests. Some of the most common are listed below.
Weld Inspection – Many weld inspections employ ultrasonic NDT for subsurface testing and a complimentary 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 aluminum aircraft skin. Low frequency probes can be used to locate corrosion on second and third layers of metal that cannot be inspected ultrasonically.
Bolt Hole Inspection – Cracking inside bolt holes can be detected using bolt hole probes, often with automated rotary scanners.
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.