Eddy Current Testing – ECT

Introduction:

Eddy current testing is a non-destructive material examination technique frequently used to detect near-surface defects of conductive materials. ECT works on the principle of electromagnetic induction to identify surface cracks, measure approximate dimensions of cracks, measure metal sheet thickness, identify corrosion in metal substrates with coatings, etc. It is widely used in aerospace and other manufacturing industries for inspection and quality control to ensure safe operation and avoid expensive equipment and component failure.

A simple single-element ECT probe consists of a copper coil that produces a magnetic field when excited with an alternating current. When this probe comes within proximity of a conductive material, its magnetic field induces currents in the material known as eddy currents. Industrial ECT probes have multiple small coils placed at various orientations, which dictates the probes’ sensitivity and applicability. ECT probes measure tiny variations in the eddy currents’ path with high sensitivity and detect even small cracks as they scan large surfaces of conductive materials. Handheld field probes and large fixed systems are available for varying applications making ECT a versatile tool for quick onsite inspections and complex laboratory studies. Remote Field Testing (RFT), Flux Leakage, and Barkhausen Noise are other testing methods that use the principle of eddy current testing.

Other eddy current testing procedures such as Eddy current array (ECA) were created with varying degrees of success to get around some of the drawbacks of traditional ECT. The fundamental principles of both eddy current arrays (ECA) and traditional ECT are the same. With the use of ECA technology, it is possible to electronically control the topology—an array of coils (many coils)—that produces a sensitivity profile appropriate for the target flaws. In order to prevent mutual inductance between the individual coils, data capture is accomplished by multiplexing the coils in a certain pattern. 

Video 01: Eddy Current Testing (ECT)

Eddy Current Testing (ECT) Common Uses:

• Detect cracks, flaws, and faults, corrosion defects in ferrous, non-ferrous metals, aluminum alloys, and other conductive materials
• Quantify wear in support structures
• Thickness measurements of thin coatings and metal sheets
• Outer diameter (OD) and inner diameter (ID) erosion
• OD and ID pitting
• Inspecting the integrity of welds and bolts
• Conductivity measurements for material identification, heat damage detection, heat treatment monitoring

Advantages:

• Detect small cracks and other defects as small as 0.5mm
• Detects surface and near-surface defects
• Fast and rapid inspection and data acquisition
• Portable equipment
• Minimal surface preparation for testing
• No contact testing for high-temperature testing
• Test complex geometries
• No interference from planar defects
• Inspection of and through multiple layers of conductive materials and coatings
• Inspects complex shapes and sizes of conductive materials
• Automated testing available

Limitations:

• It can only be used for conductive materials
• The surface must be accessible to the probe
• Surface roughness may interfere with measurements
• Expertise required to interpret signals that are relevant to the measurements
• Limited depth of penetration
• Defects parallel to the probe coil winding or scanning direction are undetectable
• Difficult to test ferromagnetic materials due to susceptibility to magnetic permeability changes

Industries:

• Aerospace
• Metals and Alloys
• Automotive
• Piping and tubing
• Heat Exchangers
• Oil and Gas
• Manufacturing

Eddy Current Testing (ECT) Laboratories:

• Intertek Group Plc
• Element Materials Technology
• Eddyfi Technologies
• Applied Technical Services (ATS)
• Magna Check

More Details

• Basics and overview of Eddy Current Testing (ECT)
• Eddy current testing and its applications
• Eddy current testing in piping industry
• Eddy current testing instrumentation and measurement standards