Eddy Current testing exposes surface and sub-surface defects whilst leaving surface coatings intact.
Since its initial mainstream adoption in the 1950s, Eddy Current testing has remained an integral non-destructive testing technique. Supported and developed through intensive research, the technology surrounding the sensors, probes and data processing has seen ongoing development and has left Eddy Current testing a widely adopted inspection technique today.
Known for delivering accuracy and efficiency, Eddy Current testing is used across industries for detecting surface defects in carbon and low alloy steels, and surface, near-surface and sub-surface defects in non-ferritic materials such as brass, copper, aluminium and stainless steel.
The technique uses electromagnetic induction to create currents in the component being inspected, from which defects can be identified by the interruption they cause to these currents. The use of induction allows Eddy Currents to be created even if the material has paint coatings in place.
Surface Eddy Current Testing
Using handheld probes, Surface Eddy Current testing uses electromagnetic induction to detect discontinuities. Surface testing does not require contact between the probes and metallic parts and in ideal situations, can detect defects as small as 1mm in length.
Defects can be detected through various non-conductive surface coatings, eliminating the need to remove coatings such as paint.
Applications for Surface Eddy Current testing include:
- Painted structures, piping, vessels and tanks
- Cranes, both fixed and mobile
- Road tankers
More recently, the use of Eddy Current array technology has been a game changer. The array technology allows for greater detection of defects by giving technicians the option to read several Eddy Current sensors aligned in one assembly, allowing us the ability to cover both the x and y axis in one pass. Data can be encoded for accurate and reliable measurement of defects. Data is also displayed in a colour C-scan image giving the technician a greater ability to resolve individual defects.
Advantages of Surface Eddy Current testing
A major advantage to Surface Eddy Current testing is its ability to detect these surface or sub-surface defects through non-conductive surface coatings. Without the need to remove coatings such as paint, Surface Eddy Current testing proves to be an extremely cost-effective, time efficient and reliable non-destructive testing method.
Other advantages include:
- Customised probes can be used for complex geometries requiring inspection.
- Eddy Current testing poses no danger to the surrounding environment.
- Testing equipment is extremely portable.
- Results are immediate.
- Detection of sub-surface defects in non-magnetic materials may also be possible.
Limitations of Surface Eddy Current testing
Surface Eddy Current testing limitations include:
- Only effective on conductive materials.
- Metallic coatings, such as galvanisation, can severely restrict reliability.
- Defects parallel to the surface, such as laminations, will not be detected.
The ALS Approach
ALS has significant expertise executing Surface Eddy Current testing and carefully interpreting the results. To explore advanced Eddy Current testing techniques, such as Pulsed Eddy Current testing (PEC) and Saturated Low Frequency Eddy Current (SLOFEC), visit Advanced NDT.