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Nondestructive Evaluation


Eddy Current


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  image of three-dimensional visualization techniques used at SwRI

To simplify and expedite flaw characterization in metal materials, SwRI engineers use three-dimensional visualization techniques to analyze eddy current signals as a function of frequency.

Three-Dimensional Eddy Current Signal Visualization

To reduce reactor pressure vessel (RPV) inspection times, Southwest Research Institute (SwRI) developed a modified inspection module and accompanying quick-change unit for use with our In-service Inspection-2 device that includes an eddy current examination capability. The quick-change unit was previously used only with ultrasonic (UT) instrumentation. The eddy current version was used successfully for the first time to inspect a cladded surface in an American-built pressurized water RPV.


Coating Thickness Measurement

Surface coatings protect many components in the harsh environment of gas turbine engines. We have demonstrated an eddy current testing technique to measure coating thickness, an important factor in determining pre-service coating quality as well as in-service degradation. The eddy current technique employs multiple-frequency eddy current technology, portable eddy current instrumentation, and specialized fixtures and probes.


Remote-Field Eddy Current

  image of graph showing outputs of RFEC sensors as a robot travels down a pipe

This color image is generated from outputs of all 48 RFEC sensors as the robot travels down a pipe. Signals from defects (in this case simulated corrosion pits in a test pipe) appear as variations in color on a green background.

Gas pipelines are typically inspected for corrosion using a device called a “pig” that is inserted into the pipeline and carried along by the gas flow. However, conventional pigs cannot be used in many lines that have internal restrictions and/or low pressure or low flow rates.


To address the need for inspecting “unpiggable” pipelines, SwRI developed a tool that couples a remote-field eddy current (RFEC) inspection system with the Explorer II robotic transport tool developed by the National Robotics Engineering Consortium at Carnegie Mellon University.


The combined Explorer II/RFEC system consists of 11 modules linked to form a self-propelled device that can travel untethered through a pipe. The system can inspect 6-inch to 8-inch diameter pipelines containing tight elbows and tee joints, and can be used while the pipeline is in operation. In addition to detecting corrosion, remote-field eddy current can also characterize its extent and depth.


image of schematic showing the SwRI-developed RFEC module containing an array of sensors image of schematic showing the SwRI-developed RFEC module containing an excitation coil

Schematic showing the SwRI-developed RFEC modules. The system consists of two modules, one containing an array of sensors (left) and an excitation coil (right) with the robot centering module in between. The sensor may expand to a 6- or 8-inch diameter for different pipeline sizes (bottom view), and it collapses to 4 inches for traversing bends and for launching (inset).

image of the RFEC inspection technology, which can detect and characterize pipeline defects such as corrosion, fitted into a robotic transport tool

The RFEC inspection technology, which can detect and characterize pipeline defects such as corrosion, is fitted into a robotic transport tool. The National Robotics and Engineering Consortium at Carnegie Mellon University developed Explorer II to inspect 6- to 8-inch-diameter pipelines that are not inspectable with current technology.


The RFEC system allows inspection of many natural gas pipelines that cannot be inspected with conventional technology, thus improving the reliability and safety of pipeline infrastructure. Plans are under way for commercialization of the technology so that routine pipeline inspections can be performed on a commercial basis by licensed contractors.


For more information about our nondestructive evaluation (NDE) capabilities , eddy current technology, or how you can contract with SwRI, please contact Jay Fisher, Ph.D., at or (210) 522-2028.


Contact Information

Jay Fisher, Ph.D.


(210) 522-2028

Related Terminology

cladding thickness

computer modeling



eddy current

magnetic sensor

nondestructive evaluation

orientation sensing

pipe wall thinning

position sensing

pulsed eddy current

reliability studies

specialized NDE system development

specialized procedure development

steel pipe inspection

| Sensor Systems and Nondestructive Evaluation (NDE) Technology Department | Mechanical Engineering Division | SwRI Home |

Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.

August 07, 2014