Eddy Current, In General...

Eddy Current Testing is the most frequently used Electromagnetic Testing technique.  It’s is a nondestructive test that can utilize a wide variety of probe types and styles making it applicable to many different materials.  In testing heat exchanger tubing it’s used to identify common problems, which left unaddressed, may cause major system malfunctions and extended down time.

Eddy Current, Very Specific...

When an alternating current is impressed across a test coil, the varying magnetic field developed by current flow in the test coil induces eddy currents to flow in an electrically conductive (metallic) test material.  The eddy current flow in the test material creates a secondary magnetic field in the material.  This secondary field opposes the primary magnetic field around the test coil, and the interaction between these two oppositely charged fields decreases the loaded coil voltage and phase shifts it in proportion to the magnitude of eddy currents in the test piece.  Thus, the loaded coil voltage is dependent upon the electrical properties of the test material.  For further technical information visit: www.ndt-ed.org

Heat Exchanger Testing

In the case of heat exchanger tube testing, an appropriate size test probe is selected and passed down the entire length of each tube. The probe, connected to the digital oscilloscope, is energized with alternating currents at the appropriate frequency.  While the probe is traveling through each tube its electrical impedance is changing due to a number of factors, the most important being discontinuities in the tube.  Discontinuities may be wear related or manufacturing flaws, each discontinuity produces a unique electromagnetic response allowing for differentiation.  These responses are displayed on the test instrument and interpreted by our analyst.  Given their high level of training each analyst can immediately identify problems and recommend corrective action at the job-site.