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Bobbin, Nonmultiplexed Array, and Multiplexed Array Eddy Current Probes for Heat Exchanger Inspection

Heat exchangers are devices used in the industry to transfer heat between two fluids by thermal conduction through the material of the exchanger. In the petrochemical and power generation industries, typical heat exchangers have tens or hundreds of tubes. Bobbin probes and multiplexed or nonmultiplexed array probes are used for the eddy current inspection of nonferromagnetic tubing in heat exchangers and condensers. In this paper, the ability of three different probe types (bobbin probes, nonmultiplexed array probes, and multiplexed array probes) to detect and depict volumetric and linear discontinuities is evaluated and compared. The signals obtained from the inspection of tube samples with those three probe types and the resulting data representations are measured and analyzed. The bobbin probe has a simple design that gave a good signal for long axial discontinuities and significant holes, but it is not sensitive to the orientation of some discontinuities or smaller discontinuities and doesn’t provide imagery of the discontinuity’s angular location or morphology. The nonmultiplexed probe allows for a low-resolution detection but can miss small angular extent discontinuities. The high-definition multiplexed array probe provided superior detection of circumferentially oriented discontinuities and detailed visualization of the surface.

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