Probe Designing for Corrosion Inspection under Insulated Surface by Using Eddy Current Method
Kittinan Sodsai 1 Mai Noipitak 2* Viboon Tangwarodomnukun 1 and Chaiya Dumkum 1
1 Department of Production Engineering, Faculty of Engineer, King Mongkut’s University of Technology Thonburi.
2 Materials and Nondestructive Testing Laboratory, Ratchaburi Learning Park, King Mongkut’s University of Technology Thonburi.

Abstract

Insulation has mostly been used for preventing heat loss of substance in metal pipeline and later introduces corrosion at the metal-insulation interface. An inspection system is designed to detect the corrosion under the insulation on the outside of pipe wall based on a nondestructive testing associated with the eddy current technique. This research was to design and develop prototype devices suitably used for testing. Detecting probes designed and manufactured were of two types. C iron core probe and pick up coil iron core probe. Flat specimen with localized uniform corrosions was machined and inspected. The signal frequency of 300 – 1000 Hz induced by a function generator was applied to detect the corrosion, and the results were demonstrated by an oscilloscope. The experimental results revealed that the pick up coil iron core probe can detect corrosion effectively more than C iron core probe and the diameter of uniform corrosion detected was equal or greater than 6 millimeters. Depth of uniform corrosion of 1 – 6 millimeters at 300 to 400 Hz frequency can be detected, and the method can also detect through the color coating and insulation with the total thickness of less than 3 millimeters.

Keywords : Eddy current, Insulation, Pick up coil, Nondestructive testing