Development and Application of Pulsed Eddy Current Testing System for Ferromagnetic Pipes

Pulsed eddy current (PEC) testing technology is widely us ed in the field of large area corrosion detection. According to the material a ttributes of detected objects, there are mainly two fields in which PEC technology is used: No n-ferromagnetic and ferromagnetic material testing. When the testing objec t is ferromagnetic, the decaying speed of the received signal differs according to the diff erence of the material’s electrical conductivity, magnetic permeability and thicknes s. This paper states the realization of a type of PEC testing system and its app lication in ferromagnetic pipe testing from inside and outside of the pipe. The system consists of an exciting module, a signal receiving module, coil probes and a personal com puter (PC). The exciting signal is generated by Direct Digital Synthesis (DDS) i ntegrated circuit and the exciting coil is powered by an integrated power operational amplifier. The received signal is filtered and amplified by low noise wide dynami c range amplifying circuit. The signal is then digitized by USB data acquisition sys tem. A PC is used for signal processing and analysis. Experiments were taken with two kinds of coil structure probes to test ferromagnetic pipe from outside and insi de of the pipe respectively. One type of coil probe which has the advantage of eliminatin g vibration effect during the well logging process in oil industry is employed to find the coupling part of casing from the inside. Another type of coil probe is used to tes t the wall thickness loss through coatings from the outside of the pipe and it is abl e to detect 10% wall thickness loss with probe lift-off up to 80mm so it can be employed to test high temperature parts without removal of coatings.