The way used in a sensor allows to reduce an error at the effect of environment temperature Development and Application of Pulsed Eddy Current Testing System for Ferromagnetic Pipes

摘要

Pulsed eddy current (PEC) testing technology is widely used in the field of large area corrosion detection. According to the material attributes of detected objects, there are mainly two fields in which PEC technology is used: Non-ferromagnetic and ferromagnetic material testing. When the testing object is ferromagnetic, the decaying speed of the received signal differs according to the difference of the material?ˉs electrical conductivity, magnetic permeability and thickness. This paper states the realization of a type of PEC testing system and its application 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 computer (PC). The exciting signal is generated by Direct Digital Synthesis (DDS) integrated circuit and the exciting coil is powered by an integrated power operational amplifier. The received signal is filtered and amplified by low noise wide dynamic range amplifying circuit. The signal is then digitized by USB data acquisition system. 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 inside of the pipe respectively. One type of coil probe which has the advantage of eliminating 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 test the wall thickness loss through coatings from the outside of the pipe and it is able 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.