Full-signature real-time corrosion detection of underground casing pipes

Corrosion monitoring and early detection of pits and wall thinning for casing pipes are considerably important to gas and petroleum industries since the frequently occurring corrosion at the internal or external parts of those steel casing pipes used in underground gas storage or oil fields causes production and environmental protection problems. In this paper, a new version of the direct current (dc) electromagnetic induction system is introduced in which a sensor system, based on the dc electromagnetic induction instrument, is coupled with an updated data acquisition system. Unlike the conventional dc induction instrument, the new system can achieve a full-signature logging response by providing all the measured flux leakage (FL) signals and eddy current (EC) signals to the computer logging system (CLS) on the surface. To transmit the information represented by large amounts of data acquired by downhole instruments to the CLS on the surface, a wavelet data compression technique has been incorporated. A VLSI integrated circuit (IC) which realizes the wavelet transform has been designed so that the real-time mode can be achieved during the logging operation. The circuit has been designed using CMOS n-well 2-/spl mu/m technology and has been fabricated by MOSIS.