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

Corrosion monitoring and early detection of pits and wall thinning for casi ng pipes are considerably important to gas and petroleum industries since t he frequently occurring corrosion at the internal or external parts of thos e steel casing pipes used in underground gas storage or oil fields causes p roduction and environmental protection problems. In this paper, a new versi on of the direct current (dc) electromagnetic induction system is introduce d in which a sensor system, based on the de electromagnetic induction instr ument, is coupled with an updated data acquisition system. Unlike the conve ntional de induction instrument, the new system can achieve a full-signatur e logging response by providing all the measured flux leakage (FL) signals and eddy current (EC) signals to the computer logging system (CLS) on the s urface. To transmit the information represented by large amounts of data acquired b y downhole instruments to the CLS on the surface, a wavelet data compressio n technique has been incorporated. A VLSI integrated circuit (IC) which rea lizes the wavelet transform has been designed so that the real-time mode ca n be achieved during the logging operation. The circuit has been designed u sing CMOS n-well 2-mu m technology and has been fabricated by MOSIS.