Detection of Localized Damage in Water Wall Tubes of Thermal Power Plants Using GMR Sensor Array Based Magnetic Flux Leakage Technique

摘要

A flexible giant magneto-resistive (GMR) sensor array based magnetic flux leakage technique has been developed for nondestructive inspection of carbon steel water wall tubes (outer diameter 64.0 mm and wall thickness 6.3 mm) used in a thermal power plant. Two saddle coils are used for magnetisation of the tube and a flexible GMR sensor array is used for detection of leakage fields from localized damage in the tube. 3D-nonlinear finite element modeling has been performed to optimize the magnetizing current, inter-coil spacing of the saddle coils and location of the GMR sensor array within the saddle coils. The performance of the technique has been evaluated by measuring the axial component of leakage flux from outer diameter (OD) erosion and inner diameter (ID) corrosion type flaws artificially machined on the water wall tube. Studies reveal that the proposed technique detects both OD erosion and ID corrosion damage in the water wall tubes.