In domestic plants, sea water is used for cooling the auxiliary coolers, the lining of sea water pipe inside as anticorrosion materials is used with rubbers, polyethylene, epoxy resins, and etc. And the lining conditions are mainly confirmed by direct visual inspection. In the sea water pip g, the once occurred the small through-holes(pin-hole) accelerate the piping degradation caused by corrosion and it is important to confirm the deterioration condition of lining at an early st age. However, to confirm the small through-holes on the lining have a difficulty in aspects from the accessibilities on inside of piping by existing direct visual inspection. MHI has developed e inspection equipment with pinhole detection function for the lining of sea water pipe inside.