Proposal of detecting for thickness method of hot spring scale inside steel pipes using vibration

Abstract

At geothermal power plants, there is a problem that hot spring water pipes are blocked by the “hot spring scale”. The hot spring water used for geothermal power generation contains calcium, sulfur, and other substances, and the solid material called the “hot spring scale” adheres to the inside of steel pipes, significantly reducing the efficiency of steam transmission. In addition, there are maintenance costs to remove the “hot spring scale” inside the steel pipes. And it is important to evaluate the thickness of the hot spring scale inside the steel pipe. In this paper, a non-destructive sensor that is evaluated the thickness of the hot spring scale inside the steel tube from the outside of the steel pipe is proposed. The proposed sensor is consisted of a permanent magnet, an alternating excitation coil and an acceleration sensor. The static magnetic field from the permanent, and eddy current inside the steel pipe are generated the vibration in the steel pipe. And the thickness of the hot spring scale is evaluated from this vibration intensity. It is shown that the thickness of hot spring scale from 0 mm to 15 mm can be inspected by this proposed method. In addition, the proposed inspection principle of this inspection method will be clarified by 3-D electromagnetic force analysis and displacement analysis.