Basic study on crack diagnosis of rotary equipment by fluid-mediated AE method

Abstract

The AE (Acoustic Emission) method is a technique for detecting ultrasonic sound waves generated by plastic deformation, crack initiation and crack growth by using an AE sensor. The AE method is used in checks of petroleum tank drawer bottom corrosion, degradation of steel and concrete structures, bearing degradation checks, etc. The purpose of this study is to apply AE to crack checks of rotary equipment (drive shaft or coupling). First, we conducted a comparative test of AE propagation characteristics, followed by a comparative test of the crack detection signal by a small rotary bending fatigue testing machine. From the AE count rate in the rotary bending fatigue test, the number of cycles of the fatigue test can be divided into three areas. In the initial stage, an AE wave is generated by the dislocation motion in the material. An AE wave is estimated to occur due to the progress of a crack generated on the test piece surface. In this study, we propose a fluid-mediated AE method with an improved S/N ratio and showed that it is possible to detect a fatigue crack in a drive shaft or coupling by the proposed method.

Keywords

• acoustic emission
• crack check
• crack diagnosis
• rotary equipment
• magnetic fluid
• pencil-lead break