Monitoring of soil corrosion of underground steel pipe by acoustic emission

Research aims to study the AE activities of the rusts produced by soil corrosion of underground steel pipes. Author compared the AE activities of three types of the rust produced by atmospheric corrosion and soil corrosion by two methods. These are the monitoring of passive AEs under natural drying and active AEs under external turbulence such as forced heat cycles and mechanical loading. The soil-corrosion rust emitted AEs much more than the atmospheric rust did when they were submitted to mechanical deformation at lower strains. AE activities of the soil-produced rusts under cyclic heating (wet-and-dry) are, however, not so high compared to those of the atmospheric rusts. The rust produced on the steel pipe by soil corrosion for 20 years produced weak and few cylinder wave AEs under natural drying, and found to be detected only by AE sensors with resonant frequencies lower than 100 kHz for short distances of few hundred mm. This rust produced a number of AE at some period under cyclic heating, but the prediction of the timing for the rapid AE generation is difficult. Thus long term AE monitoring with highly sensitive AE sensors is needed for the corrosion monitoring of underground steel structures.