Detection of Surface and Subsurface Defects in Ferrous Steel Components and New Inspection Technologies Development

摘要

Our investigations show the possibility to detect the surface and subsurface like crack defects in ferrous steel by eddy current (EC) method with new low frequency double differential probes. By this probes application 3 complicated gas turbine inspection problems connected with possibility to detect defects (1) with large clearance between probe and inspected surface; (2) through nonmagnetic conductive coating and (3) to detect subsurface defects in ferrous steel without magnetic saturation were investigated and solved. High sensitivity to subsurface defects can be explained by remote field effect when transmit and receive coils in surface EC probe are separated. Additional advantages of developed probes are high lift-off effect and structural noise suppression due double differential coils connection. For blade inspection special double differential probes with 5mm and 6 mm operational diameters and long handle were produced. The developed double differential probes were applied for detection of defects situated on sidewall of gas turbine holes. For this purpose special rotating head with double differential EC probe based on ELOTEST SR-1 rotor was developed for productive gas turbine holes inspection. Presented technologies were applied for gas turbine maintenance in different countries.