  | EPRI 2000 Session: Austenitic Component Inspection |  |
| | EPRI 2000 Session: Austenitic Component Inspection | |
Based on the development of the Remote Field Eddy Current Technique (REFCT) for flat plates or shallow bent surfaces it is possible to detect flaws at any location in the pipe wall from outside the pipe, comprehensive theoretical and experimental investigations have been made at the Institute for Nuclear Technology and Nondestructive Testing at the University of Hanover and have paid a substantial contribution to the methodical development of REFCT s for industrial applications. The presentation shows the development and application of eddy current technique for the inspection of thick walled austenitic pipes. The diameter of the considered pipes is 280 mm and the thickness of the wall is 21 mm. The material is a high alloy Cr-Ni steel (1.4550; AISI 347).
Computer Aided Probe Design and Experimental Verification of the Numerical Field Calculation
The application of the FEM-Programme for calculating gives important information about the distribution of magnetic fields and therefore considers the electromagnetic material properties. The employment of the numerical calculations allows a prediction of the interaction between the flaw geometry and the magnetic field distribution. This leads to a considerable gain in time in the development of the eddy current probes. The characteristics of the eddy current probes are verified by the use of artificial flaw geometry. Comprehensive experimental investigations lead to test parameters for separating lift-off effects from flaw signals. Therefore it is possible to examine the different contortions at the outer surface of the bent. Furthermore, the signals obtained from the artificial flaw constitute the fundamental information for the classification of the eddy current signals.
Manipulator Development and Off Line Signal Processing
A two axis manipulator is specially constructed for the inspection of the bents. The eddy current signals obtained from a digital eddy current device are assessed by off-line signal processing. For this, special software has been developed which visualizes and characterizes the eddy current signals.
Conclusion
The work presented shows the investigation and application of REFCT for the inspection of thick walled austenitic pipes up to 30mm. By combination of numerical field calculation with comprehensive experimental investigations it is possible to reduce the time effort for developing eddy current sensors. Furthermore, advanced methods of signal processing extend the capabilities for the interpretation of eddy current signals. The remote field eddy current technique was successfully qualified and applied to assess the integrity of austenitic bents in a German nuclear power plant in spring 1999. The results of this inspection have special benefits to the lifetime extension strategies of the power plant.