Fatigue monitoring systems based on direct global and local temperature measurements are successfully being applied in facilities worldwide. Local temperature measurement is carried out by way of thermocouples on the outer wall of piping sections close to fatigue relevant components. The detectability and re-solvability of the corresponding inner wall temperatures — required for the fatigue assessment — is limited in the case of fast and high frequency load cycles occurring e.g. due to non-stationary mixing or vortex penetration processes of cold and hot flows. These kind of limitations are motivation for the development of a complementary nondestructive system using electromagnetic acoustic transducers (EMATs) in order to measure the ultrasonic time-of-flight (TOF).

Recent results of a respective cooperative R&D project (Fraunhofer IZFP Saarbrücken, RPTU Kaiserslautern-Landau, MPA Stuttgart, Framatome GmbH) on the applicability of the electromagnetic acoustic transducer technology for the purpose of fatigue monitoring will be discussed in this paper. The validation of the method was realized under various laboratory and operational conditions on different test rigs (uniaxial standard fatigue tests, component bending tests, pressurized pipe tests, heated plate tests, heated pipe tests, fluid structure interaction FSI test facility at MPA Stuttgart). A new test rig at the Framatome premises allowed for the simulation of different temperature transients and the application of thermocouple based and EMAT based measurements. Furthermore, both measurement types were applied at the MPA fluid structure interaction (FSI) test rig for a realistic cold-hot mixing scenarios.

It is the final aim of the project to determine the time history of fatigue relevant loading at fatigue relevant locations as the basis for complex fatigue monitoring according to the formula fatigue monitoring = continuous load monitoring + periodic (or continuous) engineering fatigue assessment.

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