Abstract
The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR) has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, the RSE-M Code introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in loadcontrolled conditions. To this end, a device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the thermal cycle, a high frequency induction coil heats the external wall of the tube. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load. Tests have been carried out, and these tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M Code for a significant plasticity.
Highlights
In operating conditions, components such as train wheels, engine pistons, moulds, brazing of electrical devices or turbine blades are submitted to cyclic loadings which have thermal origins [1]
Investigations on thermal loading have been undertaken using specific devices [5 to 8]. This present study focuses on the crack-propagation under cyclical thermo-mechanical loadings, as may be encountered in Pressurized Water Reactor pipes: thermal loadings may correspond to an incomplete mixing between cold and warm fluids, or thermal stratification
In order to improve the estimation of crack propagation under cyclic thermal loading, a new device called PROFATH has been built in our laboratory
Summary
Components such as train wheels, engine pistons, moulds, brazing of electrical devices or turbine blades are submitted to cyclic loadings which have thermal origins [1]. Investigations on thermal loading have been undertaken using specific devices [5 to 8]. This present study focuses on the crack-propagation under cyclical thermo-mechanical loadings, as may be encountered in Pressurized Water Reactor pipes: thermal loadings may correspond to an incomplete mixing between cold and warm fluids, or thermal stratification. Crack propagation leads to some mechanical unloading in the un-cracked zone. In such way, methodologies based only on load-controlled tests cannot be very efficient. In order to improve the estimation of crack propagation under cyclic thermal loading, a new device called PROFATH has been built in our laboratory. Present study begins with a crack propagation campaign performed for isothermal conditions on CT specimens
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