Experimental investigations and numerical simulation accompanying the HWT test loop operation

A material test loop has been installed at GKM Mannheim, which enables thick-walled components of future highly-efficient power plants to be exposed to steam temperatures of up to 725 °C. The project goal was to demonstrate the feasibility of a 700 °C power plant. Based on the experience with materials and component manufacturing, operational experience and scientific investigations, fundamental knowledge of material behavior was determined which allows an assessment of the behavior of key components, such as headers, tubes, bends and valves. For this purpose, in addition to the test loop construction and its operation, extensive material characterizations and numerical analyses were carried out at the participating research institutes Materials Testing Institute (MPA) University of Stuttgart, the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg and the Institute of Materials Technology (IfW) at the Technical University Darmstadt. The determination and evaluation of material properties, which also comprise microstructural investigations, was aimed at gaining a deeper understanding of the Nickel base Alloy 617B and Alloy C263 and their welded joints. For basic material qualification and qualification of manufactured components an extensive experimental investigation program as well as tests to ensure quality of materials, welds and repair welds was initiated. The operating parameters of the test loop were first optimized by numerical simulations of component loading and lifetime with existing models [1]. An adaptation of the models to the experimental data of the project material enabled a more precise confirmation of the predictions carried out during regular operation of the test loop. To quantify service experience, numerous measuring results and findings regarding damage evolution were evaluated and compared to results from material tests and predictions from numerical analyses.