Component Testing under cyclic operation modes for martensitic steels and Ni-based alloys in the HWT3 power plant test loop

In the first and second stage of a state funded research project a test loop implemented in Unit 6 of GKM Power Plant in Mannheim was used to gain information on the behavior of components for AUSC plants made of nickel alloys at 725 °C under static and fluctuating conditions in real plant environment. Due to recent changes of the operation mode of existing coal-fired power plants the test loop was modified in the third stage of the project. To gain more knowledge on the long-term static behavior at 725 °C, existing nickel components in the static part and additional HR6W pipes and valves are in operation in the static part and bypass of the test loop. The cyclically operated part of the test loop is equipped with components made of P92, P93 and HR6W.

Up to now 5000 h of operation and appr. 600 cycles with hold times of 4 h and 6 h, respectively, have been achieved. The loop will be dismantled in late spring 2024 followed by non-destructive and destructive examinations of selected components.

From the accompanying testing program results from thermal fatigue, thermal shock and long-term creep tests describing the behavior of base materials and welds are available mainly for P92 and P93, HR6W, and other nickel base alloys. Furthermore test results on dissimilar welds between martensitic steel P92 and nickel alloy A617 and HR6W are available. Numerical assessments using standardized and numerical lifetime estimation methods complete the investigations.

The contribution provides information on test loop operation issues, material behavior and lifetime as well as operational experience of valves, armatures, piping and welds.

Keywords: high temperature test loop, components, P92, HR6W, cyclic operation, life assessment