Nickel alloys allow for higher temperatures inside power plants

In 2011, the operators of the large-scale power plant Grosskraftwerk Mannheim (GKM) built and commissioned the test track HWT II using new materials for a high-temperature power plant. They have now delivered important results on the highly loaded thick-walled components, which turn out to be largely positive. The test track has undergone over 2,500 start-up and shutdown cycles and 10,000 operating hours with superheated steam at temperatures exceeding 700 °C. During operation, the test circuit underwent 14 daily temperature cycles. With these frequent load changes, the engineers simulated a flexible, dynamic mode of operation, while consciously provoking material changes and damages such as cracks in welds and the base material in order to gain a better understanding of any weaknesses. Project manager Klaus Metzger was satisfied, saying that, “We had the goal of stressing the components to cause fatigue-related damages, so that we would be able to analyse and validate the damages. The materials in some parts of the plant fared far better than expected.”

The employed nickel alloys achieved good results and confirmed the potential use in so-called 700-degree power plants. An unplanned stoppage of the test series was caused by a valve that was built for a steam flow rate of 85 kilogrammes per second, so for much heavier use, which then had to be adapted to the test track. This modification created some significant cracks, whose hazard potential had to be analysed. The positive findings here overweigh as well. Further large-scale operation with the valve went as intended until the scheduled end of the project.