Material characterization under hydrogen influence for welded and brazed joints
The objective of this subproject is to develop a method for accounting for the influence of hydrogen on welded and brazed joints during the design of fuel-carrying components. To this end, material properties for the base materials and for the joined states are required as a reference in air and under a hydrogen atmosphere.
Based on these results, we will demonstrate the extent to which strength and service life behavior are influenced, on the one hand, by the joining process and, on the other hand, by the combined effect of a hydrogen atmosphere that causes embrittlement. This method is intended to subsequently enable preliminary design calculations for application-relevant components and to ensure the applicability of the results as well as their practical implementation in design.
Core technologies for 100 percent hydrogen gas turbines
The core focus of the H2BED project is the development of core technologies for 100% hydrogen gas turbines to accelerate the energy transition in Germany. The project is divided into three main work packages: DLE hydrogen combustion, materials, and thermal insulation layers.
These work packages are being carried out by both the consortium leader, Siemens Energy, and the partners, which include TU Berlin, DLR Stuttgart, IFINKOR, Forschungszentrum Jülich, and Fraunhofer LBF.
Together with Siemens Energy Mülheim, we are carrying out the planned work in the Materials work package. Our main focus is on analyzing and evaluating the strength and service life behavior of the base materials used and the material states created through welding and brazing.
Strength and service life behavior of hydrogen-exposed materials
Through various investigations, we are examining issues such as the influence of temperature, hydrogen concentration, microstructure formation, joining processes, notch effect, the influence of average stress, and other factors.
The results will be summarized at the end of the project and compiled into a methodology to provide a foundation for practical application in the design of hydrogen-exposed components.
Cyclic material characterization under pressurized hydrogen
Various challenges must be overcome in addressing the planned research topics. The first lies in the fabrication of the material specimens to be tested.
In addition to base material specimens (base material), specimens consisting solely of weld metal (welded state) as well as welded and brazed specimens (integral specimens) must be produced. Since production lines are used for this purpose, the effort involved in specimen production is enormous.
Subsequently, here at Fraunhofer LBF, we perform cyclic material characterization using strain-controlled fatigue tests, both in ambient atmosphere and in a pressurized hydrogen atmosphere (up to a maximum of 50 bar).
For this purpose, we operate a test facility developed in-house, which, based on full-specimen autoclave technology, enables us to conduct such tests.
Due to the very extensive test program, a second facility is currently being set up, which will enable testing at pressures up to a maximum of 100 bar.
The results obtained from cyclic material characterization are continuously compared with the results of quasi-static tests and supplemented and evaluated through analyses of hydrogen content measurements.
The goal is to identify correlations and dependencies that can be applied in the design phase to describe and extrapolate material behavior under hydrogen atmospheres.
