Pipeline flexibility analysis of a hydrogen-powered train

The focus of the thesis is the pipeline designed to convey hydrogen from tanks to the fuel cell, in the ALSTOM FNM-HMU project. Part of the piping system is exposed at outside environment temperatures, being located at the roof of the PowerCar. Pipes could face high temperature ranges during the refuelling process, generating considerable thermal stresses. Due to this reason, the case-study includes a flexibility analysis of two different pipeline layouts, performed with an empirical test involving strain gauges and thermocouples. The aim is to verify the pipeline structural integrity considering longitudinal stresses due to gravity, temperature, and pressure loads. After an introduction about the ALSTOM H2 project, an overview on pipe design is treated, considering both theoretical models and standard norms. Then, the focus is shifted to theory and properties of thermal expansion, as well as norms concerning flexibility analysis. Furthermore, the test design is presented, including load cases to be analysed, the mock-up structure development to reproduce the real pipeline constraints during train operating conditions, and the strain gauges positioning. The transition from the experimental output data to the values of bending stresses affecting the pipes is performed. These can be calculated by adopting the straight beam theory. Temperature effect on stresses is computed by considering the thermal transient from 18°C to -40°C, while the pressure effect is calculated by analysing stress values at different time instants of the pressurization phase. Superposition of temperature and pressure effects is then considered, to compare calculated bending stresses with the allowable stress range, according to norm EN 13480-3. Lastly, the thesis aims to verify the correlation between numerical and empirical results: additional operations are performed on test results, to check the presence of a possible robust comparison with FEM.