Doctoral theses of the School of Engineering at Aaltodoc (external link)
Doctoral theses of the School of Engineering are available in the open access repository maintained by Aalto, Aaltodoc.
Public defence, Mechanical Engineering, M.Sc. Maria Silva
Application of hydrogen-as-a-probe to detect early microstructural imperfections in a power plant's steel. Public defence from the Aalto University School of Engineering, Energy and Mechanical Engineering Department.
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Title of the thesis: Application of hydrogen-as-a-probe to detect early microstructural imperfections in a power plant's steel
Thesis defender: Maria Silva
Opponent: Prof. Pasi Peura, Tampere University, Finland
Custos: Prof. Pedro Vilaça, Aalto University School of Engineering
The lifespan of many energy production plants is 20–50 years, and numerous nuclear power plants are nearing their design limits. Extending their operation is a cost-effective and environmentally favourable alternative; however, it depends on reliably detecting early small-scale damage under harsh service conditions, which are often beyond the reach of conventional and advanced non-destructive testing methods.
The main purpose of the doctoral thesis research is to propose and study the feasibility and reliability of a novel probing framework, hydrogen-as-a-probe, to detect early small-scale damage in the heat-resistant steel 13CrMo4-5, which is widely used in components such as steam headers, pipes and pressure vessels in power plants. This work also contributes to new experimental evidence and a mechanistic understanding of how hydrogen interacts with microstructural features formed during long‑term operation.
The research combines hydrogen measurements, via thermal desorption spectroscopy, with microstructural characterisation. A key part of the study is the investigation of an ex‑service steam header that operated in a power plant for more than three decades. The results demonstrate strong correlations between hydrogen desorption profiles and microstructural features, including creep cavitation-type damage.
The findings highlight the sensitivity of hydrogen-as-a-probe and support the development of more sensitive inspection and life‑assessment strategies for high‑temperature components in power plants and other energy systems. Although the methods used in this work are applied to small, extracted samples, the results form a mechanistic framework that can support future non‑destructive or minimally invasive diagnostic technologies. Overall, the thesis contributes to improving the safety, reliability and sustainable operation of critical energy infrastructure.
Key words: Hydrogen-as-a-probe, TDS, Small-scale damage, 13CrMo4-5 steel
Thesis available for public display 7 days prior to the defence at Aalto University's public display page.
Contact information: mariaines.silva@vtt.fi
Doctoral theses of the School of Engineering
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