To ensure the reliable functioning of the main pipeline for water transport in hydropower, which has been operational for 50 years, a detailed analysis of the pipeline’s material condition is necessary. The pipeline material undergoes changing exploitation and working conditions, including extreme load phases such as periodic intensive emptying and filling with water for inspection. In this paper, we analyse the material resistance of NIOVAL47 steel using the method for determining R-curves for three states: Normalised state (2 samples), aged state (1 sample) which underwent 10% cold deformation and was heated for 30 min at +250 °C, and deformed state (1 sample) which underwent 10% cold deformation. The test results indicate that analysing the material’s aged and deformed states is crucial for obtaining a reliable picture of the structural integrity of the NO2500 mm pipeline, which has been in operation for five decades. The study should demonstrate the current state and level of reliability of the pipeline in order to ensure the sustainability of the energy facility. Additionally, these tests provide a realistic picture of the necessity of introducing an online monitoring system for the pipeline.
