PSI - Issue 28

838 Evgeniia Georgievskaia et al. / Procedia Structural Integrity 28 (2020) 836–842 Evgeniia Georgievskaia/ Structural Integrity Procedia 00 (2020) 000–000 Figure 1 shows the ordinary scheme of the relationship between reliability (technical possibility) and operating costs (economic feasibility). 3. Existing solutions Summing up all of the above there is need an effective predictive system to avoid the sudden damage of unique equipment and increase the reliability of the machine takes into account the actual operating modes. There are two main solutions that exist now – an expert method and diagnostic systems. 3.1. An expert method There are not special regulating documents that require approaches and methods for fatigue estimation of HT under actual functioning in a wide operational range at the hydraulic power plant (HPP). Any expert method is based on the experience of individual experts or an expert organization. As practice shows, each expert usually pays main attention to any one direction of the research: an investigation of the behavior of the base metal and welding, experimental study, computer simulation of hydraulic process or stress state, etc. Therefore, the expert method has a high level of subjectivity. The assessment of one expert may differ significantly from the assessment of another. So, the equipment owner does not often understand which estimation is more correct, what and when he (or she) should be done to prevent challenges. 3.2. Diagnostic systems Now, most of the large hydraulic units (25MW and more) are to be completed by stationary monitoring or diagnostic systems that gather and analyze information from the sensors mounted at rotating and non-rotating parts. Diagnostic techniques have been developed and refined over the years. Modern systems usually contain from 50 to 250 sensors most of them are responsible for measuring vibration parameters. There are many regulating documents that describe diagnostic techniques, data interpretation, measurement, and evaluation of hydraulic machine vibration. You can find a detailed description in the Andritz Hydro booklet (2015), Standards ISO 13373-7:2017, ISO 20816 5:2018, ISO 19283:2020, and paper Valentín et al. (2019). The main aim of such systems is to detect, identify, and evaluate the symptoms of potential failures at the early stage. However, there are many situations when these systems do not allow identifying the hazardous cracks in the main hydraulic turbine components such as runner, mechanism of turning blades, fasteners, and even shaft.

T – operating time T 0 – end of the run-in period Т (1) , Т (2) , …, Т (n-1) , Т (n) – repair data T d – design lifetime T i – individual lifetime

Fig. 1. Relationship between reliability and operating cost HT at the real operation at HPP