Reliability assessment of non-destructive testing (NDT) for the inspection of weld joints in the hydroelectric turbine industry

Due to the importance of energy production, it is critical to reduce unnecessary or unpredicted power generation equipment outages. As a major power generation company, Hydro-Québec uses models to estimate the service life of turbine runners in order to avoid such outages. The influential inputs for these models include the characteristics of flaws present in the runners. Since Non-destructive testing (NDT) methods are used to detect and characterize these flaws, this study aims to evaluate the reliability of NDT methods for inspection of weld joints in hydraulic turbine runners. Conventional ultrasonic testing (UT), radiography testing (RT), phased array ultrasonic testing (PAUT), and PAUT using total focusing method (TFM) were compared. The NDT tests were conducted on a T-joint specimen manufactured with embedded flaws. This specimen was used to determine the probability of detection (POD) curves for volumetric flaw sizes. The results showed that array technology, PAUT or TFM, has demonstrated a detection capability (a90) around 2.5 mm, which is similar to the commonly used equivalent critical flaw size for such structure.