# Capability of Advanced Ultrasonic Inspection Technologies for Hydraulic Turbine Runners
###### Abstract  
This paper presents the results of a project aimed at evaluating the performance of ultrasonic techniques for detecting flaws in Francis turbine runners. This work is the first phase of a more ambitious program aimed at improving the reliability of inspection of critical areas in turbine runners. Francis runners may be utilized to supply power during peak periods, which means that they experience additional load stress associated with start and stop sequences. Inspection during manufacturing is then of paramount importance to remove as much as feasible all flaw initiation sites before the heat treatment. This phase one objective is to collect initial data on a simplified mock-up and then to compare the experimental ultrasonic data with the results of simulations performed by CIVA, a computer simulation package. The area of interest is the region with the highest stress between the blade and the web. A welded T-joint coupon made of UNS S41500 was manufactured to represent this high-stress area. During the FCAW welding process, ceramic beads were embedded in the weld to create discontinuities whose size is in the critical range to initiate a crack. Inspection of the material was carried out by various nondestructive testing (NDT) methods namely conventional pulse-echo, phased array, total focusing method (TFM). With these results, detection rates were obtained in order to compare the effectiveness of each method. nondestructive testing; defect detection; ultrasonic testing; phased-array ultrasonic testing; detection of rate; hydroelectric turbine runner +
Footnote †: journal: Medical  
NDT is the development and application of technical methods to examine materials or components such that the pieces are not destroyed and their future usefulness and serviceability remain [5]. There is a wide range of NDT methods based on the physical principles of electromagnetic radiation, sound, and other inherent properties of the materials. The techniques selected should consider safety, economic, efficiency, and time factors [6]. Ultrasonic testing (UT) is a suitable method for detecting and sizing flaws embedded within or growing from inaccessible surfaces. Ultrasonic waves can propagate through thick solid parts [7]. Therefore, UT is suitable for flaws far beneath the inspection surface, unlike methods that can only detect defects on, or very close to, the inspection surface, e.g., Eddy current testing or methods that detect flaws connected to the inspection surface, such as visual methods and penetrant testing [8]. When defect assessment calculations require a value for how deep the defect has grown, ultrasonic testing is the primary desired method. It is used to detect various types of flaws, such as cracks and inclusions in a wide range of materials, compared to magnetic particle testing methods, which require the component to be ferromagnetic. Ultrasonic waves are inherently safe compared to radiography methods, which use ionizing radiation and thus require multiple protection types [9; 10]. The basic NDT methods, such as visual testing (VT), ultrasonic testing (UT), penetrant testing (PT), and radiography (RT), are usually used to inspect hydraulic turbine runners. However, there are difficulties involved in detecting internal flaws in complex geometries, such as the runner's weld joints. Thus, hydraulic turbine runners are generally inspected using different ultrasonic inspection methods [2; 3; 11; 12; 13; 14]. Few studies have been performed on the inspection of hydraulic turbine runners with ultrasonic phased array. However, the published studies did not focus on the high-stress area, used artificial flaws embedded in a weld mockup, and did not consider the material's properties [11; 12; 13]. [PERSON] et al. [3; 15] worked on the capability of different NDT methods and the effect of microstructure on the acoustic properties of steel grades widely used for the manufacturing of hydroelectric turbine runners. These studies concluded that phased array is a very effective technique.