Trends in Ultrasonic Testing Requirements for Heavy Rotor Forgings Over the Past Decades

Heavy forged rotor components, such as those used in land-based turbines and generators for power generation, are inspected using ultrasonic testing, among other methods, prior to commissioning. These inspections were introduced several decades ago to ensure component integrity. Initially, only manual contact inspections were performed using longitudinal-wave probes in pulse-echo mode, initially without fixed recording or decision limits. The development of inspection capabilities, changes in design requirements, advances in fracture mechanics calculations, insights gained from rotor operation, experience with the inspection method, and considerations regarding probability of detection (PoD) have brought about the changes that define today’s standard inspection requirements: Following the introduction of the first sizing methods, recording and decision limits could be established. Angular and transmitter-receiver probes were introduced, and eventually, automated equipment became a requirement. All these changes made it possible to refine sizing techniques based on theoretical guidelines (such as AVG) and to introduce modern ultrasonic methods (such as array probes) on a global scale. This publication describes the evolution of ultrasonic inspection requirements over the past decades and provides an outlook on the future.