Confirming plant integrity by specialised NDE inspections

Abstract

The UK power industry is going through a difficult period, trying to balance the demand for electricity with conforming to the new environmental regulations. Because of overcapacity, it is no longer an attractive proposition to build new power stations but, instead, it makes economic sense to keep older power stations running beyond their design life. Structural integrity is increasingly demanding greater accuracy and repeatability from NDE inspections; new equipment and technology has been developed predominantly based on ultrasonic and eddy current technology. The development of information technology has been crucial for the improvement of ultrasonic imaging techniques. Advanced specialist inspections including phased array, time-of-flight diffraction and advanced eddy current, have been developed for evaluation of steam pipework, generator end-rings, steam chests, blade roots, rotor bore and rotor discs and many other plant items. The latest phased array techniques bring considerable benefits to the inspection of complex geometries. Ultrasonic inspections on components with complex geometries can give rise to confusing signal patterns which influence the speed and integrity of inspections. Additionally, access restrictions often limit probe movement, further affecting test integrity. The development and utilisation of phased array ultrasonic hardware and analysis software, has enabled high-integrity high-speed scanning and imaging of complex components. 'Sweep Scanning' can be carried out from a static position allowing coverage where access is restricted; the data can then be stored for future interrogation if required. The phased array probe contains multiple elements, and scanning can be mechanical (probe movement), electronic (pulsed beam sweep), or a combination of both. Component drawings and geometries can be overlaid on the phased array images, enabling both inspection design and ease of analysis. Advantages are gained through scanning complex geometries quickly with high integrity. Focusing of the optimal inspection angle gives improved defect detection and electronic data storage enables an auditable inspection fingerprint. This paper concentrates on three main applications: phased array and time-of-flight diffraction applications, rotor bore applications and generator retaining ring (end-ring) applications.