Rapid Blade Pit Analysis by Blue Light Scanning

Abstract Compressor blades of gas turbines operating in aggressive and harsh environments are often subject to a higher level of erosion and corrosion than others. This type of environment often leads to the formation of blade pits which are the main root cause of crack initiation and growth in compressor blades leading to engine performance reduction and component life reduction. As a result, pit analysis is an important investigation to conduct to understand the extent of pitting, its roots and its potential for further component degradation. Pit analysis is usually performed using metallographic replicas that are analyzed by microscopes. We share in this paper our experience with a faster method of pit analysis using Blue Light Scanning (BLS) that allows the investigation to be done locally and rapidly without having to send the blade to a laboratory. BLS is a maturing optical gas turbine part inspection method that focuses on high accuracy geometrical characterization of deformation and defects. It has been gaining popularity in parts repair with leading OEMs of Gas/Steam turbines. We present in this paper our experience using mobile non-contact and non-destructive BLS for pit analysis in comparison to traditional microscopy based on destructive testing at the laboratory. The advantage of the BLS technique includes non-destructive approach, portability, speed, and appropriate precision level in comparison with conventional methods. The results show very promising potential for BLS especially for rapid on-site pit analysis.