The Condition Assessment Of In-Service Vanes Of Gas Turbine Nozzle Unit With Help Of Digital Analysis Of Vane Surface

The paper presents the methodology of condition assessment of in-service vanes of gas turbine nozzle unit with help of digital processing and analysis of vane surface. Included are 3D distribution graphs of basic RGB component colours (red, green and blue) for vane surface images registered with a digital camera (lab conditions) and with two types of commonly used videoscopes (working conditions). The graphs are coupled with results of examination of vane material. Considered were also both alteration of protective coating and core microstructure. The examinations were realised on metallographic sections with help of a SEM. The core microstructure was analysed mainly from the standpoint of modification of reinforcing phase gamma and alteration of phase gamma and carbides. Size and distribution of phase gamma particles determines creep resistance properties (material criterion as the assessment criterion of vane condition). The analysis of images of gas turbine nozzle guide vane surface consists in counting of overheating area in relation to non-overheated area – the ratio is expressed in percentage terms (the criterion – the colour of the surface of a vane considered serviceable in relation to other distributions of colours on surfaces of vanes of different degree of overheating). The proposed approach is aimed at assessment of degree of overheating by reference to discolouration of vane surfaces after certain operational period.