PSI - Issue 13

Marko Katinić et al. / Procedia Structural Integrity 13 (2018) 2040 – 2047 Author name / Structural Integrity Procedia 00 (2018) 000–000

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By analysing the steam expansion h-s diagram of this turbine, Fig.5, it was found that the 5 th rotor wheel is located in the phase transition zone (salt zone). It is well known that different salts from steam are deposited on the rotor blades in this zone, being corrosive and leading to corrosion of the blade material. Chloride deposits have a particularly role in corrosion of the rotor blade. They already in small quantities significantly reduce the fatigue strength of the material. Fig. 3 and 4 show that there are traces of corrosion products, particularly in the area of the blade roots. The chemical analysis of the corrosion deposit showed the presence of different kind of elements, but also of chlorides. 3.2. Analysis of Campbell diagram and Goodman diagram Typical mode shapes of the moving blade packs are shown in Fig. 6. The Campbell diagram for the moving blades of the 5 th rotor wheel is given in Fig. 7, indicating natural frequencies as function of rotational speed. It can be seen that there is interference between the one time nozzle passing (NPF) excitation and the 2 nd tangential mode of vibration.

Fig. 6 Typical mode shapes of the moving blade packs - Petrokemija d.d. (2009)

Fig. 7 Campbell diagram for the 5 th rotor wheel blades - Petrokemija d.d. (2009)