Material characteristics and its performance measures in turbine: A review

• Main Authors: Sathish, K., Nithyanandhan, T., Ravishankar, P., Rohith, S., Malathi, L. Krishna
• Format: Conference Proceeding
• Language: English
• Subjects: Alloying elements; Base metal; Corrosion; Corrosion mechanisms; Corrosion potential; Corrosion resistance; Corrosion resistant alloys; Corrosion resistant steels; Corrosion tests; Crack propagation; Fatigue tests; Ferrite; Ferritic stainless steel; Ferritic stainless steels; Galvanic corrosion; Marine environment; Metal fatigue; Nondestructive testing; Pitting (corrosion); Propagation modes; Scale (corrosion); Sediments; Soil erosion; Structural steels; Titanium; Titanium base alloys; Titanium dioxide; Turbines; Ultrasonic testing; Welded joints
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0235912

This paper analyzes the reaction turbines such as the Kaplan and Francis turbines. The metals present in it are the major elements of stainless steel which make the turbine corrosion resistant and the other elements are bronze alloys and a small amount of titanium. Francis turbines are widely used for hydropower plants, catering to both small and large-scale operations. However, they face erosion issues, especially in sediment-laden water, impacting performance and turbine breakdown. This study utilized the Grant model to predict sediment erosion in Francis turbine runners under various conditions. Erosion near the outlet side increased linearly with the sediment inflow rate, irrespective of operating conditions. An experimental examination was carried out in the recent revival of a Kaplan turbine utilizing structural steel St 3 (GOST standard). Both the base metal and the welded joints were subjected to mechanical property testing and non-destructive techniques (NDT). Ultrasonic testing (UT) identified problems such as lamellar ripping in the base metal and lack of penetration in the weld metal. Tensile tests revealed less base metal contraction, which is consistent with lamellar tearing. For St 3 steel, the fatigue crack threshold was lower than anticipated, and the rate of crack propagation was noticeably higher. Numerical examination of the turbine covers in several operating modes showed that structural integrity is maintained despite these difficulties. In our field investigation, ferritic stainless steels used in marine environments exhibited susceptibility to pitting corrosion. It is well known that alloying, especially with titanium, can improve resistance to pitting corrosion and change the passive film on the surface. There is disagreement though, over how titanium addition affects ferritic stainless steel's passive film and overall resistance to pitting corrosion. This study addressed these uncertainties through microstructure and corrosion properties analyses. The findings indicate a nearly linear increase in pitting potential with titanium addition. Titanium contributes to TiO2 formation in the passive film, reducing defect density. Titanium also causes the leaves phase to precipitate, which promotes micro-galvanic corrosion. The ferrite phase next to the leaves phase is where pitting corrosion in titanium-alloyed ferritic stainless steels mainly happens. The study demonstrates how titanium affects pitting corrosion, with a focus on micro-gal