Parametric Study of Slurry-Erosion of Hydroturbine Steels with and without Detonation Gun Spray Coatings using Taguchi T
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RODUCTION
SLURRY erosion is the degradation caused by the impact of the solid particles entrained in a liquid on the surface of the components. Problems from slurry erosion have been observed in many industries such as mining, marine, offshore, utility, and hydropower plants.[1–7] Most of the fluid handling equipments and machines in these sectors face the problem of reduced life and malfunctioning because of the damage of either the contacting surface or/and the whole of the component. In hydroturbines, the sand particles mixed in the river water cause the erosion of turbine components. Furthermore, it could cause the change in the surface morphology of the components. The change in the surface pattern can also produce flow irregularities causing the initiation of the cavitation, which aggravates the problems. The synergistic effect of cavitation stressing on the abrasive action of solid particles may enhance erosion damage and complicate the erosion mechanism.[8] Furthermore, erosion is a complex phenomenon, HARPREET SINGH GREWAL, Research Scholar, and HARPREET SINGH, Assistant Professor, are with the Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India. Contact e-mail: [email protected] SANJEEV BHANDARI, Assistant Professor, is with the Department of Mechanical Engineering, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 140407, India. Manuscript submitted August 31, 2011. Article published online March 28, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
which involves several simultaneous and interacting process parameters.[9,10] Various hydroturbine components under the effect of the slurry erosion are runners, guide vanes, nozzles, needles, labyrinth seal, etc. It has been learned that the hydroturbines located in the Himalayan regions of Indian subcontinent are affected severely by slurry erosion because of the high content of sand particles in the flowing water have a hardness in excess of 7 mohs.[11–13] For instance, the Naptha Jhakri hydropower plant (1500 MW), located on river Sutlej is one of the largest power plant in India, faces the deleterious effects of slurry erosion from the sand particles.[14,15] According to the government reports, the Naptha Jhakri power plant suffered a loss of $77 million on account of the closure of the station pursuant to high silt levels in river Sutlej during the period 2003 to 2005. It is worthwhile to mention that the financial losses incurred from the replacement and maintenance of the slurryaffected parts is excluded from the estimate. The concentration of sand in the river Sutlej normally varies from few ppm to 12,000 ppm. During extreme events such as landslides, blockades, and flash floods, the concentration can be as high as 30,000 ppm, and in some cases, even it crosses 1,000,000 ppm (10 wt pct). To prevent the turbines from damage, the maximum limit for the plant has been limited to 5000 ppm. Whenever the concentration of sand in river Sutlej increases beyond this value, the plant is generally shut VOLUME 43A, SEPTEMBER 2012—3387
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