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Communication Feature | January 2015

Coating technology for underwater parts

Hydro-abrasive erosion in turbine components of hydropower plants is a problem especially in young geological mountains, in which the rivers have a high concentration of hard particles. In Asia the problem is especially large in hydropower plants situated in the Himalayan region due to very high particle content. During the monsoon season the particle content can increase from 50mg/l to over 10,000mg/l in a very short time and also large particles above 1mm can then be suspended in the water. The resulting erosion can reduce the overall revenue over 10 per cent for the power plant due to reduction of the efficiency, high repairing cost and downtime.

To reduce these erosion damages significantly ANDRITZ HYDRO started in the early eighties to carry out an extensive research process. Since 1986, components have been coated, first with chromium oxide plasma sprayed coatings, which was replaced in 1996 with the development of a premium tungsten carbide coating (SXH70) deposited by the HVOF technology (high-velocity-oxy-fuel).

SXH70 offers a much higher resistance to abrasive wear and is much less sensitive to particle impact. Since 2009 SXH7X-coating for Pelton runner with a higher resistance of the splitter and cut-out was developed. In 2012 further developments have yielded a premium quality coating designated as SXH80 and SXH8X for pelton runners with 20 per cent more erosion resistance.

While in the beginning the coated parts for the Himalaya region came from ANDRITZ HYDRO, Switzerland, the success was so great that the decision was taken in 2008 to start a coating workshop in the ANDRITZ HYDRO manufacturing plant at Prithla, near Delhi. Due to this, the coating workshop is well supported by machining, welding and grinding facility with highly trained staff.

The coating workshop has the newest state-of-the-art technology from the coating technology side and a robot so that all parts can be coated with highest quality. In close collaboration with the Research & Development Centre of Coating in ANDRITZ HYDRO also further developments are made and implemented. The coating plant which is operational since 2009 has been expanded further in 2012 with a newly-commissioned MULTICOAT equipment from SULZER METCO in addition to the existing one. The coating shop has coated up till now guide vanes (500 nos.), pelton runners (3 nos.) Liner face plate segments (200 nos.), wearing segments (100 nos.), needles (100 nos.) and seat rings (100 nos.) sealing rings (25 nos).

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