CAVITATION AND CRACKING OF TURBINE RUNNERS

Abstract

Cavitation causes pitting which leads to loss of material and may even lead to cracking : Cracking can also occur due to metal fatigue; vibration; part gate operation or wide head variations: Ways and means of avoiding cavitation and cracking in a specific case can be ascertained by detailed analysis, experimental and trial and error, and this varies from power house to power house. However, a few general methods can be evolved as preventive measures. These include selec- tion of runner material, setting of turbine, design, manu- facture and operation and finally annual maintenance and tests to be carried out on turbine turnners. Case histories of cavitation and cracking in four power houses in India, two in Himachal Pradesh and two in Kerala have been studied along with the rcrnedial measures adopted there. Flow aera- tion, runner blade modifications, runner cone extension, grinding to sound metal and repair welding have proved to be good remedial measures against cavitation and cracking. Governor timing and operating the turbines at or near about full load also help in resisting cavitation and cracking of turbine runners...