Corrosion pitting at ellis and whillock stations

摘要

Arkansas Electric Cooperative Corporation's (AECC's) Clyde T. Ellis Hydroelectric Generating Station is a three unit, low head plant located on the Arkansas River near Fort Smith, Arkansas which was placed into service in late 1988. AECC's Whillock Hydroelectric Generating Station is an identical plant, also located on the Arkansas River near Morrilton, Arkansas which want into service in 1993. Both plants utilize Voest Alpine pit-type Kaplan turbines, 5.8 meter runner diameter, rated at 10.8 MW each. Each plant is unmanned, operated as run-of-river and averages about 30percent of the time off line due to either low head or inadequate flow. When the first unit at Ellis was dewatered in early 1990 for a warranty inspection, a large number of small pits were discovered on the stainless steel discharge ring and runner blades. Similar pitting was found on the other two Ellis units as they were inspected and on all three units at Whillock. This paper discusses AECC's investigation into the cause or causes of the pitting, examines procedures used in repairing the damage, and reviews attempts to prevent the damage from recurring through the installation of cathodic protection systems.