GALVANIC CORROSION OF RUBBER LINED SERVICE WATER PIPES ADJACENT TO TITANIUM HEAT EXCHANGERS

摘要

In 2010 Koeberg Nuclear Power Station successively shut down both operating units in order to conduct repairs to the essential service water system (ESWS). After the discovery of a through wall leak on one of the rubber lined pipes, ultrasonic wall thickness measurements were taken prior to the shut down of the units. Several other locations of wall thinning were reported, and the corrosion rate of the carbon steel was significantly greater than the general corrosion rate expected in flowing seawater. Evidence indicated that the corrosion rate was being accelerated through the galvanic coupling of the titanium heat exchanger plates with the carbon steel pipes at locations where the rubber lining failure had exposed the base material. Polarisation scans of representative material indicated that it is possible to accelerate the corrosion rate of carbon steel by almost two orders of magnitude provided there is a large enough cathode to anode surface area ratio. While the primary cause of the loss of ESWS integrity was the failure of the rubber lining, the subsequent accelerated galvanic corrosion resulted in premature through wall leaks. Therefore it was considered prudent to electrically isolate the heat exchanger from the pipes, thereby protecting the system through defence in depth.