Online monitoring of corrosion in slightly saline geothermal water in Iceland

Online monitoring of corrosion is a valuable tool for heating systems to minimize risk of damage due to steel corrosion. Monitoring with weight loss coupons has the limitation that it takes a while to recognize the problem and a great damage may have already happened. A cost effective device for online monitoring, not relying on electricity or telecommunication at the production site is of great value in small heating systems or at a drill sites before harnessing. The current project, aimed at development and testing of such a device, was conducted at a well site under testing. By drilling near the farm site Keldunes in rural NE Iceland in 2006, a low temperature geothermal field was verified. The production water has a temperature of approximately 76°C. The water is slightly saline, 1-2 ‰, depending on relative mixture of the different aquifers in the well. The origin of the water is mixed, partly derived from geothermal effluent water from the Krafla high temperature geothermal field further inland and partly of more local origin. Production testing of the well revealed severe calcite scaling. Scaling tests, performed over an extended period indicated some ongoing steel corrosion but appeared negligible. Since a production testing a corrosion test has run for a six month period, both with traditional weight loss coupons and also by online monitoring with differential ER equipment from MetriCorr. The data logger was powered by solar cells connected to batteries with the data being retrieved through a mobile phone connected to the data collection system. The operation of the system went very well in spite of harsh conditions. Even though the corrosion rate was low, it showed distinct changes by lowered wellhead pressure and infinitesmal air inflow. The device proved to be a useful and cost effective tool to monitor possible changes in corrosion conditions easily assembled and operated at remote sites outside the electric grid. There are many small heating systems where such a device would be of great use and may even prevent damage due to corrosion.