Abstract
Low-temperature geothermal water in Iceland generally has high pH, low conductivity, and is oxygen free, resulting in negligible corrosion. However, with ingress of oxygen, due to contamination of fresh water as an example, the corrosion rate can increase significantly. In order to establish methods of monitoring corrosion under these conditions, several corrosion monitoring methods were tested in two locations in Reykjavik, Iceland and one location in Keflavik, Iceland. It was found that electrochemical tests tended to overestimate the corrosion rate due to the slow polarization behavior of the system, while weight loss techniques required too long of an exposure to provide real-time information; although they gave reliable historical data on the corrosion that had accumulated over the previous three, six or twelve months’ time. A differential ER-probe proved to be the most promising measurement technique for these conditions. The analysis of the corrosion products using EDS and XRD further disproved the common notion that the low corrosion rate found in the geothermal water was due to the formation of a protective iron sulfide film. No iron sulfide film was detected, but with the ingress of oxygen, a thick magnetite film was detected. The low corrosion rate is therefore due to the favorable water chemistry, which leaves the carbon steel pipe surface vulnerable to corrosion if it is exposed to an oxidant.
