Materials used in high temperature geothermal wells can be subjected to corrosion due to the corrosion aggressiveness of the geothermal fluid that contains dissolved gases such as H2S and CO2 and in some cases even HCl. During monitoring and discharge testing of a new high temperature geothermal well in the Krafla geothermal area in Iceland it was discovered that the carbon steel liner in the bottom of the well was fractured and severely corroded. Parts of the steel liner were retrieved from the well to investigate the cause of failure. Examination of the parts from the steel liner and tensile testing of the material was performed. The inspection revealed that the liner was severely corroded and parts of it situated on 1600 m depth had experienced environmentally assisted cracking in the form of hydrogen embrittlement. The results from the examination and testing are revealed here and discussed.
Materials used in high temperature geothermal wells can be subjected to corrosion due to the corrosion aggressiveness of the geothermal fluid. The principal corrosive agents in geothermal fluid are the dissolved gasses hydrogen sulfide (H2S) and carbon dioxide (CO2), and chloride ions (Cl-). The source of Cl- in geothermal steam can either be from volatile chloride transported as HCl (volcanic gas) or from salt brine in geothermal areas close to the sea.1,2 The gaseous HCl and its acidic condensate are very corrosive but HCl gas is not very common in geothermal systems. Other corrosive components can be present in the geothermal fluids such as dissolved hydrogen (H2), nitrogen (N2), ammonium (NH3) and methane (CH4) gases and sulfate ions (SO4-2). Corrosion in geothermal equipment and wells is also dependent on the key parameters such as temperature, pressure and flow rate and the physical characteristic of the liquid such as pH level.3-4
