Corrosion testing in H₂S abatement system at hellisheidi geothermal power plant in Iceland

Geothermal power plants are considered to be environmentally attractive because with them renewable energy source can be utilized. But geothermal steam contains non-condensable gases (NCG) such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) which may cause environmental, safety and health problems if they are not disposed correctly. H₂S emission from power plants in Iceland has now become a problem due to new stricter legislation in Iceland regarding air quality. Recently Icelandic power companies started re-injecting H₂S and CO₂ back into the ground in a research project called SulFix to decrease H₂S emission from Icelandic geothermal power plants. The gases are dissolved in condensate at 25°C and 5 bars in a newly constructed H₂S abatement system, air-cleaning station, at Hellisheioi geothermal power plant in Iceland. In this study the corrosion behavior UNS S31603, chosen for the absorption tower in the H₂S cleaning process, was investigated as well as other materials for comparison. Corrosion experiments were done over two time periods, 4 weeks and 12 weeks. The specimens were installed into the absorption tower where the H₂S and CO₂ gases were separated from other NCG and dissolved in condensate. The susceptibility to stress corrosion cracking (SCC) of the stainless steel UNS S31603 was investigated and corrosion rates were calculated for the carbon steel S235, and the stainless steels UNS S31603 and UNS S31803 for the two time periods. The results showed that the material selection for the absorption tower seems to be sufficient; UNS S31603 showed no signs of corrosion damage. The UNS S31803 duplex stainless steel was also not effected by corrosion during the testing. On the other hand, the carbon steel S235 was severely damaged by hydrogen induced cracking (HIC) and high corrosion rate, well above the acceptable limit of 0.1 mm/year.