Corrosion testing of heat exchanger tubes in steam from the IDDP-1 exploratory geothermal well in Krafla, Iceland

The IDDP-1 well in the Krafla geothermal field in Iceland is the first well in the Icelandic deep drilling project. The superheated steam from the well is extremely hot (450°C) with a 120 bar pressure at the wellhead. The IDDP-1 steam contains acid gas and is highly corrosive when it condenses. A test unit with eight different material types of heat exchanger tubes was set up in order to investigate the possibility of using the IDDP-1 steam directly for heat exchangers without prior removal of silica, sulfur and acid gases. The tube materials were three types of stainless steel, two titanium alloys, and two nickel alloys. In addition one carbon steel tube was added as a reference. The inlet temperature and pressure were 330-350°C and 52-62 bar. The steam condensed in the tubes with an outlet temperature of about 270°C. Severe problems were encountered in the use of steam traps at the outlet end of the tubes due to clogging of silica and they had to be replaced with orifice plates. This paper reports the results from the testing and inspection of the pipes including visual inspection, and microstructural and chemical composition analysis with SEM with XEDS.