A Fluid Flow Test Rig has been designed and commissioned to simulate corrosion occurring in geothermal steam pipelines. The test rig was used to evaluate the effectiveness of a variety of corrosion monitoring techniques for application to full-scale pipelines. Although unsuccessful, the thin layer activation method, which is based on the conversion of Fe to Co-56 upon irradiation with high-energy protons, showed potential for application to geothermal systems. Corrosion rates measured in the test facility were similar to those estimated for the Ohaaki (New Zealand) steam pipelines after three years of service.