Ngati Tuwharetoa Geothermal Assets Ltd Reboiler Plant Water/steam Chemistry Improvements to Resolve Ongoing Corrosion Issues and Prevent Future Tube Failures

Abstract

The Ngati Tuwharetoa Geothermal Assets Ltd (NTGA) Kawerau reboiler plant has suffered from major corrosion and plant failure issues since commissioning, including the premature complete replacement of the tube bundles. These corrosion related failures have occurred due to water/steam chemistry issues and interactions with plant materials not being fully considered and understood in the design process of the plant.
In 2018 a major root cause analysis was undertaken into the failures that included a detailed chemical and metallurgical investigation and successfully identified the failure mechanisms. A number of simple chemical treatment changes, including hydrogen sulfide neutralization, pH correction and the application of corrosion inhibiting film forming substances (FFS), were carried out to successfully mitigate ongoing corrosion of the plant and to significantly extend asset life.