Innovative Design in Expander Wheel-Shaft Attachment Replaces Hirth Coupling for High Speed, High Temperature and High Power Applications

Abstract

Although this Case Study is focused on an Expander-Generator unit in a geothermal application, it’s findings can be used in all turbomachinery applications where other conventional shaft-wheel attachments are causing problems. This solution is a notable alternative to the Hirth coupling design for high power, high speed and high temperature applications. • An Expander-Generator unit for a geothermal power plant application experienced ongoing failures during a 10-year period. The longest run cycle for the machine was 18 months yet with less than 10 MW power production. The average time between failures was less than six months and with each failure; the wheel was completely damaged and separated from the shaft. A complete metallurgical study on previous failures showed the Hirth coupling attachment was the first to fail in all cases.