Design and Manufacture of a Very Large Hot-Gas Expander Impeller in Alloy 718 for Highly Corrosive Off-Gas

Abstract

This paper focuses on metallurgical issues and manufacturing of impellers for an integrally geared 2-stage expander for a corrosive hot-gas application. The design employs the largest single piece forging in Alloy 718 material for use in the low pressure stage impeller. Alloy 718 was chosen due to the combination of best corrosion resistance and mechanical properties. With this single piece forging it is possible to manufacture very large impellers in a "non-welddesign". Information about development of the disc production, the manufacturing process and mechanical properties are presented.