Accelerated Fatigue Phenomena in High-Horsepower Turboexpander Wheels

Abstract

Radial expansion turbines or "turboe~..panders" are widely used in the gas industry in both process and power recovery applications. The increasing cost of plant inputs such as power and feedstocks, coupled with abrupt swings in plant throughput as a function of markets and pipeline system Iinepack, places a premium on turboexpander designs capable of operating efficiently and reliably over a broad range of operating conditions. High horsepower turboexpander wheels which operate over a wide speed band are subject to fatigue failures if the wheel's operating frequency window is too narrow. The fatigue failure mechanism is accelerated by resonance. Appropriate wheel designs, which will deliver extended operating life, may require modified wheel hub profiles and the use of higher strength alloys. Strict control of forging and heat treatments must be maintained to ensure metallurgy of a uniform high quality.This case study outlines the systematic methods adopted in identifying the cause of turboexpander wheel failures at the Karr Creek Gas Plant, and the engineering design revisions required to eliminate them.2. Standard Specification for Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings.