Cryogenic Pump Survival - Liquid Oxygen Service


A manufacturer of cryogenic 2-stage overhung pumps needed a non-galling bearing material that could survive shaft contact, be oxygen compatible and perform in cryogenic temperatures. 

The manufacturer’s 2-stage, cryogenic pumps are used in the liquid gas industry. These units operate at up to 8000 rpm and can pump liquid oxygen at a temperature of minus 320°F (-195°C). The 2-stage design is required to meet the design point of 70 gpm of flow and 1,020 ft. of total differential head.

Due to the shaft length required for the 2-stage pump, shaft deflection leads to a number of issues including contact, rubbing and excessive wear. A tighter fitting bushing can add support to the shaft and can be mounted between the two impellers in the diffuser.

This solution required a material with the properties to withstand the loading and contact with minimal wear. In addition, the material had to be oxygen compatible and reliably perform within cryogenic temperature ranges. The pump manufacturer contacted Graphite Metallizing Corporation and a GRAPHALLOY nickel-grade bushing was recommended. GRAPHALLOY materials are non-galling and self-lubricating which allows for tighter clearances and improved pump efficiency.  

The diffuser and inter-stage sleeve were re-designed in order to incorporate the GRAPHALLOY nickel-grade bushing.  The bushing was press-fit into the diffuser and the inter-stage sleeve material was changed per Graphite Metallizing’s recommendation.

A test pump was assembled, tested, torn down and examined in order to verify that the GRAPHALLOY bushings would work. After several successful tests, production units were fabricated, built and shipped to the end customer.

After nearly six years, the original production units as well as several new units are running smoothly. The GRAPHALLOY bushings increased the service life of these pumps.

GRAPHALLOY bearings for CO2 Pumps