January 2018

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Reliability: Dry gas sealing technology replaces segmented carbon rings in small steam turbines

Since the late 1800s, small steam turbines have incorporated bushing-type, single-piece and/or segmented carbon gland components to reduce and prevent steam leakage along the shaft.

Bloch, Heinz P., Hydrocarbon Processing Staff

Since the late 1800s, small steam turbines have incorporated bushing-type, single-piece and/or segmented carbon gland components to reduce and prevent steam leakage along the shaft. True leakage prevention has never been achieved because turbine shafts are made from steel, and the steel’s coefficient of thermal expansion differs from that of carbon. A small amount of steam rushes through seemingly insignificant gaps at sonic velocity—an erosive effect known as “steam cutting” that causes the gap to widen. Physics, thermodynamics and hydraulics combine to explain the interacting processes. Since superheated steam at 500°F/260°C is cooler than the 740°F/400°C hydrocarbon liquid transported in

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