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On The Performance Of UNS S32100 vs N08825 Expansion Compensator Materials In Geothermal Applications

Geothermal fluid pipelines experience temperature changes on startup and shutdown that can be of the order 300 °C. Carbon steel pipeline design can include expansion loops and direction changes to allow for thermal expansion and contraction for the long lengths of pipeline commonly used from geothermal production wells to the geothermal power station and from the station to reinjection wells. In some instances, expansion compensators are used where there is insufficient area for such loops or where the pipe diameter is prohibitively large.

Product Number: 51322-17790-SG
Author: Keith Lichti, Soroor Ghaziof
Publication Date: 2022
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Stressed bellows compensators heated by the transmission of two-phase geothermal fluid were exposed to atmospheric contaminants to simulate worst case external conditions. The tests aimed to determine time to failure under increasing severity of the external environment. Failure was not observed in the time period of the tests while the bellows were operated at temperatures above 150 °C regardless of the external contaminants. Cycling from high (105 °C achieved by steam heating internally) temperature to low (ambient) temperature gave accelerated damage mechanisms and failure from the external surfaces of both materials in a similar time period through pitting and Chloride SCC of the S32100 material and pitting of the N08825 material. Internal corrosion was also observed and attributed to the ambient standby conditions with no steam flow and the presence of weld spatter.

Stressed bellows compensators heated by the transmission of two-phase geothermal fluid were exposed to atmospheric contaminants to simulate worst case external conditions. The tests aimed to determine time to failure under increasing severity of the external environment. Failure was not observed in the time period of the tests while the bellows were operated at temperatures above 150 °C regardless of the external contaminants. Cycling from high (105 °C achieved by steam heating internally) temperature to low (ambient) temperature gave accelerated damage mechanisms and failure from the external surfaces of both materials in a similar time period through pitting and Chloride SCC of the S32100 material and pitting of the N08825 material. Internal corrosion was also observed and attributed to the ambient standby conditions with no steam flow and the presence of weld spatter.

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