The effect of salt composition on the chlorine corrosion of low alloy steels

Martti Mäkipää, Th. Malkow, D. Baxter

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

Material wastage of superheater tubes made of low alloy steels is greatly accelerated under normal operating conditions if alkali chlorides are stable in the deposits. The effect of salt composition on the corrosion behavior especially that of the alkali cation, Na or K was investigated using crucible tests in a thermobalance under a flowing N2-O2-CO2-atmosphere, followed by SEM/EDS analyses and thermodynamic calculations. For both salts, rapid corrosion occurred due to the known mechanism of active oxidation. In the case of sodium chloride, a major part of the metal loss was caused by volatilization of metal chlorides even at temperatures as low as 480 °C, while in the case of potassium chloride, enhanced oxide growth almost conclusively determined the corrosion rates. Further, no evidence of significant iron or potassium evaporation was found up to a temperature of 530 °C. The different behavior of the steels when exposed to the two alkali chlorides has been explained by the difference in the thermodynamic stability of the corresponding alkali ferrites. However, the difference in the thermodynamic stability and volatility of the complex chlorides of these alkali metals and iron or various other transition metals present as alloying elements in these steels may also be important. Moreover, applying temperature cycles typical for superheater tubes in boilers enhanced the metal loss rate compared to isothermal exposures. Also, temperature cycling affects the corrosion scale morphology.
Original languageEnglish
Title of host publicationCORROSION 2001
PublisherNational Association of Corrosion Engineers (NACE)
Number of pages14
Publication statusPublished - 2001
MoE publication typeA4 Article in a conference publication
EventNACE International Annual Conference and Exposition, Corrosion 2001 - George R. Brown Convention Center, Houston, United States
Duration: 11 Mar 200116 Mar 2001

Publication series

SeriesNACE - International Corrosion Conference Series
Volume2001
ISSN0361-4409

Conference

ConferenceNACE International Annual Conference and Exposition, Corrosion 2001
Abbreviated titleCorrosion 2001
Country/TerritoryUnited States
CityHouston
Period11/03/0116/03/01

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