Are NaCl and KCl equally corrosive on superheater materials of steam boilers?

► Solid NaCl and KCl show severe corrosivity on superheater steels. ► Some differences in corrosion behaviour between the two salts were observed. ► Sanicro 28 exhibited more internal degradation during exposure to NaCl than to KCl. ► Oxide formed through vaporisation of chlorides at lower temperatures with NaCl. ► For practical applications both salts are equally corrosive. Alkali chlorides deposited on superheater tubes are known to cause corrosion in boilers burning biofuels and waste. The objective of this work was to compare the corrosivities of KCl and NaCl on commonly used superheater steels at typical superheater tube temperatures (400–650°C). Two austenitic stainless steels and one low alloy steel were tested under laboratory conditions in air. The results show some differences between the two salts in terms of corrosion behaviour and internal degradation. However, for practical applications, the two chlorides are equally corrosive on the tested steels under the experimental conditions considered.