Alkali Induced High Temperature Corrosion of Stainless Steel: The Influence of NaCl, KCl and CaCl2

• Published in: Oxidation of metals Vol. 78; no. 1-2; pp. 83 - 102
• Main Authors: Karlsson, S., Pettersson, J., Johansson, L. -G., Svensson, J. -E.
• Format: Journal Article
• Language: English
• Published: New York Springer-Verlag 01-08-2012; Springer
• Subjects: 304l; 600-degrees-c; Alkali; Applied sciences; Breakaway corrosion; Chemistry and Materials Science; Chromate; chromium; Corrosion; Corrosion and Coatings; Corrosion environments; environment; Exact sciences and technology; fired cfb boiler; Inorganic Chemistry; Materials Science; Metallic Materials; Metals. Metallurgy; Original Paper; Oxidation; oxide hydroxide evaporation; potassium; sulfur; Tribology; water-vapor; Alkali; Breakaway corrosion; Chromate; 304L; Oxidation; Austenitic stainless steel; Temperature; High temperature; Sodium chloride; Potassium chloride; Chromates; Stainless steel; Stainless steel-304L; High temperature corrosion
• ISSN: 0030-770X; 1573-4889; 1573-4889
• DOI: 10.1007/s11085-012-9293-7

The influence of KCl, NaCl and CaCl
2
on the oxidation of 304-type (Fe18Cr10Ni) stainless steel at 600 °C in 5 %O
2
 + 40 %H
2
O was investigated. Prior to exposure, a small amount of the preferred salt (cation equivalent: 1.35 μmol/cm
2
) was deposited on the samples. Exposure time was 1–168 h. The oxidized samples were analyzed by SEM/EDX, XRD, FIB and IC. The presence of KCl and NaCl strongly accelerates high temperature corrosion of 304L. Corrosion attack is initiated by the formation of alkali chromate through the reaction of alkali with the protective oxide. Chromate formation is a sink for chromium in the oxide and leads to a loss of its protective properties. Subsequently a rapidly growing scale forms, consisting of an outer hematite layer with chromate particles on top and an inner spinel oxide layer. In contrast to NaCl and KCl, CaCl
2
is not very corrosive. At temperature, CaCl
2
is rapidly converted to CaO. Small amounts of CaCrO
4
form where CaO is in direct contact with the scale. CaO also reacts with the scale to form Ca
2
Fe
2
O
5
.