Corrosion Science, Vol. 18, pp. 499 to 501 0010-938X/78/0501--0499$02.0010 © Pergamon Press Ltd. 1978. Printed in Great Britain SHORT COMMUNICATION CORROSION OF CARBON STEEL DURING CYCLICAL EXPOSURE TO WET ELEMENTAL SULPHUR AND THE ATMOSPHERE* DIGBY D. MACDONALD,'[" BRUCE ROBERTS and JAMES B. HYNE Alberta Sulphur Research Ltd., Department of Chemistry, University of Calgary, Calgary, Alberta, Canada Abstract--The corrosion of carbon steel during cyclical exposure to wet elemental sulphur (four days) and the atmosphere (six days) has been investigated. The integral corrosion rate is found to decrease with successive cycles, thereby demonstrating that oxidation of the sulphide film confers protection to the underlying steel. INTRODUCTION IN A previous paper x the results of a study of the corrosion of carbon steel in wet elemental sulphur systems were reported. This work was performed as part of a program to investigate corrosion phenomena in sulphur/iron/water systems. Briefly, it was found that catastrophic (autocatalytic) corrosion occurs under both aerobic and anaerobic conditions at a critical pH in weakly acidic systems. Since elemental sulphur/water systems are known to become acidic spontaneously, par- ticularly when subjected to UV radiation, 2 the possibility of severe corrosion of carbon steel con- tainment vessels is clear. However, many such systems, and in particular those used in transportation, are exposed in a cyclical manner to elemental sulphur (loaded vessel) and the atmosphere (empty vessel). It is well known that the various iron sulphides undergo ready atmospheric oxidation, and it was considered that this phenomenon might confer some degree of resistance to sulphidation during the next sulphur exposure period. The work reported in this paper was performed to test this hypothesis. EXPERIMENTAL METHOD Twelve carbon steel samples:~ (102 x 13 x 5 ram) were initially sand-blasted clean, weighed, and then loaded into the corrosion cell (Fig. 1). The cell was designed such that all samples experi- enced an identical environment, particularly with respect to the purge gas stream. The cell was loaded with ~ 320 g of presized (4-8 mesh) slate sulphur and ~ 170 g of distilled water. The system was then purged with nitrogen, since previous worm has demonstrated that catastrophic corrosion is most severe under anaerobic conditions. After four days of exposure to wet elemental sulphur, the steel samples were removed, dried and weighed, and then exposed to the atmosphere for a period of six days. Two samples were set aside for analysis and the other ten were returned to a freshly prepared sulphur/water slurry for a further four day period. The above cycle was then repeated until all samples had been removed from the system (i.e. six cycles). After the final atmospheric exposure, each sample was weighed, and then descaled using Clarke's solution. The samples were then reweighed to determine the total loss in weight of metal. *Manuscript received 24 February 1977; in revised form 29 April 1977. 1"To whom correspondence should be addressed. ~;Elemental analysis in wt~o: C, 0.14; P, 0.08; S, 0.02; Mn, 0.58; Si, 0.34; Cu, 0.51; Cr, 0.58; Ni, 0.51. 499