Corrosion in Sulfur Production; The Use of An Alloy Protective Coating^★

Apparatus was devised and installed in the field which permitted measurements of the rates of corrosion during the various phases of sulphur production. From these studies it was definitely established that severe corrosion occurred only when water and molten sulphur were in contact with the steel surfaces together. This was corroborated in the laboratory where it was found that the corrosive effects due to molten sulphur alone were negligible while those due to the water alone were only little more serious. When sulphur and water came into intimate contact with the steel together, however, the corrosion rate increased manyfold. During the course of these studies sections of galvanized pipe normally used in the wells were found to resist the corrosive medium better than might have been expected on the basis of the standard electrode potentials of zinc and iron and the acidic character of the water, sulphur, air mixture. It was found that in salt solutions the potentials of the coating following exposure in a well was cathodic to unexposed mild steel. Analysis of the coating showed a relatively high aluminum and magnesium content and was believed that the exceptional corrosion resistance of the galvanizing was due to these materials. Coatings containing zinc, magnesium, and aluminum were prepared and these were found to be uniformly more corrosion resistant than the galvanizing alone, both in laboratory and in field experiments. Effectiveness of the coating improved with increased concentration of the light metals. Difficulties in preparing alloys of higher concentrations and in obtaining adherent coatings have thus far imposed definite limitations on the useful alloy range.