Mercury and Its Compounds—A Corrosion Hazard

Abstract

Frequently cases of severe corrosion have been encountered with equipment fabricated of non-ferrous alloys that have long been considered standard for handling or processing a specific chemical. A review of the service history of such cases usually reveals the following pattern: 1) The equipment has functioned for considerable and even long periods of time without evidence of harmful corrosion; 2) Suddenly, in a relatively short time, severe attack occurs. Routine examination failed to disclose the reason for the failures of equipment having such service records. Modified techniques for the examination of equipment having such histories of service reveal, in most cases, the presence of mercury in either the corrosion products, or on the metal surface in the vicinity of the attack, or in the environment. This observation instigated a series of studies on the role of mercury and its compounds in promoting corrosion of metals, the concentration levels that might cause serious attack, and the manner by which such substances could be transported through chemical equipment and plants. It was found that the vapor pressure of metallic mercury even at low temperatures is sufficient to permit the mercury vapors to pass through the system and alloy with many commercial metals. This amalgamation of such metals can result in stress cracking or severe corrosion. It has been shown that metallic mercury reacts with many environments to a sufficient extent to produce compounds that are corrosive to commercial metals. It has been demonstrated that concentrations of mercury compounds as low as 0.5 ppm constitute a serious corrosion hazard for a variety of useful metals and alloys. The results of laboratory work and service experience have demonstrated that mercury contamination, either metallic or its compounds, constitutes a serious corrosion menace. It is believed that control of mercury contamination could easily be justified by the savings that would result from reduced replacement and maintenance of chemical process equipment.