Detection and Mitigation of Weight Loss Corrosion in Sour Gas Gathering Systems

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract The production of sour gas through steel gathering lines usually presents serious corrosion problems to the facility. This report discusses some of the basic corrosion mechanisms involved in such a system. Most of the available corrosion monitoring techniques are discussed with regard to their principle of operation and their advantages and disadvantages. The third section of the report deals with mitigation techniques that can be applied to sour gas systems for the purposes of corrosion control. Explanation of the technique and some advantages and disadvantages are presented. Experience gained through Shell Canada's operations is interjected throughout the report. It should be noted that experience is related to specific situations and should not be blindly applied to all other situations. II. Introduction The detection and mitigation of weight loss corrosion is a constant problem in sour gas gathering systems. Pitting corrosion rates of over 200 mil/year have caused extensive damage and necessitated the expenditure of hundreds of thousands of dollars on one particular sour gas gathering system in Shell's operation (see Figs. 4 through 8). Similar experiences have been reported by other companies operating in the hydrogen sulfide-carbon dioxide environment of Alberta's natural gas reservoirs. Every year millions of dollars are spent in the restoration of corroded systems and on the treatments that were initiated for the purposes of mitigating sour gas corrosion. Corrosion of sour gas gathering systems also presents a potential threat to human safety and potential threat to human safety and environmental damage possibilities. Most sour gas gathering systems contain sufficient quantities of hydrogen sulfide to make any escaping gas fatal to exposed humans and animal life. Thus, from the foregoing discussion, it is apparent that it is not only economically advantageous to prevent sour gas corrosion, but its prevention is also necessary to maintain prevention is also necessary to maintain environmental safety. In order to efficiently detect and mitigate corrosion in sour gas gathering systems, the corrosion mechanism occurring in the system should be understood. If the corrosion mechanism of a particular system is known, then disruption of that mechanism has a greater probability of success, since blind trial-and-error attempts at mitigation are eliminated. Due to the necessity of understanding the basic corrosion mechanisms, this report has been divided into three sections.