Laboratory Study of Sour Localized/Pitting Corrosion

Carbon steel is widely used for upstream oil and gas production facilities (e.g. piping, pipeline, downhole tubulars) because it is cost effective and easy to fabricate.  Field experience indicates that failure of carbon steel facilities in sour environments typically occur as pitting in highly localized areas, rather than as general corrosion over large surface area.  Such pitting attack has been attributed to the formation of anodic sites where the iron sulfide scale (cathodic) has been damaged.  

High pressure autoclave laboratory testing has been carried out to study sour localized / pitting corrosion mechanism.  The effects of several environmental parameters were investigated, including flow rate, chloride concentration, and temperature on the iron sulfide scale formation as well as the interaction of film forming corrosion inhibitor on the scale formation.  It was found that severe pitting / localized attacks occurred under certain test conditions that promoted a partially protective sulfide scale.