Abstract
Failure of steel materials in sour environments is of great importance in the oil and gas industry. Iron sulfide deposits created from steel corrosion in the presence of H2S complicate the corrosion failure mechanism and the ability to inhibit those mechanisms. Iron sulfide films decrease the general corrosion rate but introduce higher occurrences of pitting corrosion. Most sour failures in the field are due to pitting or underdeposit corrosion which is difficult to monitor and inhibit. Several studies have been conducted describing the bulk behavior of sour corrosion with and without chemical addition in the presence of underdeposit corrosion. However, little information exists on the sub-mechanisms involved in the underdeposit corrosion process in the presence of chemicals. The inhibition performance could be significantly affected by three main sub-mechanisms with each having variable unknown contribution to the overall mechanistic process 1) adsorption on the steel anode surface, 2) adsorption on the iron sulfide cathode surface and 3) diffusion through the porous deposit film. This paper communicates our first attempt to understand the contribution of the first two sub-mechanisms to the inhibition of the underdeposit corrosion process. It also studies the effect of three types of corrosion inhibitors on the adsorption processes. The experimental procedure used in this investigation will include galvanic coupling of a mild steel electrode to an electrode made from solid iron sulfide. The data collected will be used to quantitatively analyze the individual effects on chemical inhibition from diffusion, adsorption onto the iron surface, as well as adsorption onto the iron sulfide surface.
