Modelling the Effect of Porous Iron Sulfide Layers on Sour Corrosion Behaviour

Abstract

Surface layers and deposits of iron sulfides formed from sour corrosion may exhibit both protective and corrosive properties, depending on the types of iron sulfide formed and the physical structure of the layers. The protective barrier and blocking effects of the layers may be counteracted by significant cathodic activity on the surfaces of electrically conductive iron sulfides and galvanic corrosion of the underlying steel surface. Experimental and modelling work were performed to quantify the effects that parameters such as layer thickness and porosity, H2S partial pressure, temperature and pH can have on the electrochemical reactions, aqueous equilibria and mass-transport processes governing the corrosion rate. The results were discussed in the light of available literature and compared to relevant sour corrosion data, including both native corrosion product layers and applied iron sulfide deposits (UDC). Paper reproduced with permission from CORROSION/2019 Annual Conference and Exhibition. www.nace.org