Experimental Study of Sour Top-of-the-Line Corrosion Using a Novel Experimental Setup

Top-of-the-line corrosion (TLC) is a potential issue for carbon steel pipelines transporting natural gas. This type of corrosion is driven mostly by the gradient of temperature between the warm produced fluids and the outside environment, but also is affected strongly by the presence of corrosive species such as carbon dioxide (CO2), hydrogen sulfide (H2S), and organic acids. This paper presents an assessment of the corrosion risk of a specific sour offshore development: the Karan gas field (Arabian Gulf, Saudia Arabia). The study was performed through laboratory experiments in a large-scale flow loop as well as in a specially designed autoclave equipped for corrosion studies under dewing conditions. Corrosion rates were obtained using the weight-loss method and the surface layer was analyzed with x-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). The TLC rate was found to be low under all conditions tested, and no indications of localized corrosion were observed. Mackinawite, cubic iron sulfide, and troilite (stoichiometric pyrrhotite) were identified in the corrosion product layer.