The inhibition of under deposit corrosion (UDC) of steel X-60 (UNS K03006) was studied under field-collected sludge deposits in a simulated sour environment by means of linear polarization resistance (LPR), coupled multi-electrode array system (CMAS), and weight-loss coupons. X-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS) techniques were employed to identify the deposit composition. The adsorption of two corrosion inhibitors, fatty acid imidazoline and benzyl alkyl pyridinyl quaternary ammonium chloride (benzyl chloride quaternary), designed for steel corrosion protection in sour environments, and their inhibition activities under sludge deposits were investigated. The significance of determining the adsorption affinity of the inhibitors to field-sludge deposit in the selection of corrosion inhibitors was also demonstrated. The XRD analysis indicated that the field-sludge deposit consisted mainly of calcite phase. Fatty acid imidazoline inhibitor was found to exhibit higher affinity to the sludge deposit than did benzyl chloride quaternary. As a consequence, benzyl chloride quaternary inhibitor was more effective in inhibiting general and localized corrosion of carbon steel in the presence of sludge deposit in a simulated sour environment. The corrosion rate is increased by the deposit even in the absence of inhibition. Thus, the field-sludge deposit decreased the performance of inhibitors, as compared with inhibiting steel samples that contained no sludge deposits. A clear understanding of the inhibitor's interaction with field-sludge deposits is necessary to predict its inhibition performance under field-sludge deposits.

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