Under-deposit corrosion (UDC) due to the presence of deposits has become a major concern threatening the safe service of pipelines in oil and gas fields, causing economic loss and even irreversible damage to life and environment. Herein, we provide a critical review of UDC in terms of testing methods, corrosion mechanisms and mitigation strategies, so as to better understand and prevent UDC. Two deposit simulation methods and three UDC testing systems are summarized. Two popular UDC mechanisms are discussed based on the coverage and protectiveness of deposits, and the galvanic couple caused by the uneven distribution of deposits is found to be the root cause for the prevailed localized corrosion under deposits. The mitigation strategies for UDC are reviewed from the aspects of scale controlling and corrosion inhibition. In the last, the demands for developing accurate deposit simulation methods, effective UDC inhibitors and advanced on-site scale monitoring technologies are proposed.
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