With the continued need for fossil fuels, even as we enter energy transitions, the extraction of oil and gas from significantly abundant sour fields is increasing globally. Sour i,e, H2S –containing gas environments present several challenges to system integrity, including an accelerated rate of localized corrosion, and potential catastrophic premature failures in fluid handling equipment. This creates a risk to asset integrity, leading to financial losses, and significant risk to both human health and the environment. A major problem in sour systems is ‘underdeposit corrosion (UDC)’ which is a type of extremely rapid, localized attack observed under deposits (in this case typically iron-sulfides); it is extremely difficult to both predict and monitor. The mechanism of both iron sulfide formation and UDC in pipeline is not fully understood: the complex nature of iron sulfides along with the dynamic changes of their physical and chemical properties during the corrosion process entails that multiscale correlative investigations are needed.

1-dimensional artificial pit experiments are developed in order to study localised corrosion with the use of multi-electrode arrays; this allows high-throughput measurements such that different variables can be studied simultaneously. The artificial pit acts as an anode in a three-electrode electrochemical cell, simulating an actively dissolving pit, but with reduced dimensionality that allows quantitative extraction of kinetic data as a function of the various system parameters- essentially the deposit physical and chemical properties. Data on the role of deposit chemistry and morphology on the electrochemical dissolution behaviour are presented, and discussed in terms of a transport-controlled model for pit propagation. Complementary planar (2D) surface experiments were performed under deposits; using this blended approach, both general and localized corrosion can be assessed and related to provide a comprehensive understanding of the overall performance of steel under deposits. The dynamic physicochemical variations (surface morphology and chemical composition) in both metal and deposit are related to the electrochemical findings to explain the metal-deposit interdependent physicochemical interactions.

The findings of the study paved the way towards innovating experimental methods for example the use of micro-pH electrodes to provide real-time data on the chemistry inside actively dissolving pits under representative deposits. This study provides insights into the different scenarios of UDC phenomenon and potential protocols to develop monitoring probes for industrial application.