Mechanisms of Corrosion of Pipelines

This chapter presents fundamental concepts regarding corrosion, from thermodynamics to kinetics issues, and showcases techniques used to determine corrosion rates. In terms of pipeline corrosion, the circumstances in which a pipeline is operating impacts the frequency and severity of the corrosion events. These events may encompass both external and internal corrosion. While the latter is related to the interaction between the material of the pipe and the fluids inside of it, such as oils, natural gas, or aqueous solutions, external corrosion arises from the environment where the pipeline is installed (underground or in the seawater). Therefore, the main mechanisms related to internal corrosion in the oil and gas industry, such as sweet corrosion (corrosion processes due to the presence of CO2) and sour corrosion (when H2S concentrations can produce a partial pressure above 0.05 psia), are presented. Both are examples of composition-related corrosion. Moreover, it is also discussed other corrosion mechanisms, such as flow-related, surface deposit-related (for instance, under-deposit corrosion and microbiologically influenced corrosion (MIC), or even environmental cracking-related (for example, sulfide stress cracking (SSC) and hydrogen-induced corrosion (HIC). Lastly, top of line corrosion (TLC) and black powder, special internal corrosion mechanisms, are also mentioned. Regarding external corrosion, stress corrosion cracking (SCC) and its relation to cathodic disbondment are presented.