Failure Analysis for Internal Corrosion of Crude Oil Transporting Pipelines

Abstract

Crude oil transmission pipelines safely and reliably deliver hydrocarbon-based fuels across the globe to meet our energy needs. However, pipeline failures due to internal corrosion occur occasionally, and in some cases, such failures may be at least partly due to the activity of microorganisms, a mechanism known as microbiologically influenced corrosion (MIC). Microorganisms themselves and/or their activity can be difficult to pinpoint as the sole cause(s) of a failure because the surrounding chemistry and physical environment can greatly impact microbial activity, which in turn can impact the surrounding chemical environment – these interrelated processes can lead to a corrosion scenario. Thus, a multi-faceted approach that takes into account chemical, physical, and microbiological measurements is needed in order to provide multiple lines of evidence that attribute MIC to a pipeline failure. In this chapter, we overview internal corrosion related to low flow or intermittent flow areas, or dead legs, within crude oil transporting pipelines. Here, a phenomenon known as under deposit corrosion can occur wherein inorganic sediment materials, water, organics (e.g., from crude oil), and microorganisms form localized biologically active and corrosive deposits. We also feature a case study wherein multiple lines of evidence pointed to MIC as the predominant mechanism leading to a pinhole leak within a dead leg segment of a carbon steel pipeline (API 5L, Gr. B) transporting crude oil. The study describes the importance of collecting different kinds of evidence to support MIC and also comparing samples from corroded and non-corroded areas to provide a strong case for infrastructure failure due to MIC.