Understanding Microbial Corrosion - Part 1: Microbial Corrosion Damage

Introduction

Corrosion affects many metal and plastic compositions used in industry, including many alloys specifically selected for their corrosion resistance, such as 300 series stainless steel (SS). Worldwide, microbial-induced corrosion (MIC) and biofouling are a challenge to the oil and gas industry, both economically and technologically. Inspectors, operators, and engineers are employing state-of-the-art molecular microbial methods to identify and monitor microbes causing MIC. Microbial induced corrosion, also commonly referred to as microbiologically influenced corrosion, is any corrosion caused by microorganisms that cannot be seen individually by the unaided human eye, including bacteria, microalgae, fungi, and archaea [1,2].

Conveyance, process, and storage systems impacted by MIC may involve crude, refined products, oily and other wastewater, and other processes and chemical compositions. These systems are employed in piping and pipelines, refinery processes, cooling towers, geothermal energy, wastewater and groundwater treatment, and storage tanks. Recent advancements in molecular microbial identification methods rely on high-tech methodologies. This article, the first in a two-part series, reviews simple and advanced methods for identifying post-construction MIC damage, biofouling, and mitigation related to MIC and the microbes that cause it. A separate article will follow that specifically focuses on MIC remedies.

MIC Causes Significant Negative Monetary Impact

Concerns over the negative financial impact of MIC are not a recent development, nor are they limited to a specific geography or industry. Costs incurred by MIC can be significant. For example, it was published in:

• 2020: MIC was responsible for $3 to $7 billion annually in cost to steel infrastructure corrosion in the international oil and gas industry [3].
• 2020: Worldwide, MIC accounted for 20% of costs due to corrosion in pipelines, vessels, and structures [4].
• 2012: MIC is responsible for $300 to $500 billion in economic losses in circulating cooling water systems [5].
• 2001: MIC caused $2 billion worth of losses in the US oil and gas industry [6].
• 1996 and later in 1998: MIC was estimated to cause 20% of all corrosion failures [7,8].
• 1996 and later in 1998: MIC was responsible for 40% of internal pipeline corrosion [9, 10].
• 1986: Russian investigators estimated that MIC was responsible for 30% of the corrosion damage in equipment used for oil exploration and production [11].

MIC Impacts on Conveyance, Storage, and Process Systems

MIC and its impacts are variable and occur in nearly every conveyance, storage, and process system. The ensuing sections are provided to demonstrate this through summarized industry knowledge supported with visual examples. Each of the following sections systematically address MIC in common or typical environments. Specific visual and physical characteristics can lead to the determination that observed corrosion is caused by MIC. This article focuses on MIC. However, physical- and chemical-induced corrosion often occur simultaneously with and/or promote MIC.

Conveyance: Pipe Pitting – External

Subsurface buried piping is most often in contact with clean silica sand bedding and native soil. Bedding sand and soil are porous materials and the environmental conditions related to them widely vary. Damage from environmental conditions is mitigated by coating applications and/or cathodic protection (CP).

Figure 1 shows external corrosion on a buried carbon steel gas transmission pipeline located in bog soil [12]. The external corrosion was caused by sulfate-reducing bacteria (SRB) in an anaerobic (e.g., anoxic) environment.