MIC Microbiological Corrosion

Microbiologically Induced Corrosion in a Sour Gas Pipeline

The highly localized corrosion shown in the figure is typical of that resulting from microbial action. One of the features of this type of attack are the elongated pits which tunnel into the specimen often in an irregular manner. The pit was one of several located near the gas/water interface. The pipeline was left for a prolonged period in a shut-in (static) condition which promoted the growth of bacteria and highly localized corrosive attack. Sulfate reducing bacteria were suspected due to the combination of sulfate species in the water and anaerobic conditions. The corrosion was mitigated by a closer control of operating conditions and chemical treatment.

Localized Attack in Amine Solution

The tensile specimen exhibited extensive localized corrosion as a result of exposure to an monoethanolamine solution. The unusual localized attack was promoted by the combination of mechanical stress and chemical impurities in the environment. The impurities cause localized breakdown of the normally protective surface films. The applied tensile stress promoted the propagation of intergranular corrosion.

Fatigue Cracking

A fatigue failure was observed in a piston that initiated on the backside of the piston head as a result of the cyclic stresses of operation. The failure exhibited classic "beach marks" which delineated the discontinuous nature of the crack propagation through the thickness of the material. The final fracture resulted when the remaining ligament was insufficient to sustain the service induce stresses.

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