Two leaks were discovered in a section of 4.0-inch diameter mild steel pipe used for disposal of produced water from coal-seam gas wells. These leaks were the result of pitting-type corrosion characterized by smooth walled, overlapping, cup-like, hemispherical depressions inside a main pit of which some pits contained nodules. An examination of one of these nodules revealed the mineral siderite (ferrous carbonate) along with significant amounts of sodium, manganese and iron but no sulfur. A scale surrounding these pits contained calcareous minerals in addition to magnetite. The pits were located in the proximity of circumferential welds but many were distal to the heat-affected-zone (HAZ). Significant concentrations (104-108/cc) of aerobic heterotrophs, acid-producing bacteria (aerobic and anaerobic), as well as sulfate-reducing bacteria (SRB) (104/cc) were present in the water. The presence of settled solids, exposure to air and the periodic stagnant and flowing conditions in the pipeline created conditions favorable for the formation of differential aeration cells. It is postulated that corrosion in these differential aeration cells were catalyzed by the activity of both iron-oxidizing and metal-reducing bacteria during periods of oxic and anoxic conditions in the water.

Subject
Pits, Water, Piping, Solids, Leaks, Iron, Siderite, Nodules, Bacteria, Produced water, Brines, Oxygen, Microbiologically influenced corrosion
Keywords:
microbially influenced corrosion, coal seam, nodules, pitting, welds, siderite, metal-reducers, iron-oxidizers
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1998
Association for Materials Protection and Performance (AMPP)
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