Internal Corrosion Monitoring

Microbiologically influenced corrosion is the degradation of a material under the influence of environmental factors complicated by the metabolic activities of microorganisms. Microbiological attack on process equipment used in the petroleum industry results in increased operating expenses and reduced income. This article discusses treatment options for various production streams to prevent corrosion and downtime of assets.

Online Corrosion Monitoring (pipeline OCM) devices are equipped with Access Fittings (AFs), which enable on-stream corrosion assessment of fluids under high production pressure in oil & gas operation. AFs are precision fabricated components, usually made of bare carbon steel, that are attached to pipelines and process vessels by welding. Following weld integrity checks, appropriate hole is ‘hot- tapped’ into the fluids, on-stream, while under pressure. Unfortunately, severe internal corrosion causes AF leakage failure. Since 2011, twenty-two AF leakage failures have been recorded in Kuwait Oil Company, nineteen of which have occurred in effluent water process stream. In this paper, a prioritization maintenance-focused methodology is presented for ranking the leakage potential of pipeline OCM locations in terms of an empirical leakage potential, incorporating the combined severity of general corrosion, pitting corrosion, fluid corrosivity and sessile bacteria population density in the fluid.

Bacteria population density may provide a viable corrosion control metric for microbiologically influenced corrosion (MIC) in oilfield water handling systems. This could ensure that the population of sulfate reducing bacteria (SRB), acid producing bacteria (APB), general aerobic bacteria (GAB), and general anaerobic bacteria (GAnB) in the operating environment can be kept below a target envelop to preserve asset integrity. Consider, for example, a system that has been experiencing increased corrosion over a period of time. If the trend of increasing corrosion rate versus time parallels the corresponding plot of all bacteria population density over that same period of time, the general assumption is to ascribe the source of increased corrosion to increased bacteria population density. It is because of this pragmatic correlation that oil companies normally develop in-house guidelines for quantifying bacteria proliferation. However, there is still no generally accepted method for determining such guideline unambiguously. This paper utilizes the effects of bacteria population density on general/pitting corrosion to establish an asset integrity risk ranking for the following oilfield water handling systems: brackish water, seawater, recycle water, and effluent water.

In the oil & gas industry, key performance indicators (KPI) are used to track the efficiency of the prevailing corrosion risk management strategy for the preservation of pipeline integrity. This includes the integration of corrosion monitoring, process monitoring, inspection, mitigation, environmental control, and materials management. At Kuwait Oil Company (KOC), internal corrosion monitoring activities are carried out in 22 gathering centers, early production facilities, 5 booster stations (operating), 3 effluent water disposal plants, seawater treatment plant, seawater injection plant, and pipeline network carrying different products. Corrosion and corrosivity trends are monitored using weight-loss coupons, electronic probes, bioprobes, hydrogen patch probes, galvanic probes as well as the measurement of iron content (total and dissolved) and manganese content. Corrosivity trend is also monitored using pH, conductivity, total dissolved solids, total hardness, dissolved oxygen, H2S concentrations, CO2 concentrations, bacterial population density and corrosion inhibitor residuals. These activities consume significant resources that could otherwise be conserved. The present paper identifies bacterial population density as a key performance indicator. That is, minimizing bacterial population density could enable greater cost effectiveness, efficiency, and reliability. It would certainly enable the control of the state of corrosion integrity of oilfield water handling systems.