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ABSTRACT A sulfide oxidase enzyme electrode is proposed for monitoring of biogenic sulfide resulting from the activities of sulfate-reducing bacteria (SRB). The enzyme which is immobilized in a carbon (graphite) paste with 1,1? dimethylferrocene, catalyses the oxidation of sulfide to sulfur. Amperometric measurements were carried out at a fixed potential of 0.3 V, and room temperature, using Tris-HCl buffer (pH 7.5) as the electrolyte, and sodium sulfide solution as the substrate. Under deaerated conditions, the biosensor responded linearly to the tested sulfide concentration in the range of 0?130 ppm. The results indicate that the procedures adopted for the enzyme production and electrode development were reproducible. INTRODUCTION Corrosion resulting from the attachment and activities of microorganisms on metal surfaces is referred to as microbiologically influenced corrosion (MIC) or biocorrosion. It occurs in diverse environments and is not limited to aqueous submerged conditions, but also takes place in humid atmospheres. MIC is a result of the interactions that are often synergistic between the metal surface, abiotic corrosion products, and microbial cells and their metabolites. The latter includes organic and inorganic acids, and volatile compounds, such as ammonia and hydrogen sulfide. Despite the evidence that a number of different groups of microorganisms are capable of accelerating corrosion, and the recognition that most MIC occurs in the presence of a consortium of bacteria, sulfate-reducing bacteria (SRB) have received the most attention as the causative agents of MIC. They oxidize organic substances to organic acids or carbon dioxide by reducing sulfate to sulfide through anaerobic respiration. In addition to being highly corrosive to many materials, biogenic sulfide production leads to health and safety problems, environmental hazards, and severe economic losses due to reservoir souring1. MIC monitoring methods can be categorized by the primary characteristics of the process that is monitored. For example, there are techniques that monitor the microbiology, those that detect microbiological influences, and those that track only corrosion. These techniques have recently been reviewed. Often these techniques must be used in combination in order to obtain the best results. This is due primarily to a lack of analytical techniques that can be used to characterize microbes or their activity in-situ while still providing adequate information of the corroding metal surface. Biosensors are powerful tools having the ability of performing fast and specific, on-site monitoring of a wide range of analytes. These devices have many favorable analytical characteristics, such as selectivity, sensitivity, portability, speed, low cost and potential for miniaturization. They have potentials for continuous, and in-situ applications, and are suitable for a variety of matrices including soil extracts,groundwater, blood, and urine. Recently, a patent was issued for the development of a biosensor for in-situ monitoring of sulfide. It is a biosensor which is based on the enzyme sulfide oxidase. This probe could be extremely valuable in correlating MIC with SRB activities, for which at present no suitable method is available. Development of the correlation is an important step in the strategy of enhancing process safety by understanding and preventing MIC.
- North America > United States (0.69)
- North America > Canada (0.47)
ABSTRACT Corrosion is one of the main threats to the integrity of oil and gas pipelines. It can occur both on the inside wall and outside surface of the pipelines. The control of corrosion is an ongoing challenge in pipeline operations. Predicting and assuring pipeline integrity and serviceability entail the use of sensors and monitoring tools as well as predictive models. Our aim is to develop an integrated internal pitting corrosion model, which incorporates the aspect of microbiologically influenced corrosion (MIC) in addition to non-MIC pitting corrosion. This paper presents the two components of this integrated model designed to predict internal corrosion in oil and gas pipelines. The first module, a pitting-corrosion model predicts when localized corrosion conditions (not related to MIC) will result in pipeline failures. The second module predicts the susceptibility of microbiologically influenced corrosion (MIC) inside pipelines. An evaluation of the MIC model based on four case histories of pipeline failures indicates that the occurrence of MIC can be predicted. INTRODUCTION According to the U.S. Office of Pipeline Safety statistics, internal corrosion caused approximately 15% of oil and gas transmission pipeline incidents in the U.S.A. between 1994 and 2000. According to a Canadian report by the Alberta Energy and Utilities Board (AUEB), the total number of failures in Alberta, Canada, due to internal corrosion in both gathering and transmission pipelines (gas and liquid) for the past 20 years is more than 5,000, averaging almost one failure per day. The failure of a transmission pipeline due to internal corrosion resulted in 12 casualties in Carlsbad, New Mexico, U.S.A. in 2000. In March 2006, another pipeline failure due to internal corrosion leaked 270,000 gallons of crude oil into Prudhoe Bay, Alaska. Environmentalists described the spill, the largest ever in Alaska's North Slope region, as a "catastrophe". At the Banff/2005 Pipeline Workshop: Managing Pipeline Integrity, there was agreement that advances in improving control of internal corrosion for all pipelines (gas transmission, gas production, oil transmission, and oil production pipelines) are important. CAUSES OF INTERNAL PITTING CORROSION Carbon and low-alloys steels used in constructing pipelines and other equipment in the oil and gas industry, although cost-effective, are susceptible to corrosion. Several factors influence the corrosion rate including flow; compositions of steel, oil and formation water; temperature; pH; and the wettability of the steel surface itself. The corrosion rate of a steel surface that is completely coated with oil (i.e., oil wet) is low, whereas the corrosion rate of a steel surface that is completely coated with water (i.e., water wet) is usually significantly higher. If a steel surface corrodes generally, but corrosion-product layers do not deposit forming a passive layer that covers the surface, then general corrosion may continue. If, as commonly occurs, corrosion-product layers deposit and form a layer that covers the surface, then the steel may become susceptible to pitting corrosion. The degree of susceptibility depends on the stability of the surface layer, temperature, brine composition, and flow. The penetration of a pipe wall by a pit is a three-stage process: Formation, growth, breakdown, and reformation of the surface layer(s) on the steel surface; Initiation of pits at localized regions on the steel surface where breakdown of the surface layer occurs; and Pit propagation and eventual penetration of the pipe wall
- North America > United States > New Mexico > Eddy County > Carlsbad (0.24)
- North America > United States > Alaska > North Slope Borough > Prudhoe Bay (0.24)
- North America > United States > Texas > Harris County > Houston (0.16)
- Information Technology > Modeling & Simulation (0.60)
- Information Technology > Data Science > Data Mining (0.60)