ABSTRACT

A laboratory flow loop is used to evaluate the ability of an on-line, electrochemical, biofilm-activity probe to monitor biofilm activity in synthetic oilfield brine and correlate its activity to localized pitting corrosion. In addition, bio-traps containing porous polymer beads for trapping biomass are evaluated as a rapid means to evaluate biofilm community structure using phospholipid fatty acid (PLFA) and DNA analysis. Results suggest that applied current as measured by the electrochemical probe can be used to detect biofilm activity in produced oilfield brine and can be used to evaluate the effectiveness of biocide treatments. However, biofilm activity did not always correlate with pitting corrosion conditions. Biofilms collected by biotraps during periods of pitting and non-corrosive conditions, however, displayed distinctly different microbial communities as determined by PLFA and DNA analysis. Furthermore, the biofilm microbial communities in bio-traps and on metal coupons were similar, except during biocide application, suggesting that bio-traps could be used as a rapid means to evaluate biofilm community structure on metal surfaces.

INTRODUCTION

It was recently estimated that almost 50% of production pipeline leaks result from internal corrosion, of which 75 to 90% are estimated to be due to localized (pitting, crevice, SCC) corrosion 1. Microbiologically influenced corrosion (MIC) results in a sustained, localized, pitting attack and has been implicated as a possible mechanism in as many as 10 to 30% of all serious corrosion cases. Traditionally, monitoring for MIC activity has been conducted by examining pits on weight loss coupons and by performance monitoring of such parameters as water chemistry and planktonic bacteria that are indirectly related to MIC activity. These methods are also historical in nature, meaning the analyses and interpretations are completed days and even months after the corrosion event took place. Therefore the need for real-time, on-line monitoring of MIC activity is warranted.

Borenstein and Licina 2 provided an overview of monitoring techniques for the study of MIC and discussed the pros and cons of typical on-line corrosion methods for monitoring MIC. They concluded that while several of these techniques (e.g, EIS, ECN) may be useful for on-line detection, none are specific for MIC. However a device that could monitor biofilm activity should be a more direct indicator of MIC activity since biofilms are known precursors of MIC. Nivens et al. 3 reviewed various continuous, nondestructi ve methods for monitoring biofilms including microscopic, spectrochemical, electrochemical, and piezoelectrical analysis. More recently, H.-C Flemming 4 reviewed additional biofilm monitoring devices (fibre optics and turbidimetry) while Schmid et. al. 5 describe a photoacoustical technique for in-situ monitoring of biofilms. Many of these devices are good tools for laboratory use, but according to Borenstein and Licina 2, for industrial or commercial use, these devices must be simple to install, simple to use, simple to interpret, accurate, economical, and capable of withstanding the operating conditions of use. One such biofilm-monitoring device that has gained acceptance in industry for meeting many of these criteria is the BIoGEORGE biofilm activity monitor (BAM). This monitor is an electrochemical device that detects the online, real time, activity of a biofilm by measuring the amount of current necessary to offset the decrease in polarization resistance when a biofilm forms on a nonactive metal (e.g., titanium); and measures the current that flows between two nominally identical electrodes when no potential is app

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