Effectiveness of ultraviolet treatment in mitigating microbiologically influenced corrosion

Abstract

The destructive effect of microbiologically influenced corrosion (MIC) of carbon steel in pipelines has been widely found in soil and water environments. Chemical biocides are normally used for MIC mitigation in pipelines. However, many problems were encountered in its application, causing biocides usage to remain controversial. Ultraviolet (UV) radiation is seen as a possible alternative for chemical biocides. Nevertheless, information on the efficiency of UV treatment and the influences of UV parameters on corrosion process is limited, thus restricting any efforts to explore the potential application of UV as a chemical biocide replacement. This study aims to identify the effectiveness of UV disinfection against MIC caused by Sulfate Reducing Bacteria (SRB) strain. The investigation utilized two different samples of SRB sources: Baram-C and ATCC7757 strains. The Baram-C SRB consortium sample was cultivated from raw crude oil gathered from one of the main trunk lines at Baram Delta Operation, Sarawak, Malaysia, while the ATCC7757 SRB sample was sourced from the American Type Culture Collection (ATCC). The observation on bacteria growth revealed that the preferred pH and temperature for the active cultivation of Baram-C and ATCC7757 strains were pH 8.5 and 37°C, respectively inside the Modified Baar’s media. The corrosion process was found more severe in biotic condition by approximately 50% based on metal loss results. The maximum corrosion rate in biotic environment was recorded at 0.3209 mm/year and 0.5042 mm/year for Baram-C and ATCC7757 strains, respectively, as compared to the 0.1791 mm/year corrosion rate in an abiotic sample. One-Factor-At-a-Time (OFAT) analysis was performed under the influence of UV time of exposure, types of UV lamps, numbers of UV lamps and treated volume. The optical density reading showed that UV treatment was able to suppress the number of bacteria up to almost 99% after 28 days of incubation. The effect on bacteria growth was similar for both strains. However, when a variety of UV treatment parameters were applied, different bacterial strains indicated different rates of metal loss. Furthermore, Response Surface Methodology (RSM) was used as a tool to determine the relationship between UV parameter and metal loss by using two different types of UV lamps (10 watts and 14 watts). The RSM models were successfully developed with R2 of 0.8990 and 0.9020 for UV lamps with 10 watts and 14 watts, respectively. ANOVA results indicate that the effects of treated volume do not depend on the level of factors contact time and numbers of UV lamp for 10 watts lamps, whereas for 14 watts lamps, the contact time and number of UV lamp do affect each other. The result also suggests that the effectiveness of UV treatment does not only depend on UV lamp’s intensity to provide optimum curing. The experimental test and numerical analysis performed in this research has provided a comprehensive understanding of the efficiency of UV treatment on the extermination of SRB strains and reduction of metal loss rates. The findings also produced a numerical measurement of metal loss rate due to SRB as a function of UV radiation. This can serve as an impetus for the transition of UV technology from its infancy level to the real-world practice of corrosion mitigation in the oil and gas industry.