Investigation of Microbiologically Influenced Corrosion (MIC) by Sulfate Reducing Bacteria (SRB) Biofilms and Its Mitigation Using Enhanced Biocides

摘要

Microbiologically influenced corrosion (MIC) has been a challenge in the oil and gas industry as well as other industries such as water treatment facilities, nuclear power plants and pulp and paper plants. Sulfate-reducing bacteria (SRB) are considered a major factor because sulfate is a widely available oxidant in anaerobic environments.;This work studied the influence of flow effects on SRB biofilm growth in a glass cell bioreactor. Correlation between the cylindrical coupon rotation rate in the glass cell and the average flow velocity in the pipeline was theoretically derived with rough surface taken into account. Deadlegs attached to pipelines often are more prone to MIC. Because there is often no flow or low flow near the bottom of a deadleg, an open flow loop for MIC investigation in deadlegs using small flow rates to achieve similar mass transfer effects to fast flow pipeline was proposed. Mass transfer simulation using the computational fluid dynamics (CFD) software FLUENT was employed. Unlike regular recirculating flow loops used in most MIC studies, this setup was better at emulating real MIC in pipelines, avoiding the recycling of metabolic byproducts and damage of cells due to the high shear stress in the recycling pump.;MIC treatment is usually about biocide treatment. Because of increasing environmental concerns and tightening regulations, a more environmentally benign treatment to mitigate MIC was evaluated in this work, utilizing biodegradable chelators such as ethylenediaminedisuccinate (EDDS) and N-(2-Hydroxyethyl)iminodiacetic acid disodium salts (HEIDA) to enhance biocide performance against planktonic and sessile SRB. It showed that biocide dosage to control biofilm growth could be reduced considerably when a chelator was used with the biocide. Furthermore, when 10% to 15% (v/v) methanol was added to the binary combination of biocide and EDDS treatment, mitigation of planktonic SRB growth was improved from an inhibiting effect to a kill effect. D-amino acids as signaling molecules to disassemble biofilms were also investigated as biocide enhancers. It was found that 10 microM of a mixture of D-amino acids combined with 500 ppm EDDS successfully enhanced 30 ppm THPS to remove an established SRB biofilm. They showed great promise to enhance biocides for the mitigation of SRB biofilms.;Lab investigation of MIC after simulated hydrotesting revealed that severe pitting, as high as 40 microm pit depth in 30 days, occurred with greater pit depth when it was spiked with SRB. CO2 and H 2S/CO2 combined with MIC were also found to accelerate corrosion. A mechanistic model for MIC in the presence of CO2 was presented based on the electrochemical model for general CO2 corrosion. A localized MIC pitting rate can be predicted with the help of biofilm porosity indicators.