Frank Cheng

Biocide-mediated corrosion of coiled tubing.

Coiled tubing corrosion was investigated for 16 field water samples (S5 to S20) from a Canadian shale gas field. Weight loss corrosion rates of carbon steel beads incubated with these field water samples averaged 0.2 mm/yr, but injection water sample S19 had 1.25±0.07 mm/yr. S19 had a most probable number of zero acid-producing bacteria and incubation of S19 with carbon steel beads or coupons did not lead to big changes in microbial community composition. In contrast other field water samples had most probable numbers of APB of 102/mL to 107/mL and incubation of these field water samples with carbon steel beads or coupons often gave large changes in microbial community composition. HPLC analysis indicated that all field water samples had elevated concentrations of bromide (average 1.6 mM), which may be derived from bronopol, which was used as a biocide. S19 had the highest bromide concentration (4.2 mM) and was the only water sample with a high concentration of active bronopol (13.8 mM, 2760 ppm). Corrosion rates increased linearly with bronopol concentration, as determined by weight loss of carbon steel beads, for experiments with S19, with filtered S19 and with bronopol dissolved in defined medium. This indicated that the high corrosion rate found for S19 was due to its high bronopol concentration. The corrosion rate of coiled tubing coupons also increased linearly with bronopol concentration as determined by electrochemical methods. Profilometry measurements also showed formation of multiple pits on the surface of coiled tubing coupon with an average pit depth of 60 μm after 1 week of incubation with 1 mM bronopol. At the recommended dosage of 100 ppm the corrosiveness of bronopol towards carbon steel beads was modest (0.011 mm/yr). Higher concentrations, resulting if biocide is added repeatedly as commonly done in shale gas operations, are more corrosive and should be avoided. Overdosing may be avoided by assaying the presence of residual biocide by HPLC, rather than by assaying the presence of residual surviving bacteria.

AgNP-coordinated glucosamine-grafted carbon nanotubes with enhanced antibacterial properties

An MWCNT–glucosamine–AgNP composite with long-term antibacterial properties, good dispersity, and stability in aqueous solutions was synthesized by a grafting method. Various surface analysis techniques were used to determine the successful preparation of MWCNT–glucosamine–AgNPs. The release behavior of Ag was detected by ICP-Q, and the long-term antibacterial effect against Staphylococcus aureus was characterized by the counting method. It was found that, after modification of the MWCNTs with glucosamine, the interfacial adsorption of Ag was significantly enhanced. The concentration of Ag ions released in the PBS solution was only 0.0643 ppm after 35 days of immersion. The MWCNT–glucosamine–AgNPs maintained effective antibacterial properties, and the bacteriostatic percentage of S. aureus was maintained at 90% after 35 days. This study demonstrated the great potential of MWCNT–glucosamine–AgNPs as a long-term antibacterial agent for use in the public health and antibacterial coating fields.

Interfacial potential barrier driven electrochemical detection of Cr6

3D NiO/polyaniline p-p junction foam was prepared and applied for electrochemical detection of Cr6+. The electrochemical detection using interfacial potential barrier was illustrated and a mature theoretical model was built to demonstrate the mechanism. Electrochemical sensing signals of targets can be revealed by changing the height of potential barrier after specific adsorption. The extra high sensitivity (0.78 μA nM-1) and low detection limit (3.96 × 10-4 nM) of Cr6+ were achieved by applying the p-p junction interfacial potential barrier as driven factors. This work proposes a model to apply the potential barrier for electrochemical detection of metal ions, which can be further developed for a wide range of specific substance detection.

A Real-Time AC/DC Measurement Technique for Assessment of AC Corrosion of Buried Pipelines

In this work, a real-time AC/DC signal data acquisition (DAQ) technique was developed, which is capable of separating the DC and AC potential components from the recorded total potential, providing mechanistic information about the steel corrosion in the presence of AC interference. It was found that the corrosion of the steel is enhanced by the applied AC current density from 0 to 400 A/m2. With the further increase to 600 A/m2 and 800 A/m2, the corrosion rate of the steel decreases, which is attributed to passivation of the steel at sufficiently high AC current densities, and a compact film is formed on the steel surface. Moreover, the derived mathematic relationships between AC potential and AC current density provides a potential alternative to determine AC current density on pipelines based on measurements of AC potential in the field.Copyright