Rolf Gubner

Study of the interaction of sulphate-reducing bacteria exopolymers with iron using X-ray photoelectron spectroscopy and time-of-flight secondary ionisation mass spectrometry.

Time-of-flight secondary ionisation mass spectrometry and X-ray photoelectron spectroscopy were employed to determine the interaction of crude extracellular polymeric substances recovered from static batch cultures of two isolates of marine sulphate-reducing bacteria of the genus Desulfovibrio, grown in the presence of and without mild steel surfaces, with Fe ions released from steel. The results demonstrated that exopolymers synthesised by different strains of sulphate-reducers varied in their ability to bind iron originating from steel. Based on the X-ray photoelectron spectroscopy analysis it is proposed that Fe released from steel was associated with bacterial exopolymers such as Fe(III) ion. The application of surface science techniques to study exopolymer/metal interaction allowed quantitative evaluation of Fe binding using small sample size.

The Initial Steps of Atmospheric Corrosion on Magnesium Alloy AZ91D

Magnesium, with its low density, is a very interesting metal in applications in which weight is important. In this work the initiation of corrosion attacks on magnesium alloy AZ91D has been inves ...

Characterization of phases in duplex stainless steel by magnetic force microscopy/scanning kelvin probe force microscopy

A 2205 duplex stainless steel, which had undergone a slow cooling process in order to precipitate intermetallic phases, was characterized by means of magnetic force microscopy (MFM) and scanning Ke ...

Direct involvement of an extracellular complex produced by a marine sulfate‐reducing bacterium in deterioration of steel

A thermostable polysaccharide‐protein complex capable of accelerating the deterioration of mild steel was produced by a marine strain of sulfate‐reducing bacterium of the genus Desulfovibrio, and partially purified using low‐pressure chromatography. This complex induced pitting of steel in oxic aqueous solution. The increase in the corrosion rate of steel exposed to the complex, determined using linear polarization resistance measurements, correlated with the inferred increase in production of ex‐opolymer during the stationary phase of Desulfovibrio growth. Atomic absorption analysis confirmed that the complex caused rapid dissolution of iron from the steel surface, while light microscopy observations demonstrated that the complex caused grain boundary and intercrystalline attack of the steel, which did not occur in control solutions. The molecular mass of the corrosive complex, determined using gel filtration, was greater than 200 kD.

Characterisation of conditioning layers formed by exopolymeric substances of Pseudomonas NCIMB 2021 on surfaces of AISI 316 stainless steel

This investigation aimed to characterise conditioning layers formed on AISI 316 stainless steel by different types of extracellular polymeric substances (EPS), i.e. biofilm, planktonic and capsular exopolymers, isolated from continuous cultures of marine Pseudomonas received from the National Collection of Industrial and Marine Bacteria (strain NCIMB 2021). Colorimetric assays and gas chromatography‐mass spectrometry analysis confirmed previously obtained results based on a FTIR and SDS‐PAGE study of Pseudomonas NCIMB 2021 EPS demonstrating the presence of protein, neutral and amino sugars and uronic acids. The content and the ratio of these macromolecules differed depending on the type of EPS. X‐ray photoelectron spectroscopy revealed that conditioning layers formed upon exposure of steel to EPS solutions were chemically dissimilar. It is proposed that the observed difference in the chemistry of conditioning layers is the likely reason for reported differences in attachment of Pseudomonas cells to EPS‐conditioned steel surfaces.

The effect of Pseudomonas NCIMB 2021 biofilm on AISI 316 stainless steel

A bioreactor system operating in a continuous mode was designed to generate biofilms on polished and as‐received surfaces of AISI 316 stainless steel coupons exposed for 36 d to a pure culture of marine Pseudomonas NCIMB 2021. Scanning electron microscopy (SEM) and atomic force microscopy were employed to determine the degree of surface colonisation and to examine corrosion damage of the steel. X‐ray photoelectron spectroscopy analysis was carried out to characterise the chemistry of the passive layers on polished steel stored for a period of time, freshly re‐polished coupons, and as‐received steel. The effect of biofilms on the composition of layers formed on the steel specimens was evaluated. SEM revealed that the surfaces of polished and stored steel appeared to accumulate more biofilm compared to as‐received specimens. Micropitting of steel occurred underneath the biofilm, regardless of surface finish. The concentration of elements in the passive layers differed significantly between freshly re‐polished and as‐received or polished and stored coupons. In the presence of Pseudomonas NCIMB 2021 biofilm, the composition of the passive layer on the as‐received steel surface was considerably altered compared to unexposed steel or steel exposed to abiotic medium.

Corrosion Inhibitor and Oxygen Scavenger for use as MEG Additives in the Inhibition of Wet Gas Pipelines

The transportation of wet gas fluid in carbon steel pipelines for onshore processing offers an economically attractive strategy. Although a substantial saving in capital cost can be realized, the risks of hydrate formation and corrosion damage are two of the main issues with such an approach. The standard industrial practice is to apply chemical solutions to reduce the risks. A thermodynamic hydrate inhibitor, such as monoethylene glycol (MEG) and corrosion inhibitors are commonly utilized to provide hydrate and corrosion control, respectively. Other production chemicals, such as an oxygen scavenger, may also be deployed as part of the risk management process. Consequently, the main challenge to the corrosion inhibitor is to provide corrosion protection throughout the production and processing facility while subjected to high temperatures in the MEG regeneration process and exposure to other production chemicals. Thermal stability and performance assessments should be an important aspect of the qualification process in the selection of corrosion inhibitors. This paper presents data from a laboratory corrosion inhibitor evaluation program, using thermally stressed MEG/chemicals fluids under simulated wet gas pipeline operating conditions, which resulted in the successful qualification of a corrosion inhibitor for the production facility.

Influence of magnetic fields on calcium carbonate scaling in aqueous solutions at 150 °C and 1 bar

The experiments performed as a part of this study were conducted to evaluate the effect of magnetic field treatment upon the scale forming tendency of brine solution composed primarily of calcium bicarbonate ions. The reported results were generated using a Dynamic Scale Loop system with the brine solution exposed to a magnetic field generated by a 6480 Gauss magnet of grade N45SH in a diametrical orientation for 2.5s. Following magnetic exposure, the brine solution was exposed to an elevated temperature 150°C at 1bar to promote the formation of scale within a capillary tube. The extent of scaling was measured by recording the differential pressure across the tube as scaling proceeded. Three important conclusions regarding the effect of magnetic field treatment upon scale formation in calcium bicarbonate solutions were reached. Firstly, the ratio of calcium to bicarbonate plays a key role in determining how magnetic fields influence scale formation, whether promoting or inhibiting it. Solutions containing high concentrations of the bicarbonate, or equal concentrations of the bicarbonate and calcium species showed inhibited scale formation following magnetic exposure. Secondly, the electrical conductivity of the calcium carbonate solution was noticeably impacted by the exposure to the magnetic field through manipulation of the ionic hydration shell and may also provide a measure of the extent of scale formation. Finally, the application of magnetic field treatment for scale inhibition may provide an alternative eco-friendly scale inhibition strategy in place of traditional chemical scale inhibitors.

Microbial Corrosion Resistance of Stainless Steels for Marine Energy Installations

A range of stainless steels has been investigated for resistance to microbiologically influenced corrosion in seawater. The corrosion potential was monitored for stainless steel coupons exposed to sterilized seawater and to microbiologically active seawater, which showed the effect of the growth of microorganisms. Cyclic potentiodynamic polarization scans confirmed that 13%Cr stainless steel is very susceptible to localized corrosion under these conditions. 316L stainless steel was also quite susceptible to localized corrosion, whereas 2205 duplex stainless displayed good resistance to localized corrosion. Naturally occurring microorganisms in the seawater were shown to exacerbate the localized corrosion.

Removal of monoethylene glycol from wastewater by using Zr-metal organic frameworks

Mono-ethylene glycol (MEG), used in the oil and gas industries as a gas hydrate inhibitor, is a hazardous chemical present in wastewater from those processes. Metal-organic frameworks (MOFs) (modified UiO-66∗ and UiO-66-2OH) were used for the effective removal of MEG waste from effluents of distillation columns (MEG recovery units). Batch contact adsorption method was used to study the adsorption behavior toward these types of MOFs. Adsorption experiments showed that these MOFs had very high affinity toward MEG. Significant adsorption capacity was demonstrated on UiO-66-2OH and modified UiO-66 at 1000 mg·g-1 and 800 mg·g-1 respectively. The adsorption kinetics were fitted to a pseudo first-order model. UiO-66-2OH showed a higher adsorption capacity due to the presence of hydroxyl groups in its structure. A Langmuir model gave the best fitting for isotherm of experimental data at pH = 7.