Egil Gulbrandsen

The Effect of Straight Chain Alcohols and Ethylene Glycol on the Adsorption of CTAB on Gold

The adsorption of the cationic surfactant CTAB (cetyltrimethylammonium+ bromide−), together with alcohols CnH2n+1OH (n=3–6) at different concentrations, onto a gold surface, was measured with the QCM technique. The effect of low concentrations (≤500 ppm) ethylene glycol was also investigated. The pure CTAB has a maximum adsorption of ∼110 ng cm−2 at the critical micelle concentration in solution, and adsorption/desorption takes place within seconds. At high concentrations of alcohols (shorter than hexanol) the adsorbed mass was about 30% of the one observed for the pure CTAB. The presence of 10 mM hexanol gave approximately the same amount adsorbed as pure CTAB. At 25 mM hexanol the amount adsorbed increased to 270–300 ng cm−2 and the desorption process was significantly slower than for the other conditions. Upon rinsing, the desorption proceeded in two steps, halting around 140 ng cm−2 before it was further reduced. It is in agreement with other work that surfactant adsorption is reduced by addition of shorter alcohols. The addition of hexanol changes the molecular packing ratio, and the adsorbate changes from discrete spherical aggregates to a bilayer film analogous to the lamellar crystalline D phase. Ethylene glycol does not affect the adsorption significantly at these low concentrations.

Propagation and Arrest of Localized Attacks in Carbon Dioxide Corrosion of Carbon Steel in the Presence of Acetic Acid

Abstract The presence of acetic acid (HAc) has been identified as one factor that may contribute to enhance localized top-of-the-line corrosion attacks in gas condensate pipelines. The role of free HAc on the growth of localized attacks in carbon dioxide (CO2) corrosion of carbon steel pipelines therefore was studied by means of a preinitiated localized attack electrode assembly (“artificial pit electrode”). The current flowing between the localized attack and the outer surface was measured with a zero-resistance ammeter. It is shown that the corrosion potential increases with increasing free HAc concentration. Depletion of free HAc inside the attack imposed a potential difference that triggered the propagation of the attack at room temperature. The pit growth was self-sustained in CO2 and HAc environments only to a certain depth, beyond which the dissolution current at the bottom of the attack vanished. This is in good agreement with field observations in the case of top-of-the-line corrosion phenomena.

Effect of Corrosion Inhibitors and Oil on Carbon Dioxide Corrosion and Wetting of Carbon Steel with Ferrous Carbonate Deposits

Abstract The wettability of the steel surface is an important factor codetermining the risk of corrosion in multiphase pipelines for transportation of oil and gas. The present paper deals with the ...

Effect of Oxygen Contamination on Inhibition Studies in Carbon Dioxide Corrosion

Abstract The effect of oxygen (O2) contamination on the inhibition of carbon dioxide (CO2) corrosion was studied using carbon steel rotating cylinder electrodes (RCE). The test conditions were 40°C, 1 bar CO2, pH 5.5, and 1 wt% sodium chloride (NaCl) solution. The uninhibited CO2 corrosion rate was 1.5 mm/y to 2 mm/y under these conditions. Three organic, film-forming corrosion inhibitor formulations were tested in the concentration range from 20 ppm to 50 ppm. With less than 1 ppb of dissolved O2 in the test brine, the inhibitors reduced the corrosion rate by two orders of magnitude, and the inhibited corrosion rates were insensitive to the RCE rotation rate (100 rpm to 5,000 rpm). In the presence of 100 ppb O2 with 20 ppm to 30 ppm inhibitor, the corrosion rates depended on the RCE rotation rate, the corrosion rate being under partial or full O2 diffusion control with some contribution of CO2 corrosion. The O2 corrosion rate was reduced by increasing the inhibitor concentration. The consequences of the ...

Oil Wetting and Carbon Dioxide Corrosion Inhibition of Carbon Steel with Ferric Corrosion Products Deposits

Abstract Wettability of carbon steel with corrosion product films (iron carbonate [FeCO3], FeCO3 with oxidized surface, and rust [FeO(OH)]) was investigated through contact angle and inhibitor perf...

Alteration of Wettability of Corroding Carbon Steel Surface by Carbon Dioxide Corrosion Inhibitors-Effect on Carbon Dioxide Corrosion Rate and Contact Angle

Abstract The wettability of the steel surface is an important factor co-determining the risk of corrosion in multiphase pipelines for transportation of oil and gas. The effect of carbon dioxide (CO2) corrosion inhibitors on the wettability of carbon steel was investigated in the present paper. Also investigated was the effect of oil on the performance of these inhibitors. Three inhibitors were investigated. Two of them were commercial inhibitor-based chemicals: an oleic imidazoline salt (OI) and a phosphate ester (PE). The third was cetyltrimethylammonium bromide (CTAB), a well-characterized quaternary ammonium compound. A refined, low-aromatic oil product was used in the tests. The wettability of the corroding carbon steel surface was studied by contact angle measurements (25°C, 1 bar CO2, 3 wt% sodium chloride [NaCl]). Both oil-in-water and water-in-oil experiments were performed. The effect of the inhibitor/oil interactions were also studied in CO2 corrosion tests where the steel specimens were alterna...

Partitioning of a Model Corrosion Inhibitor in Emulsions

As the majority of corrosion inhibitors used in oil production are surfactants, they are are not only adsorbing to metal surfaces, but also at the oil/water (o/w) interface and onto dispersed solid particles. In the present work, the partitioning of cetyltrimethylammonium bromide (CTAB) between the aqueous bulk and the o/w interface is investigated. Zeta potential measurement of oil droplets at different CTAB concentrations has been utilized to study the adsorption process at the o/w interface. The CTAB reached an adsorption maximum at the critical micelle concentration. Upon dilution, the CTAB desorbed to equilibrium values within minutes. A new method has been utilized for determining the concentration of CTAB in the continuous phase of an o/w emulsion. The effects of some selected parameters were investigated in a fractional factorial experimental design, and the main effects were determined by blocking the experiments for each effect. The average loss of CTAB due to emulsification of 5% oil was found to be 0.34 and 0.24 mmol dm−3, 15 minutes and 315 minutes after emulsification, respectively. The loss of CTAB was higher for samples with an initial concentration of 3 mmol dm−3 than for those with an initial concentration of 1 mmol dm−3. Of the parameters investigated, the presence of 3% NaCl had the highest impact on the CTAB loss for the samples taken 15 minutes after emulsification, while the presence of 100 ppm MEG had the highest impact 315 minutes after emulsification. The presence of NaCl and MEG increased the aqueous concentration of CTAB.

Adsorption of Corrosion Inhibitors onto Iron Carbonate (FeCO3) Studied by Zeta Potential Measurements

The adsorption of cetyl trimethyl ammonium bromide (CTAB) and two commercial inhibitor base chemicals, an oleic imidazoline salt (OI) and a phosphate ester (PE), onto iron carbonate (FeCO3), was studied by zeta potential measurements in a 0.1 wt% sodium chloride (NaCl) solution under 1 bar CO2 at 22°C, in the absence and presence of a refined low-aromatic oil. The zeta potential of oil-in-water emulsion droplets was also determined. Surface tension of 0.1 wt% and 3 wt% brines was measured as a function of inhibitor concentration. The isoelectric point was pH 6.0 in the 0.1 wt% NaCl solution under 1 bar CO2. The results show that all three inhibitor compounds adsorbed onto the iron carbonate particles both at pH 4.0 and pH 6.0. Adsorption on both negatively charged surfaces and surfaces with no charge were thus found for all inhibitors. The addition of oil had no significant effect on the measured zeta potential on iron carbonate particles.

Measurements of Zeta Potential on Corroding, High-Purity Iron Particles: Influence of Corrosion Inhibitors

Adsorption of cetyl trimethyl ammonium bromide (CTAB), and two commercial inhibitor base chemicals; an oleic imidazoline salt (OI) and a phosphate ester (PE), onto high purity, corroding iron particles was studied by zeta potential measurements in a 0.1 Wt% sodium chloride (NaCl) solution under 1 bar CO2 at 22°C. The particles were exposed to the inhibitor compounds for 24 hours before measurements were done. The results show that the measured zeta potential in the absence of inhibitor is zero at both pH 4.0 ± 0.2 and pH 5.8 ± 0.2. It is concluded that this might be caused by the electrochemical reactions occurring at the steel surface when placed in an electrical field. When adding inhibitor, which slows the electrochemical reactions at the steel surface, the zeta potential moves away from zero and an adsorption isotherm is obtained for all three inhibitors. The measured potential is probably a mixed potential where the apparent potential measured is a combination of the potential at the shear plane and a contribution form the electrochemical reactions occurring on the surface.

Adsorption of Polycation and Anionic Surfactant onto Iron Surfaces and the Inhibition of Carbon Dioxide Corrosion

The adsorption process of two polycations (pDADMAC and C‐PAM) with different charge densities has been investigated using the quartz crystal microbalance technique with dissipation monitoring (QCM‐D). The effect of the charge density of the polycation, the NaCl concentration, and the complexation with an anionic surfactant are addressed in this work. X‐ray photoelectron spectroscopy and atomic force microscopy were utilized to analyze the adsorbate with respect to the film coverage and film structure. The corrosion‐inhibiting performance of the films on high‐purity iron in a CO2 saturated brine, at 25°C, 1 bar CO2, and pH 4, was investigated by the linear polarization resistance technique. It was found that the polycations adsorbed onto the iron surface, but the corrosion rate of 1 mm yr−1 was not lowered. However, the polycations formed a complex with an anionic surfactant, and such films showed excellent inhibition performance. Both films, of pDADMAC/SDS and of C‐PAM/SDS, lowered the corrosion rate of iron below 0.01 mm yr−1. The SDS concentration was below the cmc. It is believed that the SDS adsorbed into the preadsorbed polycation film, forming a complex structure resulting in a hydrophobic and dense film.