Harvey J. Flitt

Computer simulation of the corrosion inhibition of copper in acidic solution by alkyl esters of 5-carboxybenzotriazole

A series of alkyl esters (methyl, butyl, hexyl, and octyl) synthesised from a mixture of 4- and 5-carboxybenzotriazole (4-CBTAH and 5-CBTAH) inhibited copper corrosion in aerated solution (pH � 0). Inhibition efficiency (IE%) of the protonated esters (CBTAH þ -R) increased with hydrocarbon chain length and this is attributed to chemisorption (through azole ring N) and increased physical adsorption as more methyl groups are introduced. A modelling package employing molecular mechanics and molecular dynamics has been used to simulate the docking of a single protonated species (5-CBTAH þ -R) onto a clean copper (1 1 0) surface. A decrease in potential energy was associated with the flattening of the ester ring system onto the surface and further decreases in energy were associated with the extension of the aliphatic chain onto the surface. The crude binding energy (Ebind) of each ester with the surface was estimated and this energy also increased regularly with carbon chain length. The study suggests that molecular modelling and calculation of Ebind of a single molecule on a specified metallic surface can be used to predict the inhibition performance of compounds whose structures change in a regular way. 2002 Elsevier Science Ltd. All rights reserved.

The effect of potential scan rate on the parameters used to synthesize anodic polarization curves

Abstract The anodic polarization behaviour of pure iron in near neutral 0.1 M sodium benzoate with and without 0.007 M Cl − at different potential scan rates has been studied. The suitability of a computerized curve matching routine for systems exhibiting the typical active-passive transition and subsequent film breakdown has been demonstrated. The effect of potential scan rate on the input parameters required to generate the anodic polarization curve was established and empirical linear relationships were derived. This leads to the prediction of curves at other scan rates and good matches between the predicted and experimental curves are obtained provided the scan rate is not too far outside the initial range chosen.

The corrosion of a low alloy steel in a steam turbine environment : the effect of oxygen concentration and potential scan rate on input parameters used to computer match the experimental polarization curves

Abstract The corrosion behaviour of A-470 low alloy steel in a simulated low pressure steam turbine environment at ambient temperature has been examined as a function of dissolved oxygen (DO 2 ) concentration. A computerized routine was used to synthesize, match and deconvolute experimental potentiodynamic polarization curves. The empirical relationships between the input parameters required to match the experimental polarization curves at different potential scan rate (v) and DO 2 levels has been established. The effect of increasing DO 2 level and v parallel one another. The DO 2 concentration resulting in spontaneous passivation was between 0.05 and 0.10 ppm whilst concentrations between 2.50 and 3.00 ppm led to instantaneous pitting.

The effect of hydroquinone and methoxypropylamine on the pitting corrosion behaviour of A-470 low alloy turbine disc steel

Abstract Electrochemical techniques have been used to study the pitting corrosion behaviour of A-470 turbine rotor disc low alloy steel (LAS) in a simulated aggressive turbine environment containing 2 ppm NaCl + 2 ppm Na 2 SO 4 + 2 ppm NaOH + 5 ppm SiO 2 (30°C) in the presence of hydroquinone (HQ) and methoxypropylamine (MPA), alone or in combination. Addition of HQ to N 2 purged solutions shifts the corrosion potential in the positive direction and spontaneous passivation is observed at concentrations of approximately 100 ppb. HQ concentrations as low as 150 ppb can induce pitting and Scanning Electron Microscopy studies revealed these pits to have been formed primarily at MnS inclusions. Potentiodynamic polarization has been used to determine the pitting potential ( E pit ) of the alloy in N 2 purged solutions containing different concentrations of MPA between 1 × 10 −4 and 1 × 10 −3 M. E pit increased with increasing MPA concentration and immunity to pitting corrosion is evident at concentrations above 4 × 10 −4 M. Surface analysis studies show this inhibition to be due to the chemisorption of MPA on the metal. In case of HQ/MPA mixtures, the pitting corrosion of the alloy by 200 ppb HQ is completely inhibited by 2 × 10 −4 M MPA. The normal practice of adding amines to adjust the pH of turbine feed water acts to counteract the pitting characteristics of HQ at higher concentrations.

The corrosion resistance of low carbon steel in flowing sugar juice: The analysis of polarization curves from a laboratory flow system

Abstract A study of the corrosion of mild steel in sugar juice in a laboratory flow rig has shown that oxygen reduction, which is the dominant cathodic reaction and comes under mixed activation and mass transport control, remains the dominant cathodic reaction at flow rates corresponding to normal factory operation and as combined polarization was still observed, the linear polarization resistance method is not applicable. The surface film whose resistance increases with time deposits on the working electrode, leads to a reduction in the corrosion rate and counteracts the increase in corrosion rate expected with an increase in flow rate.

The pitting of low alloy turbine disc steel

Blades and discs in low pressure (LP) steam turbines are subject to stress corrosion cracking. Pitting may be a precursor to failure and this is influenced by ionic contaminant build up in the steam. This paper addresses the main and interaction effects of four common contaminants on the pitting susceptibility of NiCrMoV disc steel in a typical steam impurity environment. A two-level full factorial experimental design was used to study the influence of chloride, sulphate, fluoride and carbonate. A solution containing 2 ppm sodium chloride, 2 ppm sodium sulphate, 2 ppm sodium hydroxide and 5 ppm SiO2 and ofpH= 9.0 ± 0.1 was employed as a background electrolyte and low levels of each contaminant corresponded to 0 ppm or to that in the background electrolyte. The high level was set at 2500 ppm. The pitting tendency of the background electrolyte at different dissolved oxygen levels was evaluated from corrosion potential-time curves and potentiodynamic polarization was used to determine the relative pitting susceptibility of the alloy at 30°C in the various nitrogen purged solutions. The solutions were also saturated with air to evaluate the tendency towards spontaneous pitting. Chloride, fluoride and sulphate were found to promote localized corrosion whilst carbonate was an inhibitor. The statistical analysis shows that no significant synergistic effect is operative between the contaminants. Some contaminants, however, do interact to reduce or prevent the tendency to pit. Instantaneous pitting was observed in air saturated solutions of the background electrolyte. This behaviour was also exhibited in the presence of high levels of chloride, fluoride and sulphate, alone or in combination. A high level of carbonate alone or in combination with high levels of chloride, fluoride and sulphate prevents pitting.