Some basic considerations concerning the origin of the contribution of the ohmic drop to the electrode potential are developed. A simple electrical scheme of the solution-metal interphase is proposed in order to give an analytical representation of the kinetic law and to study the dependence of the corrosion current density and the Tafel slopes on the solution resistance. The analytical expression of the dependence of the current density on the solution resistance is established. The experimental applications concern the behaviour of some carbon steels in solutions containing 100 g l−1 EDTA at different pH and 100°C. These results have shown that the corrosion current density and the Tafel slopes depend in a critical way on the solution resistance. However, in the case of low alloy steel SA 213 grade T9, which exhibits a small corrosion rate, the previous quantities keep a constant value. These electrochemical systems were considered in order to introduce an extrapolation technique, based on the best-fitting of the reckoned values of Ic, Ba and Bc as a function of the solution resistance.
ZINC ELECTRO deposits of 5, 10, and 15 microns thickness were obtained using an alkaline non-cyanide zincate bath, and some of the samples were chromated. The corrosion behaviour of the zinc deposits was studied in 3.5% NaCl solution, by both electrochemical and non-electrochemical techniques such as galvanostatic, potentiodynamic, impedance, salt-spray, and weight-loss methods. Three specimens under identical conditions were subjected to the test. Similar studies were carried out for the chromated specimens, and the results are discussed.
THE INHIBITION effect of a naturally-occurring petrophorum pterocarpum extract on the corrosion of mild steel in 1M HCl has been studied using the weight-loss and electrochemical methods. The inhibition efficiency is found to increase with the concentration and is a maximum at 2 % concentration of the extract. The optimum time for maximum efficiency was found to be 2 hours. The inhibitor was found to behave like anodic inhibitor, and the mechanism of the inhibition was the adsorption process.
THREE REDUCING sugars-glucose, fructose, and maltose-were tested as inhibitors of carbon-steel corrosion in alkaline solution. Their inhibition efficiencies were measured using weight-loss and potentiostatic polarization, and it was found that the. addition of any of the three reduced the corrosion rate of the steel. The inhibition efficiency decreased according in the order glucose > fructose > maltose. The adsorption of glucose molecules on the steel surface followed the Langmuir adsorption isotherm, whereas the adsorption of fructose and maltose do not. It was also found that the three sugars acted as anodic inhibitors, where their oxidation reactions interfered with the anodic corrosion reaction of the steel The inhibitive effects of the tested sugars are discussed in view of their relative reducing-power. UV-visible spectra were recorded for the test solutions after the completion of the weight-loss experiments, and the spectra suggested a formation of metal-sugar complexes.
SOME GENERAL considerations on the use of computerized systems in the corrosion field for performing electrochemical measurements, and collecting and processing data, using suitable software are given, and the usefulness of determining instantaneous corrosion rates for metallic materials using the polarization-resistance method is emphasized. It has been stressed that the use of the Stern and Geary method is empirically justified by its ability to provide reliable information. A useful hint for computing the actual value of E-m when experimental data are stored on a magnetic support is given, and their selection criterion is illustrated. Some results relating to the behaviour of iron in 0.5M H2SO4 solutions containing aliphatic amines at various concentration and at 25 degrees C demonstrate clearly that the best-fit with the monomial i = R(p)(-1)Delta E over the [-10, 10]mV interval associated to the Stern and Geary scheme fairly faithfully reproduces the theoretical values of I-c obtained using the POLCURFIT program, as illustrated by a numerical case, and the relative error never exceeds the value of 4%. Furthermore, as documented by a graphic example, it has been proved that in the vicinity of Delta E = 0, the trend of experimental points is very close to the best-fit straight line, in agreement with Skold and Larson's observations.The scheme for determining R-p through the best-fit with the polynomial i = a Delta E + b Delta E-2 + c Delta E-3 was adopted in the SOFTCOR-DC-PSI program. In this case, the reproduction of the trend of polarization curves over the Delta E [-20, 20]mV interval is very satisfactory, as documented by the case of iron in 5% by weight HCl solutions containing a commercial product and at temperature values ranging from 35 to 90 degrees C.Finally, it should be stressed that the use of a third-degree polynomial allows application of the Bonhoffer and Jena definition with a high level of confidence.
THE CORROSION behaviour of Ti-6Al-4V alloy in 2.5M H2SO4 and 5.0M HCl solutions containing different concentrations of methanol was investigated using polarization and electrochemical-impedance spectroscopy (EIS). The corrosion rate of the alloy was found to decrease with increasing alcohol content in the acid solution. Also, the effect of a cationic surfactant - such as Bradoral - on the corrosion rate of the alloy in methanolic sulphuric and hydrochloric acid solutions was studied. The corrosion inhibition efficiency at different concentrations of the surfactant was calculated: it turned out that Bradoral has a maximum corrosion inhibition efficiency for the alloy at a concentration of 7.5 x 10(-4)M in 2.5M H2SO4 and 7.5 x 10(-3)M in 5.0M HCl. Scanning-electron micrographs indicated that the patches and flawed regions on the alloy surface were reduced greatly in the presence of Bradoral. The activation energy values of alloy corrosion in methanolic 2.5M H2SO4 and 5.0M HCl solutions were found to be 69 and 56kJmol(-1), respectively.
MICROBIAL CONTAMINATION of fuels has been the cause of intermittent operation problems and corrosion throughout the world for many years, and more recently the frequency and severity of the cases appears to have been dramatically increasing. This study emphasizes the role of fungi on diesel degradation and its influence on corrosion of mild steel: fungal strains were isolated from diesel oil collected from storage tanks and were identified as Penicillium sp., Candida sp.., and Aspergillus sp.. The degraded diesel was characterized and analyzed by Fourier transform infra-red spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The corrosion studies were carried out by gravimetric methods, and the product of the corrosion analysed using XRD to find out the nature of the corrosion product. The biodegradation and corrosion studies showed that all the strains were aliphatic protons and aromatic protons in refined diesel, capable of oxidizing ferrous ion into ferric oxide. This is the first report that discloses the involvement of fungal strains on biodegradation of diesel and its influence on corrosion.
THE CORROSION behaviour of carbon steel was investigated in seawater. A suitable mechanism of corrosion is proposed based on the results obtained from the electrochemical and weight-loss measurements. The nature of the formed protective film on the alloy surface was been analysed by X-ray diffraction (XRD) and was found to be a double layer consisting of Fe2O3 and Fe3O4. A metallographic study using scanning-electron microscopy showed the existence of pits along the alloy surface after ageing in seawater.
VINYL-CHLORIDE monomer and poly-vinyl chloride are extensively used as raw materials by the plastic industry. Petrochemical plants that produce these raw materials are often highly structured units employing a wide variety of engineering materials in their construction and design. The selection of a particular material is based on the performance of a component required under specific conditions. This paper describes the materials' evaluation of a dryer support component used in the drying unit of a PVC plant.The component was made of 304-type stainless steel and was fractured after a relatively-short period of service. Various techniques used for materials analysis included scanning-electron microscopy combined with energy dispersive X-ray spectroscopy and diffraction. The dryer support appeared to fail by hydrogen-induced cracking (HIC). Based upon the results obtained, it was recommended to use an alloy more resistant to hydrogen-induced cracking such as the 309-type stainless steel.
ELECTROCHEMICAL CREVICE corrosion experiments were carried out on 304 stainless steel in ground water in order to assess the crevice-corrosion inhibition of various inhibitors, including phosphonates, bivalent cation, and surfactants. These studies were made in conjunction with a surface-morphology study by scanning-electron microscopy and a solution analysis by inductively-coupled plasma-atomic emission spectrometry so as to determine the amount of metal ions leached out at different imposed potentials. These two techniques proved the beneficial action of inhibitor application in improving the crevice-corrosion resistance of 304 stainless steel in ground water.
A NUMBER OF high-profile pipeline failures across Canada and the United States have brought the issue of pipeline safety to the forefront. Every year in Alberta, more than 750 pipelines fail, potentially causing harm to both people and the environment. The Energy and Utilities Board (EUB) that regulates pipelines in Alberta attributes these failures to three primary causes: internal corrosion, external corrosion, and third-party damage.Upstream pipelines account for approximately two thirds of the pipeline failures that occur in Alberta, and over half of those failures are due to internal corrosion. For the operators of these pipelines, integrity maintenance is problematic due to three factors:Upstream pipelines are typically multiphase and have a corrosive environment caused by the CO2, H2S, and chloride-containing water that comes directly from the production reservoir.Most of these pipelines cannot be easily inspected with smart tools, and determination of the location and severity of internal corrosion is difficult by other means.The sheer volume of pipelines (H circle 200,000km in Alberta) makes it difficult for operators to know where to concentrate their efforts to ensure the best value and highest impact.In the latest release of their pipeline integrity software, PipeCraft, GreenPipe Industries Ltd has developed an internal corrosion model (ICM) to help operators manage its internal corrosion issues using information from the operator's records and the public domain (such as the EUB). The ICM combines the power of a geographic-information system (GIS) with corrosion prediction and hydraulic analysis tools to determine the locations for direct assessment for internal corrosion.In a joint project, GreenPipe and Talisman Energy Inc have worked together to validate the algorithms in the internal corrosion model using the results from actual inline inspection data. The results of this project demonstrated an excellent correlation between the predicted and measured severity of the major corrosion defects. PipeCraft also includes a comprehensive GIS-based consequence algorithm which, when used in conjunction with the ICM, provides the risk based methodology to prioritize pipelines for direct assessment as recommended by ASME B31.8S-2000, as well as verify the effectiveness of corrosion inhibition and monitoring programs.
T HE CORROSION behaviour of a cadmium electrode in Na2CO3 and HCl solutions was studied in the absence and presence of five compounds of cationic surfactants of olyelamido derivatives using potentiostatic polarization technique. The inhibition efficiency was found to increase with increasing the inhibitor concentration and the number of polyethylene diamine units, and decrease with rising temperature. These compounds are more effective in HCl than in Na2CO3 solutions. This can be attributed to the synergistic effect of Cl- ions with the cationic surfactant compounds. The inhibitors are adsorbed on the surface of Cd in both HCl and Na2CO3 solutions according to Langmuir adsorption isotherm. The effect of temperatures was studied to evaluate some activated thermodynamic parameters.
COPPER TUBES used in a commercial air-conditioning system were analysed to assess the reasons for their premature corrosion failure during leakage tests after installation and during their first two months in service. Scanning-electron microscopy, energy dispersive Xray analysis, and X-ray photoelectron spectroscopy were the techniques used. Volatile organic acids, chlorine, and sulphur, originated by the manufacturing processes, were identified as possible sources of the premature copper corrosion failure.
THE ATMOSPHERIC corrosion behaviour of engineering materials such as mild steel, zinc, galvanized steel, and aluminium has been studied at 40 exposure stations in India, and corrosion data from the sites have been collected for over 11 years, from 1993-2004. The data collected from these sites have been analyzed and presented in the form of updated corrosion maps of India. In these maps, the annual corrosion rate for each particular material have been arranged in four ranges, which are colour coded. An interesting feature of the maps is that the corrosion is area-specific, and not region-specific.The durability factor is defined as the ratio between the corrosion rate of mild steel and that of a non-ferrous metal exposed at a particular location. The durability data have been analyzed and are presented as durability maps of India. The data clearly indicate that non-ferrous metals, such as galvanized steel, zinc, and aluminium, have better corrosion resistance than bare mild steel. However, the factors vary from area to area. These data were calculated from one-year exposure studies. If the durability and the cost factors are taken together, it can be clearly seen that aluminium has an appreciable cost-benefit ratio; at certain locations, galvanized steel may also prove to be a cost-effective material.
EVEN THOUGH corrosion can manifest itself in many forms, the impact of uniform corrosion on the cost of corrosion will be quite different. Out of 11 different forms of corrosion, only uniform corrosion plays an important role. By suitable illustration, the impact of uniform corrosion on corrosion economics has been evaluated and is presented in this paper.
THE EFFECT of ethoxylated fatty amines on the corrosion behaviour of mild steel-which is used in petroleum pipelines-in I M HCl has been investigated using weight loss and potentiostatic-polarization techniques. The values of inhibition efficiency obtained from the weight-loss measurements was found to be in good agreement with those obtained from the potentiostatic polarization study. They increased with increasing concentration, number of ethylene oxide units, and with decreasing temperature. Inhibition is explained on the basis of adsorption of these compounds on the steel surface through their ethoxy groups, and the adsorption obeys the Langmuir adsorption isotherm. Some thermodynamic parameters were calculated and are discussed.
The inhibition of juice extract of cashews (Anacardium Occidentale) on the corrosion of mild steel test specimens immersed in 0.5M H2SO4 at ambient temperature was evaluated. The weight-loss method and potential-measurement technique were used for the experimental work. The juice was obtained from the bark, apples, and nuts of the tree: the bark juice extract provided a fairly good inhibition performance at a concentration of only 0.5ml juice per 100ml of acid; the nut juice extract, at all concentrations used, provided very minimal corrosion inhibition of the test specimen in the acid; the cashew apple juice gave more-than-average performance of inhibition of the test specimen at all the concentrations used.
THE BASIC ASPECTS of the theories proposed by North and Pryor [12] and Gaparini et al. [14] to explain the growth of a protective lepidocrocite layer on the surface of copper and its alloys exposed to seawater conditioned with ferrous salts, and the approach dealing with a heterogeneous reaction occurring through an electrochemical path, are discussed. Some general considerations concerning the physical meaning of aluminium brass corrosion monitoring are developed, and the usefulness of performing in-field measurements to detect anomalous situations during the operation of steam condensers cooled with seawater is carefully examined in order to check the actual validity of information produced using suitable electrochemical techniques. The monitoring system, constituted by three- and five-electrode probes and a computerized corrosion rate meter, installed on the steam condensers of two units of an Italian power station, is described in detail. Concise considerations concerning the computer program developed to control the operation of the corrosion meter and collect experimental data are also given.Some data obtained from the electrode probes installed on the tube sheets of the second pass of the Unit 3 condenser are examined in detail to establish empirical guidelines for an optimal injection of Fe2+ ions into seawater. Finally, experimental data collected during a three-year period were rather useful for proper operation of the ferrous chloride injection system, for defining the optimal length of the continuous seawater treatment, detecting failures of the protective film, and carrying out discontinuous conditioning operations.
