Anti-Corrosion Methods and Materials

Application of the inverse wavelet transform on electrochemical current signals to demonstrate the essence of high-frequency variations : Table of Contents

Mehdi Khodayari, Saeed Reza Allahkaram, Alex A. Volinsky — Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – One way to analyze electrochemical signals is the wavelet transform, which transforms a signal into another representation whereby the signal information is presented in a multi-scale manner. Using the inverse wavelet transform, it is also possible to split a signal into different components of different frequency intervals. The inverse wavelet transform is the concept underpinning this paper, the aim of which is to demonstrate that high-frequency variations in current signals are as valuable as low-frequency variations. Design/methodology/approach – The set-up for the experiments carried out consisted of two identical carbon steel working electrodes exposed to simulated concrete pore solution, sparged simultaneously with SO2 and CO2. The corresponding electrochemical current signal was studied using wavelet transform. Findings – High-frequency components of current signals are as informative as low-frequency components. High-frequency variations could show some electrochemical activities that are not obvious in the other parts. Originality/value – This paper shows that high-frequency variations can be taken into consideration along with low-frequency variations, since both can provide complementary information about electrochemical activities.

Quantitative analysis of the effect of coarse aggregate diffusivity on reinforcing steel corrosion initiation with a finite element model : Table of Contents

Hui Yu, William H. Hartt — Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – The purpose of this paper is to explore and compare the influence of diverse coarse aggregate (CA) diffusivities on reinforcing steel corrosion initiation through a quantitative modeling analysis approach. Design/methodology/approach – Finite element analysis was used to solve two-dimensional chloride diffusion processes, which follow the Fick's second law within the concrete cover. Two non-dimensional time-derating factors were employed to quantify the time-to-corrosion of steel rebar, Ti, for different models. Findings – The finite diffusivity CA exhibits variable effects on Ti, depending upon: diffusivity ratio between the CA and mortar; CA type; reinforcement corrosion resistance; and cover thickness. The intent of the effects are expressed quantitatively and their implications discussed. Originality/value – The methodology and results presented in this paper provide insights on the variable reinforcement Ti values as a function of CA diffusivity. The approach employed herein provides an effective tool to select CA materials for reinforced concrete structure where chloride-induced corrosion is a concern.

Stress corrosion cracking of sensitized austenitic stainless steels in Kuwait petroleum refineries : Table of Contents

A. Almubarak, M. Belkharchouche, A. Hussain — Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – The purpose of this paper is to investigate stress corrosion cracking (SCC) for 304, 316, and 321 stainless steels in petroleum-processing environments. Design/methodology/approach – Sensitized austenitic stainless steels were subjected to a microstructure investigation and electrochemical test. Stressed sensitized 304, 316, and 321 stainless steels were selected and subjected to various environments that included polythionic acid, sour solution, and chloride solution that were prepared in the laboratory to simulate service environments in the petroleum refinery. Findings – Microstructure investigation reveals more severe SCC in polythionic acid than in the sour and chloride solutions. Type 321 SS gives better resistance to SCC than do 304 and 316 SS in the three solutions. It is concluded that acidity of solutions has a relatively minor influence in promoting cracking. However, polythionic acid is found to be the primary causative agent. Originality/value – The results demonstrated that SCC is more severe in polythionic acid than in chloride and sour solutions.

Effect of cryogenic cooling on corrosion of friction stir welded AA7010-T7651 : Table of Contents

Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – The purpose of this paper is to study how cryogenic CO2 cooling during the welding process affects corrosion behaviour of friction stir welding (FSW) AA7010-T7651. Design/methodology/approach – Friction stir welded AA7010-T7651 was produced with a rotation speed of 288?rpm and a travel speed of 58?mm/min. The liquid CO2 was sprayed onto the weld centre line immediately after the toolpiece. The microstructures of welds in different regions were observed using Field Emission Gun Scanning Electron Microscope (FEG-SEM). The effect on the corrosion susceptibility was investigated using a gel visualisation test and potentiodynamic polarisation measurements using a micro-electrochemical technique. Findings – The main corrosion region for both FSWs AA7010-T7651 produced with and without cryogenic CO2 cooling is in the HAZ region, which exhibited intergranular attack. Cryogenic cooling does not show any influence on anodic reactivity of the weld region (both nugget and HAZ) compared to uncooled weld metal. However, the width of the reactive HAZ is reduced after cooling, as compared to the uncooled weld. The cooled welds show higher cathodic reactivity in the nugget region than does the nugget region of uncooled welds. Originality/value – There has been no previous work to investigate the effect of cryogenic CO2 cooling on the corrosion behaviour of FSW AA7010-T7651. The paper relates the microstructures of both uncooled and cooled welds to their anodic and cathodic reactivities using a micro-electrochemical technique.

Effect of the relative velocity between ship hull and seawater on the performance of sacrificial cathodic protection : Table of Contents

G.H. Sedahmed, H.A. Farag, M.A. Hassan, I. Hassan — Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – The purpose of this paper is to study the effect of the relative velocity between ship hull and seawater on the rate of zinc consumption and degree of cathodic protection during sacrificial cathodic protection of steel hulls using zinc anodes. Design/methodology/approach – The rate of zinc consumption under different relative velocities was determined by the loss in weight technique while the degree of cathodic protection of the ship hull at different distances from the anode was determined by measuring the cathode potential of the hull cathode against a silver/silver chloride reference electrode. Findings – Within the present range of conditions, the rate of zinc consumption (R) was found to increase with increasing the relative velocity according to equations: R=3.9×10-4 Re0.0126; for Re<3,500, and R=7.36×10-6 Re0.5; for Re>3,500, where Re is the Reynolds number. The degree of cathodic protection represented by the hull (cathode) potential at a given distance from the anode was found to decrease slightly with increasing the relative velocity. Originality/value – The present results would make it possible for the designer of sacrificial cathodic protection systems to assess the amount of zinc required to protect the ship hull under certain operating conditions more accurately than the situation where the effect of the relative velocity was not considered.

Enhancement of corrosion protection of micro-arc oxidation by applying nanostructured TiO2 thin film via the “sol-gel” method : Table of Contents

M. Aliofkhazraei, A. Sabour Rouhaghdam, M. Laleh, A. Shanaghi — Mon Mar 08 02:05:32 GMT 2010

Abstract:
Purpose – Uniform nanostructured TiO2 thin film has been applied as an over coat on micro-arc oxidized substrate, using the sol-gel method. The anticorrosion performance of the coating have been evaluated using electrochemical techniques. Owing to increasing application of light alloys in industry, the purpose of this paper is to report effort to increase the corrosion and wear resistance properties of these alloys by applying a TiO2 nanostructured coating using the sol-gel method on the micro-arc oxidation (MAO) surface. This approach will decrease the time for the MAO process, especially for achieving good mechanical properties, and will minimize energy consumption as well as achieving better results from the obtained coatings. Design/methodology/approach – Sol-gel coatings were deposited (on titanium substrates) by spin coating techniques. The morphologies and nanostructures of thin films were analyzed using scanning electron microscope, atomic force microscopy and grazing incidence X-ray diffraction (XRD). The anticorrosion performance of the coating has been evaluated by using electrochemical techniques. Tafel polarization measurements provide an explanation for the increased resistance of nanostructured TiO2 coated specimen against corrosion. Effective sol-gel coating parameters were optimized with respect to this enhancement. Electrochemical impedance spectroscopy measurements showed the role of barrier layer on corrosion resistance of MAO and nanostructured TiO2 coating. Findings – The results showed that icorr is decreased from 0.258 to 0.169 (µA/cm2). An optimized TiO2 nanostructured coating with thickness of 74?nm will shift the open circuit potential (OCP) about 165?mV and will improve the corrosion prevention properties of coated samples. Corrosion resistance by these duplex coatings can be improved by a factor of more than three times, compared to that of the uncoated substrate. Increasing the coating thickness to more than 74?nm will decrease the physical and corrosion properties of coated samples. It can be concluded that samples with the optimized coating showed higher values of charge transfer resistance, due to the presence of a newly formed layer that accounted for the greater corrosion protection. Practical implications – The results obtained in this research into nanostructured coating can be used wherever good corrosion and wear resistances are required. Originality/value – The speed of treatment by this technique makes this method very suitable for industrial surface treatment of different components.