Anti-Corrosion Methods and Materials

Mechanism of degradation of stabilized corrosion-resistant steel during the welding cycle : Table of Contents

Eva Schmidova, Pavel Svanda, David Vesely, Andrea Kalendova — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to clarify the destabilisation mechanism that occurs with two types of ferritic corrosion-resistant steel during the welding cycle. Design/methodology/approach – A series of experimental weld joints was made to verify the actual response of non-stabilised corrosion-resistant steel, and of the same steel that had been stabilised by added titanium. The character and extent of the ensuing structural changes were analysed. The essential characteristics of degradation in the heat-affected zone are evaluated using optical and scanning electron microscopy; individual phases are identified by means of EDX microanalysis. The underlying mechanism for the loss of stability is induced experimentally in several stages; depending on the thermal doping level and interaction with the environment during the welding process, phases of various types are precipitated. These phases subsequently are studied in connection with the original microstructural characteristics of the steel and the induced grain boundary decohesion of the surface layer. The scope and character of the damage are analysed and the results verified by analysing the actual operating damage to the weldment. Findings – A degradation mechanism of stabilised corrosion-resistant steel 1.4510 is induced that is associated with destabilisation of titanium phases. The importance is demonstrated of ensuring that a protective atmosphere is maintained during welding, and various phase changes in the surface layers are identified that can delimit the use of appropriate post-weld passivation procedures. Practical implications – Identification of the mechanism underlying the damage to the surface layer in welded stabilised ferritic steel will find application in development of welding technology, specifically in designing a technology process and subsequent surface treatment. Originality/value – The results bring new knowledge of material response of steel 1.4510 under specific material processing conditions; a destabilisation mechanism related to precipitation of several titanium-containing phases is identified. The result enables the fatigue limit of the welded material as a function of the welding technology employed, which offers increased service life under specific application conditions.

The corrosion of silver in indoor conditions of an assembly process in the microelectronics industry : Table of Contents

O.L. Vargas, S.B. Valdez, M.L. Veleva, K.R. Zlatev, W.M. Schorr, G.J. Terrazas — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to evaluate the corrosion of silver due to hydrogen sulphide pollutant in indoor conditions at a microelectronics plant located in Mexicali, Baja California, a semi-arid zone in the northwest of Mexico. Design/methodology/approach – Silver coupons and silver plated on to copper-lead frames are exposed in the assembly process building of a microelectronics company during a period of 60 days and also in a sheltered test chamber that simulates indoor conditions with ambient concentrations of atmospheric pollutants, temperature and relative humidity (rH). Other exposures are made in the test chamber to study the corrosion behaviour of silver coupons over a duration of 24 months. The corrosion products were analysed using the Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Corrosion rates were measured by Quartz Crystal Microbalance (QCM) under laboratory-controlled conditions. Findings – The presence of silver sulphide corrosion products, dendrites and whiskers is observed on the exposed samples using SEM and EDS analysis. Practical implications – The paper is designed to establish whether the company, where the exposure is taking place, constituted an indoor environment with outdoor hydrogen sulphide pollutant in sufficient concentration to induce silver corrosion. Originality/value – The methodology used in this work can be applied to study the indoor corrosion behaviour of other metals, which will be of interest to the microelectronics industry.

Factors affecting pulsed-cathodic protection effectiveness for deep well casings : Table of Contents

I.A. Metwally, A. Al-Badi — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to introduce a theoretical investigation of the pulse-cathodic protection (PCP) systems to show how they behave under different operating conditions. The effectiveness of the PCP system also is highlighted for a typical large-scale configuration. The principal technical objectives of this paper are to answer three questions: Are the PCP systems effective in the desert fields? Although they have been approved, what is the reason for their lack of effectiveness in some coastal areas? What are the operation recommendations for the currently installed PCP systems and their future application? Design/methodology/approach – The factors affecting the cathodic protection of well casings have been investigated theoretically by using a 3D field approach software package current distribution, electromagnetic fields, grounding and soil structure analysis. Cathodic interference with nearby well casings has been investigated thoroughly because corrosion of this kind is more serious than the anodic type. The performance of PCP systems has been analyzed with respect to obtaining better protection-current distribution along the protected well casing at reduced anode current, together with reduced stray current (corrosion) at any nearby unprotected structure(s). Findings – For uncoated well casings, protection current pulses are attenuated significantly and are smoothed out to be pure direct current after about 10 percent of the well-casing buried length. High-magnitude stray current can be found affecting any switched-off well casings and hence they can be corroded faster from the top part than unprotected/remote wells, as are deeper well casings that may sustain considerable localized corrosion attack on the upper portions of the casing. Without the formation of a natural protective coating with high resistivity, the PCP system becomes malfunctioning, i.e. its performance becomes very similar to that of the conventional cathodic protection (CP) systems. This effect has been confirmed by field measurements in Oman, where magnesium hydroxide is minimally formed (in desert areas). Research limitations/implications – In reality, some of the PCP modules at the same station can have a slight deviation in the operating frequency and/or voltage. It is planned, therefore, that the investigation will be extended to simulate such cases and take into account the effect of multi-layer soils. Practical implications – Knowing the performance of PCP systems for protecting deep well casings is a critical issue for the oil industry. Originality/value – The paper provides a sound basis on which oil producers can take decisions about the future application of the PCP systems, optimize their performance, and introduce application restrictions by studying all factors that affect PCP performance. The effectiveness of PCP in desert (sandy/rocky) soil, where calcium-carbonate deposition predominates over magnesium-hydroxide formation, has proven to be very similar to that of a conventional CP system. The reliability of artificial oil-lifting systems will be increased by reducing oil production losses (“oil deferment”) and the rig mobilization, which has very high rent cost.

Corrosion studies on the plasma-sprayed nanostructured titanium dioxide coatings : Table of Contents

Z. Ahmad, M. Ahsan — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to report the resistance of plasma-sprayed titanium dioxide (TiO2) nanostructured coatings in a corrosive environment. Design/methodology/approach – Weight loss studies are performed according to ASTM G31 specifications in 3.5?wt% NaCl. Electrochemical polarization resistance measurements are made according to ASTM G59-91 specifications. Corrosion resistance in a humid and corrosive environment is determined by exposing the samples in a salt spray chamber for 100?h. Microstructural studies are carried out using an atomic force microscope and scanning electron microscope. Findings – The nanostructured TiO2 coatings offer good resistance to corrosion, as shown by the results of immersion, electrochemical and salt spray studies. The corrosion resistance of the coating is dictated primarily by the geometry of splat lamellae, density of unmelted nanoparticles, magnitude of porosity and surface homogeneity. Practical implications – The TiO2 nanostructured coatings show promising potential for use as abrasion, wear-resistant and thermal barrier coatings for service in harsh environments. Originality/value – The paper relates the corrosion resistance of nanostructured TiO2 coatings to their structure and surface morphology.

Preparation of non-chromium polymer films on zinc for corrosion protection due to a compound effect between silane and cerium salt : Table of Contents

Da-jing Fang, Xu-hui Mao, Ye-ming Zhang, Zhi-liang Chen, Min Liu, Fu-xing Gan — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to study the compound effect between silane and cerium salts in the passivation process of chemical conversion treatment of zinc. Design/methodology/approach – Chemical conversion treatment using 3-Glycidoxypropyltrimethoxysilane on zinc is investigated as an alternative treatment to chromate conversion. The surface chemistry of the silane-treated samples is investigated with mass change measurements, polarization curves, electrochemical impedance spectroscopy (EIS) and the salt spray tests (SST). The surface morphology of samples was studied using a scanning electron microscope. Findings – The polarization curves, EIS and SST data are in agreement. On the surface of zinc, the silane formed a compound with the cerium, thus enhancing the adhesion and corrosion resistance of the polymer film. Originality/value – There have been few reports on the compound effects of silanes and cerium salts in the passivation process. The mechanism of this compound effect may be due to the ability of Ce3?+?ions to gain access to the interface through tiny cracks or micropores in the cross-linking structure of GPS polymer films on zinc, and the subsequent oxidation of Ce3?+?to Ce4?+?by H2O2 may result in a barrier effect between the electrolyte and the metallic substrate.

Inhibition of the corrosion of cold rolled steel in hydrochloric acid solution by Tween-40 : Table of Contents

Li Xianghong, Deng Shuduan, Fu Hui, Li Taohong, Mu Guannan — Sun Jun 28 14:15:06 BST 2009

Abstract:
Purpose – The purpose of this paper is to study the inhibition effect of Tween-40 on the corrosion of cold rolled steel (CRS) in 1.0-8.0?M HCl over the temperature range of 20-50°C. It also aims to make an attempt to correlate both thermodynamic parameters and kinetic parameters with the inhibition effect. Design/methodology/approach – The inhibition efficiencies of Tween-40 are investigated by weight loss and potentiodynamic polarization methods. Findings – Tween-40 acts as a good inhibitor in 1.0?M HCl, and inhibition efficiency increases with the inhibitor concentration, while it decreases with HCl concentration and temperature. The adsorption of inhibitor on the CRS surface obeys the Langmuir adsorption isotherm equation. The inhibition effect is satisfactorily explained by both thermodynamic and kinetic parameters. Polarization curves show that Tween-40 is a mixed-type inhibitor in hydrochloric acid. Originality/value – The experimental data have been treated with adsorption theory and kinetic equations successfully. Both the thermodynamic and kinetic parameters can be obtained, and used in explaining the inhibition effect satisfactorily.