Innovations in Corrosion and Materials Science (Discontinued) - Volume 7, Issue 1, 2017

Coating application is one of the traditional methods of protecting materials against corrosion. Using polymeric materials for structures and coatings increasingly dominates corrosion- protection technology. The most effective method of improving protective properties of coatings is to reduce their permeability by using special additives, reducing the rate of diffusion of electrolytes in polymers and anti-corrosive silicate compounds. We have proposed the set of inorganic substances of composite polymeric materials which selectively interact with the water or water solutions of acids, salts, and alkalis in order to decrease their penetrability and increase their chemical resistance simultaneously. The article offers a brief review of published works of the authors and their colleagues.

Shallow geothermal energy can be exploited in any location by ground heat exchangers (GHE), which consist of pipes placed either horizontally in trenches or vertically in boreholes in the ground. The cost of the GHE is primarily determined by the pipe cost per unit length and the total required length. For a given type of ground and completion conditions, the main parameter that affects the required length of a GHE is the thermal conductivity of the pipe material. The preferred pipe construction materials are usually high density polyethylene (HDPE) as the plastic with the highest thermal conductivity, in a much lesser extent cross-linked polyethylene (PEX) for relatively higher temperature applications, and even stainless or galvanized steel in some other installations. In this paper, alternative metallic materials with higher thermal conductivity as well as thermoplastics available in market were evaluated for shallow geothermal use. The evaluation was made in terms of expected GHE service life based on literature review of buried piping systems, estimation of the required GHE length per unit energy output by computer simulations and cost estimation using current market prices.

Background: We analyse here the well-known U-shaped form of pH-dependence of glass corrosion rates U(t) focusing on changes of U-shaped form with time. Methods: We account for the two main mechanisms of glass corrosion which play dominant role at different times - ion exchange and hydrolysis. Results: We reveal that the pH dependence evolves even for solutions ostensibly kept at constant pH. The U(t) dependence is caused by changes of concentration profiles of elements in the nearsurface layers of glasses in contact with water. The change is most evident within the initial stages of glass corrosion at relatively low temperatures. Numerical examples are given for the Russian nuclear waste borosilicate glass K-26 characterised in experiment by an effective diffusion coefficient for caesium DCs = 4.5 10-12 cm2/day and by a rate of glass hydrolysis in non-saturated groundwater as high as rh = 100 nm/year. Conclusion: The changes of the U-shaped form of glass corrosion rates need to be accounted for when assessing the performance of glasses in contact with water solutions.

Background: Some corrosion damage may occur on the steel tubes of a pipeline that is buried underground to transport petroleum and natural gases. This damage may result from the natural corrosion and/or the electrolytic corrosion that is usually assumed to be caused by the stray current leaking from the railway tracks of the DC (direct current) drive train. A pipeline with mild steel tubes, 350 mm in nominal diameter and 9.5 mm in thickness, was built underground to transport natural gas for a distance of 30 km. The outer surface of the pipeline was coated with a coating of polyethylene resin 2 mm in depth. Methods: To inspect the performance of the lining, the potentials of the steel tubes were monitored by potentiometers with the copper/saturated copper sulfate reference electrode which were provided in terminal boxes throughout the pipeline. Results: Fluctuation with the large amplitude of approximately 3000 mV was observed which was maintained day and night at every terminal box: most base levels were far lower than -2500 mV vs. the copper reference electrode, the lowest limiting potential to avoid heavy production of hydrogen gas. The highest levels were higher than -850 mV, which indicated the possibility of corrosion. In contrast, the DC currents in the pipeline wall determined by the clamp ammeter did not fluctuate at all, which revealed a limited association between these currents and the potentials displayed in the potentiometers. Consequently, it was interpreted that not the pipeline potential but the equilibrium potential of the copper electrode did fluctuate intensely with a high frequency. It was theoretically explained that the equilibrium potential of reference electrode be possibly changed by the effect of electric field. It was further made clear that the cause of the equilibrium potential fluctuation must come from the fluctuation of the electric field which was formed by a larger electric charge which may be attributed, on reasonable grounds, to the electrostatic precipitators and/or the electrostatic coating facility located near the pipeline. Adequate reasons for suspecting the existence of the stray current were given based on basic theories of the electromagnetics and the electrochemistry: according to the theory of electromagnetism the existence of any current crossing the boundary between a metal and a solution is impossible. This was interpreted to indicate that the current leaking from the railway track, i.e., the stray current cannot exist. Conclusion: On the grounds of theory and the actual situation mentioned above electrolytic corrosion may be caused not by stray current but by electric fields.

Background: Optical interferometry based methods have been used to monitor electrochemical corrosion and protection processes. Quantitative and qualitative information related to these processes, is obtained by using a Michelson interferometer technique configuration. This technique without the need of direct physical contact with the sample during reaction time is based on a simple inspection of intensity patterns. Methods: Evaluation of corrosion phenomenon of bare copper corrosion protection by ABS (Acrylonitrile- butadiene-styrene) coating using Michelson interferometry, was obtained. Bare and coated samples were exposed to different conditions in chloride solution and immersed as a function of time, and electrochemical noise and impedance methods and interferometric measurements were obtained and correlated. Results: Experimental results suggest important kinetic information regarding copper corrosion and coating protection performance taking place, corroborated and correlated with electrochemical methods. Interferometric measurements reflect the changing corrosion conditions and coating performance. Conclusions: Good corrosion protection of ABS coating performance through the Michelson interferometric technique was demonstrated.

Background: Trial productions of API-X65, API-X70 steels have been undertaken at Rourkela steel plant (RSP) and Bokaro steel limited (BSL) in collaboration with R Center for iron and steel and the requisite mechanical properties have been successfully met in industrial heats. One of the important aspects to assure good performance of pipeline steels is to minimize cracking susceptibility when exposed to sour environments. Hence, the present work focuses on characterization of newly developed API X65 and 70-line pipe steels on terms of HIC and SSC phenomenon in sour gas media and possibility to develop HIC and SSC resistant steel. Methods: Hydrogen-induced cracking (HIC) resistance and sulphide stress corrosion (SSC) behavior of commercially produced API X65 and API X70 steels were characterized as per NACE standards. Results: Newly produced API X65 and API X70 line pipe steels showed poor resistant to HIC and SSC in sour gas environment. From Electrochemical corrosion studies it was concluded that chemisorbtion film formed on the surface responsible for auto-catalytically generating hydrogen at the surface, increasing the probability for diffusion of hydrogen. To explore the possibility of improving the HIC and SSC performance of these steels in hydrogenated and sour gas environments, laboratory heat making trial was undertaken with controlled addition of Cu at levels of 0.14, 0.26 and 0.36 wt% to API X65 steel. The addition of Cu to API X65 steel has immensely beneficial by increasing the corrosion resistant of the steel by altering the surface film and restricts the hydrogen diffusion. Also the Cu has improved the HIC and SSC resistant of the steel because of low diffusion of hydrogen.

Background: Acid hydrolysis is a common process used for the production of microcrystalline and nanocrystalline cellulose. When the starting cellulose feedstock is treated with dilute mineral acid (2-3 M), a sharp decrease in degree of polymerization (DP) is observed until a minimum constant value called level-off degree of polymerization (DPm) is achieved, which is associated with DP of elementary nanocrystallites. After such chemical treatment, despite achieving Pm, the particles of microcrystalline cellulose (MCC) are formed instead of cellulose nanocrystallites (CNCs), which require further explanation. Methods: Observation of DP, crystallinity degree, particle size and charge depending on the acid concentration and type. Results: It was found that dilute acid causes a selective degradation of non-crystalline domains (NCD), which leads to transverse splitting of relatively long fibers and obtaining of shorter low-molecular fragments of the fibers, namely micron-size particles of MCC. On the other hand, concentrated acid causes not only the degradation of NCD, but also tightly packed lateral surfaces between nanocrystallites connected via strong inter-crystalline contacts, thus facilitating the release of free CNCs.

Background: Pipeline steels such as the API 5L X80 grade can be subjected to corrosion in contact with either acidic or alkaline sour brines. The surfaces oxides formed in each case can have a protective or non-protective character against corrosion. This behavior is not understood and gives rise to conflicting reports in the literature. The aim of the present work was to investigate the electrochemical response of anodic films formed by cyclic voltammetry on the surface of the API 5L X80 pipeline steel. Methods: The anodic films were formed by cyclic voltammetry under different pH conditions and switching potentials. The corrosion behavior was assessed using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis. Results: Mott-Schottky analysis revealed that the doping densities were higher for the films formed in the acidic solution whereas those formed in the alkaline solution were less defective. SEM micrographs suggest the formation of a defective and porous surface as the switching potential becomes more positive. Conclusion: The poorest protective properties are associated with films formed under high switching potentials and low pH.

Background: A simple criterion for the efficiency evaluation of KGR-134 corrosion inhibitor of carbon steel samples in seawater solutions has been applied and compared with a numerical model along with a screening method of the percentage protection efficiency. The criterion, lim (ρ ;ins/ρ ;s) =1, has been applied, when the resistivity of carbon steel sample in inhibited seawater (ρ ;ins) becomes equal to the resistivity of the carbon steel sample in blank seawater (ρ ;s), as a function of the exposure time of the sample to the inhibited solutions. The criterion was used to determine the efficiency of 5-20 ppm of KGR-134 corrosion inhibitor in seawater. The analytical criterion, numerical modelling, and screening method of corrosion inhibitors were used in the present investigation. Efficiency variations of the KGR-134 corrosion inhibitor as a function of the inhibitor concentration and exposure time were calculated by fitting the experimental data to a numerical model incorporating a nonlinear regression method. The screening method of the percentage protection efficiency of corrosion inhibitors was found in a good agreement with the analytical criterion. Conclusions: The analytical criterion a long with numerical modelling were found concise ways of predicting the corrosion inhibitors efficiency of carbon steel in seawater in a comparison with the classical way of the screening method of corrosion inhibitors. 10.2174/2352094906666161103124935