Siderite micro-modification for enhanced corrosion protection

Production of oil and gas results in the creation of carbon dioxide (CO₂) which when wet is extremely corrosive owing to the speciation of carbonic acid. Severe production losses and safety incidents occur when carbon steel (CS) is used as a pipeline material if corrosion is not properly managed. Currently corrosion inhibitor (CI) chemicals are used to ensure that the material degradation rates are properly controlled; this imposes operational constraints, costs of deployment and environmental issues. In specific conditions, a naturally growing corrosion product known as siderite or iron carbonate (FeCO₃) precipitates onto the internal pipe wall providing protection from electrochemical degradation. Many parameters influence the thermodynamics of FeCO₃ precipitation which is generally favoured at high values of temperatures, pressure and pH. In this paper, a new approach for corrosion management is presented; micro-modifying the corrosion product. This novel mitigation approach relies on enhancing the crystallisation of FeCO₃ and improving its density, protectiveness and mechanical properties. The addition of a silicon-rich nanofiller is shown to augment the growth of FeCO₃ at lower pH and temperature without affecting the bulk pH. The hybrid FeCO₃ exhibits superior general and localised corrosion properties. The findings herein indicate that it is possible to locally alter the environment in the vicinity of the corroding steel in order to grow a dense and therefore protective FeCO₃ film via the incorporation of hybrid organic-inorganic silsesquioxane moieties. The durability and mechanical integrity of the film is also significantly improved

A fresh look at ASTM g 1-90 solution recommended for cleaning of corrosion products formed on iron and steels

ASTM G 1-90 solution, also popularly known as Clarke solution, which contains concentrated hydrochloric acid (HCl, specific gravity [sp.gr] 1.19) + 2% antimony trioxide (Sb2O3) and 5% stannous chloride (SnCl2), shows considerable variation in its corrosive effect toward steels having different chemical compositions. Plain carbon steels (PCS) and some low-alloy steels (LAS) experience faster dissolution in comparison to LAS having copper, manganese, silicon, chromium, etc., as alloying elements. The presence of phosphorous in steels has an accelerating effect on corrosion rate. An attempt has been made to bring down the corrosion rate of different types of steels to an equal level by modifying the composition of the ASTM-recommended cleaning solution. Addition of 0.5% copper salt (cuprous chloride [CuCl]) to the Clarke solution has dramatically improved the performance of the solution, and an almost identical rate of corrosion is recorded for all the studied steels. This addition also accelerates the dissolution rate of oxide of steels with variations in their chemical compositions. Electrochemical direct current (DC) polarization and alternating current impedance spectroscopic (EIS) studies have been performed to understand the mechanism of the action of the original and modified solutions in controlling the corrosion of steels

Influence of Zn and Mg Alloying on the Corrosion Resistance Properties of Al Coating Applied by Arc Thermal Spray Process in Simulated Weather Solution

In this study, Al–Zn and Al–Mg coatings were deposited on steel substrates by an arc thermal spray process. X-ray diffraction and scanning electr on microscopy were used to characterize the deposited coatings and corrosion products. Open circuit potential (OCP), electrochemical impedance spectroscopy, and potentiodynamic studies were used to assess the corrosion characteristics of these coatings after exposure according to the Society of Automotive Engineers (SAE) J2334 solution of varying durations. This solution simulates an industrial environment and contains chloride and carbonate ions that induce corrosion of the deposited coatings. However, the Al–Mg alloy coating maintained an OCP of approximately - 0.911 V versus Ag/AgCl in the SAE J2334 solution even after 792 h of exposure. This indicates that it protects the steel sacrificially, whereas the Al–Zn coating provides only barrier-type protection through the deposition of corrosion products. The Al–Mg coating acts as a self-healing coating and provides protection by forming Mg 6 Al 2 (OH) 16 CO 3 (Al–Mg layered double hydroxides). Mg 6 Al 2 (OH) 16 CO 3 has interlocking characteristics with a morphology of plate-like nanostructures and an ion-exchange ability that can improve the corrosion resistance properties of the coating. The presence of Zn in the corrosion products of the Al–Zn coating allows dissolution, but, at the same time, Zn 5 (OH) 6 (CO 3 ) 2 and Zn 6 Al 2 (OH) 16 CO 3 are formed and act to reduce the corrosion rate