Abstract
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.
Highlights
While energy demands keep rising, hydrocarbons are set to remain the core power source for the 50 years renewable alternatives and nuclear options evolve but are not sufficient to close the gap.[1]
The registered corrosion rate (CR) drop remains much slower if compared to tests where octa-ammonium polyhedral oligomeric silsesquioxane (POSS) (OA-POSS) is added (Fig. 1a) and this is explained by the FeCO3 protective film growth (Figs. 2b and 3b)
As the nanofiller is seen to provide better electrochemical results after a pre-corrosion period, it is assumed that the increased surface roughness will help the OAPOSS adsorb onto the carbon steel exposed surface as evidenced by the growth of the inductive loops as per the electrochemical impedance spectroscopy (EIS) data (Supplementary Fig. 2b)
Summary
While energy demands keep rising, hydrocarbons are set to remain the core power source for the 50 years renewable alternatives and nuclear options evolve but are not sufficient to close the gap.[1]. The current primary mode of managing corrosion in oil and gas is the deployment of chemicals in batch or continuous treatments for a typical well and these imply huge operational expenditure but are often harmful to the environment. As such, being able to reduce chemical deployment and engineer the corrosion product would present a paradigm shift in corrosion management. Physical and metallurgical influencing factors act interdependently to affect the formation of a protective FeCO3 corrosion layer.[4,5,6,7] FeCO3 can develop as an amorphous or crystalline structure; in the latter case, it forms as a crystalline system which is identical to calcite scale[8] especially when both pH and temperatures are high.[9,10,11] FeCO3 can reduce the corrosion rate (CR) to values that are 10 times lower,[12] when compared to the CR achieved when common CI are administered (Supplementary Table S1) but far, there has been no attempt to chemically modify its structure or adapt its density in-situ
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