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In gas-oil separation plants (GOSPs), multiphase crude is separated, degassed and then dehydrated before being shipped to stabilization plants for further processing. Typically, in ageing oil fields, the crude is accompanied by large volumes of formation water that is separated in GOSPs using three-phase production traps, which are large horizontal vessels, using a gravimetric separation process where water collects and settles at the vessel’s lower part.
After six years in continuous operation, early indication of depleted sacrificial anodes inside a three-phase separation vessel was revealed by the vessel’s anode monitoring system (AMS). The vessel, which was constructed of carbon steel, has been subjected to a highly corrosive environment due to the presence of acidic gases (CO2 and H2S) and high-salinity formation water typically encountered in upstream crude processing plants.A qualitative corrosion assessment was conducted to evaluate the need to open the vessel one year ahead of the scheduled turnaround and inspection (T&I). The study included a review of the previous inspection history and the existing corrosion protection layers; namely, internal coating, sacrificial anodes cathodic protection, and corrosion inhibition. It was concluded that the vessel can be safely maintained in continuous operation for the proposed period with a recommendation to conduct frequent external inspections to screen for any localized corrosion. Inspecting the vessel one year later (i.e., after seven-year continuous operation) revealed that the sacrificial anodes depletion was between 80-90%, providing the necessary protection to the vessel. Consequently, this assessment led to avoiding unplanned lengthy shutdowns and unnecessary production loss.
The hydrocarbon exploration in the ocean and deep sea was started as early as early as the 1850s, when the first drilling was carried out in California, USA. Other early oil explorations activities were later recorded in Pakistan (1886), Peru (1869), India (1890) and Dutch East Indies (1893). The development of an offshore industry is directly related to the development of subsea pipelines as well. As the industry expands towards deeper waters, the pipelines are required to have better materials, designs, operation practices and maintenance strategies to withstand the challenging environments. These pipelines are exposed to elevated temperatures, high pressures, and corrosive fluids.
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When a metal or metal alloy is immersed in an electrolyte made of a conducting material of sufficient oxidizing power, such as moist soil, it will corrode according to a well-defined electrochemical mechanism. dc corrosion is a result of dissolution of material due to oxidizing reactions, liberating electrons and forming positive ions transported into the electrolyte, leading to material loss. The current-potential relationship governing this electrochemical process termed polarization, is non-linear. This relationship is often represented by a polarization curve, which is typically, an experimentally determined function. There are a number of parameters that can contribute to the final characteristics of the polarization curve within a system ranging from material parameters (e.g. material, geometry) to environmental factors (e.g. composition of the electrolyte).
Recently, the nickel-based alloy UNS N08827, commercially known as VDM ® Alloy 825 CTP(3), has been presented to the oil and gas industry as an alloy that has been developed to fill in the existing gap between both UNS N08825 and UNS N06625 in terms of localized corrosion resistance. It is a solid-solution nickel alloy with chemical composition similar to UNS N08825, except for its doubled molybdenum content and the no addition of titanium.