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Top of line corrosion (TLC) is a degradation mechanism predominantly encountered in the oil and gas industry. Initiation of TLC requires a stratified flow regime with wet gas transportation and the existence of a significant temperature gradient between the hot fluid inside the pipeline and the colder external environment.1,2,3 This temperature difference results in the condensation of water vapor, present in the gas phase, onto the cooler, upper internal section of the pipeline. The condensed water can be particularly aggressive as it lacks dissolved salts (e.g. bicarbonates), some of which are able to buffer the bulk electrolyte, increasing the pH and suppressing corrosivity.4,5,6 The absence of such salts typically results in a very low pH condensate (<pH 4), often containing dissolved acidic gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S), and also acetic acid (HAc), which can cause severe degradation, particularly in the form of localized corrosion.5
Carbon dioxide (CO2) Top of Line Corrosion (TLC) poses a significant problem in oil and gas fields, resulting in both economic losses and health and safety issues. The use of conventional corrosion inhibitors does not typically ensure effective protection against this particular type of corrosion, limiting the working lifetime of carbon steel pipelines. The main chemistry of inhibitors used for such application relies on volatile chemicals that can be transported through the vapor phase to reach the top of the pipeline. Studies have shown that alkanethiol compounds may form self-assembled monolayers in acid environments with good efficiency in mitigating steel corrosion. Recently, long chain thiols (> C6) have been investigated as potential volatile corrosion inhibitors (VCIs), demonstrating good efficiency. This work seeks to evaluate the efficiency, mechanism and bulk-vapor partitioning behavior of volatile thiol corrosion inhibitors through the implementation of a biochemical technique which targets sulphydryl groups, coupled with a miniature electrode configuration for real time, in situ electrochemical TLC measurements. The proposed assay results in a rapid, cost effective screening technique that can monitor thiol-based chemistries that are partitioned in the condensate. The implementation of these methods enables the performance and mechanisms of volatile inhibitors to be better characterized and understood, shedding new light on their behavior, whilst also facilitating more effective optimization of their dose rate.
The work carried out to develop test methods suitable for assessing inhibitor performance in controlling TOL corrosion. New corrosion inhibitors have been developed that effectively mitigate TOL corrosion.
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A visual inspection of a subsea field development, transporting wet gas, containing approximately 1.5 to 2 mol% of CO2 to shore, was conducted via ROV (remotely operated vehicle). The pipeline system is largely carbon steel with only short lengths of CRA (corrosion resistant alloy) piping from the wellhead to the production/pigging manifold. Downstream of the pigging manifold the system has 20” carbon steel spools leading to the FTA (flowline termination assembly) and then 20” carbon steel flowlines to the riser platform.
Deep well casing is an important part of oilfield production. In the long service life of well casing, corrosion can result in wall thinning and even perforation of the casing due to contacting with soil, water and other naturally occurring substances within the formation. The most economic and effective method to decrease corrosion of well casing is cathodic protection (CP). However, the vertical depth of casing is several kilometers, and CP current requirements of casing in different layers are quite different. At the same time, the conductivity of different formations will affect the distribution of CP current.