Chemical applications as corrosion inhibitors are widely adopted in production and processing operations in the Oil and Gas Industry. Particularly challenging is the protection of materials at and near the welds and joints from preferential corrosion and, especially, under conditions of high flow and high sheer. Additionally, successful application to gas production can also be difficult, as most inhibitors are designed to be oil and / or water-soluble.
This paper outlines the development of an inhibitor class which demonstrates good general inhibitor performance in gas lines, shows good filming characteristics under conditions of high sheer and also appears to exhibit preferential protection at weldments. The paper will discuss the laboratory testing methods employed and detail the in field performance of the chemistry. The paper will explore a rational for further development and experimental work. Due to reasons of commercial confidentiality the paper will not disclose the detailed nature of the proprietary chemistry involved.
Preferential corrosion of weldments has been a well documented and particularly difficult corrosion problem to deal with in all sorts of environments. [1,2,3] Offshore oil and gas production leads to a variety of difficult corrosion problems both within the drilling and near well bore environment [4], in subsurface flow and pipelines [5] and throughout processing and topsides facilities [6].
Oil and Gas production presents a number of challenges in the development of effective inhibitors for mitigating corrosion in carbon steels and this is doubly true for weldments due to both electrochemical environments and variations in acidity of fluids and gases. In addition to this, in particular within the gas production systems, vapors and small amounts of condensate liquids are at high flow and further add to the inability of any chemistry to be persistent. Particular challenges are also present in oil processing facilities on standing or floating production systems, where many angles and bends are present, leading to the possibility of localized corrosion and preferred weldment corrosion failures.
This paper, in particular, concentrates on the environment present on the Curlew FPSO owned by Maersk Contractors, at present producing gas on behalf of Shell Europe from the Curlew Field, and both oil and gas from the Kyle field, which is owned and operated by CNR International.
NEW CHEMISTRY The chemistry behind oil and gas field corrosion inhibitors [7-9] has not changed significantly in the last 40 years and product development in many cases has constituted refinement and "clever" formulation; nevertheless they have served the industry well. However, the latter has undoubtedly had a blinkering effect on the search for and introduction of step out chemistries. In the area of specialized small use problems, such as preferential weld corrosion, the application of radically different chemistries has not been examined as commercial drivers and rewards are low. Nonetheless solutions to these and other problems may exist away from the traditional filming and surfactant persistency performance chemicals. The application of non-traditional chemistry is described in the particular problem of weld corrosion in high gas flow in the Curlew FPSO. The chemistry that has been established in Product A, as described in this paper, has novel chemical constituents namely a small molecule, heterocyclic in nature. This in combination with the more traditional amine surfactant chemistry is explored and also comparison with quaternary ammonium salts, which are known to be the active inhibitory component of Product B
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