Passive Layer Stability of 2205 Duplex Stainless Steel in Oilfield-Produced Water: Potentiostatic Critical Pitting Tempe
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INTRODUCTION
CORROSION is one of the most significant problems in all oil and gas industry sectors. Corrosion control in oil and gas production is reviewed in depth and related failures are well documented.[1–5] Produced water, as the first aqueous phase separated from the crude oil in the upstream sector, has a complex chemical composition and contains high concentrations of corrosive agents such as chloride and sulfate; hence, it is highly corrosive for many conventional industrial alloys. Nowadays, produced water is commonly employed as a replacement for fresh water in water flooding to increase the oil production from the reservoirs. The composition of the water used in water flooding must be such that it does not damage the reservoir rocks.[6–9] In this respect, the produced water separated from crude oil is stored and treated in special upstream desalination plants.[8,9] The alloys employed for construction of such plants should be resistant to corrosion by the contained fluid.
M. SABOURI and H. HOSEINY are with the Corrosion Research Group, Research Institute of Petroleum Industry (RIPI), P.O. Box 14665-137, Tehran, Iran. Contact email: [email protected] Manuscript submitted September 28, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
In oil and gas industries, steel alloys are the most used materials for construction of equipment for transportation and storage of processing fluids. However, the use of these alloys is restricted particularly when the temperature is high and high concentrations of corrosive agents, such as chloride ions, are present in the processing fluids.[10–15] For instance, the presence of high concentrations of chloride in some fluids, such as produced waters, can lead to severe pitting in stainless steels series 300 and limitation in use of these alloys in construction of desalination units in upstream sectors.[10,11] Duplex stainless steels, particularly grade 2205, are extensively used in applications that require good corrosion resistance and strength, particularly in the chloride containing environments such as produced waters. They are usually employed as a replacement to austenitic grades, especially in corrosive environments such as in oil and gas industries.[16] Much research has been conducted on pitting corrosion in the last decades.[17–22] Galvele[18] performed a detailed analysis on the influence of pit chemistry variations on pit growth and stability. Phenomenology of pitting and its critical factors are investigated comprehensively by Frankel,[19] Alvarez and Galvele,[21] and Soltis.[22] Pitting behavior of metals and alloys is strongly influenced by the solution temperature.[19,21] The critical
pitting temperature (CPT) test is a promising technique used for determining the lowest temperature at which the pitting occurs in a stable manner.[23–27] This test is generally performed potentiostatically or galvanostatically on a prepassivated alloy sample, while the electrolyte temperature is increased. In fact, the test can be considered as a typical electrochemical noise experime
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