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ABSTRACT
Produced water can be much more aggressive in terms of corrosion than sea water, presenting high levels of chloride and carbon dioxide. In addition to bring corrosion risks for oil and gas production systems, it contains harmful components to environment. This way, it is crucial a materials selection that guarantees a good performance of produced water treatment systems. Although there are many studies evaluating the strength of stainless steels in seawater medium, resistance of these materials in produced water has not been fully investigated. Pitting Resistance Equivalent Number (PREN) is usually used as an indicator of localized corrosion resistance of stainless steels. However this parameter is only function of alloys composition and does not take into account the variations of the corrosive medium. This study investigates the correlation between PREN and some parameters obtained by the electrochemical techniques of anodic polarization and electrochemical impedance spectroscopy. It is also proposed a modified pitting resistance parameter (R pit). Then, classification of evaluated stainless steel according to PREN and R P|T criteria was compared.
Key words: corrosion, stainless steel, materials selection, produced water, Electrochemical Techniques
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INTRODUCTION
Produced water (PW) is a mixture of formation water, re-injected water and treatment chemicals during drilling, production, and processes like oil-water separation. It is also the largest volume of the waste stream from oil and gas production. 1
Produced water composition depends on the geological formation, hydrocarbon type, localization and field age. It also depends on the operational process and its chemicals. In general, PW may contain oil components, dissolved minerals (e.g. +, Cl", S042', CO32, HCO3, K+, Ca2+, Ba2+, Mg2+, Fe2+, e Sr2"1"), chemicals (e.g. corrosion inhibitors, demulsifying, etc), solid products (e.g. sand, clays, precipitated solids, waxes, bacteria, carbonates, corrosion and scale products, proppant and formation solids) and dissolved gases (e.g. oxygen, carbon dioxide and hydrogen sulfide).2
From literature review, Ahmadun et al3 indicate that pH of PW vary from 4.3 to 10 and chloride content may vary from 80 to 200,000 mg/L. The presence of chloride in PW has an important role in the corrosion of a exposed equipment, because 0 its high chloride contents that leads to high rates of localized corrosion.4 In terms of corrosion, it is important to highlight the...