This work discusses the case of corrosion in a copper-nickel alloy used in seawater, where chlorination is necessary to control micro- and macro-organism growth that can render inoperable the seawater supply system used in an offshore platform. Studies developed in the last 30 years have shown copper-nickel’s adequateness in seawater, with a corrosion rate of about 0.001mm/year. However, annual equipment inspection showed localized corrosion in an internal chamber in a stand-by pump. Such corrosion occurred due to high-concentration of sodium hypochlorite (NaClO) injection into the operational system, even for pumps that were out of operation. To evaluate this corrosive process, gravimetric (mass loss) and electrochemical tests were developed in synthetic seawater with NaClO at concentrations of 100, 500, 1000 and 5000mg/L. The results indicated that the corrosiveness varied from low to moderate. The presence of pitting and crevices observed in the laboratory tests derails or compromises material use in seawater. It was concluded that there is a need for continuous monitoring of the NaClO injection in seawater pumps, and a method was proposed in order to minimize or avoid a high concentration of chlorine in standby pumps.
ASTM A182 F51 duplex stainless steel with a 50:50 ratio of austenite to ferrite microstructure is a material used in mechanical engineering. Its uses include the manufacturing of equipment and components subject to acidification or acid stimulation for oil and gas industries. During acid stimulation or acidification, hydrochloric acid (HCl) solution with concentrations ranging from 5% to 28% (by volume) is injected into the limestone (CaCO 3) and dolomite (CaCO 3 •MgCO 3) reservoir rock to restore permeability and consequently increase oil well productivity. Therefore, it is important to use a corrosion inhibitor, such as propargyl alcohol, to prevent or inhibit the aggressive attack of HCl on duplex stainless steel. The present study evaluates the corrosion resistance of ASTM A182 F51 stainless steel using gravimetric (mass loss) and electrochemical (polarization) tests. Studies were completed with and without the addition of 500 and 1,000 mg/L propargyl alcohol in HCl solutions with concentrations of 10% and 15% (by volume) at temperatures of 25, 40 and 55 °C. The good protection by propargyl alcohol of duplex steel immersed in HCl is observed.
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