Abstract
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.
Highlights
The seawater system used in maritime oil production facilities located on the coast of South America is designed to supply units and equipment with water injection
Depending on the purpose of each maritime installation project, seawater can be independent from the utilities and injection wells, except for the fire ring main systems, where pressurization can be used for an extension of the seawater intake system
Copper-nickel alloys have been used as materials for pipes and equipment for seawater systems, mainly in shipbuilding, offshore oil production platforms, and desalination plants
Summary
The seawater system used in maritime oil production facilities located on the coast of South America is designed to supply units and equipment with water injection. The novelty of this paper is to alert marine equipment inspectors that high concentrations of NaClO can damage the rotors and internal pumps made of copper-nickel alloy Operational failures of these seawater suction pumps can cause disruption of oil production. Despite the appropriate properties of this alloy, some failures can occur and compromise the pumping of seawater [1,2,3,4] In this particular case evaluation, the intake and transfer of sea water to different equipment and processes of the platform consists, essentially, of four submerged pumps to a depth of 20m protected by a screen to avoid the penetration of sea animals.
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