CorrOcean's RCP anode installed on a seawater pump.
A new resistor controlled cathodic protection (RCP) system from Trondheim-based CorrOcean prevents the localized corrosion of stainless steel in chlorinated sea-water and produced water systems.
The basic principle of the RCP method is to provide cathodic protection to a stainless steel pipe system by using a resistor in series with the anode to control both the potential of the stainless steel and the anode output.
The method is based on the observation that the protection potential for preventing localized stainless steel corrosion is more positive than the potentials typically offered by sacrificial anodes, according to managing director Roe Stroemmen. Protection can therefore be provided by designing the voltage drop over the resistor to obtain a sufficient, though not excessive, negative polarisation of the stainless steel.
The system, which was developed in conjunction with the Sintef research institute in Trondheim, is proving a great success, Stroemmen says. Its first commercial application was as a retrofit to sea-water filters made of AISI 316 stainless steel on Norske Shell's Draugen platform. And the first system incorporating the RCP into the design from the outset is to be installed on Statoil's production ship for the Lufeng Field in China. It will provide protection for the sea-water/fire-water system, which also uses 316 steel.
The RCP can extend the life of existing stainless steel piping systems and allows the use of inexpensive, low alloyed stainless steel in new systems, Stroemmen says. It has a low anode consumption life and a long anode life. Because the resistor control keeps the stainless steel in a protective potential range in which the current requirements are very small, a single anode can protect long lengths of a pipe system.
Meanwhile, CorrOcean has enjoyed continuing success with its well established Field Signature Method (FSM) for corrosion monitoring. Later this year, it is due to deliver five FSM systems for BP's ETAP development in the UK. It also has orders to supply systems to Amoco's new Valhall pipeline and BP's Schiehallion development west of the Shetlands.
A new portable version of the FSM has been developed for topside use, Stroemmen reports. The sensors, which are installed as usual at critical locations on the pipework, are interrogated using a portable electronic unit. Each reading takes three-four minutes. This means a single interrogation unit can be used for multiple pipework systems, thus lowering the cost per location.
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