Cathodic protection
James Horton, consultant at Frazer-Nash explains how Impressed
Current Cathodic Protection adapts to the changing local
environment to protect oil and gas assets from corrosion
Protecting your assets
anodes were placed on oil and gas platforms 25 years ago to protect them against corrosion. The fact that these anodes
E
are now nearing the end of their lives gives operators a chance to revisit their protec- tion systems and make an in- formed choice on what will give their assets the most reliable form of defence against corro- sion.
Cathodic Protection (CP)
systems are used to provide pro- tection against corrosion of off- shore structures. Depending on
ngineering analysis has moved on signif- icantly since the original sacrificial
the application, either active or passive systems can be used. Active Impressed Current
Cathodic Protection (ICCP) sys- tems require anodes to be strategically placed on the struc- ture and connected to a power supply and control system, which outputs current to sup- press the local corrosive gal- vanic cells.
The major advantage of ICCP systems over passive sac- rificial anodes is that the higher driving voltage allows for fewer anodes to be more widely spaced, significantly reducing installation costs. However, this does have its
drawbacks, making the system more sensitive to local environ- mental conditions. Its effectiveness will also de- pend on what part of the system you may be protecting, whether it’s pipelines, jacket structures, subsea manifolds or even sup- port vessels; each part will pro- vide their own challenges, and require specific CP design.
Making the right choice At the outset of any CP choice must be an understanding of the area of the ocean in which the platform will be placed. It is important to prepare for the changes in the environment of a structure over its lifetime – in order to do this, careful model- ling and verification of the sys- tem must take place.
Understanding the com-
plexities of a subsea environ- ment and the intricacies of corrosion mechanisms enables facilities to be better protected. This means informed decisions can be made and early identifi- cation for potential shortfalls in the protection systems can be identified that will allow better forward planning.
Installation and mainte- nance of offshore structures in- curs significant costs to operators. Take into considera- tion the hire of specialist vessels and trained crew members and these costs can run into mil- lions of pounds – far exceeding the cost for development and purchase of a corrosion protec- tion system. ICCP systems, while more expensive than the sacrificial alternative, have sig- nificantly fewer components. Therefore, when installation costs are included they can be- come a much cheaper retrofit option than replacing like for like. Their lower mass also places less stress on an ageing and potentially corroded plat- form.
ICCP – a new beginning?
The primary function of ICCP is to prevent the corrosion of structures that spend their life in harsh offshore conditions. This protection system can lead to huge savings as structures will remain protected and reach
The ICCP system is able to protect the monopile against corrosion, as shown by the colour gradient over the surface which is between minus 800mV and 1.1mV
18 November/December 2012 Offshore Technology
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