Cost Saving Offshore Cathodic Protection Retrofits
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Many offshore structures, platforms and pipelines will require a cathodic protection retrofit in the next several years. The required life extension will vary from one or two years through adding over 20 years to the original design life of the equipment. Historical approach to retrofit has been to replace anodes on a one for one basis; this approach is very costly and completely un-necessary.
There is a tendency for the industry to misinterpret the reasons why CP systems for new structures are designed the way they are, they are invariably designed to satisfy installation requirements.
For example, a pipeline bracelet anode is designed to look the way it does to facilitate pre-installation of the cathodic protection system on the pipeline, the shape of the anode is designed so that the pipe can be easily laid with the anodes in place. In truth, the bracelet anode is possibly the worst that an anode could be (from the cathodic protection engineers’ standpoint). The resistance is high, the utilization factor is low, the manufacturing cost is high and the "throwing power" is poor.
Another example is the conventional platform anode. They are attached by welding extremely stout pipe cores to the structure, why…to withstand launch forces and/or pile driving during installation. Again the CP design is predicated on the installation method. Is this the best way to install an anode on a large bare steel structure…well of course not, utilization is reduced, the standoff distance is not optimized and the cost of all those welds is very significant.
When we are charged with designing a retrofit system, most of these constraints disappear because the structure is already in place, so we should not be constrained in any way by the original design methodology when designing the retrofit.
By Jim Britton, CEO, Deepwater Corrosion Services
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