As part of a sacrificial CP design the anodes could (in normal circumstances) be optimised to maximise the initial/mean/final current outputs and the design life of the system. This can be achieved by selecting the correct anode material and taking the anode dimensions into account. A general rule of thumb is to aim towards long slender anodes for maximum current output. However, there are many other constraints to consider as part of any design.
It is also essential to take account of where the anodes are to be installed as this can dictate their dimensions, which will in turn affect their current outputs and ultimately the protection level achieved.
Impressed current anodes are generally selected by their application suitability and maximum current output and as such they do not require to be optimised in this manner.
The Question.
How can we ensure that the anodes have been optimised for the system?
The Challenge.
In general, sacrificial anodes should always be optimised for a CP design in order to ensure that the maximum current can be applied to the steelwork over the CP design life. This will help ensure that the maximum level of cathodic protection can be applied to the steelwork. However, as an example for a sacrificial system, a compromise may be required between the anode dimensions or installation layout and the current outputs. In this instance, the main constraint may relate to physically placing the anodes “out of harms way”.
The Fix.
It is important to include the Client during the CP design to ensure that their requirements are met, whilst giving advice as to the most suitable and practical solution. Future maintenance and retrofit considerations should also be taken into account. However, experience plays a large part in designing any robust and effective CP system and it is important to ensure a suitable system has been designed to cope with all eventualities over what could be a considerable lifetime (20 to 30 years or more!).
Subsea Corrosion engineers have the qualifications and experience to ensure these considerations are taken into account and confirm that the system will operate satisfactorily over its lifetime.
