their designed life span. There are many factors to be


taken into consideration before understanding how far from the anodes the corrosion protection system can provide protection. These include changing envi- ronmental conditions. The system must therefore


be flexible and able to provide changing outputs to match the changing conditions.


While it is important that


the structure is fully protected, there is the danger with ICCP systems that the structure around anodes can be overpro- tected leading to hydrogen em- brittlement and coating disbondment. This is where modelling and verification come into play.


ICCP systems feature a


feedback loop which measures the protection levels at certain points across the structure. This informs the system of any changes to output that need to be made as seasonal variations take place. However, just because an ICCP system tells you your structure is protected at a few points, it is not sufficient to as- sume you are completely pro- tected. So even with feedback, it is probable that as the environ- mental conditions change the distribution of protection across the structure will also change. Detailed modelling is used


to develop CP system designs, verify that they provide com- plete protection in all condi- tions through the changing seasons, and predict how the re- quired current output changes over the year. Our work has shown that


some layouts are very sensitive to environmental conditions and are not suitable for provid- ing complete protection all year round. Over and under exposure of


a structure can cause problems if changes in condition go un- detected. This can result in cor- rosion reducing structural integrity and damaged coatings


exposing more metal to sea water and exacerbating corro- sion. These contribute to in- creased maintenance, reduced life and potentially large finan- cial losses. It is therefore extremely im- portant to understand the envi- ronment around your structure and plan to protect it accord- ingly.


ICCP systems can work in combination with other corro- sion protection systems to en- sure exceptionally good levels of protection. For instance, anti-corrosion


coatings have become more ad- vanced in recent years with some very good options avail- able which are impermeable and isolate the steel structure from the seawater. Anti-corro- sion coatings are, however, sus- ceptible to damage from conditions such as including bio-fouling, impact damage, and sand-scouring. ICCP sys- tems can help protect the ex- posed areas of the structure where the coating has been damaged, and will increase the protection as more coating is damaged over the life of the structure.


Offshore Technology November/December 2012


Simulations show that adequate protection can be achieved across a wind turbine jacket with ICCP


ICCP modelling includes being able to predict the effects of damage to anti-corrosion coatings on structure-wide pro- tection. This may mean that at the beginning of the life of a jacket with a new anti-corro- sion coating only a small ICCP current is required, whereas 20 years on when more damage has be sustained to the coating the ICCP currents will need to be increased to ensure optimum protection.


Protecting against a force of nature Seawater, with its high conduc- tivity, is a perfect medium for galvanic corrosion – but it is also an ever-changing environ- ment. Consider a vessel which itself moves through different environments from dock to deep waters and it becomes ap- parent that careful planning and engineering must be car- ried out at the beginning of the project to ensure ICCP systems work efficiently and provide


complete protection during transitions.


The main factors that affect


seawater conductivity are tem- perature and salinity, which change on a seasonal basis. The performance of corro-


sion protection systems is highly non-linear and it is therefore not simple to accu- rately predict how performance changes over the seasons. It needs to be modelled to cor- rectly gauge the changes due to these environmental factors and determine how the system should be configured to gener- ate the required protection lev- els.


Physical as well as environ- mental differences must also be taken into consideration. For illustration purposes, let us look at a pipeline. It is not enough to say that a certain amount of ICCP current will be sufficient. Some pipelines are laid under the seabed, others on top of the seabed with concrete mattresses holding them in place while others can be fixed in place with steel structures. So, not only must the environ- mental factors of the ocean be looked at, it is also imperative to understand the implications of how the pipeline is laid. Oil and gas structures are


complex by nature with differ- ent metals coming in contact with each other, along with in- teractions from mooring chains and exposure to air in the splash zone. Effective modelling and verification can take each of these points and ensure the correct level of protection is pro- vided at all times.


Here’s to the future For offshore oil and gas opera- tors, now is the time to con- sider protection options for the future. Modelling and verifica- tion is an important part of ca- thodic protection systems and this must not be overlooked if structures, pipelines and ves- sels are to safely exceed their design lives.


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