Sacrificial anode retrofitting to aging structures is routinely performed for life extension of offshore assets in mature fields. Indeed, the stage has been reached where ‘original’ retrofit systems are now being replaced or supplemented. Understanding when remnant CP systems can no longer prevent depolarization is important as timely intervention can reduce overall retrofit cost. This principle can also be applied to an assessment of the impact of new ‘tie-ins’.
Computer modeling can be used to:
- Assess the present state of an existing CP system, including the state of the calcareous deposits and remaining anode life, including calibration against survey data where appropriate
- Forward predict the future condition of the structure over its remaining life to provide data to support the timing of the installation of a retrofit system
- Assess the short term impact of a retrofit system
- Provide ‘what-if’ evaluations to assist engineers in the selection of the final design. For example, anode distribution could be varied to ensure that no anode gets consumed much earlier than others, and to ensure that all areas of the structure are adequately protected
- Forward predict effective life of the combined retrofit plus remnant CP system
- Enable parameter studies to be undertaken to assist engineers in the selection of lower cost design alternatives, whilst still being assured that the configuration satisfies its design limits
The image above shows a jacket structure which had an original CP system, and was subsequently fitted with a retrofit system after 15 years (“previous retrofit CP system”). The “previous retrofit system” was approaching end of life, and simulation was used as a key input to the design and optimization process for the new retrofit system, which is to have a design life of 15 years.
The picture shows that the original anodes are capable of depolarizing the structure to a range between 750 and 900 mV vs Ag/Ag Cl. Note red indicates unacceptable potentials.
The key demonstrated values are:
- Retrofit requirements can be successfully reduced. Hence, significant cost savings are achievable
- Better CP current distribution can be obtained despite a reduction in the number of anodes used by better strategic anode positioning
- Assured targeted life extension of the CP system
- The ability to optimize the frequency of subsequent CP surveys and thereby minimize costs.
- Improved planning of retrofits and surveys
The Sigmoidal or Long Term Polarization curve can be used to determine how a structure will respond to changes over the long term
The picture shows the predicted potentials on the structure after 15 years following a new retrofit. The colours indicate that the potentials are in the acceptable range.
Jain A K, Peratta C, Baynham J, Adey R A ‘Optimization of Retrofit Cathodic Protection (CP) Systems using Computational Modeling by Evaluating Performance of Remnant and Retrofit CP Systems, Taking into Account Long-Term Polarization Effects’ NACE Corrosion 2011
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BEASY, a world leader in corrosion modeling provides both corrosion modeling software and modeling services. With today’s need to reduce risk and uncertainty, we can quickly provide the answers you need on the effectiveness of corrosion control solutions.
Corrosion Modeling - What can it do?
Computer modeling provides the tools to predict how a particular system will perform even for the most complex situations. It can provide quantitative information on the protection potentials achieved and the life of the system, thus reducing the risk of systems not meeting the design goals and enabling future management of assets to be planned effectively.
How can BEASY help you?
BEASY’s Services offer specialized analysis in the area of Corrosion Modeling. Available services range from performing specific modeling tasks to comprehensive studies to determine the optimum design solution. Our engineers have extensive expertise in applying state-of the-art BEASY Corrosion
Modeling to solve complex corrosion control problems. BEASY engineers can quantify the level of protection provided to the structure without any simplifying assumptions.
What type of structures and materials can be assessed?
There are no restrictions on the structure geometry that can be modelled, and these can be offshore, subsea or onshore including shallow coastal waters. Materials include steel - coated or uncoated; other metals; reinforced concrete & hybrid structures. We can help determine how the CP system will perform over time so that you can improve the timing and quality of your estimate the service life of sacrificial anodes and the optimum location of ICCP.
Optimize CP System Designs
Computer models are the ideal solution to test the sensitivity of a proposed design to environmental factors and long term coating degradation. The protection potential distribution achieved and the current demand on the anodes can be predicted, for example, under different coating conditions and the most cost effective system identified.
Verify Performance of Retrofits
Retrofits are a common requirement, driven by changing requirements and the need to extend the life of structures. Computer modeling can provide the information you need to identify the most cost effective solution which meets the design goals.
Predict Long Term Performance of CP Systems
Modeling can predict the long term effectiveness of the CP system, including changes in the environmental conditions, coating degradation and possible damage scenarios.
Assess Anode Consumption Rates
The service life of individual sacrificial anodes and their performance over the life of the structure can be predicted by computer modeling.