Case Study - Predicting the Effectiveness of CP on a PCCP Transmission Pipeline

The Challenge

Prestressed Concrete Cylinder Pipe (PCCP) is a rigid pipe designed to take optimum advantage of the tensile strength of steel and of the compressive strength and corrosion inhibiting properties of concrete and is frequently used for water transmission.

While the cement mortar and additional coatings usually protect the prestressing wire from corrosion, in certain circumstances chlorides can diffuse into the mortar, reach the wire, and cause chloride-induced corrosion of the prestressing wire. Therefore the challenge is to design a robust cathodic protection (CP) system to mitigate the risk of corrosion damage to the wire in high chloride environments.

The Solution

When specifying a CP system, the CP engineer will be defining the following parameters, amongst others:

  • Type and characteristics of any coating applied to the pipe
  • Type of CP system
  • Sacrificial anode arrangement (material, dimensions and distribution of anode ground beds)
  • Impressed Current Cathodic Protection (ICCP) arrangement (eg discrete locations or ribbon type anodes buried near the pipe)
  • Attenuation losses in the cabling connections to the ground beds and the return path from the pipeline

A computer modelling study was designed to determine the protection provided by the CP system, to evaluate different design options, and to optimize the design.

The Value

The study demonstrated how a multiscale modeling study can support the design of a CP system to test the effectiveness and the robustness of the design under various conditions. The information provided by the model can be used to identify the key design variables and to optimize the final design.

Model results have been validated on similar studies where correlation with subsequent field data has been good. Such a study provides the means to interpret pipeline survey potential data in order to determine the potential and current densities on the prestressing wire and steel liner within the PCCP.

Adey R A, Peratta A, and Baynham J W ‘Application of Computational Modeling to Predict the Effectiveness of CP on a PCCP Transmission Pipeline’ NACE Corrosion 2011

Corrosion Modeling Services & Software

BEASY – using computer modeling expertise to support corrosion engineers solving the world’s corrosion problems

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.

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