CorrCAD is the latest addition to SES’s powerful software packages aimed at solving practical scientific and engineering problems realistically and accurately.

Applicable Software Computation Modules

RESAP MALZ

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Technical Description

CorrCAD is the latest addition to SES’s powerful software packages aimed at solving practical scientific and engineering problems realistically and accurately. CorrCAD has been developed to tackle a large variety of cathodic protection design tasks and related issues on land and offshore. CorrCAD’s main function is to determine the degree of corrosion control provided by a system. Typical applications of CorrCAD for corrosion control include impressed cathodic current protection systems (ICCP) and use of sacrificial anodes in anodic protection systems, where anodic current is impressed on corroding material to enforce passivation.

Another application of CorrCAD is to estimate the effect of stray currents such as those produced by HVDC electrodes or DC rail traction systems on the corrosion of buried metallic structures. It can evaluate the corrosion status of the structure and help optimize the location and characteristics of the corrosion protective system (such as ICCP or Sacrificial Anode) to minimize stray current interference effects on protected structures such as pipelines.

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Technical Highlights

The CAD based graphical user interface offers a complete and simple solution for defining complex networks accurately, displaying and editing the protected structures and their protection systems, computing and examining the results. CorrCAD integrates the computational power of the MALZ module, including its capability to calculate conductor currents of large conductor networks, and the resolution of non-linear electrochemical boundary conditions, using a fixed-point iteration approach. The MALZ computation module is the main engine that calculates conductor currents and electromagnetic fields in an arbitrary network. The resolution of CP problems uses the numerical methods of MALZ and the simple fixed-point iteration. It starts with an initial value of potential or current, and solves the non-linear boundary conditions. The polarization curve (non-linear boundary condition) is used during the iterative process to compute the new entry (potential or current) for the next iteration. The iteration is stopped when the difference of two successive steps is smaller than a specified tolerance threshold, or when a maximum number of iterations is reached.

The CorrCAD computation modules consider polarization effects, i.e., they do consider the polarization resistance. The computed coating stress voltage is the potential difference between the protected structure metal potential and soil potential at the reference point, and it includes the polarization potential. The potential drop across the coating and the soil potential drop to remote soil, i.e., the “ON” reading, are both considered as IR drop that should be eliminated from the cathodic protection effectiveness evaluation. The real effectiveness measure of the CP or direct characterization of stray current interference level is the polarization potential, i.e., the “OFF” reading. That being said, CorrCAD:

• Accounts for the polarization resistance in the computation.
• Provides the polarization potential that is the most significant value for corrosion evaluation.

CorrCAD offers the possibility of determining the corrosion effectiveness considering experimental polarization data such as polarization curves. When there is a good coating on the pipe, CorrCAD computes the current density by using the provided coated steel polarization curve, then eliminates the effects of IR drops, so that the coating protection current density and corresponding over-potential (responding to the “OFF” reading) are accurately obtained.

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CorrCAD Capabilities

The following summarizes the capabilities of the CorrCAD software package.

• It accurately models large metallic ground networks in complex soil structures such as horizontally and vertically layered soils with, optionally, embedded finite volumes of soils having arbitrary resistivities without the need to use time-consuming finite element based solutions. Presently, although CorrCAD can use the capabilities of vertical soil models and embedded finite volumes of soil to account for soil characteristics variations, it is usually more efficient to use one soil model for the entire system and to then account for soil model variations by defining appropriate coating characteristics along the length of the modeled metallic structures.
• It computes leakage currents, earth potentials and electric fields associated with a buried network of metallic conductors or structures and can account for a large range of frequencies, in addition to DC.
• It accounts for the attenuation along conductors and determines potential drops from one part of a system to another as well as transfer voltages to other buried structures. This makes it possible to accurately compute potentials along the lengths of the pipeline. The presence of lumped impedances (resistors, capacitors and inductances) can be taken into account as well.
• It models coated pipes, each with different coating characteristics (i.e., effective coating resistivity, permittivity and thickness), if desired. Thus, buried pipes can be accurately represented.
• Finally it accounts for the polarization electrochemical potential, which is the most significant indicator of the cathodic protection effectiveness and the adequacy of the mitigation methods deployed to minimize the effects of stray current interference.

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Intuitive Interface and Powerful Functionalities

CorrCAD provides a highly intuitive graphical user interface that simplifies and reduce the time needed to specify the parameters of the system to be analyzed. The main features and functionalities of this interface are:

This interface allows you to import or define metallic structure path coordinates in graphical or tabular form using various standard formats, such as Excel CSV, a MALT, MALZ or HIFREQ SES SICL files and Google Earth™ KML files. Appropriate names and colors can be assigned to each path.

Appropriate energization of a network of metallic structures is essential when performing corrosion protection studies. CorrCAD provides the ability to energize the system at defined intervals or arbitrary locations. This capability provides an easy way to compute pipe-to-soil potentials (this simulates the CP “on” readings in the field) along pipelines and similar structures and to verify that pipe-to-soil potentials do not attenuate to inadequate levels far from the rectifiers and that pipe-to-soil potentials are not excessive at current feed locations (i.e., rectifiers).

CorrCAD provides detailed information on the performance of individual sacrificial anodes, such as the anode consumption rate, life expectancy and remaining life. Furthermore, a detailed analysis of anode beds is available. All analyses can be carried out for multi-layered and arbitrary soil models and a soil model can be easily imported from a RESAP output file, a MALZ input file or it can be simply defined in the Soil Definition panel for a uniform soil model.

Native (Galvanic Series) potentials can be specified in CorrCAD to account for a metal’s natural potential with respect to soil. In the present version, values measured with respect to Copper Sulfate Electrodes (CSE) and Standard Hydrogen Electrodes (SHE) can be defined for convenience. Polarization effects representing the behavior of both metallic structures and anodes are considered, if applicable.

Polarization curves for each individual electrochemical reaction, cathodic and anodic reactions and polarization can optionally be specified and displayed and will be used in the computations. CorrCAD provides a digitization tool, named SESCurveFit, which can digitize polarization curves in standard image formats in order to obtain the polarization curve parameters needed to perform a complete corrosion analysis according to the type of function selected.

The relevant computed values can be displayed in 2D curve, 2D-Spot or 3D plot. Most of the results can be exported to an Excel CSV file format.

When you need an explanation or a rapid reminder of what any portion of a screen is for, simply click on that part of the screen, press the F1 function key, and a context-sensitive help screen pops up instantly. If you have questions that the help file and the manuals do not immediately answer, SES experts are a toll-free phone call away or, if you prefer, you may email or fax your inquiries to us and we will promptly reply with a detailed answer.