Development of Tools to Estimate Actual Corrosion Growth Rates (Internal and External) of Gas Pipelines

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• Onshore Transmission Pipeline
• Gas Pipeline
• Pipeline Condition
• Internal Corrosion
• External Corrosion

Main Objective

SwRI recently completed a PHMSA project on Modeling Reassessment Intervals and is conducting a PRCI project on Internal Corrosion and has identified the needs, consistent with the current PHMSA BAA, for developing guidelines for more reliably predicting field corrosion growth rates. The main objectives of the proposed work are: (1) Improving the current existing internal corrosion rate model for wet gas pipelines and further verifying the model using field corrosion growth rate data, (2) Developing a thin-film internal corrosion model to predict corrosion rates in dry gas pipelines with gas quality upsets, and verifying the model using field corrosion growth rate data, and (3) Using the existing external corrosion model to predict external corrosion rates with including the effect of CO2 permeation from soil into a disbonded region through a holiday and through the coating itself.

Public Abstract

Both internal and external corrosion of gas pipelines can pose significant threats to pipeline safety by thinning the pipe wall, leading to leaks or ruptures. Many approaches have been explored in the past to estimate internal and external corrosion growth rates. A review showed that no single approach in the current practice allows for a confident prediction of the rates that are necessary for determining reassessment intervals. A reliable prediction of the corrosion growth rates can, however, lead to significant cost-savings while maintaining the safe operation of pipelines.

Southwest Research Institute® (SwRI®) recently completed a PHMSA contract where, building on fundamental principles, mechanistic corrosion models were developed, and then simplified into an easy-to-use format, from which guidelines for field application of the model were developed. For the first time, a simple methodology and procedure was developed that permits easy estimation of corrosion potential and rate distributions in coating-disbonded regions.

Continuing on from the success of the above PHMSA work, this proposed project expands the scope to include predictions of wet gas internal corrosion rates, dry gas internal corrosion rates, and external corrosion rates. The external corrosion rate model will further include CO2 and CP current penetration through the disbonded coating and a holiday.

Guidelines, methodologies, and procedures for corrosion rate estimations will be developed based on the models, and recommendations will be made for their implementation in the field. The goal is to improve pipeline safety to benefit pipeline operators, regulators and service providers.

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