Top-of-line corrosion (TLC) is known as one of the main corrosion threats in wet gas pipelines operating in stratified flow conditions. Using a corrosion model is one of the key tools to identify and quantify the threat and to identify the potential need for mitigation and control of this risk.

This paper will describe a new TLC model that can be used to assess the TLC risk for sweet wet gas pipelines. This model is based on the mechanistic understanding from the latest literature and knowledge generated in a JIP (Joint Industry Project with Ohio University). The new model addresses the following relevant physicochemical phenomena:

  • The latest electrochemical CO₂ corrosion model for the bare steel corrosion rate, including the effect of organic acids as a pH buffering agent.

  • The Fe2+ flux balance

  • The condensation rate, condensation regime and condensing droplet size

  • FeCO3 formation and its effect on the corrosion rate

  • Incomplete substrate coverage during low condensation rates

Three sources or sinks in the Fe2+ flux balance equation are distinguished:

  • Fe2+ formation by corrosion

  • Fe2+removal by FeCO3 precipitation

  • Fe2+ transportation by condensed water film convection

This model has been implemented into our in-house corrosion prediction software Hydrocor (HC). The performance has been verified with a database compiled from the literature. The new TLC Model shows a very good agreement with both experimental and field data on top of line corrosion.

Subject
Mechanistic models, Steel surfaces, Water, Droplets, Precipitation (solids), Corrosion rate, Electrochemical models, Top of the line corrosion, Condensation, Condensation rates, Experimental data, Corrosion modeling, De Waard corrosion model
Keywords:
corrosion, prediction, top of line, TLC, oil and gas, carbon steel, pipelines
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2021
Association for Materials Protection and Performance (AMPP)
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