Estimating Internal Corrosion Rates

Internal corrosion is most likely to occur where water first accumulates. Predicting these locations of water accumulation serve as a method for prioritizing local examinations. Predicting where water first accumulates requires knowledge about the multiphase flow behavior in the pipe requiring certain data.  The following are some general calculations based on flow conditions.  Keep in mind that these are strictly estimates and do not consider the effects of temperature, wettability, MIC, pressure, hydrocarbon characterization, gas composition, etc.

 Corrosion Rate for Annular Flow:

 The corrosion rate for flowlines under annular flow can calculated as follows.

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Corrosion Rate for Intermittent Flow:

 The corrosion rate is calculated based on the fraction of the stratified form and the fraction of the film that is in full liquid flow.

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Corrosion Rate for Stratified Flow:

 Stratified flow is characterized by liquid flowing at the bottom of the pipe with gas at the top. The stratified flow regime is further classified into stratified wavy when the gas liquid interface is wavy and stratified smooth when the liquid surface is smooth.

References

 J. D. Garber and Bob Winters, Internal Corrosion Rate Prediction Pipelines and Flowlines Using a Computer Model, Corrosion Paper 4155, 2004