PR-186-213600-R01 Generic External Corrosion Growth Rate Distributions for Buried Pipelines

External corrosion growth rates in buried pipelines are influenced by a vast quantity of parameters, and the interaction of these parameters creates complexities that can be challenging to understand. As a result, external corrosion growth rates are difficult to estimate and measure. Further, the detailed actual conditions where external corrosion growth is occurring are often not known. When external corrosion growth rates cannot be calculated (i.e., using a corrosion growth rate model) or measured (i.e., ILI run-to-run comparisons), default corrosion growth rates are frequently utilized in making Integrity Management decisions. Often, these default, or assumed, corrosion growth rates are overly conservative. Using overly conservative external corrosion rates can result in a poor utilization of resources. However, there may be locations of isolated and accelerated corrosion growth in which the assumed rates are non-conservative. Non-conservative assumed external corrosion growth rates can result in lack of awareness of locations that may become critical prior to the next planned integrity assessment. Therefore, it is ideal to evaluate appropriate external corrosion growth rates along the length of a given pipeline. Applied external corrosion growth rates are utilized in making Integrity Management decisions on a pipeline, such as optimizing excavation programs and establishing integrity reassessment intervals, and therefore, it is important to utilize realistic rates that are accurate and not overly conservative. This report describes a methodology for establishing generic external corrosion growth rate distributions based on empirical ILI and corrosion modeling data. The report describes key parameters that affect, or can be utilized to establish, external corrosion growth rates. The identified key parameters include data that should be understood and/or readily available to pipeline operators. The authors of this report have created external corrosion growth rate distribution curves for each combination of the identified key parameters. The results of this project can be utilized by pipeline operators to establish data driven and justifiable external corrosion growth rates on pipelines in which rates are not able to be calculated from historical and/or ILI run-to-run comparisons.