Effective integrity management of a corroded pipeline requires a significant quantity of data. Common data sources include in-line inspection (ILI), process monitoring, or external surveys. The key challenge for an integrity engineer is to leverage the data to understand the level of corrosion activity along the pipeline route, and make optimal decisions on future repair, mitigation and monitoring. This practice of gaining business insights from historical datasets is often referred to as ‘data analytics’.
In this paper, a single application of data analytics is investigated — that of improving the estimation of corrosion growth rates (CGRs) from ILI data. When two or more sets of ILI data are available for the same pipeline, a process known as ‘box matching’ is typically used to estimate CGRs. Corresponding feature ‘boxes’ are linked between the two ILIs and a population of CGRs is generated based on changes in reported depth. While this is a well-established technique, there are uncertainties related to ILI sizing, detection limitations, and data censoring. Great care is required if these uncertain CGRs are used to predict future pipeline integrity.
A superior technique is ‘signal matching’, which involves the direct alignment, normalization and comparison of magnetic flux leakage (MFL) signals. This delivers CGRs with a higher accuracy than box matching. However, signal matching is not always feasible (e.g. when conducting a cross-vendor or cross-technology comparison). When box matching is the only option for a pipeline, there is great value in understanding how the box matching CGRs can be improved in order to more closely resemble those from signal matching. This limits the extent to which uncertainties are propagated into any subsequent analyses, such as repair plan generation or remaining life assessment.
Given their relative accuracy, signal matching CGRs can be utilized as a ‘ground truth’ against which box matching results can be validated. This is analogous to the ILI verification process, where in-field measurements (e.g. with laser scan) are used to validate feature depths reported by an ILI. By extension, a model to estimate CGRs following a box matching analysis can be trained with CGRs from a signal matching analysis, using supervised machine learning. The outcome is an enhanced output from box matching, which more closely resembles the true state of corrosion growth in a pipeline.
Through testing on real pipeline data, it is shown that this new technique has the potential to improve pipeline integrity management decisions and support economical, safe and compliant operation.