When conducting ongoing pipeline integrity management programmes, it is vital for operators to have access to as much information regarding potential corrosive activity on their pipeline as possible. The data provided from river bottom profiles (RBP) offers a more in-depth look at anomalies in a pipeline that occurred because of corrosion.
An ultrasonic inline inspection (ILI) reliably detects and sizes corrosion anomalies in pipelines. The recorded ultrasonic technology (UT) inspection data provides a solid basis for a RBP, as this data directly extracts into a RBP. RBPs, i.e. the plot of remaining wall thickness versus distance, provide a detailed description of the actual shape of a corrosion anomaly, at an axial resolution down to 0.75 mm. In contrast, magnetic flux leakage (MFL) data does not typically offer such detailed data, nor the same data accuracy.
Following an inspection run, NDT Global's experienced data analysis team analyzes the recorded inspection data to detect, classify and size anomalies. For metal loss anomalies, this sizing procedure determines: the peak depth of the anomaly present, the minimum remaining wall thickness and the total length of the anomaly.
The feature list, or pipeline register, of the inspection report provides this information. However, the information from this feature list does not provide a detailed description of the actual shape of the metal loss anomalies. For instance, the peak depth may only be observed at a small pit-like deepest point in an extended shallow corrosion area. Alternatively, the depth of the metal loss feature could be close to the maximum depth in a significant portion of the corroded area.
Providing accurate information on metal loss anomalies
The proliferation of RBPs in pressure capacity and corrosion growth assessment enables operators access to more complete data regarding the status of their pipelines. This data provides greater insights into the description and characterisation of any metal loss anomalies present in their pipelines.
Using river bottom profiles for pressure capacity assessment
Advanced assessment methods for the calculation of the pressure capacity (safe operating pressure, burst pressure) consider the detailed RBP profiles of metal loss anomalies. Therefore, these methods yield more accurate and less conservative results when compared to list-based assessment methods (e.g. B31.G) that only account for the reported length and depth of the features. The most predominant advanced assessment methods for calculating the pressure capacity of metal loss anomalies, based on the RBP, are: RSTRENG Effective Area, DNV-RP-F101 Complex Shape and DNV-RP-F101 Appendix D (special assessment method for pipelines with channeling corrosion).
Using river bottom profiles for corrosion growth assessment
In keeping with this, for a detailed corrosion growth assessment, merely comparing the reported peak dimensions of metal loss features is insufficient. This is simply because the growth outside the deepest point is undetectable. A high level corrosion growth assessment, therefore, includes the comparison of inspection data. This includes RBPs, e.g. DNV-RP-F101 Appendix D.
Corrosion that goes unchecked leads to potentially calamitous impact on an operator's integrity management programme, which underlines the integral role that accurate data – such as the data provided by high resolution ultrasonic ILI tools – plays in a proactive pipeline management program. The proliferation of RBP comparisons increases the accessibility of accurate data regarding the presence and location of corrosion. Knowing the presence of corrosion in their pipelines, as well as the growth rate of such defects, enables pipeline operators to proactively and intelligently plan their maintenance, operate their pipelines and manage costs, all of which greatly aid long-term planning and safety.
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