Gains with Advanced Data Assessment in ILI: Leveraging pipeline data to eliminate risk, prioritize and schedule necessary repairs

Introduction

For traditional in-line inspection (ILI) vendors, considering 21.4 miles of a piggable 4” diesel pipeline is typically not a big deal.  However, significant threats like 3rd party damage and external corrosion seem to come with the territory in nearly any pipeline territory.  Often times, the assumption of standard piggability can be challenged when considering additional variables. For one Gulf of Mexico pipeline operator, who previously had a pig stuck in one of their lines, the risk associated with another pig run in a subsea environment was worrisome. Another pig getting stuck and blocking the flow of fuel critical to operations was simply not an option.

Quest Integrity’s InVistaTM technology was selected to perform the inspection based on these specialized conditions, along with a preference for collecting comprehensive data in one pass. As a result, the integrity survey was carried out in a flawless, uneventful manner, providing complete deformation and metal-loss data. Accordingly, the line’s integrity goals were met; but what else could be leveraged?

The ultrasonic in-line inspection identified a total of 45 geometry anomalies (dents and ovalities). Data indicated that 16 of these were larger than the common depth based criteria threshold of 6% of OD, which is used to develop a conservative dig repair program. However, an assessment based on depth alone does not identify the factors that can quantify their severity, because the amount of stress concentration caused by the dent and the amount of pressure cycling the dent experiences can vary.

The life cycle assessment of each area of concern is started by engineering finite element analysis (FEA) models using the ultrasonic ILI data, and then applying pressure cycling results to stress concentration factors. These advanced engineering calculations allow for a remaining life assessment based upon the time for a crack to initiate and grow to failure. The results of the advanced assessment showed that only 3 dents had a calculated remaining life less than 50 years. The assessment reduced the number of anomalies not meeting criteria by over 80% - from 16 to 3. Furthermore, the remaining 3 locations were able to be prioritized based on risk profile for scheduled attention from the operator’s preferred timeline.