Multi-diameter Inline Tool Inspects The Previously Unpiggable

Around the world, almost 30% of oil and gas transmission pipelines are not suitable for inspection using conventional inline inspection (ILI) tools. In fact, many of these lines were built before intelligent pigging had even been invented. The challenges facing “unpiggable” pipelines are often associated with reduced bore valves, miter bends or changes in diameter. PII Pipeline Solutions has identified this as an opportunity to combine its pipeline inspection experience with the requirement of pipeline operating companies to develop technologies to inspect these challenging pipelines.

One example of this cooperation arose in 2007 when El Paso Pipeline Group contracted PII to conduct metal-loss inspections of 13 natural gas pipelines located in the United States.
The segments ranged in length from 30 to 89 miles with at least two diameters in each segment. Many of them contained full-bore tees and 1.5D back-to-back bends. Although the lines had been in service for several decades, none had been inspected previously. El Paso had a requirement to complete inspections mandated under U.S. Department of Transportation regulation CFR 49 Part 192 for High Consequence Areas (HCA) and also for internal requirements.

The project timeline required that GE be capable of designing, building and testing a fully functional, multi-diameter SmartScan tool within eight months. The tool was promised and expected to be on site ready for the first inspection by Nov. 7, 2007.

GE has developed its SmartScan inspection tool using the well-proven MFL (Magnetic Flux Leakage) principle. The tool is configured with extremely short and compact magnetizing modules compared with conventional ILI tools.

Pipeline configuration was among the challenges. Up to this effort, the typical solutions for inspecting a pipeline with diameter changes was to adapt an existing MFL single-diameter tool to inspect the nominal diameter and traverse through the other diameter(s) or break up the segment into multiple segments of single diameter pipeline by adding pig launcher/receiver sets. The limitation of this approach is largely due to the existing MFL technology and magnetizers designed for these tools. If the variation in bore is large, the data collected in the extreme diameters is usually compromised. Ultrasonic wall measurement inline inspection tools have performed better in these situations but costly tool modifications are often required and were not applicable in El Paso’s gas pipeline network.

Although there are several pipeline inspection companies that do have multi-diameter inspection tools, there were no tools on the market that could traverse and inspect these 24-inch through 31-inch pipelines. El Paso required that all diameters be inspected within the segment, preferably, within one run. Some of these pipelines contained full-bore offtakes, 1.5D bends and to further complicate the issue, there were lines with true 31-inch OD.