Track Record of In-Line Inspection as a Means of ERW Seam Assessment in Response to NTSB Recommendation P-09-1, Arising From the Carmichael, MS Rupture

The track record of in-line inspection crack detection technology with respect to locating and characterizing seam defects in electric-resistance-welded (ERW) pipe was examined on the basis of 13 tool runs on 741 miles of hazardous liquid and natural gas pipelines. Results for three types of tools were examined: (ultrasonic angle beam, circumferential magnetic flux, and electromagnetic acoustic transducer (EMAT). The methods for validating the locations, types, and sizes of anomalies included in-the-ditch NDE (UT and MT), and removal of pipe for metallurgical investigation and/or burst testing. The work indicates that in-the-ditch NDE is not always reliable for confirming the ILI findings. The metallographic examinations and burst tests sometimes confirmed the ILI findings, but in other cases, they revealed defects did not compare well in size with the anomalies indicated by the ILI or the in-the-ditch NDE. In some cases, anomalies that caused failures in burst tests had not been identified by the ILI. Because the toughness of the bond line region may differ significantly from that of adjacent material, predictions of failure pressure based on ILI-indicated dimensions using a single toughness level are unreliable. It is concluded that significant improvements in ILI crack-detection technologies will be needed in order for pipeline operators to be able to have adequate confidence in the ERW seam integrity of a pipeline inspected by means of an ILI crack-detection tool. It is also concluded that significant improvements of in-the-ditch NDE methods are needed for such methods to be considered a reliable means of validating ERW seam anomalies found by ILI. These results should not discourage the use of technologies for ERW seam integrity assessment. The tools clearly are useful for finding and eliminating some seam defects. Only by continuing to use and develop the tools can pipeline operators expect to see the technologies improve to the point where operators can have a high degree of confidence in the ERW seam integrity of an inspected pipeline.