In-line Inspection Performance Validation Pipe Experiment


You’ve just completed the first in-line inspection (ILI) of a new pipeline asset. The ILI tool results are in, and there are no required repairs! However, how sure are we of the accuracy of the results? Could the tool have under-called some of the reported anomalies? Are there any regulatory requirements beyond the “response criteria” mentioned in CFR 192 and 195 for operators of hazard-ous transmission pipelines? These are the problems that ILI verification is trying to solve.

Traditionally, validations can be done using costly excavations of anomalies found by the tool. In cases where those anomalies need to be repaired, this approach is effective, and the validation does not require any further excavations. For some ILI inspections, the tool does not call any anomalies that need to be repaired. The traditional approach, in this case, has been to excavate sub-critical anomalies just for validation. In such cases, an ILI validation spool can be a valuable asset. ILI validation spools can be designed to quantify the uncertainty of the full spectrum of anomaly types without additional excavations, thus freeing up valuable resources to be allocated elsewhere to improve safety, minimizing the exposure risk of excavating pipeline assets while under full operating pressure.

ili Validation Spool vs Validating Anomalies

Validating an ILI inspection by excavating anomalies the tool called raises several problems. For one thing, the NDE methods used to characterize some anomalies have their level of uncertainty. Secondly, it is difficult to excavate enough anomalies to cover the full spectrum of anomalies the inspection is looking for if all that is available to validate the tool results is “pitting” anomaly types; the performance may not be within the stated specifications for “pinhole” anomalies. Finally, excavating a small number of anomalies only provides a low level of confidence from a statistical perspective.

Validation spools offer an alternate approach. A validation spool is a spool of pipe with artificial anomalies that can be dropped in and out of the active system. This spool can be designed to validate the full spectrum of anomaly types the ILI tool may encounter within the inspection. The data that the tool collects on these known anomalies can then demonstrate to stakeholders the actual performance of the inspection. Validation spools do not suffer from the issues of variety, quantity, and uncertainty that plague the anomaly validation approach.

Engineering and Design Case Study

Structural Integrity (SI) was recently contracted to design a validation spool for a major pipeline operator. The scope of the project was to design a pipe spool five feet in length that could be installed as part of the inspection activities before the tool launch date.

SI used the guidance provided in API 1163 2nd edition to engineer the ILI validation spool. Table 1 is an example of what the stated specifications ILI companies will deliver with their inspections. The dimensional classes are found within API 1163 and shown in Figure 1.

FIGURE 1. Dimensional Classes for Metal Loss Indications

Fifteen manufactured flaws were used to validate the inspection results in this case – three to five times more anomalies than the typical operator would excavate to validate an ILI run. The manufactured flaws for this project were designed to meet an ANSI 600 class system and Maximum Operating Pressure (MOP) of 1480. All 15 anomalies were manufactured with a tolerance of ±0.001 inch, using a proprietary manufacturing process.

One of the challenges of this approach is manufacturing defects that are representative of actual degradation in a pipeline. Using a naïve approach such as a grinder may produce anomalies with the desired length and depth, but to the ILI tool such anomalies may look different from real-world anomalies. One could use a cutout with real-world anomalies, but it may be challenging to acquire pipe that has enough actual degradation to test the full spectrum of anomaly types.

To address these concerns, SI partnered with FlawTech to simulate corrosion flaws representative of real-world corrosion. The defects were manufactured to specified dimensions while closely representing actual corrosion degradation of the pipeline asset. The figures below provide some examples of the metal loss defects manufactured for this project.


Pipeline operators can recognize the significant value in having a calibrated test spool to quickly and effectively validate ILI performance. Validation spools offer several advantages over traditional validation approaches, and improvements in technology are reducing their drawbacks. In particular, the variety, quantity, and measurement accuracy of manufactured anomalies can be far superior to traditional approaches. Furthermore, a validation spool reduces the safety risk associated with excavating on an operational asset. SI believes that adoption of validation spools will help the industry in achieving compliance, better qualifying inspection tools, and improving pipeline safety.

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