Image of newly manufactured pipes to represent blog post Deceptive Dents: Characterizing a Manufacturing Anomaly
Complex Corrosion

Deceptive Dents: Characterizing a Manufacturing Anomaly

As operators know, pipeline dents vary in severity, and being able to prioritize which dents to act on first is crucial to any integrity plan. The ENTEGRA® True Ultra-High Resolution ILI system includes both sophisticated data-gathering tools and highly skilled interpretation. Together, these components can help you understand what kind of dent you’re facing, and …

Jun 24, 2025

As operators know, pipeline dents vary in severity, and being able to prioritize which dents to act on first is crucial to any integrity plan. The ENTEGRA® True Ultra-High Resolution ILI system includes both sophisticated data-gathering tools and highly skilled interpretation. Together, these components can help you understand what kind of dent you’re facing, and in this rather unusual case, whether it’s even a dent at all.

Field inspection complemented by True UHR ILI data

In this case, a pipeline field excavation revealed a thumbprint indentation. It appeared this anomaly was caused during pipe manufacturing and was paired with interior mill-related metal loss. Measurements showed the wall around the indentation was just 2 mm thick compared to other areas of the pipe where the thinnest reading was 4.8 mm. This indicated a 58% metal loss. Based on the field study, this anomaly needed to be added to the operator’s watchlist.

Image of measurements written on outside of pipe showing a dent with metal loss
Figure 1: A close visual inspection of a thumbprint indentation in this pipeline indicated a dent with 58% interior metal loss, likely due to a manufacturing issue.

ENTEGRA® True UHR ILI was deployed to provide additional analysis. The ENTEGRA UHR ILI tool also revealed internal mill-related metal loss, predicted at a depth of 53%. However, the tool did not detect any inside diameter restriction, which would usually accompany a dent-like feature. The ENTEGRA team agreed that the dent was mostly likely a milling anomaly. This, however, was only telling part of the story.

Same pipe, similar anomalies

Other areas of the pipe had also been excavated, showing similar anomalies. As with the first anomaly, these were characterized as dents with internal metal loss, although the loss was not quite as deep. Once again, the UHR ILI analysis found no indication of ID restriction. These indentations were also accompanied by linear surface laminations. When these were ground out, very little material was removed from the pipe. This was another clue that these might not be typical dents.

The ENTEGRA team quickly noted that while the primary sensors clearly picked up the problem areas, nothing was indicated in the caliper data. How is it that anomalies very obviously present in the visual and ILI inspections were not causing any ID restrictions? The ENTEGRA analysts had a hunch.

True UHR In-Line Inspection data from Entegra showing an internal metal loss mill anomaly on a pipeline
Figure 2: Two other thumbprint anomalies were also excavated. ENTEGRA True UHR ILI predicted these anomalies were 33% and 36% deep, respectively, but found no ID restriction.

A manufacturing anomaly origin story

The ENTEGRA team brought together the data gathered from the True UHR ILI process and field inspections and looked at it in context with decades of experience working with pipelines of all makes and characteristics. The team landed on a highly probably explanation.

In each anomaly instance, a void had likely formed during pipe manufacturing, trapping liquid or gas in the metal. This took up volume in the thickness of the pipe. Then, still during manufacturing, the void is close enough to the surface of the interior of the pipe that it breaks through. As the pressure was released, there was less support for the thickness of the wall. This caused the outside area to sink down, creating a thumbprint indentation but not reducing the wall thickness. The metal in the pipe hadn’t been lost; it had simply migrated.

Illustration showing a void movement in a pipeline wall.
Figure 3: Drawing on decades of real-world experience with pipelines and a robust set of ILI and field data, the ENTEGRA team concluded these anomalies were likely caused by voids produced during manufacturing. During the same manufacturing phase, the void is close enough to the internal surface that it breaks through, releasing the pressure and support for the thickness of the wall, causing the same area outside the pipe to sink down. The pipe had not lost any metal, but the metal had moved.

Successfully characterizing these anomalies took a combination of data, experience and collaboration with the operator. It was only by having the initial excavation reports that the ENTEGRA team was able to truly understand this anomaly, saving the operator downtime and repair costs, and putting their minds at ease that the pipe itself was not experiencing any metal loss.