Detecting the Undetectable: New Frontiers in Small-Diameter Pipeline Inspection

Last month Dr Chris Peyton presented his paper titled “Enhancing the Probability of Detection for Small Diameter Ultrasonic Intelligent PIGs” at the 20^th PTC (Pipeline Technology Conference) in Berlin. The presentation provided insight into some of the work that Cokebusters’ Technology Team is undergoing along with partners at the University of Strathclyde and Square Wave Technology. This article provides an overview of the paper and presentation.

The demand for more comprehensive inspection of small-diameter piping and pipelines is continuously increasing. This presents unique technical and operational challenges that require constant evolution in both the tools we use and the processes we employ. Small-diameter pipelines pose a number of inspection difficulties, including limited accessibility, tighter bends, and more restrictive internal geometries, which also limit the space available within the inspection tool to house the sensors and control electronics.

To ensure that new tools are suitable for to meet the required inspection criteria, their performance needs to be evaluated. A quantitative metric that is commonly used to do this is probability of detection (POD); the likelihood of an inspection method detecting a feature of a specific size.

Bespoke test pieces have been designed and manufactured to allow for comprehensive characterisation of tools performance. Testing is possible in both static and dynamic set ups. When investigating the factors of the intelligent UT PIG design with enhancing the probability of detection; static testing was used to understand the offset between the ultrasonic beam and defect size as well as testing prototypes during the product development lifecycle. The dynamic testing allows for accurate POD calculations in real testing conditions.

The results presented focused on multiple areas. The impact of defect alignment with respect to the ultrasonic beam was investigated. It was found that 11% of the ultrasonic beam needs to interact with a region of wall thinning to ensure that it can be detected.

In addition, the POD was calculated for two different capture rates, both tools had match circumferential coverage, but one tool had an axial measuring density four times greater. The POD for the tool with the higher capture rate was over 5 mm smaller. The differences in the axial coverage are comparable to running tools at differing inspection speeds. A tool running at 0.2 ms^-1 will have a four times greater axial measurement density in comparison to a tool running at 0.8 ms^-1. This highlights the variation in tools performance depending on the operating conditions, and the importance of having highly trained and qualified operators.

The paper also introduced preliminary results for the development of a small diameter (<6”) ultrasonic phased array PIG. As highlighted in the results from conventional UT intelligent PIGs, increasing to coverage and decreasing the spot size increases the likelihood of detecting small features. Phased array technology allows you to increase the coverage of the tool and provide the flexibility to vary the spot size. The preliminary results showed the phased tool capable of detecting defects 2 mm in diameter in the static test jig.

Whilst developing new tools and optimising the operating conditions, the volume of date required to process and interrogate increases. As a result, more advance signal processing routines are being developed which can also help reduced the POD of the tool. In addition, the volume of data being gathered lends itself to machine learning.

The work presented in the paper showed key factors that impact the probability of detection of small diameter ultrasonic tools as well current work on developing the next generation of ultrasonic intelligent PIGs. The work highlights the continued innovation in tool design, signal processing and robust experimental validation taking place at Cokebusters.