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Dr. Mike Kirkwood
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Mike Kirkwood, Aaron Lockey, Susannah Turner
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Abstract

Dents in onshore pipelines are relatively common. They can be caused during pipe manufacture, transportation, construction, or during operations. Most dents are benign, but some are not. Dents can fail immediately due to cracking when they are formed, or after many years of operation due to cyclic loading. The factors that determine whether a dent fails can be complex, and the size of the dent is only one aspect to consider. Excavating and remediating is expensive and time-consuming, so being able to appropriately sentence dents for repair really is valuable. Until around 15 years ago, dents were usually assessed using simple methods based solely on their depth. Dents are formed by objects that are not smooth, such as rocks and excavator buckets. Dents therefore often have complex shapes including multiple peaks. The simple depth-based assessment methods needed to be highly conservative to account for the large variability in dent shape hidden behind this single parameter. ILI can accurately measure the shape of the pipe wall over a dense grid of points, allowing the unique shape of each dent to be assessed directly. Methodologies were developed to assess dents based on their unique shapes, taking advantage of the data produced by advances in ILI resolution and accuracy. Although complex, the calculations involved in these assessments can be automated. These methodologies greatly reduced the excess conservatism in many dent assessments, and therefore reduced the costs associated with excavating and repairing dents unnecessarily. However, these methodologies were proprietary, lacked standardisation, and could be difficult for regulators to accept. In the words of Mater (Pixar movie Cars 2) “I don't get them dents buffed, pulled, filled or painted by nobody. They are way too valuable.". This paper discusses why it is important to value your dents and to assess them carefully and considers current industry best practice.

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