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  Title Techniques for the enhanced assessment of pipeline dents
  Author(s) Jane Dawson, Ian Murray, and Julie Hedger  
  Abstract DENTS CAN OCCUR DURING PIPELINE construction or in-service causing a local stress and strain concentration and a local reduction in the pipe diameter. If failure as a result of a dent is not immediate, it is possible that the damage can deteriorate in service and cause failure at some time after the initial impact. The challenge to the pipeline operator is the identification of the dents that may threaten the future integrity of the pipeline from those that are dormant and require no further action.

In recent years, there has been a shift from simple depth-based assessment of plain dents to the use of strain-based assessment that uses the dent local radius of curvature to define severity. Furthermore, as pipeline dents subject to cyclic pressure loading can also develop fatigue cracks it is necessary to assess dent fatigue life. Up until recently, the options for dent fatigue assessment were limited to published assessment methods that tend to be based on dent depth or the alternative has been expensive and time consuming finite element analysis (FEA) modelling of each individual dent. A new approach developed in a PRCI research project [1] uses measurements from the dent axial and circumferential profiles to predict dent fatigue severity and the cyclic pressure spectrum to derive the dent remaining life. This approach has been validated based on extensive FEA studies and full scale dent fatigue testing.

This paper discusses the new approaches that can be used to evaluate dent severity and fatigue life. Real case studies are provided to illustrate the new approaches and to compare the findings to the older depth-based methodologies used previously.

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