Abstract
This research investigated the strain-based dent evaluation approach for thin-walled, low-grade steel pipeline, with a particular focus on the assessment models proposed in the American Society of Mechanical Engineers B31.8 (ASME B31.8), the European Pipeline Research Group (EPRG), and the Pipeline Defect Assessment Manual (PDAM). The primary aim was to assess the accuracy and limitations of existing depth-based acceptance criteria by examining the influence of dent geometry, dent depth, and internal pressure on induced strain and dent recovery.
A combined experimental and numerical approach was employed. A practical denting experiment was conducted on a steel pipe using a Toweye indenter, followed by finite element analysis (FEA) to validate and extend the investigation. The validated FEA model was then used to perform parametric studies, simulating different dent geometries, depths, and internal pressures to evaluate their effects on strain distribution and dent reformation.
The results revealed that dent geometry and dent depth are the dominant factors influencing strain concentration. Sharp dents formed by the Toweye produced significantly higher strain levels than spherical dents, with peak strain values increasing from 25.42% at 2% dent depth to 32.80% at 12% depth. Under equivalent conditions, spherical dents exhibited lower strain levels, ranging from 24.34% to 26.77%, indicating a more uniform stress distribution. Increasing internal pressure promoted dent recovery but had only a moderate effect on strain. At 11 MPa, the maximum dent depth reduction reached 6.86 mm for spherical dents and 6.48 mm for Toweye dents, while the corresponding maximum strain increases were 3.57% and 1.93%, respectively.
Comparison with existing assessment models showed that strain levels in sharp dents exceeded the ASME B31.8 strain limit (16.2%) at a dent depth of 6%, confirming that the 6% depth criterion is not overly conservative for severe dents. In contrast, spherical dents remained closer to code thresholds, indicating that dent shape should be a key consideration in integrity evaluations...