Full Scale Cyclic Fatigue Testing of Dented Pipelines and Development of a Validated Dented Pipe Finite Element Model

Abstract

Dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling, amongst others. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support, pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The paper discusses the full-scale dent testing being completed to support the development of pipeline integrity management criteria and is a continuation of the work discussed in previous IPC papers [1,2]. The material and structural response of the pipe test segments during dent formation and pressure loading has been recorded to support numerical model development. The full scale experimental testing is being completed for pipe test specimens in the unrestrained and restrained condition using different indentation depths and indenter sizes. The dents are pressure cycled until fatigue failure in the dent. This paper presents typical data recorded during trial including indentation load/displacement curves, applied pressures, strain gauges along the axial and circumferential centerlines, as well as dent profiles. The use of the full-scale mechanical damage test data described in this paper in calibrating and validating a finite element model based integrity assessment model is outlined. The details of the integrity assessment model are described along with the level of agreement of the finite element model with the full scale trial results. Current and future applications of the integrity assessment model are described along with recommendations for further development and testing to support pipeline integrity management.

Pipeline Mechanical Damage Assessment Using Finite Element Methods

“…9, there also exists discrepancy in the predicted residual dent depth between the current study and the investigations conducted by Tiku et al (2012). The reasons for a much higher elastic rebound observed in the study by Tiku et al (2012) are unclear but it is stated the FE model had scatter that lay outside the ± 10 % range. elastic rebound after removal of the indenter for an unconstrained dent with no internal pressure, was 70 mm in the present study and ~50 mm in the Tiku et al (2012) investigation.…”

“…9, there also exists discrepancy in the predicted residual dent depth between the current study and the investigations conducted by Tiku et al (2012). 9, there also exists discrepancy in the predicted residual dent depth between the current study and the investigations conducted by Tiku et al (2012).…”

“…The calibrated model was extended to analyse recent investigations for different parameters including pipe diameter, pipe wall thickness, indenter diameter and indentation depth (Tiku et al, 2012). Test 57 was selected and the parameters are summarized in Table 2; however, this reference study did not provide sufficient details on the physical testing and numerical modelling procedures.…”

“…Future work will aim at initially addressing the discrepancies observed in comparison study with Tiku et al (2012). Research efforts will be carried out to reduce the uncertainties associated with the model.…”

Investigation and Recommendations on Bottom-Dented Petroleum Pipelines

“…Recent studies on constrained (impinged by a hard object) and unconstrained (free to flex) pipe segments have attempted to model fatigue fracture in pipes [29]. Fatigue studies on dented pipes have been shown to develop colonies of parallel cracks that visually appear to be SCC, but are only fatigue.…”