Study of a Plastic Strain Limit Damage Criterion for Pipeline Mechanical Damage Using FEA and Full-Scale Denting Tests

Abstract

Pipeline constructed in rocky terrain is vulnerable to damages such as denting, gouging and other mechanical damages. In-line inspection (ILI) of these pipelines often reported several hundreds or even thousands of dents. Although most of these reported dents are well below 6% outside diameter (OD) depth limit as per ASME B31.8, few dents (sharp rock dents) with high strain could pose threat to integrity of the pipeline. Recently, strain-based models have been proposed to assess mechanical damage severity in pipelines. Attempts have also been made to characterize cracking susceptibility in rock dents using the critical strain based ductile failure damage indicator (DFDI) model. The objective of this study is to validate this model using full-scale denting tests conducted at the laboratory. Additionally, validation also extends to against the simplified DFDI model without finite element analysis (FEA). In this paper, the existing ASME strain limit and strain limit damage models are reviewed. The critical strain based strain damage model known as Ductile Failure Damage Indicator (DFDI) is then presented. The theoretical aspect of this model, including early work by Hancock and Mackenzie on strain limit (εf, reference failure strain) for ductile failure, is reviewed. The experimental aspect of material critical strain and its measurement using uni-axial tensile testing are then described. An elastic-plastic finite element analysis is employed to calculate DFDI, which is used to quantify the accumulated plastic strain damage and its susceptibility to cracking, and is validated using six full scale denting tests. Finally, the simplified strain limits for plain dent is proposed and validated.

Fatigue Life Models for Pipelines Containing Dents and Gouges

“…where (SCF)m and (SCF)b are the function of residual dent depth at MAOP expressed in Eqs ( 13) and (14). Equation ( 26) is an approximate solution of fatigue crack driving force expressed by the stress intensity factor range, ΔK, for an axial outside surface crack or gouge in dent in a pipeline.…”

“…In 2012, at the IPC conference, Zarea et al [11] presented the experimental and analytical results for dents and gouges obtained by those MD-4 projects over the four years. Since then, PRCI and U.S. Department of Transportation (DOT), Pipeline and Hazardous Materials Safety Administration (PHMSA) continues to sponsor the MD programs, and significant results have been obtained over the decade through great efforts by many investigators from different organizations using experimental, numerical, and analytical methods [5][6][7][8][9][10][11][12][13][14][15][16]. Recently, these MD assessment results were incorporated with other R&D results and the MD management practice from the pipeline operators' experience.…”

Corrosion informatics: an integrated approach to modelling corrosion

“…For example, dents characterised via inline inspection technologies have been used as input geometries for finite element elastic-plastic models to assess the susceptibility of physical dents to initiate cracks. 132 The use of 'ISVs' is critical to the application of finite element models for simulating the effects of damage, history and plasticity and to represent the growth of, for example, voids, slip-systems and dislocation densities. The development of ISV theory and its implementation in finite element simulations of materials is reviewed by Horstemeyer and Bammann, 133 who mention that the current state of the art allows the prediction of structure-property relations at such a high level that now it is possible for machine component materials to be optimised (an example was given of a Cadillac control arm that was reduced in weight by 25%, cost by 12% and, at the same time, increased in load-bearing capacity by 50% and fatigue life by 100%).…”

“…For example, dents characterised via inline inspection technologies have been used as input geometries for finite element elastic–plastic models to assess the susceptibility of physical dents to initiate cracks. 132…”

Comparison of Fatigue Models in API 1183 for Predicting Fatigue Life of Pipeline Dents

“…At the IPC2012 conference, Zarea et al [13] summarized the experimental and analytical results for dents and gouges obtained by those MD-4 projects over the four years from 2008 to 2012. Since then, both PRCI and U.S. Department of Transportation (USDOT) Pipeline and Hazardous Materials Safety Administration (PHMSA) have continued to sponsor the MD programs, and numerous results have been obtained over the 10 years through great efforts by many researchers from different organizations using experimental, numerical, and analytical methods [14][15][16][17][18][19][20][21][22][23][24][25][26]. Recently, these results were incorporated with the pipeline dent management practice from operators, and a recommended practice (RP) code was developed by API and designated as API RP 1183 [27] with an objective for assessment and management of pipeline dents.…”