Development of a Tensile Strain Capacity Predictive Model for American Petroleum Institute 5L X42 Welded Vintage Pipelines

Abstract Pipelines can be exposed to a wide variety of loads, depending on the environments and the area of application. These loads may impose large longitudinal plastic strain on pipelines, which could constitute a significant threat to the structural capacity of the pipeline. Reliable calibration of the strain capacity of pipelines plays an important role in the strain-based design (SBD) method. In this paper, a tensile strain capacity (TSC) predictive model (an equation) for welded X42 vintage pipes has been developed by conducting nonlinear parametric analysis followed by nonlinear regression analysis. First, our previously validated extended finite element method (XFEM) model was used to demonstrate the applicability of the XFEM in simulating full-scale ductile fracture response of pipelines subjected to biaxial loading, using pressurized American Petroleum Institute (API) 5L X42 vintage pipes subjected to four-point bending. Second, a parametric study investigating the effects of pipe and defect geometries as well as loading on the pipe TSC is presented. The nonlinear parameterization using XFEM was conducted in abaqus/standard. The TSC trends obtained for the various parameters considered were examined to derive appropriate individual variable functions for each parameter while taking any significant interactions between the parameters into consideration. Also, a nonlinear regression analysis is employed to develop a nonlinear semi-empirical model for predicting the TSC. The results obtained from the developed TSC predictive model (TSCvin.) was compared with those evaluated using the validated XFEM models. The results showed good agreement. Finally, statistical analysis was conducted to ensure the model is unbiased and predicts conservative TSCs by modifying the model using probabilistic error analysis. The modified model is capable of increasing the confidence level in the predicted TSC hence becoming a practical tool for reliable prediction of TSC of X42 vintage pipes needed for conducting pipeline integrity assessment. This modified predictive model is useful in practical applications because it provides a quantifiable degree of conservatism and reliability to the predicted TSCs.

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Effects of Biaxial Loading on the Tensile Strain Capacity of Girth Welds With Weld Strength Undermatching and HAZ Softening

Volume 2: Pipeline Safety Management Systems; Project Management, Design, Construction, and Environmental Issues; Strain Based Design; Risk and Reliability; Northern, Offshore, and Production Pipelines ◽

10.1115/ipc2020-9663 ◽

2020 ◽

Author(s):

Banglin Liu ◽

Yong-Yi Wang ◽

Xiaotong Chen ◽

David Warman

Keyword(s):

Internal Pressure ◽

Tensile Strain ◽

Biaxial Loading ◽

Reduction Factor ◽

Pressure Level ◽

Weld Strength ◽

Strain Capacity ◽

Weld Region ◽

Girth Welds ◽

Tensile Strain Capacity

Abstract The ability to accurately estimate the tensile strain capacity (TSC) of a girth weld is critical to performing strain-based assessment (SBA). A wide range of geometry, material, and loading factors can affect the TSC of a girth weld. Among the influencing factors, an increase in the internal pressure level has been shown to have a detrimental effect on the TSC. The overall influence of internal pressure is usually quantified by a TSC reduction factor, defined as the ratio of the TSC at zero pressure to the lowest TSC typically attained at pressure factors around 0.5–0.6. Here the pressure factor is defined as the ratio of the nominal hoop stress induced by pressure to the yield strength (YS) of the pipe material. A number of numeric and experiment studies have reported a TSC reduction factor of 1.5–2.5. These studies generally focused on strain-based designed pipelines with evenmatching or overmatching welds, minimum heat affected zone (HAZ) softening, and a surface breaking flaw at the weld centerline or the fusion boundary. This paper examines the effects of pipe internal pressure on the TSC of girth welds under the premise of weld strength undermatching and HAZ softening. The interaction of biaxial loading and the local stress concentration at the girth weld region was quantified using full-pipe finite element analysis (FEA). The relationship between TSC and the internal pressure level was obtained under several combinations of weld strength mismatch and HAZ softening. Results from the FEA show that the effects of the internal pressure on the TSC are highly sensitive to the material attributes in the girth weld region. Under less favorable weld strength undermatching and HAZ softening conditions, the traditionally assumed reduction factor or 1.5–2.5 may not be applicable. Further, the location of tensile failure is found to depend on both the weld material attributes and the internal pressure. It is possible for the failure location to shift from pipe body at zero internal pressure to the girth weld at elevated internal pressure levels. The implications of the results for both girth weld qualification and integrity assessment are discussed.

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Nonlinear Regression Analysis Methodology for the Estimation of Detection Probabilities from Empirical Data.

10.21236/ada134078 ◽

1982 ◽

Author(s):

J. L. Hofmockel

Keyword(s):

Regression Analysis ◽

Nonlinear Regression ◽

Empirical Data ◽

Nonlinear Regression Analysis ◽

Analysis Methodology ◽

Detection Probabilities

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Software Effort Estimation from Use Case Diagrams Using Nonlinear Regression Analysis

2020 IEEE Canadian Conference on Electrical and Computer Engineering (CCECE) ◽

10.1109/ccece47787.2020.9255712 ◽

2020 ◽

Author(s):

Ali Bou Nassif ◽

Manar AbuTalib ◽

Luiz Fernando Capretz

Keyword(s):

Regression Analysis ◽

Nonlinear Regression ◽

Use Case ◽

Effort Estimation ◽

Nonlinear Regression Analysis ◽

Software Effort Estimation

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Multi-Tier Tensile Strain Models for Strain-Based Design: Part 2 — Development and Formulation of Tensile Strain Capacity Models

Volume 4: Pipelining in Northern and Offshore Environments; Strain-Based Design; Risk and Reliability; Standards and Regulations ◽

10.1115/ipc2012-90659 ◽

2012 ◽

Cited By ~ 4

Author(s):

Ming Liu ◽

Yong-Yi Wang ◽

Yaxin Song ◽

David Horsley ◽

Steve Nanney

Keyword(s):

Driving Force ◽

Tensile Strain ◽

Weld Strength ◽

Experiment Data ◽

Pipe Wall Thickness ◽

Crack Driving Force ◽

Strain Capacity ◽

Welding Processes ◽

Tensile Strain Capacity

This is the second paper in a three-paper series related to the development of tensile strain models. The fundamental basis of the models [1] and evaluation of the models against experiment data [2] are presented in two companion papers. This paper presents the structure and formulation of the models. The philosophy and development of the multi-tier tensile strain models are described. The tensile strain models are applicable for linepipe grades from X65 to X100 and two welding processes, i.e., mechanized GMAW and FCAW/SMAW. The tensile strain capacity (TSC) is given as a function of key material properties and weld and flaw geometric parameters, including pipe wall thickness, girth weld high-low misalignment, pipe strain hardening (Y/T ratio), weld strength mismatch, girth weld flaw size, toughness, and internal pressure. Two essential parts of the tensile strain models are the crack driving force and material’s toughness. This paper covers principally the crack driving force. The significance and determination of material’s toughness are covered in the companion papers [1,2].

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