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To comprehensively investigate the tensile properties of cold bends, full-scale cold bending experiments, tensile tests using prestrained small-scale specimens, and finite element (FE) analyses of the cold bending processes were conducted on API 5L X60 and X80 grade line pipes. The tensile tests revealed that the tensile properties of the cold bends were comparable to the uniaxially prestrained specimens machined from the straight part of the pipes. A FE model simulating the cold bending process was verified with the full-scale experimental results in terms of the distributions of residual strains. These results supported a procedure for estimating the tensile properties of the cold bends with a combination of the FE model and the tensile tests using the pre-strained specimens; the residual strains obtained from the FE model are transformed into the tensile properties based on the relationship between the residual strains and the tensile properties. This study clarified that the tensile properties come close to being uniformly distributed by reducing the distance between the bending locations; the distance between the bending locations has a significant influence on the overlap of adjacent deformed areas, which governs the distribution of the tensile properties of the cold bends. [DOI: 10.111511.2746395]

To investigate the mechanical properties of pipeline subjected to plastic deformation, tensile tests and crack-tip-opening displacement (CTOD) tests were conducted on X60, X65, and X80 line pipe steels with uniaxial tensile or compressive prestrain, [[epsilon].sub.pr]. The tensile tests revealed that the Bauschinger effect and work hardening were dependent on the yield-to-tensile ratio (Y/T) of the steels; the change in yield stress due to prestrain linearly depended on the Y/T of the base metal. A critical CTOD for crack initiation decreased with increasing \[[epsilon].sub.pr]\. Compressive prestrain had a larger effect on the reduction of the critical CTOD than tensile prestrain. The test results showed that the reduction in the critical CTOD due to tensile prestrain was predictable with a simplified theoretical model employing a critical fracture strain of the base metal. [DOI: 10.1115/1.1894405]

In order to clarify the significant parameters to control the deformability of high-grade induction bend pipes, finite element analyses simulating the deformation behavior subjected to an internal pressure and bending moment were carried out. Parametric studies were conducted using the finite element models with various mechanical properties and geometric imperfections. The change in the integrity of the buried pipeline due to the quality of the induction bend pipe was then quantitatively examined. Consequently, this study indicated that the mechanical properties, the dimensions and tolerance and the properties of the 'transition' part should be appropriately designed in proportion to the ground deformation. [DOI: 10.1115/1.1839881]

Leak-before-break (LBB) behavior was evaluated for two series of API 5L X65 line pipes and three series of X80 line pipes with various levels of Charpy V-notch (CVN) absorbed energy. Full-scale hydrostatic burst tests were conducted for the line pipes with an axial through-wall (TW) notch to determine LBB criteria, that is, the relationship between the axial TW notch length and hoop stress for LBB. The determined LBB criteria were verified by full-scale partial gas burst tests for line pipes with an axial part-through-wall (PTW) notch and were then compared to the estimation using the CVN energy-based equation that Kiefner et al. have proposed. The present study demonstrated that the estimation using the CVN-based equation was in good agreement with the experimental results for the pipes with a relatively low CVN energy of less than 130 J. On the contrary, the equation was not applicable to the pipes with a relatively high CVN energy of more than 130 J. The results of instrumented Charpy tests clarified that the load versus load-point displacement curves for Charpy specimens from the high CVN energy pipes were different from those from the low CVN energy pipes. Therefore, the applicability of the CVN-based equation was dependent on the load versus load-point displacement curve for a Charpy specimen. [DOI: 10.1115/1.1834619]

In this study, the deformability of high-grade pipelines subjected to an axial compressive deformation was experimentally and analytically discussed. Six cases of axial compression experiments with high-grade line pipe were carried out. The pipe specimens had various material properties and wall thickness. Finite-element analyses were also carried out and verified the reliability. Then, a finite-element analysis method for evaluating the deformability of the line pipe was established. By using this method, parametric studies were carried out. The effects of the strain-hardening behavior and pipe geometry on the deformability of the high-grade pipelines were examined.

The behavior during the cold bending of pipelines was experimentally and analytically investigated. Full-scale cold bending experiments were performed on API X60 and X80 grade line pipes. Finite element (FE) analyses simulated the cold bending process by considering the contact interactions between a pipe and the components of the bending machine. The results of the simulation were in good agreement with the full-scale experiments. The stress-strain relationship and yield to tensile ratio (Y/T) had no obvious effect on the strain distribution after cold bending. The tensile tests quantitatively evaluated the decrease in the yield stress along the longitudinal direction on the cold bends due to the Bauschinger effect. [DOI: 10.1115/1.1554701]

Crack-tip-opening displacement (CTOD) and fatigue-crack growth tests were conducted for several line pipe steels with uniaxial tensile or compressive prestrain, [[Epsilon].sub.pr]. Critical CTOD decreased with increasing |[[Epsilon].sub.pr]|. The reduction of critical CTOD due to prestrain was dependent on the ductile-brittle transition temperature of the steels without prestrain. A few percent of [[Epsilon].sub.pr] induced the ductile-brittle transition for the steels with a higher transition temperature. The compressive [[Epsilon].sub.pr] had larger effects on both reduction of critical CTOD and strain induced ductile-brittle transition than the tensile [[Epsilon].sub.pr]. Only the high compressive [[Epsilon].sub.pr] accelerated both fatigue crack initiation and growth, and no obvious effect of the tensile [[Epsilon].sub.pr] on the fatigue properties was observed. [DOI: 10.1115/1.1379531]