Search

In this paper, the deformability of line pipe with local metal loss was examined. A full-scale experiment and a finite element (FE) analysis were carried out for line pipe with local metal loss subjected to an axial compressive load. As a result, a good agreement was obtained between the analytical and experimental results. This indicated that the present analytical method was applicable to evaluate the deformability of line pipes with local metal loss subjected to a large ground movement. Parametric studies were then conducted to clarify the relationship between the geometry of the local metal loss and the deformability using the FE analytical method. Keywords: pipelines, compressive deformation, local metal loss, peak load strain, experiment, finite element analysis

By conducting curved wide plate tensile tests for girth welded joints of X80 line pipe containing a surface notch in the weld metal the effects of strength matching on fracture performance were evaluated. Parametric studies were also conducted using a finite element method simulating the experiments to clarify the effects of strain hardening capacity of the base metal, softening in the heat affected zone, and groove configuration on fracture performance. A strain at failure significantly decreased with the decreasing strength matching. This was expected to be due to a difference in local straining behavior at the notch tip caused by the shielding effect. The analytical studies revealed that the strain hardening capacity of the base metal the softening in the heat affected zone, and the groove configuration affected the allowable strain for a given toughness level in the case of overmatching. However, these factors hardly affected the allowable strain in the case of undermatching. [DOI: 10. I 115/1.2746402]

A method of predicting the leak/rupture criteria for AP1 5L X80 and X100 line pipes was evaluated based on the results of hydrostatic full-scale tests for X60, X65, X80, and X100 line pipes with an axially through-wall (TW) notch. The TW notch test results defined the leak/rupture criteria, that is, the relationship between the initial notch lengths and the maximum hoop stresses during the TW notch tests. The defined leak/rupture criteria were then compared to the prediction of the Charpy V-notch (CVN) absorbed energy-based equation, which has been proposed by Kiefner, Maxey et al. This comparison revealed that the CVN-based equation was not applicable to the pipes having both a CVN energy greater than 120 or 130 J and flow stress greater than the level of X65. In order to predict the leak/rupture criteria for these line pipes, the static absorbed energy for ductile cracking, [([C.sub.vs]).sub.i], was introduced as representing the fracture toughness of a pipe material The [([C.sub.vs]).sub.i] value was determined from the microscopic observation of the cut and polished Charpy V-notch specimens after static three-point bending tests. The CVN energy in the original CVN-based equation was replaced by an equivalent CVN energy, [([C.sub.v]).sub.eq], which was defined as follows: [([C.sub.v]).sub.eq]=4.5 [([C.sub.vs]).sub.i]. The leak/rupture criteria for the X80 and X100 line pipes with higher CVN energies were reasonably predicted by the modified equation using the [([C.sub.vs]).sub.i] value. [DOI: 10.1115/1.2349570]

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]

This paper presents an analytical procedure to predict the conditional probability of dynamic ductile axial crack arrest within one pipe joint length for pipeline materials operating at temperature above the brittle-to-ductile transition temperature. The analysis assumes there is an event to initiate a rupture with probability of one, so that the probability of a fracture event occurring is the probability of the rupture event (i.e., from mechanical damage) times the conditional probability of arrest within one pipe joint. The underlying deterministic model centers on the Battelle Two-Curve approach with a correction to predict the arrest length given the actual material toughness relative to the minimum arrest toughness. Past full-scale experimental results were used to develop statistical parameters that were used with the deterministic model in a Monte Carlo analysis. This model was calibrated for linepipe materials with a toughness less than 150J and a grade less than X65. Example cases are presented to demonstrate the variation of the probability of arrest with the pipeline operating conditions. [DOI:101115/1.1858924]

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]

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]