This paper presents a numerical study of plastic hardening models used in the stresses, strains and fatigue life simulation of a pipeline elbow under operating internal pressure and cyclic in-plane bending. To determine more accurate... more
This paper presents a numerical study of plastic hardening models used in the stresses, strains and fatigue life simulation of a pipeline elbow under operating internal pressure and cyclic in-plane bending. To determine more accurate stresses, strains and fatigue life of the elbow in cyclic loading, the material plastic hardening response and the Bauschinger effect need to be considered properly in the numerical simulation. Thus, the isotropic, kinematic and combined isotropic/kinematic hardening models are evaluated in the elastic-plastic finite element analysis (FEA) of a benchmark beam. On this basis, those plastic hardening models are applied to simulate the elbow under combined loading of constant internal pressure and cyclic in-plane bending. With the FEA results and the selected fatigue models that are commonly used in the pipeline industry, fatigue life of the elbow is predicted for each hardening model. As such, the appropriate plastic hardening model and fatigue life model...
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ABSTRACT Normalization method is adopted in this paper to determine fracture resistance curves, i.e. J-R curves for dissimilar metal (DM) welds involved in nuclear reactor pressure vessels. Due to the restriction of material availability,... more
ABSTRACT Normalization method is adopted in this paper to determine fracture resistance curves, i.e. J-R curves for dissimilar metal (DM) welds involved in nuclear reactor pressure vessels. Due to the restriction of material availability, three compact tension (CT) specimens containing a DM weld with a crack were utilized and tested under the guideline of ASTM fracture toughness test standard E1820 [1]. The test data of load versus load-line displacement were recorded during the tests, and directly applied to estimate crack extension using the normalization procedures. The J-R curves are then developed without the need of online crack extension measurement.Three J-R curves of DM welds were obtained using the standard 1T CT specimens and the normalization method. These resistance curves were evaluated through comparison with those obtained from small sized ½T CT specimens via ASTM E1820 standard procedures and those obtained from the electrical potential drop method. The results showed that the normalization method, ASTM E1820 standard procedures, and the electrical potential drop method can determine similar fracture resistance curves for DM welds in a good agreement. Among the three methods, the normalization method is of most attractive because it is the only one that does not need crack extension measurements, and thus test costs are saved.
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This paper presents an elastic stress analysis for miter joints in a pipeline under internal pressure or in-plane bending. Using the three-dimensional theory of elasticity, Green and Emmerson [1] obtained two general expressions of hoop... more
This paper presents an elastic stress analysis for miter joints in a pipeline under internal pressure or in-plane bending. Using the three-dimensional theory of elasticity, Green and Emmerson [1] obtained two general expressions of hoop and axial stresses for a mitered pipe, and two specific solutions at the plane of joint for the loading cases of internal pressure and in-plane bending. However, their solution of axial stress for bending case is incorrect, and the stress variations with the pipe axis are not provided. Based on their general expressions, the closed-form solutions of hoop and axial stresses are obtained as functions of the radial location r, the circumferential angle θ, and the half miter angle α, in addition to the applied loading, geometry and material parameters. From these results, the solutions of hoop and normal stresses are obtained at the plane of joint for the two loading scenarios. The proposed theoretical solutions are then validated by three-dimensional fi...
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ABSTRACT The normalization method is adopted in this paper to determine J-R curves for X60 pipeline steel using single-edge notched tension (SENT) specimens. A resistance curve procedure associated with the normalization method is... more
ABSTRACT The normalization method is adopted in this paper to determine J-R curves for X60 pipeline steel using single-edge notched tension (SENT) specimens. A resistance curve procedure associated with the normalization method is developed to estimate crack extension, calculate crack growth corrected J-integral and generate a J-R curve directly using load-displacement data from a single test on SENT specimens. Based on experimental data for a typical pin-loaded SENT specimen, J-R curve for X60 pipeline steel is obtained by the normalization method and the conventional elastic unloading compliance method. The results show that the normalization method is simple and cost-effective, and can obtain J-R curves equivalent to the unloading compliance method in use of SENT specimens.
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Historic pipeline construction utilized miter joints to enable small directional changes in pipeline routing, and this legacy construction remains in today’s pipelines. Current codes and regulations impose a limit on the maximum miter... more
Historic pipeline construction utilized miter joints to enable small directional changes in pipeline routing, and this legacy construction remains in today’s pipelines. Current codes and regulations impose a limit on the maximum miter angle to less than three degrees of the total pipeline direction change, for pipeline operating with pressure over 30-percent SMYS (Specified Minimum Yield Stress). In anticipation of an operational pressure increase, an experimental and simulation effort was undertaken recently to determine the stress amplification due to miters in 30-inch diameter, 0.5-inch thick gas transmission pipelines. Experiments were conducted on six miter joints ranging in miter angle from 0° to 8° degrees of total pipeline direction change. Three of the miter joints were removed from the field (1950’s original installation), while the remaining three were specifically fabricated for the testing. All the miters considered were X42 pipeline steel. The miter pipe joint specimen...
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... For power-law hardening materials, (Gao and Nemat-Nasser, 1983b) and (Zhu andHwang, 1996) proposed dynamic near-tip fields with discontinuous and logarithmically singular stresses and strains. However, Leighton et al. ...
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