• Title/Summary/Keyword: API X65 Linepipe

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Plastic Collapse Solution for API 5L X65 Natural Gas Linepipe (천연가스 수송용 API 5L X65 배관에 대한 소성붕괴해)

  • Kim Woo-sik;Shim Do-jun;Choi Jae-boong;Baek Jong-hyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.10
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    • pp.1483-1491
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    • 2004
  • To assess the integrity of the pipeline is the most important problem to be solved first of all for prevention of any fracture accident of the pipeline. As a result of exerting such efforts, a number of plastic collapse assessment equations have been suggested, however, the scope of using or applying such assessment equations has not been exactly defined. In this study, the case that a surface crack existed in the circumferential direction in the external side of the natural gas pipeline and a bending load was applied to the pipeline was analytically identified as the most critical condition, and a plastic collapse assessment equation fur it was suggested. The flow stress of the API X65 linepipe was defined through the experiment conducted on SENT specimens. Also, a local assessing criterion of a 3-dimensional crack behavior considering not only the crack depth but also the crack length was suggested. Finally, a plastic collapse assessment equation for the API X65 linepipe was developed by performing the 3-dimensional finite element analysis.

Hydrogen Diffusion in APX X65 Grade Linepipe Steels

  • Park, Gyu Tae;Koh, Seong Ung;Kim, Kyoo Young;Jung, Hwan Gyo
    • Corrosion Science and Technology
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    • v.5 no.4
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    • pp.117-122
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    • 2006
  • Hydrogen permeation measurements have been carried out on API X65 grade linepipe steel. In order to study the effect of steel microstructure on hydrogen diffusion behavior in linepipe steel, the accelerated cooling condition was applied and then three different kinds of microstructures were obtained. Hydrogen permeation measurement has been performed in reference to modified ISO17081 (2004) and ZIS Z3113 method. Hydrogen trapping parameters in these steels were evaluated in terms of the effective diffusivity ($D_{eff}$), permeability ($J_{ss}L$) and the amount of diffusible hydrogen. In this study, microstructures which affect both hydrogen trapping and diffusion were degenerated pearlite (DP), acicular ferrite (AF), bainite and martensite/austenite constituents (MA). The low $D_{eff}$ and $J_{ss}L$ mean that more hydrogen can be trapped reversibly or irreversibly and the corresponding steel microstructure is dominant hydrogen trapping site. The large amount of diffusible hydrogen means that corresponding steel microstructure is predominantly reversible. The results of this study suggest that the hydrogen trapping efficiency increases in the order of DP, bainite and AF, while AF is the most efficient reversible trap.

Estimation of fracture toughness of X65 and X70 steels by DWTT (X65 및 X70강 가스배관의 DWTT 및 파괴인성평가)

  • Cho, Ye-Won;Song, Young-Ho;Kim, Jeong-Min;Kim, Woo-Sik;Park, Joon-Sik
    • Journal of the Korean Institute of Gas
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    • v.16 no.3
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    • pp.54-64
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    • 2012
  • DWTT (Drop Weigh Tearing Test) is one critical method that can exhibit the fracture properties of line pipe steel, since it estimates the properties with real pipe steel. In this study, the ductile portion, inverse fracture ratio and absorbed energy of API X65 and X70 line pipe steels were estimated with temperature variation. Both steels showed that the ratio of ductile area and absorbed energy were decreased with respect to decreasing the test temperature. However, while the ductile fracture behavior exhibited until $-40^{\circ}C$ for the X70 steel, but it showed until $-30^{\circ}C$ for the X65 steel. The fracture properties were discussed with respect to test temperatures.