• Title/Summary/Keyword: API X65 강

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Development of Stress-Modified Fracture Strain Criterion for Ductile Fracture of API X65 Steel (API X65 강의 연성파괴 해석을 위한 삼축응력 영향을 고려한 파괴변형률 기준 개발)

  • Oh Chang-Kyun;Kim Yun-Jae;Park Jin-Moo;Baek Jong-Hyun;Kim Woo-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.12 s.243
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    • pp.1621-1628
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    • 2005
  • This paper presents a stress-modified fracture strain for API X65 steel used for gas pipeline, as a function of stress triaxiality. To determine the stress-modified fracture strain, tension test of bars with four different notch radii, made of API X65 steel, is firstly performed, from which true fracture strains are determined as a function of notch radius. Then detailed elastic-plastic, large strain finite element (FE) analyses are performed to estimate variations of stress triaxiality in the notched bars with load. Combining experimental with FE results provides the true fracture strain as a function of stress triaxiality, which is regarded as a criterion of ductile fracture. Application of the developed stress-modified fracture strain to failure prediction of gas pipes made of API X65 steel with various types of defects is discussed.

Finite Element Ductile Failure Simulations of Tensile and Bend Bars made of API X65 Steels (API X65 강의 인장 및 굽힘 시편에 대한 유한요소 연성파괴 해석)

  • Oh, Chang-Kyun;Jin, Te-Eun;Kim, Yun-Jae
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1696-1701
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    • 2007
  • This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.

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Ductile Failure Analysis of Defective API X65 Pipes Based on Stress-Modified Fracture Strain Criterion (파괴변형률모델에 기초한 결함이 존재하는 API X65 배관의 연성파괴 해석)

  • Oh, Chang-Kyun;Baek, Jong-Hyun;Kim, Young-Pyo;Kim, Woo-Sik;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.9 s.252
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    • pp.1086-1093
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    • 2006
  • A local failure criterion for the API X65 steel is applied to predict ductile failure of full-scale API X65 pipes with simulated corrosion and gouge defects under internal pressure. The local failure criterion is the stress-modified fracture strain for the API X65 steel as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the effective stress). Based on detailed FE analyses with the proposed local failure criteria, burst pressures of defective pipes are estimated and compared with experimental data. The predicted burst pressures are in good agreement with experimental data. Noting that an assessment equation against the gouge defect is not yet available, parametric study is performed, from which a simple equation is proposed to predict burst pressure fur API X65 pipes with gouge defects.

Study on Hydrogen Embrittlement for API 5L X65 Steel Using Small Punch Test I : Base Metal (소형펀치 시험을 이용한 API 5L X65 강의 수소취화에 관한 연구 I : 모재부)

  • Jang, Sang-Yup;Yoon, Kee-Bong
    • Journal of Energy Engineering
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    • v.18 no.1
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    • pp.49-55
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    • 2009
  • Occurrence of hydrogen embrittlement could be one of the main obstacles for using structural equipment under hydrogen environment. It is required to develop assessment methods of hydrogen embrittlement for the metals used in production, storage, transmission and application utilities of hydrogen. The most probable method of hydrogen mass transmission is using existing natural gas pipeline. Base or weld part of the pipeline can be damaged by mixed gas of hydrogen in the pipeline. In this study small punch (SP) testing was employed to evaluate the hydrogen embrittlement behavior for a line pipe steel (API X65) with electrochemically hydrogen charged specimens. Results showed that the SP test can be a good candidate test method for hydrogen damage evaluation method. Strength of steel is known to be decreased with the level of hydrogen charging. However, for API X65 steel base metal need in this study, the effect of hydrogen to strength was not significant. It can be negligible regardless of the hydrogen contents in the steel. With this test different strength levels with various hydrogen charging conditions were observed. It can also be anticipated that more sensitive evaluation of material behavior be obtainable by the SP test method.

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.

Study on Hydrogen Embrittlement for API 5L X65 Steel Using Small Punch Test II : Weld Metal (소형펀치 시험을 이용한 API 5L X65 강의 수소취화에 관한 연구 II : 용접부)

  • Jang, Sang-Yup;Yoon, Kee-Bong
    • Journal of Energy Engineering
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    • v.18 no.1
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    • pp.56-62
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    • 2009
  • With weld metal of X65 steel, hydrogen was charged by electro-chemical method and mechanical behavior such as strength was measured by the small punch test. The weld metal was more sensitive to hydrogen charging than the case of base metal. The small punch (SP) strength was decreased as the hydrogen contents increased. Magnitude of strength decrease was dependent on current density, temperature, charging time. Current density and charging time have significant effect on the mechanical properties but temperature of electrolyte has limited effect. Fractured surfaces of the tested specimens were observed by SEM (scanning electron microscope). In the hydrogen charged specimens cleavage fracture were observed, which is consistent with the SP test results. Since the testing procedure for studying hydrogen embrittlement proposed in this study has shown good reproducibility of test results, the proposed method can be assumed to be a reliable test procedure. Using the electrochemical charging and the small punch test, the change of SP strength for X65 weld metal due to hydrogen embritlement could be evaluated sensitively.