Journal of High Pressure Institute of Japan
Online ISSN : 1347-9598
Print ISSN : 0387-0154
ISSN-L : 0387-0154
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Volume 48, Issue 3
Displaying 1-6 of 6 articles from this issue
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Original Paper
  • STUDY ON COLLAPSE CHARACTERISTICS OF CYLINDER-TO-CYLINDER INTERSECTIONS BY INELASTIC FINITE ELEMENT ANALYSIS
    Shunji KATAOKA, Asako MIYAKAWA
    Article type: Original paper
    2010 Volume 48 Issue 3 Pages 114-121
    Published: May 25, 2010
    Released on J-STAGE: July 23, 2010
    DOIhttps://doi.org/10.11181/hpi.48.114
    JOURNAL FREE ACCESS
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    It is known that the collapse strength of complex three-dimensional structures cannot be evaluated accurately with elastic analysis, and more accurate results require the use of inelastic analysis. A typical example is cylinder-to-cylinder intersection.
    In this study, the relationship of collapse loads and local primary membrane stresses of cylinder-to-cylinder intersections was examined.
    First, elastic analysis on the cylinder-to-cylinder intersections with various combinations of diameter and thickness under internal pressure was conducted. The local primary membrane stress (PL) obtained from the analysis was normalized by the general primary membrane stress (Pm) . The ratio of PL⁄Pm is defined as Stress Intensification Factor (SIF) which was directly influenced by the geometries.
    Secondly, limit load analysis was conducted on the same structures as elastic analysis and collapse pressure was obtained. The Collapse Strength Reduction Factor (CSRF) defined as the ratio of the run pipe collapse pressure to the cylinder-to-cylinder collapse pressure was proposed. The CSRF was also directly influenced by the geometries.
    Comparing the results of SIF with CSRF, it is clear that the evaluation by method is overly-conservative and the proposed concept of CSRF method provides more accurate evaluation for the cylinder-to-cylinder intersections. Furthermore, these analysis results can be extended to the reinforced intersections. SIF or CSRF values on the reinforced intersection were predicted from the basic data.
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  • Effects of Nut thinning due to Corrosion on the Strength Characteristic and the Sealing Performance in Bolted Flange Joints under Internal Pressure
    Tsutomu KIKUCHI, Mitsuo HITOMI, Toshiyuki SAWA, Yuya OMIYA
    Article type: Original paper
    2010 Volume 48 Issue 3 Pages 122-131
    Published: May 25, 2010
    Released on J-STAGE: July 23, 2010
    DOIhttps://doi.org/10.11181/hpi.48.122
    JOURNAL FREE ACCESS
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    In the depreciation evaluations for pressure equipment, it is important for engineers to evaluate the reduction in strength and the sealing performance in bolted flange joints. In this study the effects of nut thinning due to corrosion on the strength characteristic and the sealing performance in 3B bolted flange joints under internal pressure are examined from both FEM calculations and experiments. The following results are obtained. When the bolted flange joint has been tightened by the bolt force of 50% yield stress, the tolerance yield force of the screws will not be surpassed, but when tightened by the 90% of yield stress, a small-scale yield region occurred from the nut washers to the three threads. During the tests, when the nut height decreased, the fracture position of the bolts and nuts changed from the free-threaded part of a bolt screw to the thread engagement. While verifying this phenomenon using FEM, it was newly discovered that when the height of the nut was reduced to 1⁄3 (equivalent to approximately two threads) of the original dimensions according to the standards, the sealing performance could no longer be assured.
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  • Long Term Estimation for Sealing Performance of Gasketed Connections by using Finite Element Analysis
    Kouji SATOU, Takahito NISHIDA
    Article type: Original paper
    2010 Volume 48 Issue 3 Pages 132-139
    Published: May 25, 2010
    Released on J-STAGE: July 23, 2010
    DOIhttps://doi.org/10.11181/hpi.48.132
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    Non-asbestos gasket is recently widely used as a substitute of compressed asbestos sheet gasket. Even though the PTFE gasket has excellent seal performance, heat resistance, and chemical resistance, a large reduction of axial bolt force under high temperature condition is a serious problem for a bolted connection with PTFE gasket. There is no method of evaluating the long-term and high temperature characteristic of the gasket. What is a dominant factor for bolt force reduction in the connection is not clear because of complex high temperature performance of such soft gasket.
    In this study, method of estimate sealing life of bolted connection with soft gasket, finite element simulations to investigate gasket contact stress reduction of bolted flange connection with soft gasket are performed under high temperature conditions, where temperature and time dependent gasket material properties, such as stress-strain relation, thermal expansion factor and creep performance, are measured and employed. And, sealing performance under high temperature conditions are testes.
    As a result, method of estimate sealing life and examine maintenance of bolted connection with soft gasket is performed. The method give information of sealing life and method for extend life. Here, the gasket that can be applied is limited to the PTFE gasket.
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Review
  • The development trend of non asbestos sheet gasketing
    Shinya KUROKAWA, Takahito NISHIDA
    Article type: Review
    2010 Volume 48 Issue 3 Pages 140-147
    Published: May 25, 2010
    Released on J-STAGE: July 23, 2010
    DOIhttps://doi.org/10.11181/hpi.48.140
    JOURNAL FREE ACCESS
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    Before the 1990"s the compressed asbestos sheet gasketing has been used widely in comparatively mild conditions. Since the 1980"s the gasketing manufacturers have developed non asbestos products that substitute the compressed asbestos sheet gasketing. Recently such movement is accelerated. The gasketings that consist of many kinds of materials are commercialized. This report introduces the characteristics of various products.
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  • Hydrogen Embrittlement of Austenitic Stainless Steels
    Michihiko NAGUMO
    Article type: Review
    2010 Volume 48 Issue 3 Pages 154-165
    Published: May 25, 2010
    Released on J-STAGE: July 23, 2010
    DOIhttps://doi.org/10.11181/hpi.48.154
    JOURNAL FREE ACCESS
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    Recent studies on hydrogen embrittlement (HE) of austenitic stainless steels have been reviewed with a brief summary of fundamentals of hydrogen behaviors. The hydrogen states are characterized by high solubility and low diffusivity, occasionally leading to a high local concentration of hydrogen. The high concentration of hydrogen leads to the formation of hydrides, which transform into martensites on increasing hydrogen concentration or degassing. The susceptibility to HE is critically dependent on the stability of austenite, i. e. the composition of steels, and the test temperature. The effects of inhomogeneity of alloy distributions and of microstructures have been presented.
    The mechanism of HE has been examined from fractographic features, microstructures around the crack path and the amount of transformed martensite. Contradictory observations have been reported on the role of α' martensite in the crack propagation. It is noticed that apparent correlation of the embrittlement with the amount of α' does not necessarily imply the essential function of α' serving as the crack path. The instability of austenite is associated with the extent of stacking fault the formation of which precedes martensitic transformation. A possibility is suggested that hydrogen-enhanced creation of strain-induced lattice defects results in both HE and the instability of austenite.
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