Journal of High Pressure Institute of Japan
Online ISSN : 1347-9598
Print ISSN : 0387-0154
ISSN-L : 0387-0154
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Original Paper
  • Atsushi IWASAKI
    2021 Volume 59 Issue 5 Pages 230-237
    Published: 2021
    Released: October 28, 2021
    In this study, evaluation method of the probability of failure of a structure from qualitative inspection data, such as visual inspection, is proposed. In recent years, the aging of social infrastructure structures and the resulting increase in maintenance costs have become a problem. RBM is a method of optimiz-ing the timing and content of maintenance by defining the risk as the product of the probability of failure of the structure and the consequence of the failure. For the Risk Based Maintenance, optimization is done by homogenizing risk, which requires the calculation of risk, i.e., the probability of failure. Corrosion is a problem in outdoor structures such as bridges and roadway ancillary facili-ties. However, unlike structures in factories, quantitative thickness control is not used in many target structures, and only qualitative inspections such as visu-al inspections are used to rank the thickness. However, in such inspections, un-like in the case of control by thickness measurement, a method for evaluat-ing the probability of failure from inspection results has not been established. In this paper, we propose a method to evaluate the quantitative wall thin-ning rate from discrete qualitative inspection data using Bayesian estimation, and examine the effectiveness of the proposed method by comparing it with the evaluation of quantitative inspection data. The method is based on the probabilistic estimation of the inspection results obtained from any combi-nation of the year when the wall thinning started and the wall thinning rate. In this paper, the effectiveness of the proposed method, the evaluation accuracy, and the influence of the qualitative method are clarified by examining the evaluation of the qualitative inspection classified into four ranks, the number of rank divi-sions in the qualitative inspection, and the influence of the rank division method on the evaluation accuracy.
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  • Yutaka TSUCHIDA, Tetsushi CHIDA, Tomohiko OMURA, Daisuke HIRAKAMI
    2021 Volume 59 Issue 5 Pages 238-249
    Published: 2021
    Released: October 28, 2021
    Combining the peak separation of TDA (Thermal Desorption Analysis) curve with Fermi-Dirac statistics, the published TDA curves on a cold-rolled pure iron, which were hydrogen-charged by exposure to gaseous hydrogen or cathodic polarization, have been analyzed.
    When hydrogen is charged at 60 and 90℃ for 4 hours by cathodic polar-ization, dis-location trap density is decreased by segregation of carbon atoms along dislocation. With the prolonged exposure to gaseous hydrogen up to 90 hours, the decreased trap site density is restored and the trapping ability is recovered. This recovery is certainly due to the removal of carbon atoms fa-cilitated by methane forming reaction with hydrogen. Accordingly, the state of hydrogen is transitioned, whether by cathodic polarization or gaseous hydrogen exposure. In both cases, hydrogen is reallocated in ac-cordance with the equilibrium Fermi-Dirac relation at room temperature, showing that the details of cooling practice do not impinge.
    Other than dislocation trap, grain boundary or vacancy trap is also affected by tem-perature and duration of hydrogen charging; both temperature and duration rendered grain boundary and vacancy traps increased, except-ing the decrease of grain boundary trap site density by prolonged exposure to gaseous hydrogen.
    Present analyzing method can further predict the state of hydrogen at the high temper-ature of hydrogen charging. The predicted equilibrium hy-drogen concentration in lattice site is in accordance with the result obtained by da Silva upon thermodynamic consideration.
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  • Hironori OGATA, Yuichi YAMAMOTO, Hiromi ANDO, Masayuki KANEKO, Ryotaro ...
    2021 Volume 59 Issue 5 Pages 250-264
    Published: 2021
    Released: October 28, 2021
    In the cargo tank structure of the chemical tanker, the cruciform welded joints between the trans-verse bulkhead and the double bottom requires the most attention to prevent fatigue crack initiation because of its severe stress condition. By the way, laser scanning measuring instruments are becom-ing smaller and lighter and handheld types are being commercialized.
    We have studied practical application of a technology to estimate stress concentration factors by measuring the shape of welds in cargo tank structure of chemical tanker with a weld bead laser scanner during construction at a shipbuilding site.
    In this study, the welded joint surface shapes of fatigue test specimens simulated as the cruciform welded joints between the transverse bulkhead and the double bottom were measured by a weld bead laser scanner and the stress concentration factors (KtL) of the welded joint of the specimens were calculated by using the conventional estimating equation with the measured geometrical data of the welded parts. In addition, the static FEM analysis was also conducted to obtain the stress concen-tration factors (KtF) using the same measured data. Comparing the stress concentration factors KtL and KtF with the stress concentration factor KtS calculated by the conventional estimating method with silicon mold, it was shown that KtL and KtF values were about the same as that of KtS. In addi-tion, the representative value of the fatigue strength at 2×106 cycles for cruciform welded joint was derived considering the fatigue test results using the cruciform welded joint specimens and the re-sults of previous studies, the allowable stress concentration factor (KtA) was presumed based on the representative value of fatigue strength and design S-N curve for cruciform welded joints. As a re-sult, it is proposed that the guarantee which fatigue crack initiation does not occur at the toe of welded joint can be valid when the geometry of weld joints in the cargo tank structure under con-struction at shipbuilding site is measured by using the weld bead laser scanner and immediately the stress concentration factor KtL or KtF is calculated and the value is evaluated less than KtA.
    This is a revolutionary technique in terms of quality control and assurance of shipbuilding.
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