HPIS Z101-2, “Assessment Procedure for Crack-Like Flaws in Pressure Equipment-Level 2”provides the methodology for the evaluation of fitness-for-service for detected flaws in structural components such as pressure vessels, piping, storage tanks during in-service inspection. In this context, the solutions of reference stress, which represent the margin of loading state against limit load condition with respect to stress dimension, are required. Therefore, the HPIS Z101-2 adopted existing proposed reference stress solutions, which was derived based on appropriate theoretical basis. In this paper, the reference stress solutions for axially and circumferentially inner-surface cracked cylinders in HPIS Z101-2 were compared with those in other referable codes⁄standards, including FBR Guideline, R6 Procedure, BS7910, and API579. The HPIS Z101-2 solutions were generally consistent with the other solutions, thus, the adequacy of the HPIS Z101-2 solutions were verified.
The finite element method is applied to buckling analysis of cylindrical shells subjected to asymmetric external and axisymmetric internal liquid pressures. The axisymmetric shell element is used and the load distribution, prebuckling and buckling displacements are represented by Fourier series expansion in the circumferential angle. The analyses are performed for cylindrical shells under axisymmetric and asymmetric external and axisymmetric internal liquid pressures and the accuracy of the previously proposed simplified equations is investigated. The asymmetric and axisymmetric analyses and the simplified equations are applied to the tanks under tsunami and axisymmetric internal liquid pressures. The validity and effectiveness of the axisymmetric analysis and the simplified equations are demonstrated.
This paper describes the results of development regarding AE global diagnostics on corrosion damage in bottom plates of aboveground storage tanks. It is sometimes difficult to evaluate the corrosion damage by conventional measurement methods such as HPIS because the measured AE data includes various noise. Regarding our study for the layout of AE sensors as double layer which are installed on shell plates, the removal of AE data reflected by bottom plates made it possible to identify a liquid drop noise from cone roof tanks. In addition, the accuracy of the identification of AE source was improved with the AE waveform classification processing. The AE data by shell and annular sensors could facilitate the removing of some noise to evaluate the location of corrosion. As well known, the corrosion risk parameter (CRP) is correlated with the actual corrosion rate obtained by the overall UT scanning system for thickness measurement of bottom plates. The CRP can predict the average maximum corrosion rate based on the actual measuring data. The average maximum corrosion rate can also be predicted with AE activity since the relationship between CRP and AE activity is verified by another study. The referential curve for prediction of the average maximum corrosion rate based on AE activity was developed as quantitative evaluation technique without opening tank under plant operation. The AE Global Diagnostics enables to plan of the maintenance before opening the tanks by determining the elements of repair work, preparing materials and establishing procedures for maintenance plan.
The expansion bellows is used as a heat stress relief and displacement mitigation equipment of a pipe that is connected to an exit side of equipment operated in a high temperature. ASTM International Alloy625LCF has been used in consideration of corrosion resistance and heat resistance. However, as the operating temperature changes, the refractories deform so that the internal high temperature gas fluid and the bellows are in direct contact, and the Alloy625LCF is cracked due to the synergistic effect of high temperature embrittlement and thermal stress, resulting in mechanical failure. This paper describes the knowledge of the equipment diagnostic inspection technology of life prediction for high temperature embrittlement by conducting in-furnace examination similar to the real environment above on the Alloy625LCF, from the experience that the high temperature embrittlement of the expansion bellows and cracking occurred in the above environment. The inspection method and the maintenance period setting for the damage mode and the risk reduction that cause breakage of the expansion device become an effective inspection plan by visualizing damage mechanism during operation and stoppage period.
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