Proposal of Revision of Upper Limit of Hydrostatic Test Pressure in KD-236 and KT-312.3 of ASME Section VIII Division 3

Abstract

Abstract Regarding the upper limit of hydrostatic test pressure, KD-236 of Section VIII Division 3 prescribes that an elastic-plastic analysis using an elastic-perfectly plastic material model with the specified yield strength at test temperature shall be performed on a vessel. The reason why such material model shall be used for hydrostatic test criteria in KD-236 is to match the analysis to the criteria for the upper limit of the hydrostatic test pressure in KT-312. The upper limit of the hydrostatic test pressure for an open-end and closed-end cylindrical shell was based on general yielding using Gangling’s and Nadai’s equations with yield strength and design factor Kut for the upper limit of hydrostatic test pressure in KT-312. Especially for SA-372 Gr. E Class 70, the ratio of burst pressure to the upper limit of the hydrostatic test pressure becomes more than 1.5. There is a large amount of strain hardening which occurs in the deformation process of this material and the perfectly plastic limit makes it impossible to utilize the materials in a practical manner. The new hydrostatic test criteria for elastic-plastic analysis using an elastic-plastic stress-strain material model are proposed to reduce this conservativeness, instead of an elastic-perfectly plastic material model in current KD-236. The new load factor for the upper limit of the hydrostatic test should be 1.25 since the maximum equivalent plastic strain is less than 5 % and the shake-down on the inside surface is achieved by the subsequent design pressure. The revisions of KD-236 and KT-312 were proposed. The background of these revisions is described in this paper.