Study on the Strength of Type B Semi-Membrane Tank

Abstract

This is the report on the strength analyses of Type B semi-membrane tank based on the requirements of the IMCO (the present IMO) Gas Carrier Code (the present IGC Code). The IMCO Code became effective in 1980, and then, it became compulsory for Type B semi-membrane tank with partial secondary barrier to prove its reliability using model tests, refined analytical tools and analysis methods to determine stress levels, fatigue life and crack propagation characteristics. The authors, therefore, made the following extensive strength analyses with regard to a semi-membrane type tank of a 77,400m^3 LPG carrier, including various studies and tests concerned. (1) Development of an FEM program for contact problems involving a thin-plate structure like a semi-membrane tank (2) Stress analysis by the FEM program for contact problems (3) Fatigue strength analysis (4) Brittle fracture strength analysis (5) Study on partial secondary barrier (6) Tests to obtain necessary data for these analyses (fatigue test, crack propagation test, brittle fracture test, leak test etc.) It was proved through these analyses that this tank satisfies all the requirements of the IMCO Code for Type B Tank. This tank was approved by Nippon Kaiji Kyokai and the U.S. Coast Guard as Type B Tank. Based on the results of this study, we built, first in the world, an LPG carrier with Type B semi-membrane tanks, M.S. "Clean River", under the supervision of NK.