Research Papers: Design and Analysis

Plastic Collapse Load for Vessel With External Flaw Simultaneously Subjected to Internal Pressure and External Bending Moment: Experimental and FEA Results

[+] Author and Article Information
Shinji Konosu

 Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japankonosu@mx.ibaraki.ac.jp

Masato Kano

 Sumitomo Metal Technology, Inc., 16-1 Sunayama, Kamisu, Ibaraki 314-0255, Japankano-mst@smt-co.com

Norihiko Mukaimachi

 JGC Corporation, 2-3-1 Minatomirai, Nishiku, Yokohama 220-6001, Japanmukaimachi.norihiko@jgc.co.jp

Hiroyuki Komura

 Kashima Vinyl Chloride Monomer, Co. Ltd., 2 Towada, Kamisu, Ibaraki 314-0102, Japanẖkomura@shinetsu.jp

Hiroyuki Takada

 Ibaraki Prefecture Office, 978-6 Kasahara, Mito, Ibaraki 310-8555, Japantakada-hiroyuki@pref.ibaraki.jp

J. Pressure Vessel Technol 131(2), 021206 (Jan 05, 2009) (10 pages) doi:10.1115/1.3027472 History: Received May 14, 2007; Revised October 24, 2007; Published January 05, 2009

This paper is based on work done to establish the validity of a simple engineering approach to assess plastic collapse for a vessel with a local thin area (LTA). The approach is based on a recently developed p-M (internal pressure ratio and external bending moment ratio) diagram, which is an easy way to visualize the status of a vessel with a LTA simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. If the assessment point (Mr,pr) lies inside the p-M line, the vessel with the LTA is judged to be safe. Numerous experiments and finite element analyses for a cylinder with an external flaw were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic initiation load and plastic collapse load by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are similar to those calculated under the proposed p-M line based on the measured yield stress. The p-M line adopted in the Ibaraki fitness for service (FFS) rule based on the specified minimum yield stress with a safety factor of 1.5 indicates that the safety margin for the plastic initiation loads at LTA is about 1.0–3.0, about 1.5–4.0 for the TES loads at LTA, and 2.5–6.5 for the plastic instability (break) loads.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Definition of various limit loads

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Figure 2

Plastic deformation process of a cylinder with a local thin area

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Figure 3

p-M diagram in Ibaraki FFS rule

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Figure 4

True stress-true strain curve used in FEA

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Figure 5

Typical rectangular LTA geometry used for experimental test and FEA

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Figure 6

(a) Schematic representation with internally pressurized cylinder and (b) apparatus for bending cylinder

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Figure 7

Positions of strain gauges

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Figure 8

Typical plastic initiation and twice-elastic slope definitions and von Mises stress distribution at these stages (black region is elastic)

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Figure 9

Comparison of TES loads at LTA determined by experiment and FEA versus p-M line based on σf=σysmean

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Figure 10

Plastic initiation, TES, and plastic instability loads at LTA plotted on Ibaraki FFS p-M diagram based on σf=σysmin∕1.5




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