Abstract
The author has recently been involved in the analysis of the seismic performance of several standard types of cryogenic pressure vessel which were originally designed in the United States. Particular attention was accorded to the magnitude and distribution of the localised membrane and bending stresses developed in the inner and outer vessels near the points at which the internal and external support systems are attached. The analyses revealed that reinforcement would be required in certain critical areas in order to meet the design rules established by the relevant New Zealand government agency. Suitable modifications were made in these areas, although there seems reason to believe that the design rules may in some respects be unduly conservative.
Highlights
The pressure vessels concerned are cryogenic storage units for liquid oxygen, nitrogen or argon
The inner vessel is connected to the outer vessel through compact supporting members fabricated from steel and reinforced glass fibre tubes and welded to the end caps via reinforcing plates
The outer vessel is supported on three symmetrically located members, each of which is fabricated from mild steel plate to form a tapered channel section
Summary
The pressure vessels concerned are cryogenic storage units for liquid oxygen, nitrogen or argon. No allowance is permitted for the considerable material strength increase which occurs at cryogenic temperatures These design rules are stringent, and substantial modifications had to be made to the pressure vessels discussed in this paper in order to achieve the required strength levels. Evison and Mowat (1982) have suggested that NZS 4203 should be extended to provide structural type factors and risk factors appropriate to industrial plant, while, on the other hand, Norton, Gillies and Edmonds (1982) have prepared recommendations for the seismic design of petrochemical plant which are based on the selection of an earthquake return period and a direct assessment of the structural displacement ductility The latter approach appears to the author to have some significant advantages, and the suggested design procedure may usefully be examined in more detail. The alternative design method is used and, since the vessels are at least potentially relocatable, a uniform seismic coefficient equal to 0.60 *Senior Lecturer, School of Architecture, Victoria University of Wellington
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