Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-05-11
2003-10-07
Nutter, Nathan M. (Department: 1711)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S594000, C428S596000, C428S425800, C427S142000, C114S069000, C156S091000
Reexamination Certificate
active
06630249
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a flexible impact and tear resistant composite sandwich plate and construction system for vessels, such as, for example, tankers, bulk carriers or ships for which it is desirable to contain the vessel contents during conditions of extreme or accidental load or for which it is desirable to prevent failure (e.g., sinking of bulk carriers, ruptured members) or for which it is desirable to reduce costly repairs from fatigue cracks; and for civil or maritime structures, such as, for example, orthotropic bridge decks, railway bridges or tanks for which it is desirable to minimize strain concentration, reduce fatigue problems, improve thermal insulation and acoustical insulation or vibration characteristics, or where it is desirable to connect similar or dissimilar metals without welding.
DESCRIPTION OF THE PRIOR ART
Increased social, economic and political pressure has led to the development of technology to reduce or eliminate the risks of pollution and resulting damage to the marine environment, as well as the loss of valuable cargo, that may result from cargo leaking due to rupture of a vessel under extreme or accidental loads such as collisions, grounding, fire and explosion. In particular, vessels carrying hazardous materials are increasingly subject to additional requirements imposed by regulatory agencies, ship and cargo insurers, and ship owners and financiers. The high cost of hazardous spill liability and increasing cargo values has further encouraged the development of leak and rupture resistant vessels.
One approach to containing vessel contents is the provision of double hulls for oil tankers. An inner cargo containing hull of a stiffened single plate construction is supported within an outer protective hull, which is also a stiffened single plate construction. A conventional double hull has longitudinal and transverse frames between the inner and outer hulls. A more advanced, alternative double hull has only longitudinal frames between the inner and outer hulls, allowing for simplified construction suitable for assembly line production by robotic devices. Both conventional and advanced double hull designs have transverse bulkheads between cargo compartments in the inner hull, and may have bulkheads between ballast compartments which are generally located between the inner and outer hulls. Variations in double hull design include constructions with a double bottom only, or with a double bottom and double hull sides. To reduce weight, the deck is generally a single plate construction. Alternatively, convexly curved hull plates between longitudinal frames may provide high energy absorption in the curved plate double hull.
FIG. 1
shows a cross-section of a typical double hull oil tanker designed according to conventional naval architecture.
FIG. 2
illustrates the arrangement of cargo tanks and other sections for a typical double hull vessel.
The advantages of double hull construction over conventional single hull designs are also well known. These advantages include improved cargo handling efficiency, better cargo purity, and reduced water pollution by isolating ballast tanks from cargo holds. Furthermore, double hulls constructed to international standards which require a two meter space between inner and outer hulls also offer reduced risk of leakage or rupture due to penetration of the outer hull during collisions or groundings. The claimed innovative features of advanced double hulls are improved strength, ease of manufacture and reduced welding and steel surface areas in ballast tanks, increased accessibility to ballast tanks which results in better inspection and improved maintenance and inner hull retention of oil during high energy grounding. With current technology, double hull vessels involved in low energy, low velocity impacts are less likely to be compromised and less likely to cause pollution than a single hull vessel. The improved tanker designs, such as double-bottom, double sides, double hull, mid-deck, etc. are known to reduce but not eliminate the risk of oil spills in accidents. Although tests indicate that an advanced all steel double hull design will dissipate more energy than a conventional all steel double hull design, both designs are subject to compromise of the inner hull due to crack propagation resulting from fatigue cracks or from cracks that propagate from a ruptured plate during extreme load events.
Patents related to improving the energy absorption capacity of double hull construction due to accidental or extreme load events such as grounding or collision include U.S. Pat. Nos. 5,218,919 to Krulikowski III et al. and 5,477,797 to Stuart. Both patents are directed to retrofitting existing single hull tankers with external hulls to make a double hull tanker. Krulikowski III et al. describe the use of energy absorbing telescoping members arranged in a truss-like formation to support a laminated steel auxiliary hull to the outside of an existing oil tanker hull. Construction details of attachments to transverse bulkheads and deflection control devices are also described. The void between hulls is filled with polyurethane foam/balls to distribute impact forces, to support the auxiliary hull under hydrostatic loads and to provide additional buoyancy in the case where the auxiliary hull is ruptured. Stuart describes the construction of an auxiliary hull attached to the outside hull of an existing oil tanker. It is composed of a series of longitudinally framed steel plates that form a honeycomb configuration, when viewed in section, between the hulls. The combination of stress relief joints, which make the outer hull discontinuous, and the honeycomb inner hull structure create a damage resistant hull. The construction also allows the inner hull space to be flooded to any level to provide the appropriate ballast by means of a pressurized inert gas and a vacuum pressure system. These retrofitted external hull structures fail to address the possibility of crack propagation into the inner hull due to rupture of the outer hull, and inadequately address the cost and practicality of fabrication and maintenance of the auxiliary hull structure. In current retrofit designs, access between the hulls for inspection and corrosion maintenance is difficult, if not impossible. The external hull in a retrofit design generally does not participate in carrying all of the operational loads, and adds significant dead weight to the tanker with limited structural functionality.
U.S. Pat. Nos. 4,083,318 to Verolme and 4,672,906 to Asai are directed to LNG (liquid natural gas) tankers and to tankers carrying cryogenic or high temperature freight in which the cargo tanks are separate structures from the tanker and do not form part of the load carrying hull girder system of the tanker.
Current all steel double hull construction has serious disadvantages which lower the likelihood that these design types will meet the performance criteria of zero oil outflow after accidental or extreme load events such as collisions, groundings, explosions or fire, and remain competitive relative to construction, maintenance and service life costs. One disadvantage is that current double hull construction is based on traditional naval architecture design concepts in conjunction with international agreements and national standards that stipulate the use of double hull construction with a minimum separation between hulls which is related to statistical data of measured rock penetrations from recorded tanker casualties.
Hulls constructed according to traditional naval architecture standards generally provide a complex system of steel plates and plate steel structural members, such as frames, bulkheads and girders. The carrying capacity of the steel plates and supporting members is increased by reinforcing the plates and structural members with multiple stiffeners of the type well known in the art, such as flat, angle or channel metal stock fastened to plate surfaces. This complex hull structure and plate stiffener system is a source of
Bissett Melanie
Darby & Darby
Fern Investments Limited
Nutter Nathan M.
LandOfFree
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