AU2008100654A4 - Explosion-proof enclosure design with extreme overpressure capability - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT EXPLOSION-PROOF ENCLOSURE DESIGN WITH EXTREME OVERPRESSURE CAPABILITY The following statement is a full description of this invention, Inclusive of its variants and different implementation methods COMS ID No: ARCS-198768 Received by IP Australia: Time 19:22 Date 2008-07-17 00 0 0 c EXPLOSION-PROOF ENCLOSURE

DESIGN

WITH EXTREME OVERPRESSURE

CAPABILITY

SExplosion-proof (also called flarmeproof) enclosures have been manufactured since the SSbeinning of the last century as a method of containing explosions that might be generated by internal sparking devices in presence of an explosive atmosphere.

One of the essential requirements of flameproof enclosures is their capability to withstand internal pressure, which is generated in the event of an internal explosion- Applicationat very low temperature, which is a requirement in cold Countries, requires capability of the i enclosure to withstand even higher internal overpressure. Typical minimum pressure test values required for rectangular enclosures for surface application subject to mandatory overpressure test are between I100 kPa and 2000 kPa. In order to be exempted from 00 individual routine testing, the enclosure shall be able to withstand an internal pressure in 0 excess of 3000 kPa, SThe most popular designs of explosion proof enclosures for surface application have CA rectangular shape where lid is bolted to the base of the box on a flanged joint. The walls of these enclosures are flat with constant thickness (unifonrm cross-section) and their capability to withstand internal pressure relies on the strength of the material, the thickness of the walls and when these are not sufficient ribs are added to reinforce the walls, the base or the lid of the box. The internal pressure that could be experienced during a gas explosion causes flexural stress in the walls of the enclosure. The larger the dimensions of the enclosure, the more it will tend to deform when subject to internal overpressure. The side walls, the lid and the back face tend to bend (sag) under internal pressure, potentially causing deformation of the flanged joint and failure at the corners where the yield stress of the material is exceeded. Ribs can reduce the deformation adding rigidity to the enclosure, but can cause weak points where they join the sides and reduce the internal usable volume.

An Explosion-proof enclosure according to this invention has side walls and/or base and/or lid, with shape curved like a dome inside of the enclosure. The side walls and the lid have non-uniform cross section, with the maximum thickness in the center. Ribs are not required to reinforce the enclosure with this dcsign. The cross section of the walls (or lid or base) decreases from the center to the corners, to achieve constant or nearly constant equivalent stress distribution through the material. The thicker cross section is achieved by increasing the thickness inside the enclosure. Additional strength can be achieved for very large enclosures by a similar dome shape of the outside of the enclosure (the outside is subject to mainly tensile stress, and the tensile strength of metallic alloys is generally similar to their compressive strength).

Changing the section from "flat" to "convex" in a domed shape, changes the stress through the sides of the enclosure from mainly flexural (bending) to compressive. Since compressive strength of materials are genrally much greater than bending strengths, the increase in rigidity and pressure resistance capability of the enclosure with such new shape is remarkable.

COMS ID No: ARCS-198768 Received by IP Australia: Time 19:22 Date 2008-07-17

Claims (3)

1. An Explosion-Proof (Flameproof, Ex d) enclosure having a rectangular or square shape with a flanged joint and bolted lid, in which one or more internal faces are convex.

2. An Explosion-Proof (Flameproof, Ex d) enclosure having a rectangular or square shape with a flanged joint and bolted lid, in which one or more internal and external faces are convex.

3. An Explosion-Proof (Flameproof, Ex d) enclosure having a rectangular or square shape with a flanged joint and bolted lid, in which the flanged joint has non- uniform width, being wider at the center of the sides and where the internal edge of each side is not straight but follows an arc. The following drawings illustrate the invention: COMS ID No: ARCS-198768 Received by IP Australia: Time 19:22 Date 2008-07-17