WO2000056406A1

WO2000056406A1 - Detonation flame arrester

Info

Publication number: WO2000056406A1
Application number: PCT/GB2000/001048
Authority: WO
Inventors: Jeffery Boardman
Original assignee: A.G. Marvac Limited
Priority date: 1999-03-24
Filing date: 2000-03-21
Publication date: 2000-09-28
Also published as: GB0006202D0; GB2348604A; GB2348604B; GB9906669D0

Abstract

A detonation flame arrester comprises a tubular housing (10) and arrester elements (14, 15) removably disposed within the housing between element supports (16, 17 and 18). A first element support (16) is a close circumferential fit within the housing (10) and is placed within the housing by a shrink-fitting operation. The element support (18) is threaded at its circumference and engages a matching thread on the inner cylindrical surface of the housing (10), which allows the support to be screwed into the end of the housing until its outer face is aligned with the end of the housing.

Description

DETONATION FLAME ARRESTER

The present invention is a detonation flame arrester, that is a unit for installation in a pipeline to prevent the passage of a fast-moving flame front from the point of ignition to a point where damaging detonation of the associated vapour or gas could occur. More specifically, the invention is an improved form of detonation flame arrester.

Detonation flame arresters are usually of significantly greater cross-section than the pipelines in which they are installed and they function by subdividing the flame front into a large number of flamelets and quenching the resulting flamelets such that the vapour or gas downstream of the arrester is not ignited and flame transmission is thus prevented. The subdividing of the flame front is achieved by means of arrester elements in the form of blocks comprising a large number of narrow passages of such a length that the flame front cannot pass through them.

The arrester elements are usually of metal, in particular of stainless steel, and their fine construction is such that it is usual to provide greater strength by securing the elements within an enclosing outer wall, which typically may be of stainless steel. The outer wall of each element performs the additional very important function of providing a tight fit between the element and the inner face of the flame arrester housing .

The required tight fit between the arrester element and the housing is usually achieved by constructing the element outer wall of a diameter very close to the internal diameter of the housing. Unfortunately, in practice, it is extremely difficult to achieve the required close correlation between these two diameters. However, if the arrester element diameter is too small, then the whole purpose of the arrester is defeated and a flame front may pass through any resulting gap or gaps. On the other hand, if the diameter of the arrester element is greater than required, then only the application of force or pressure can enable the element to be installed in the housing. Such force or pressure is likely to distort the element and may adversely influence the effectiveness of the flame arrester in use. Moreover, if the arrester element is over-sized in this way, it is likely to be very difficult subsequently to remove the element for cleaning, inspection or replacement.

However, the potentially conflicting requirements of current internationally-imposed standards for application to detonation arresters are firstly, that the elements should be so tightly fitted that flame cannot pass between the element and the housing but also, secondly, that the elements should be readily removable for inspection and maintenance purposes. These two specific requirements are difficult to reconcile using detonation arresters of current design.

One proposal which has been made to overcome some of the disadvantages associated with existing detonation arresters is to provide for each element block a pair of supports, each having four or more radial arms, which supports are braced together by means of an axial link and together enclose the arrester element under limited pressure. Arrester elements of this construction have been retained under peripheral pressure by trapping them between inwardly-directed peripheral flanges on reducers which are secured at the respective ends of the tubular housing in which the element is retained. However, arrester elements of this construction have proved to be vulnerable to longitudinal deformation, with associated reduction in effectiveness as detonation arresters. Moreover the retaining of the element between the flanges of the reducers requires the external retaining bolts by which the arrester is held together to be tightened uniformly if distortion of the element, and consequential loss of performance, is to be avoided.

Thus there remains a need for a detonation flame arrester in which the risk of deformation of the element in use is minimised and in which nonetheless the element is readily inspected and, if necessary, replaced. It is an object of the present invention to provide an improved detonation flame arrester which is better able to meet these requirements than many existing forms of arrester.

According to the present invention, there is provided a detonation flame arrester comprising a tubular housing, at least one flame arrester element removably disposed within said housing, a first arrester element support having a circumferential section which has notional external dimensions greater than those of the inner face of the housing in a direction transverse to the axis of said housing and disposed within the housing, and a respective second arrester element support, disposed within the housing on that side of the or each arrester element which is remote from the first said support and having a peripheral surface removably engaging the inner face of the housing.

Thus, in the detonation flame arrester of the present invention, the arrester element is not required to be the very close interference fit which it is required to be in many prior detonation flame arresters in that security against peripheral escape of the detonation flame and/or vapours is afforded by the first arrester element support. The element itself may therefore be more readily inspected and/or removed than in other such flame arresters, by simple disengagement of the second arrester element suppor . The circumferential section may be substantially annular.

The or each said arrester element support may comprise a circumferential rim supported upon a substantially central boss by a plurality of substantially radial spokes.

In a preferred embodiment, installation of the first arrester element support in the tubular housing is effected by changing the temperature of one or both of these two components.

For example the support may be cooled or the tubular housing may be heated or both of these temperature changes may be undertaken. When the flame arrester comprises just one element and two supports, or when the inner diameter of the housing is relatively small, for example less than about 20 cm diameter, it is preferred that the support be installed such that one of its flat faces is aligned with the end of the housing. The bond between the support and the housing may be enhanced by welding these two components together. However, as described below, the flame arrester may comprise two or more elements, supported by three or more supports. In such forms of the flame arrester and/or when the housing inner diameter exceeds about 20 cm, the first support is preferably located at the middle of the sequence of arresters and supports.

The second support for the detonation flame arrester element is removably engaged with the tubular housing. This second support may, for example, be removably retained in position by means of screws extending radially through the tubular housing into the periphery of the support. However, in a preferred form of the present invention, the support is threadedly engaged with the housing by means of a thread on the periphery of the support engaging a matching thread cut on the inner surface of the housing. Preferably the extent of the housing thread in a direction parallel to the axis of the tubular housing is approximately equal to, or slightly exceeds, the thickness of the second support such that, when the support has been installed, its outer face is level with, or slightly within, the end of the housing.

The first and second arrester element supports may be of any metal or alloy such as is appropriate for the conditions under which the detonation flame arrester is required to function. However, it is particularly preferred to produce the supports of carbon steel or of a heat- and corrosion-resistant stainless steel. These supports may be made by casting from molten metal, by cutting from solid plate or sheet material, or by assembly from the required component parts.

The arrester element itself may be of any desired construction appropriate to its function. Such elements are already well known and may be of a range of diverse types . The element comprises a large number of narrow passages of such cross- section and length that any flame front is sub-divided and cannot pass through to the downstream side of the element. Typically, such detonation flame arrester elements are assembled from layers of crimped metal strip or from suitably deformed wire mesh. The element may be of any metal or alloy appropriate to its required function and typically will be of stainless steel .

The arrester element is very preferably enclosed by a peripheral annular wall, whereby to impart a uniform cylindrical shape to the element and also to give peripheral strength to the construction. However, it is possible to dispense with the outer wall by spot welding the ends of the wound strips from which the element is constructed. Further strength may be imparted by welding together selected adjacent sections of the element, preferably along narrow radial tracks.

As indicated above the detonation flame arrester according to the present invention may comprise just a single arrester element, retained within the housing between the first and second arrester element supports already described. However, it may alternatively comprise two or more axially aligned elements, retained between three or more supports including the two already specified. Thus, by way of example, the flame arrester may comprise, in linear sequence along the housing, the first element support secured in place by shrink-fitting and optionally by welding, a first arrester element, an additional support, which may be a close fit within the housing, a second arrester element and then the specified second element support removably engaging the inner face of the housing. The preferred alternative, especially with the larger housing diameters, is to construct the flame arrester with the first support at the centre of the assembly and with one element and a second support at each side of the first element .

The housing may, if desired, be formed with an inner circumferential shoulder, against which one of the element supports may abut and/or be welded.

The invention will now be further described and illustrated, by way of example only, with reference to the accompanying drawings, which show one preferred form of detonation flame arrester according to the present invention and wherein: -

Fig. 1 is an axial sectional view of the detonation flame arrester;

Fig. 2 is an axial elevation of one form of arrester element; and

Fig. 3 is an axial elevation of one form of element support .

The illustrated detonation flame arrester comprises a generally tubular housing 10 retained between tapered reducers 11, 12 by means of external bolts 13. Within the housing 10 are secured arrester elements 14, 15 and element supports 16, 17 and 18. The element supports are all of generally similar elevation as illustrated in Fig. 3. However element support 16 is a close circumferential fit within the housing 10 and is placed within the latter by a shrink-fitting operation. It is secured in position against a shoulder 19 within the housing by welding. The arrester elements 14, 15 are of circular profile and are a close sliding fit within the housing 10. As illustrated in Fig. 2, these elements are formed of closely-packed crimped stainless steel strip 20, confined within a cylindrical steel outer wall 21.

Between the arrester elements 14 and 15 is disposed the element support 17 which is generally similar to the element supports 16 and 18 but is of such a radial dimension as makes it a close sliding fit within the housing 10. The element support 18 is threaded at its circumference and engages a matching thread on the inner cylindrical surface of the housing 10, which allows the support to be screwed into the end of the housing until its outer face is aligned with the end of the housing.

Each of the element supports 16, 17 and 18 is braced by radial arms 22, of which there are four in the illustrated embodiment, and the assembly of elements and supports within the housing are held securely together by axial bolt 23.

In use of the illustrated detonation flame arrester, any leakage of detonation flame, which in a conventional flame arrester could occur past the periphery of a distorted arrester element, is prevented by the very close fit of the element supports 19 and 18 within the housing. However the elements may be removed as required for inspection and possible replacement by disengagement of the bolt 23, unscrewing of the support 18 and the sliding removal of the elements and of the support 17.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

1. A detonation flame arrester comprising a tubular housing, at least one flame arrester element removably disposed within said housing, a first arrester element support having a circumferential section which has notional external dimensions greater than those of the inner face of the housing in a direction transverse to the axis of said housing and disposed within the housing, and a respective second arrester element support, disposed within the housing on that side of the or each arrester element which is remote from the first said support and having a peripheral surface removably engaging the inner face of the housing.

2. A flame arrester according to claim 1, wherein said circumferential section is substantially annular.

3. A flame arrester according to claim 1 or 2 , wherein the or each said arrester element support comprises a circumferential rim supported upon a substantially central boss by a plurality of substantially radial spokes.

4. A flame arrester according to any one of the preceding claims, wherein installation of the first arrester element support in the tubular housing is effected by changing the temperature of one or both of these two components.

5. A flame arrester according to any one of the preceding claims, wherein the first arrester element support has a flat face aligned in use with the end of the housing.

6. A flame arrester according to any one of the preceding claims, wherein the bond between the first arrester element support and the housing is enhanced by welding these two components together.

7. A flame arrester according to any one of the preceding claims, comprising two or more flame arrester elements, supported by three or more supports.

8. A flame arrester according to claim 7, wherein the first arrester element support is located at the middle of the sequence of arresters and supports.

9. A flame arrester according to any one of the preceding claims, wherein the or each said second arrester element support is removably retained in position in use by means of screws extending radially through the tubular housing into the periphery of the support .

10. A flame arrester according to any one of claims 1 to 8 , wherein the or each said second arrester element support is threadedly engaged in use with the housing by means of a thread on the periphery of the support engaging a matching thread cut on the inner surface of the housing.

11. A flame arrester according to claim 10, wherein the extent of the housing thread in a direction parallel to the axis of the tubular housing is approximately equal to, or slightly exceeds, the thickness of the second support such that, when the support has been installed, its outer face is level with, or slightly within, the end of the housing.

12. A flame arrester according to any one of the preceding claims, wherein the first and second arrester element supports are produced of carbon steel or of a heat- and corrosion- resistant stainless steel .

13. A flame arrester according to any one of the preceding claims, wherein the or each flame arrester element is assembled from layers of crimped metal strip or from suitably deformed wire mesh.

14. A flame arrester according to any one of the preceding claims, wherein the or each flame arrester element is enclosed by a peripheral wall.

15. A flame arrester according to any one of the preceding claims, wherein the housing is formed with an inner circumferential shoulder, against which one of the element supports may abut and/or be welded.

16. A detonation flame arrester substantially as hereinbefore described with reference to the accompanying drawings .