GB2182985A - Gaskets - Google Patents

Abstract

A gasket comprises an essentially flat metal core 10 having laminated to each opposed face at least one layer of an expanded graphite foil, the or each such layer containing a thin reinforcing core of metal 11. <IMAGE>

Description

SPECIFICATION Gaskets This invention relates to gaskets for use in flanged connections such as pipework.

A particular problem which is encountered in flanged connections is where there is a need for not only an external, peripheral seal, (usually to atmosphere) but also an internal seal, between separate passageways wholly contained within the pipework. An example of this is a heat exchange vessel with two, three or more separate internal sections or elements. At each joint in such a case there has to be an effective seal between these internal sections, or "pass partitions".

In the past, this problem has often been met by using an internal back-up seal comprising a sealant material such as asbestos encapsulated inside a metal jacket.

This back-up seal is located radially inside the main peripheral seal. It will usually include one or more pass partition bar seals extending across the interior of the pipework and disposed to lie along the pass partition bars. The latter are at the ends of the internal section dividers, or pass partitions. The back-up seal can in some circumstances also act as the main peripheral seal, but only for relatively light duty applications. It is usual to provide a separate peripheral seal to take the bolt loading of the joint, as well as sealing the system to atmosphere.

Unfortunately, the use of a separate outer seal in conjunction with an internal back-up seal for the pass partitions is not always successful, especially where high temperatures and pressures are involved. The outer seal is not the problem, which is that conventional back-up gasket constructions simply do not accommodate the thermal movement encountered. The internal seal between partitions breaks down, although the outer seal does not. The resultant internal leakage may or may not have serious consequences; it may or may not be readily detectable. But whatever happens, the system has to be completely shut down and dismantled in order to even inspect the internal seals, of which there may be many in any one installation.

Attempts to overcome the problem by using complex seals including resilient materials such as rubbers have been unsuccessful, mainly due to the problem of achieving high elastic recovery at elevated temperatures and pressures.

It is an object of the invention to provide an improved gasket construction especially but not exclusively useful as an internal pass partition seal for multi-pass pipework and/or vessels.

According to this invention, a gasket comprises an essentially flat metal core having laminated to each opposed face thereof at least one layer of an expanded graphite foil, the or each layer containing a thin reinforcing core of metal. "Thin" in this present context means preferably less than 25 microns thick.

There are preferably two such layers laminated to each side of the flat metal core. The latter may be a plane sheet, or it may be corrugated, grooved or serrated. Lamination may be achieved by use of an adhesive, but the nature of the latter is not a critical factor, since it is mainly used to achieve ease of handling. Once the gasket is installed, the adhesive is no longer needed, of course.

The flat metal core may be of stainless steel, nickel or other material appropriate to the anticipated working environment. It will normally be cut or blanked from sheet as a unit, complete with all pass partition bars required to suit the end use in a particular joint/vessel. However, in some cases it may be necessary to make a rim portion separately and then add the pass partition bars by welding. This is really a matter of size and/or manufacturing convenience. The whole gasket could be blanked out from a pre-formed laminate sheet including the metal core, although this would be suitable only for relatively small gaskets.

Normally, the graphite elements will be made separately and cut to match the metal core. Laminating the assembly together may be done by simple pressing, after appiying the adhesive, if necessary.

Particularly suitable graphite foils are described in our co-pending application GB 2154675 A.

It has been found that gaskets constructed according to the invention exhibit relatively high elastic recovery, even under severe conditions of thermal cycling, thereby enabling an effective pass partition bar seal to be established and maintained. A recovery of at least three times that normally encountered with conventional metal jacketed gasket constructions has been observed with two metal reinforced graphite foils on each face of a stainless steel core. This was a very significant improvement.

The invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a plan view of a gasket according to the invention, and Figure 2 is a cross-sectional side view of part of the gasket of Fig. 1.

In the Figures, the gasket comprises a generally circular rim 1, with three radially directed pass partition bars 2 extending across it to define three internal sections 3, 4 and 5 corresponding to the internal sections of the heat exchange vessel (not shown) between those longitudinal parts this gasket is to effect a seal. It will be understood that the rim 1 is to be located, in use, inside a main outer peripheral seal between the vessel and atmos phere.

However, the main seal is conventional and will not be further described here.

In Fig. 2, the internal construction of the rim 1 and the bars 2 is more clearly shown. A central flat metal core 10 has on each of its faces two layers of expanded graphite foil, each comprising a thin nickel core 11 and graphite foil facings 12, 13. These particular foils were made according to the disclosure of GB 2154 675 A which was referred to earlier.

The flat core was of stainless steel 1.5mm thick the overall gasket thickness prior to use was about 7mm inch thick.

Claims (5)

1. A gasket comprising an essentially flat metal core having laminated to each opposed face thereof at least one layer of an expanded graphite foil, the or each such layer containing a thin reinforcing core of metal.

2. A gasket according to Claim 1 wherein there are at least two layers of graphite foil on each side of the flat core.

3. A gasket according to Claim 1 or Claim 2 wherein the graphite foils contain a nickel foil core less than 25 microns thick.

4. A gasket according to any preceding claim wherein the essentially flat metal core is of stainless steel.

5. A gasket substantially as described with reference to the drawing.