Patent Description:
During such long time period, up to several years or decades, the tube assembly might be subjected to variations of temperature, to vibrations, mechanical stress variations, so that the tube joint might be subjected to variable clamping stress or force (also called seating force or seating stress), and leaks might occur if the seating force becomes too low or null.

Document <CIT> describes a gasket with a sealing portion which is compressible, but the disclosed gasket will leak if the seating force becomes too low or null during its service life.

Document <CIT> discloses a gasket according to the preamble of claim <NUM>.

The present invention aims to address the above mentioned drawbacks of the prior art, and to propose first a gasket having the capacity to help for avoidance of leaks, even if, during a long or very long service life, the seating force varies and decreases too much.

In this aim, a first aspect of the invention relates to a gasket for sealing an assembly of two tubes each comprising an extremity with a seating surface,.

The gasket according to the above embodiment comprises an optical fiber with a sensing portion enclosed in the compressible portion. Thus, the optical fiber provides the capacity to monitor or measure the seating stress (via a detected compression strain or compression stress, creating the compression force), so that in case of strong decrease of the compression force, an alarm can be sent so as to invite an operator to check / repair the clamping of the tubes. In other words, if the optical fiber with the sensing portion detects a too low seating force, the bolts/nuts maintaining the tube together can be changed, screwed again to the proper value/torque so as to avoid any leak. In addition, the sensing portion of the fiber is enclosed in the compressible portion, so that the risk of leakage due to the presence of the fiber is prevented.

According to the invention, the gasket comprises guiding means arranged to provide guiding of the optical fiber out of the sealing portion. The guiding means are part of the gasket, and not linked to the tubes. Therefore, the tubes and their flanges do not need to be modified to receive the gasket according to the invention, equipped with the optical fiber.

Advantageously, the guiding means are arranged to provide guiding of the optical fiber towards a space arranged between two planes defined by the two opposite faces. In the above embodiment, the optical fiber is guided out of the gasket and positioned between the seating surfaces of the tubes (typically flanges), so that the optical fiber is directly maintained by the gasket itself within a space where there is no interference with the tubes. In other words, the tubes are free of any connector for guiding the optical fiber.

Advantageously, the optical fiber comprises a connector arranged to be connected to a monitoring unit, so as to monitor the compression force generated by the assembly of the two tubes. Typically, the sensing portion is located at an extremity of the optical fiber, and the connector is located at the opposite extremity.

According to the invention, the compressible portion comprises a strip spirally wound, and the sensing portion is at least partially wound with the strip. In such embodiment, the optical fiber is wound with the strip, so as to minimize the process changes, and this takes advantage of the flexible / elastic properties of the optical fiber, to be included in the spiral part of the gasket.

Advantageously, the optical fiber is enclosed only in an outer portion of the strip spirally wound. Thus, the optical fiber and its sensing portion are remote from the inner portion of the compressible portion, the latter being usually exposed to the fluid to seal. Therefore, the sealing is not compromised by the optical fiber.

Advantageously, the sensing portion of the optical fiber is arranged between two adjacent portions of the strip.

Advantageously, a cross section of the strip comprises a portion in V shape or U-shape.

Advantageously, the sensing portion of the optical fiber arranged between two adjacent portions of the strip is located in a central part of the V shape. In other words, the sensing portion is located in the middle portion of the gasket, thus minimizing the impact onto the sealing capacity of the gasket.

Advantageously, the strip comprises a metallic layer and a filler layer, the filler layer comprising a material such as graphite, polytetrafluoroethylene, or mica, or rubber.

Advantageously, the sensing portion of the optical fiber is at least partially located within the filler layer.

Advantageously, the sensing portion of the optical fiber is at least partially surrounded with the material of the filler layer.

Advantageously, the compressible portion comprises a solid portion, made of an homogenous material at least partially enclosing the sensing portion of the optical fiber. In other words, the solid portion is made of a single material. According to an embodiment, the compressible portion is made only of one single solid portion.

Advantageously, the homogenous material comprises polytetrafluoroethylene (PTFE), or mica, or rubber.

Advantageously, the compressible portion comprises a composite portion comprising at least one fibrous material and at least partially enclosing the sensing portion of the optical fiber. In other words, the composite portion is made of a fibrous material and resin. According to an embodiment, the compressible portion is made only of one single composite portion, made of a fibrous material and resin.

Advantageously, the composite portion comprises aramid fibers and/or glass fibers, and/or carbon fibers.

Advantageously, the gasket comprises an inner ring, preferably made of metal.

Advantageously, the gasket comprises an outer ring, preferably made of metal.

Advantageously, the outer ring comprises a slot or a hole, and the optical fiber is at least partially arranged in the hole or groove. The outer ring holds the fiber from exterior to interior of the gasket, to minimize the risk of mechanical damage of the fiber. This embodiment provides a path for the fiber for being directed to the inner part of the gasket, without compromising the tightness.

Advantageously, the sensing portion of the optical fiber comprises one or more fiber Bragg grating sensors (FBGs). A FBG is a type of Bragg reflector constructed in a short segment of an optical fiber that reflects particular wavelengths of light and transmits all others, and that is sensitive to strain as well as to temperature changes. The sensor will also detect the temperature and if any medium (gas/liquid) will diffuse through the gasket, a second kind of alarm might be generated, based on temperature changes or values.

The first aspect of the invention is then the use, in a gasket for sealing a tube joint, of such optical fiber comprising a sensing portion with a fiber Bragg grating sensor.

A second aspect of the invention is directed to a tube assembly, comprising:.

In other words, the second aspect of the invention is directed to a tube assembly, comprising:.

A third aspect of the invention is related to a monitoring system, comprising:.

Other features and advantages of the present invention will appear more clearly from the following detailed description of particular non-limitative examples of the invention, illustrated by the appended drawings where:.

The <FIG> is a simplified sketch and represents an assembly of two tubes <NUM>, <NUM>, maintained together by nuts and bolts <NUM>. The tubes <NUM>, <NUM> are typically used to convey fluids, such as liquids, water, oil. and tightness at the tube joint is provided by a gasket G. Nuts and bolts <NUM> provide a seating stress which compresses the gasket G which in return seals the tube joint.

Typically, the gasket G comprises a sealing portion which is in contact with the tubes <NUM> and <NUM>, via a seating surface of these tubes <NUM> and <NUM>. The sealing portion is a compressible portion <NUM>, also shown in <FIG>, and in this example, is made of a strip wound in spiral. This strip comprises a steel band <NUM>, and a filler <NUM>, typically made of graphite, polytetrafluoroethylene (ptfe) or mica. The strip and in particular the metallic band have a portion in V-shape or U-shape. It has to be noted that a W-shape is possible and can be considered as two portions in V-shape. In this example of construction of <FIG>, the gasket G comprises an outer ring <NUM>, which is made of steel, or stainless steel.

As shown <FIG>, the sealing portion comprises two opposite faces 21A and 21B, each being in contact with one of the respective extremity of tubes <NUM> and <NUM>, to seal the tube assembly. In other words, the gasket G is sandwiched between the two tubes <NUM> and <NUM> via its opposite faces 21a, 21B.

During service life, especially if the tube joint is subjected to temperature changes, and/or pressure changes, and/or vibrations, and/or mechanical stress, it might be that the seating stress applied by the tube assembly onto the gasket G will vary, and if the seating stress decreases too much, leaks could occur.

To prevent such risk, the invention provides a gasket G with seating stress measurement capacity. In this aim, an optical fiber <NUM> is implemented in the outer part of the compressible portion <NUM>. To provide capacity to measure variations of the seating stress, the optical fiber <NUM> comprises a sensing portion which is enclosed into the compressible portion <NUM>, and which comprises fiber Bragg grating sensors.

Such sensor is sensitive to strain, and when connected to a monitoring unit M as shown on <FIG> (this <FIG> does not show the nuts and bolts <NUM> for clarity), the optical fiber <NUM> provides the capacity to measure the seating stress (σ) applied to the compressible portion <NUM> of the gasket G along time (t). if the seating stress becomes too low, it is possible to send an alarm to an operator for inspection and possibly adjusting the seating stress by screwing or exchanging the nuts and bolts <NUM>, so as to avoid the risk of leak, in advance. Also the sensor will detect the temperature and if any medium (gas/liquid) will diffuse through the gasket, a second kind of alarm might be generated, based on temperature changes.

<FIG> shows a detail of the outer ring <NUM>, comprising a hole 23A to guide and give access to the optical fiber <NUM> to the compressible portion <NUM> from exterior, and <FIG> shows the optical fiber <NUM> output from the compressible portion <NUM>, made of the V shape metallic strip, wound with a soft filler, graphite.

In detail, the optical fiber <NUM> is added to the spiral wound gasket during production of the spiral. Before the last winding with graphite will be produced; the optical fiber <NUM> will be added and wound with the filler <NUM> and metal spiral <NUM>. When adding the optical fiber <NUM>, it will be placed in the V-shape of the metal band <NUM>. The optical fiber <NUM> will be added 'above' the filler <NUM>. The filler <NUM> will be cut off after minimum one circular winding. The optical fiber <NUM> will be wound together with the metal windings till the outer diameter has been reached. In this part of the gasket, the optical fiber may be protected with a tube, in particular a plastic tube, and preferably a tube made of polytetrafluoroethylene (PTFE). There might have three minimum 'extra' windings of the metallic band <NUM>. It can also be limited to a much shorter section (<NUM>/<NUM> of a winding or even less). The sensing portion of optical fiber <NUM> has to be placed in the part with the filler <NUM>.

The fiber will be guided to the 'outside' of the flange. In this aim, an outer ring <NUM> (or guide ring) is used for the spiral wound gasket, the optical fiber <NUM> is guided to the outside of the guide ring <NUM> by a groove in the ring or a hole 23A will be drilled in the guide ring <NUM>.

<FIG> represent alternative constructions of gaskets (not claimed), using homogeneous materials for the compressible portion <NUM>. As a result, and as shown <FIG>, the optical fiber <NUM> is guided out of the compressible portion <NUM> in a tangential direction, but as shown <FIG>, radial direction guiding is also an alternative.

<FIG> shows a hole 23A, but it is also possible to implement a groove in the outer ring <NUM> to guide the optical fiber <NUM>.

<FIG> represents a first possible design for the tube assembly, where tubes <NUM> and <NUM> have same flange design, and gasket G comprises an outer ring and an inner ring, the compressible portion of the gasket G being in contact with the tubes <NUM> and <NUM>.

<FIG> represents a second possible design for the tube assembly, where tubes <NUM> and <NUM> have different flange design, and gasket G comprises only a compressible portion, with no outer or inner ring. In such case, one of the tube flange might be adapted to allow a passage for the optical fiber <NUM>, with an opening such as a groove or a hole.

<FIG> represents a third possible design for the tube assembly, where tubes <NUM> and <NUM> have different flange design, and gasket G comprises only a compressible portion, and an inner ring. In such case, one of the tube flange might also be adapted to allow a passage for the optical fiber <NUM>, with an opening such as a groove or a hole.

<FIG> represents another alternative gasket (not claimed), comprising a serrated core <NUM> sandwiched between two washers of compressible portions <NUM>. As an example, the core <NUM> might be metallic (stainless steel), and the compressible portions <NUM> might be of graphite or polytetrafluoroethylene (PTFE), or mica, or rubber. The core <NUM> presents a serrated or corrugated or wavy interface with the compressible portions <NUM>, the wavy interface being provided by successive grooves 26A, 26B. Alternatively, the wavy interface might be provided by a spiral groove.

Sealing between the tubes is provided by deformation of the compressible portions <NUM>, which can penetrate the grooves 26A, 26B, when the tubes are clamped together.

An optical fiber <NUM> is provided in the groove 26B forming a receiving recess, so that the top compressible portion <NUM> will apply a residual pressure onto the optical fiber, which can be detected as explained above for <FIG>. It might be noticed that the groove 26B (or the part of the spiral groove receiving the optical fibre) might be deeper than the rest of grooves 26A forming sealing recesses, to avoid overstress of the optical fiber <NUM>. In particular, groove 26B might present a depth equal to or smaller than the depth of groove 26A added to the size (diameter) of the optical fiber <NUM>.

Finally, grooves 23B are provided on core <NUM> to allow guiding of the optical fiber <NUM> out of the gasket, towards a space between opposite faces 21A, 21B, so that the tube flanges do not need to be modified for optical fiber <NUM> presence. It should be noticed that two grooves 23B are provided on each side of core <NUM>, so that the gasket can be equipped with two optical fibers <NUM> if necessary.

<FIG> shows an alternative gasket of <FIG> (not claimed), comprising a core <NUM> sandwiched between two washers of compressible portions <NUM>, and equipped with an outer ring <NUM>. Compared to the gasket of <FIG>, only the optional outer ring <NUM> will be described in detail.

The outer ring <NUM> might be metallic (stainless steel for example), and comprises two holes 23A to provide guiding of the optical fiber <NUM>. The holes 23A are aligned with the grooves 23B of the core <NUM> to provide adequate guiding of the optical fiber <NUM>. The outer ring <NUM> might be attached to the core <NUM> as shown on <FIG> (internal diameter of outer ring <NUM> fits to outer diameter of core <NUM>), but the outer ring <NUM> might be installed into a peripheral groove of the core <NUM>.

It is of course understood that obvious improvements and/or modifications for one skilled in the art may be implemented, still being under the scope of the invention as defined by the claims.

Claim 1:
Gasket (G) for sealing an assembly of two tubes (<NUM>, <NUM>) each comprising an extremity with a seating surface,
the gasket (G) comprising a sealing portion with two opposite faces (21A, 21B), each being arranged to contact a respective seating surface,
the sealing portion comprising at least a compressible portion (<NUM>),
wherein the gasket (G) comprises an optical fiber (<NUM>) comprising a sensing portion at least partially enclosed in the compressible portion (<NUM>) and arranged to detect a compression force applied by the tube assembly to the compressible portion (<NUM>) via the opposite faces (21A, 21B), wherein the compressible portion (<NUM>) comprises a strip spirally wound,
characterized in
that the gasket comprises guiding means arranged to provide guiding of the optical fiber (<NUM>) out of the sealing portion,
wherein the sensing portion is at least partially wound with the strip.