GB1594756A

GB1594756A - Flexible expansion joint

Info

Publication number: GB1594756A
Application number: GB1916578A
Authority: GB
Original assignee: Industrie Pirelli SpA; Pirelli SpA
Current assignee: Industrie Pirelli SpA; Pirelli and C SpA
Priority date: 1977-08-30
Filing date: 1978-05-12
Publication date: 1981-08-05
Also published as: FR2402150A1; DE2834136A1; IT1114411B; AU3886078A; DE2834136C2; FR2402150B1

Description

(54) FLEXIBLE EXPANSION JOINT (71) We, INDUSTRIE PIRELLI SOCIETA PER AZIONI, an Italian Company, of Centro Pirelli, Piazza Duca d'Aosta No 3, 20100 Milan, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a flexible expansion joint, and in particular, though not exclusively, to a flexible expansion joint for non-flexible pipes, as for example metallic pipes.

There exist 'known' flexible expansion joints for non-flexible pipes, formed with a body of elastomeric material having a corrugation protruding radially towards the outside, two cylindrical portions placed symmetrically with respect to said corrugation, and two terminal portions protruding radially outwards and placed one at each extremity of the said body of elastomeric material, capable of being pressed between a counterflange and the flange of the non-flexible pipes to be connected. The reinforcing structures incorporated in the said bodies of elastomeric material are of various types.

In addition to having one or more layers of fabric cord that can either be metallic or textile cords, the reinforcing structures that are incorporated in the said 'known' flexible expansion joints for non-flexible pipes consist of a further reinforcement inserted into each cylindrical portion, or placed outside the said cylindrical portion. Said reinforcement was at first formed by a steel wire wound helically around the cylindrical portion and embedded therein. The increase in the working pressures in the pipes into which the said joints are inserted, and fatigue stresses due to the pressure variations, cause the steel wire helix to open, in the joints that are provided with reinforcements of this type, with the consequent failure of the rubbermetal connection, which leads to a breaking of the joint after a short period of time.

An improvement has been obtained by inserting into the cylindrical portion instead of a steel wire wound around helically, closed metallic rings having a circular cross-section.

No further opening of the rings was to be had with these joints; but owing to the repeated stresses as a result of the pressure variations in the pipes said joints have the defect of migration of said rings from the cylindrical portion towards the two terminal portions placed at the extremities of the joint, with the consequent breaking of the joint itself.

For averting this problem of a migration of the rings, attempts were made to substitute the closed metallic rings having circular cross-sections, with closed metallic rings having square cross-sections, and to insert between one ring and the next, very hard rubber inserts. However, even this solution did not produce the desired results, since it did not succeed in eliminating a migration of said rings towards the two terminal portions.

Moreover, this solution has a drawback for the rings made in this way because of the manufacturing process which they must undergo cannot be made out of a very strong and stress resistant material. Hence, said joints cannot be subjected to very high working pressures.

Subsequently attempts were made to surround the cylindrical portion with a tubular metallic structure, outside the joint body made in elastomeric material, connected to the counter-flange. This solution however does not provide any support for the cylindrical portion when the pipe functions under depression or vacuum.

The aim of the present invention is to overcome or mitigate the previously indicated drawbacks of the 'known' flexible expansion joints.

In accordance with one aspect of the present invention a flexible expansion joint comprises a substantially tubular body of elastomeric material incorporating a reinforcement structure, said body comprising: two cylindrical portions having positioned therebetween a corrugation which extends radially outwards of the two cylindrical portions, and two terminal portions protruding radially outwardly, positioned one at each extremity of said body and capable of being pressed bet ween a flange and a counterflange for carrying out the watertight joining of the pipes to be connected, wherein in each cylindrical portion of said substantially tubular body the reinforcing structure embedded therein comprises a spiral of at least one overlapping turn formed by a continuous tape of a flexible inextensible material wound with the turns in contact one with the other, and means that impede relative axial movements between said turns of the spiral.

The present invention will be better understood from the following detailed description given by way of non-limiting example, referring to the accompanying drawings, in which: Figure 1 shows in longitudinal crosssection part of a joint according to the present invention interconnecting two nonflexible pipes, and Figure 2 shows in cross-section in an enlarged scale a detail of the joint shown in Figure 1.

Referring to Figure 1, a flexible expansion joint according to the present invention, formed by a substantially tubular body of elastomeric material 1, is connected to nonflexible pipes 2 and 3. Said body of elastomeric material is formed by two cylindrical portions 5, placed symmetrically with respect to a corrugation 4, and by two terminal portions 6, protruding radially outwards. Said two terminal portions 6 are pressed between the flanges 7 of each pipe connected by the joint and counter-flanges 8, the clamping pressure being provided by a series of bolts 9 and nuts 10 placed circumferentially in holes 11 made both in the flanges 7 and in the counter-flanges 8 as well as in the terminal portions 6.

The structure of the body of elastomeric material 1, comprises (as shown in Figure 1), from the inside towards the outside of the joint, a layer of elastomeric material 12, at least a couple of layers of rubberised cord fabric 13 that extend with continuity from one terminal portion 6 of the joint to the other. Said rubberised cord fabric can be either metallic or textile; examples of textile cords are NYLON-66 or KEVLAR (which is an aromatic polyamide produced by Du Pont). The cords of each layer of rubberised fabric cord 13 are crossed with respect to the cords of the adjacent layers, and they form equal angles with respect to a generatrix of the cylindrical portion itself. Preferably, said angles are 15". A spiral 14, comprising at least one turn of flexible and inextensible tape, is inserted into the cylindrical portion in such a way as to form a substantially rigid sleeve that extends for the or substantially the entire length of the said cylindrical portion. Around the said spiral 14 there are comprised means (not shown) known per se to any technician of the field, that maintain in mutual contact at least the two radially outermost turns of the said spiral. Said means can be for example a welding, a wire wound one or more times around the spiral, or even a strip of rubberised fabric wound either around the spiral or disposed astride the surmounting zone of the two radially outermost turns. To the spiral 14 there are moreover associated means (described later on) that impede any relative axial movement between the turns themselves of the spiral.

Finally, at least another couple of layers of rubberised cord fabric 15 disposed as the previous layers and a covering layer of elastomeric material 16.

The detailed description of the structure of the cylindrical portion according to the present invention is shown to a larger scale in Figure 2. Besides the various layers of elastomeric material and the rubberised cord fabric as previously described, in the said Figure 2 is clearly shown the spiral 14 of a tape of flexible and inextensible material.

Said spiral of tape is formed for example by three turns 14a, 14b and 14c, wound around the radially innermost structure of the cylindrical portion that is over the couple of layers of rubberised cord 13, each turn being in close contact with the next. The tape material of the said turn can be for example a continuous tape in metallic material, or a continuous tape in plastics material. The selection of the metallic material is done on the basis of the stresses that are applied to said joint i.e. practically on the basis of the working pressures, and above all on the variations that the said pressures are subjected to during operation.

For example, for high stresses during operation with great pressure variations there can be utilised a tempered steel alloy having a breaking load higher than 140 Kg/cm2, having a tape thickness of 0.5 to 0.8 mm.

For lower stresses on the other hand a plastics material tape can suffice. It is not necessary (though it is preferable) to effect a rubber-metal connection (or plastic-rubber) between the tape that forms the spiral and the elastomeric material which surrounds it since the friction that is created between the contacting turns of the spiral is sufficient enough for preventing them from unwinding.

For maintaining said friction, the means described previously for maintaining in contact one with the other at least the two radially outermost turns of the spiral are sufficient In Figure 2 there is given a particular form of the means disposed around the said spiral 14 for impeding the turns 14a, 14b and 14c of the said spiral 14 from shifting axially one with respect to the other. Said means consists of a winding of rubberised cord fabric 17, with the cords disposed parallel to the axis of the cylindrical portion. Said cords 17 are preferably metallic since these provide a greater resistance to the cutting stresses to which they are subjected by the turns of the spiral 14. Moreover, said rubberised fabric cords 17 also have the function of blocking between them the radially outermost turns of the said spiral 14.

Another form (not shown in the Figures) of the means for impeding any relative axial shifting between the turns, consists of the insertion between the single turns formed by the continuous metallic tape of a thermoplastic material strip slightly larger than the metallic tape in such a way that during the vulcanising phase by fusing the surplus portion of the said strip of thermoplastic material can envelop and keep fixed together the turns of the metallic tape that form the spiral 14. The insertion of said thermoplastic strip only between the radially outermost turns of the spiral 14 of metallic tape constitutes another example of the means capable of holding in mutual contact at least the said two radially outermost turns.

The operation of the flexible expansion joint according to the present invention is as follows: The stresses due to the high working pressures and especially to the pressure variations inside the pipes can be divided into their radial and axial components. Purely radial stresses are those that are applied on the inside of the cylindrical portions. These stresses are withstood by the spiral 14 which provides a practically equal resistance as that of a rigid sleeve with a slightly lesser thickness. The stresses that originate in the corrugation 4 on the contrary can be divided into the radial direction and the axial direction. The radial component of these stresses being of a modest entity it is withstood by the body itself of the corrugation. The axial stresses on the other hand are those which to date have created the greatest problems for the 'known' flexible expansion joints because especially if repeated they cause a migration of the reinforcement structure i.e.

of the rings from the cylindrical portion to the terminal portions. In the solution adopted for the joints according to the present invention on the other hand thanks to the presence of the rigid sleeves, said stresses are transmitted directly onto the flanges 7 from where they then pass onto the non-flexible pipes connected by the joint. It is the particular structure of the rigid sleeve formed by the spiral of tape 14 (said spiral having in its whole the same characteristics of a rigid sleeve with a slightly lesser thickness than that of the effective thickness of the spiral itself) that since the sleeve is subjected to buckling loads from the axial stresses allows the structure according to the present invention to resist adequately said stresses because considering the same resistance the corresponding rigid sleeve (formed by the spiral 14) has a greater thickness.

Likewise this can also be said for the stresses originating when the pipes and hence also the joint functions under depression. In such cases, since the cylindrical portions of the joints according to the present invention are very rigid, the resistance of the joints themselves against the radial stresses directed towards the joint axis (which tend to cause the collapse of the corrugation and of the adjacent cylindrical portions towards the inside of the joint itself) is increased.

By being able to unload the axial stresses onto the non-flexible pipes connected by the said joints in the manner described above, i.e. through the buckling load being distributed uniformly along the circumference of the sleeve formed by the spiral, it is believed there is a longer lifetime for the joint, since said reinforcing structures of the joint are less stressed. Besides this it appears from the results of experimental tests carried out on the joints according to the present invention that said joints can resist repeated pressure variations and, in a still more efficacious way than the 'known' joints, they can resist conditions where the pressure existing within the joint is considerably lower than that outside the pipes. Finally, the particular constructive solution adopted, permits an easy production of the joints according to the present invention.

WHAT WE CLAIM IS: 1. A flexible expansion joint comprising a substantially tubular body of elastomeric material incorporating a reinforcement structure, said body comprising: two cylindrical portions having positioned therebetween a corrugation which extends radially outwards of the two cylindrical portions, and two terminal portions protruding radially outwardly, positioned one at each extremity of said body and capable of being pressed between a flange and a counterflange for carrying out the watertight joining of the pipes to be connected, wherein in each cylindrical portion of said substantially tubular body the reinforcing structure embedded therein comprises a spiral of at least one overlapping turn formed by a continuous tape of a flexible inextensible material wound with the turns in contact one with the other, and means that impede relative axial movements between said turns of the spiral.

2. A flexible expansion joint according to claim 1 wherein the means for impeding the relative axial movements between the turns of the spiral formed of a flexible and inextensible material comprises a winding of rubberised cord fabric, with the cords disposed parallel to the axis of the cylindrical portion, wound around the spiral formed by said inextensible and flexible material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

provide a greater resistance to the cutting stresses to which they are subjected by the turns of the spiral 14. Moreover, said rubberised fabric cords 17 also have the function of blocking between them the radially outermost turns of the said spiral 14.

Another form (not shown in the Figures) of the means for impeding any relative axial shifting between the turns, consists of the insertion between the single turns formed by the continuous metallic tape of a thermoplastic material strip slightly larger than the metallic tape in such a way that during the vulcanising phase by fusing the surplus portion of the said strip of thermoplastic material can envelop and keep fixed together the turns of the metallic tape that form the spiral 14. The insertion of said thermoplastic strip only between the radially outermost turns of the spiral 14 of metallic tape constitutes another example of the means capable of holding in mutual contact at least the said two radially outermost turns.

The operation of the flexible expansion joint according to the present invention is as follows: The stresses due to the high working pressures and especially to the pressure variations inside the pipes can be divided into their radial and axial components. Purely radial stresses are those that are applied on the inside of the cylindrical portions. These stresses are withstood by the spiral 14 which provides a practically equal resistance as that of a rigid sleeve with a slightly lesser thickness. The stresses that originate in the corrugation 4 on the contrary can be divided into the radial direction and the axial direction. The radial component of these stresses being of a modest entity it is withstood by the body itself of the corrugation. The axial stresses on the other hand are those which to date have created the greatest problems for the 'known' flexible expansion joints because especially if repeated they cause a migration of the reinforcement structure i.e.

of the rings from the cylindrical portion to the terminal portions. In the solution adopted for the joints according to the present invention on the other hand thanks to the presence of the rigid sleeves, said stresses are transmitted directly onto the flanges 7 from where they then pass onto the non-flexible pipes connected by the joint. It is the particular structure of the rigid sleeve formed by the spiral of tape 14 (said spiral having in its whole the same characteristics of a rigid sleeve with a slightly lesser thickness than that of the effective thickness of the spiral itself) that since the sleeve is subjected to buckling loads from the axial stresses allows the structure according to the present invention to resist adequately said stresses because considering the same resistance the corresponding rigid sleeve (formed by the spiral

14) has a greater thickness.

Likewise this can also be said for the stresses originating when the pipes and hence also the joint functions under depression. In such cases, since the cylindrical portions of the joints according to the present invention are very rigid, the resistance of the joints themselves against the radial stresses directed towards the joint axis (which tend to cause the collapse of the corrugation and of the adjacent cylindrical portions towards the inside of the joint itself) is increased.

By being able to unload the axial stresses onto the non-flexible pipes connected by the said joints in the manner described above, i.e. through the buckling load being distributed uniformly along the circumference of the sleeve formed by the spiral, it is believed there is a longer lifetime for the joint, since said reinforcing structures of the joint are less stressed. Besides this it appears from the results of experimental tests carried out on the joints according to the present invention that said joints can resist repeated pressure variations and, in a still more efficacious way than the 'known' joints, they can resist conditions where the pressure existing within the joint is considerably lower than that outside the pipes. Finally, the particular constructive solution adopted, permits an easy production of the joints according to the present invention.

WHAT WE CLAIM IS: 1. A flexible expansion joint comprising a substantially tubular body of elastomeric material incorporating a reinforcement structure, said body comprising: two cylindrical portions having positioned therebetween a corrugation which extends radially outwards of the two cylindrical portions, and two terminal portions protruding radially outwardly, positioned one at each extremity of said body and capable of being pressed between a flange and a counterflange for carrying out the watertight joining of the pipes to be connected, wherein in each cylindrical portion of said substantially tubular body the reinforcing structure embedded therein comprises a spiral of at least one overlapping turn formed by a continuous tape of a flexible inextensible material wound with the turns in contact one with the other, and means that impede relative axial movements between said turns of the spiral.
2. A flexible expansion joint according to claim 1 wherein the means for impeding the relative axial movements between the turns of the spiral formed of a flexible and inextensible material comprises a winding of rubberised cord fabric, with the cords disposed parallel to the axis of the cylindrical portion, wound around the spiral formed by said inextensible and flexible material.
3. A flexible expansion joint according

to claim 1 or claim 2 wherein the rigid sleeve inserted into each cylindrical portion extends substantially axially for substantially the entire length of the said cylindrical portion.
4. A flexible expansion joint according to any one of the preceding claims wherein means is provided for maintaining in contact at least two radially outermost turns of the spiral formed by the continuous tape of flexible and inextensible material.
5. A flexible expansion joint according to any one of the preceding claims and comprising, from inside the joint towards outside, a layer of elastomeric material, at least a couple of layers of rubberised cord fabric disposed with the cords of each layer crossed with respect to the other layer, in such a way as to form equal angles with respect to a generatrix of the cylindrical portion, a spiral formed by a continuous tape of flexible and inextensible material placed in each cylindrical portion, a winding of rubberised cord fabric with the cords disposed parallel to the axis of the cylindrical portion wrapped around said spiral of flexible and inextensible material, a couple of rubberised cord fabrics disposed with the cords of each layer crossed with respect to those of the other layer, in such a way as to form equal angles with respect to a generatrix of the cylindrical portion, and a covering layer in elastomeric material.
6. A flexible expansion joint constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.