IT201800006714A1 - MULTI-LAYER PIPE FOR THE TRANSPORT OF PRESSURE FLUIDS. - Google Patents

Description

MULTILAYER PIPE FOR THE TRANSPORT OF FLUIDS UNDER PRESSURE

The present invention relates to a multilayer pipe for conveying pressurized fluids. In particular, the present invention relates to a multilayer pipe for the transport of pressurized fluids, such as hydrocarbons (e.g. mineral oils, lubricants, glycols, etc.), which is preferably used in the sectors of hydraulic systems, industrial machines, handling machines, lifting machines.

It is well known that to allow adequate transport of fluids, especially when these are oily fluids or hydrocarbons under pressure, it is necessary to use a multilayer pipe with specific structural and chemical-physical characteristics. The material that constitutes the layer of the pipe in direct contact with the transported fluid must in fact have a high impermeability to oils and hydrocarbons, as well as having high resistance to attack by the constituent components of the transported fluid. Multilayer pipes known for conveying pressurized fluids, in addition to possessing this chemical resistance, must also possess high mechanical performance, for example high bursting resistance due to an increase in internal pressure, compression and impact. Finally, these tubes must be endowed with such flexibility that they can be handled with a certain ease during both production and use and be wound on reels for their storage and transport.

There are numerous combinations of materials proposed in the known art for the production of multilayer pipes for applications in the aforesaid fields.

For example, multilayer pipes are known comprising from the inside to the outside: an internal layer made of elastomeric material, placed in contact with the fluid to be transported; an intermediate reinforcement layer made of metallic or textile material and an outer layer of elastomeric material.

Usually the reinforcement layer has the mechanical function of counteracting the pressure exerted by the fluid under pressure transported, thus preventing the pipe from bursting, while the internal layer in elastomeric material has characteristics of impermeability and resistance to attack by the transported fluids . The outer layer, on the other hand, acts as a protective layer of the inner layers.

Also known are the so-called hybrid multilayer pipes comprising an internal layer made of elastomeric material, an intermediate reinforcing layer made of metallic or textile material and an external layer made of thermoplastic material.

An example of these hybrid multilayer pipes is described in EP 2290278, which describes a multilayer pipe comprising an inner layer made of elastomeric material, one or more interwoven or spiral reinforcement intermediate layers made of metallic or textile material and an outer layer made of thermoplastic material, such as polyurethane.

The temperature range within which a multilayer pipe can be used depends mainly on the material with which the inner and outer layers are made. Each material, be it elastomeric or thermoplastic, in fact has its own temperature range within which its performance remains constant. At temperatures outside the aforementioned range, the material can degrade, for example by melting, thus making its use inadequate at those temperatures.

Depending on the temperatures within which the pipe is expected to be used, it is therefore necessary to choose a particular combination of materials for the inner and outer layers, such as to make the pipe suitable for use in those specific temperatures.

For example, a hybrid multilayer pipe comprising an elastomeric inner layer and an outer layer of polyurethane has the limit that it cannot be used at relatively high temperatures, for example above about 80 ° C, since beyond that temperature the polyurethane begins to deteriorate.

In general, pipes whose performance is correctly maintained at low temperatures have the disadvantage of losing the aforementioned performance when the temperature rises and, conversely, pipes that operate correctly at high temperatures exhibit poor performance at low temperatures. This limits the choice of the type of pipe to be installed to the temperature range of use and forces the user to install pipes of different structure and composition for different temperature ranges of use.

On the other hand, it would be desirable to have multilayer pipes capable of being used indifferently at low or high temperatures, that is, in a wider temperature range than that of the pipes of the known art.

The Applicant therefore posed the problem of developing a multilayer pipe for the transport of pressurized fluids that was suitable for use in a wide range of temperatures, for example from -60 ° C to 150 ° C.

The Applicant has now found that this problem, and others that will be better illustrated below, can be solved by a hybrid multilayer pipe in which the inner layer is made of elastomeric material and the outer layer is composed of a polymeric material comprising cross-linked polyethylene with silanes. ; between the two layers there is interposed at least one intermediate reinforcing layer comprising metal threads or textile fibers.

It has been found, in fact, that the use of a polymeric material comprising cross-linked polyethylene with silanes as an external layer allows to obtain pipes that can be used in a wider range of temperatures. The tubes also maintain a high flexibility and are significantly lighter than the tubes of the known art, in particular the tubes having the inner and outer layers of elastomeric material, with the same required performance. In fact, cross-linked polyethylene confers adequate mechanical and thermal resistance despite being used in the form of a thin layer. Furthermore, by carrying out the cross-linking of polyethylene by means of the “silane” technique, the production process is easy and economical to implement.

In a first aspect, the present invention therefore relates to a multilayer pipe for the transport of pressurized fluids which includes, from the inside to the outside:

- an internal layer comprising a vulcanized elastomeric material;

- at least one reinforcing layer comprising a plurality of metal threads and / or textile fibers;

- an external extruded layer comprising silane cross-linked polyethylene.

In a second aspect, the present invention concerns the use of the aforementioned multilayer pipe for the transport of a fluid under pressure.

In the context of this description and the attached claims, with "pressurized" fluids we mean the fluids circulating in a pipe at a pressure in the range of 20 - 1300 bar.

Preferably, the pressurized fluids transported are selected from: hydrocarbons, mineral oils, lubricants, glycols, water and similar fluids.

The elastomeric material that forms the inner layer can be chosen without particular limitations among the elastomeric materials commonly used to make the multilayer pipes of the known art. The elastomeric material can be a vulcanizable natural rubber or a synthetic rubber, such as for example nitrile rubber, styrene-butadiene rubber (SBR), butadiene-acrylonitrile copolymers (NBR), chlorobutadiene polymers (neoprene®). More preferably, the elastomeric material is an acrylonitrile butadiene copolymer.

The elastomeric material that forms the inner layer is in vulcanized form.

The internal layer defines, internally with respect to the tube, a cavity for the transport of pressurized fluids. Preferably, the diameter of this cavity is between 3/16 of an inch and 2 inches. The inner layer is therefore in direct contact with the transported fluid.

The elastomeric material preferably has a hardness value between 60 and 95 Shore A (UNI EN ISO 868).

The elastomeric material preferably has a tensile strength of between 5 and 30 MPa (UNI 6065).

The elastomeric material preferably has an elongation at break value between 100 and 300% (UNI 6065).

The elastomeric material preferably has a 100% modulus value between 1.0 and 15.0 MPa (UNI 6065).

In accordance with an embodiment of the present invention, the multilayer pipe comprises one or more reinforcing layers (or sheaths), each comprising metal threads or textile fibers. The metal wires are preferably twisted or spiraled. In accordance with another embodiment of the invention, the textile fibers are preferably intertwined or spiraled.

Preferably, the metal threads are steel threads, while the textile fibers are preferably selected from: aramid fibers, nylon fibers, polyvinyl alcohol fibers, polyester fibers and their combinations.

The at least one reinforcement layer surrounding the inner layer is designed to increase the mechanical strength of the multilayer pipe; in particular, the at least one reinforcement layer is chosen in such a way as to allow the pipe to comply with the burst resistance requirements established by the specific industry standards.

The reinforcement layer can comprise one or more of the following elements: a sheath of steel wires or textile fibers, optionally intertwined or spiraled. The reinforcing layer can also comprise a plurality of intertwined or spiral sheaths, possibly superimposed on each other and formed for example by metal threads or intertwined textile fibers. In this case, a thin layer of natural or synthetic rubber is preferably interposed between two successive sheaths, commonly referred to as a "sheet", with the purpose of increasing the adhesion of the two or more sheaths.

Preferably, the reinforcement layer is able to adhere to the inner and outer layers, allowing the layers to be mechanically fixed and avoiding reciprocal sliding.

Advantageously, the reinforcement layer and any sheaths can be impregnated with the elastomeric material of the inner layer and / or with the polyethylene of the outer layer, for example following the production process of the multilayer pipe by extrusion. This further improves the adhesion of the various layers to each other.

The outer layer surrounding the at least one reinforcement layer of the multilayer pipe according to the present invention is made of a material comprising cross-linked polyethylene with silanes.

The polyethylene that can be used for the purposes of the present invention preferably has a hardness value between 60 and 95 Shore A (UNI EN ISO 868).

The polyethylene preferably has a tensile strength higher than 5, more preferably between 5 and 30 MPa (ISO 527-2).

The polyethylene preferably has an elongation at break value higher than 400%, more preferably between 400% and 800% (ISO 527-2).

The polyethylene preferably has a 100% modulus value comprised between 1.0 and 15.0 MPa (ISO 527-2).

In accordance with a preferred embodiment, the outer layer of the silane cross-linked polyethylene pipe advantageously has a thickness of between 0.2 and 1.5 mm, even more preferably it has a thickness of between 0.3 and 1.0 mm. . This thickness of the cross-linked polyethylene layer gives the pipe adequate mechanical and thermal resistance, without either excessively stiffening the pipe, which therefore maintains adequate flexibility, or significantly increasing its weight.

In particular, the multilayer pipes according to the present invention can be used continuously at temperatures in a wide range of values, for example in the range from -55 ° C to 145 ° C.

For the purposes of the present description and the annexed claims, the term "with continuity" means that the tube can operate for an indefinite time at the aforementioned temperatures, without interruption. Furthermore, when used for short periods of time, the multilayer pipe can also be used at a lower temperature, such as at -60 ° C, or at a higher temperature, such as at 150 ° C.

The characteristic of the outer layer of having a thickness between 0.2 and 1.5 mm also allows to reduce the weight per unit of length of the multilayer pipe with respect to the multilayer pipes known in the known art. The weight reduction advantageously makes the tube of the invention easy to handle.

The multilayer pipe according to the present invention can be made with the devices and techniques known to those skilled in the art.

In accordance with a further aspect of the present invention, the multilayer pipe is preferably produced by means of a process which comprises the steps of:

a) extruding an inner annular layer of elastomeric material;

b) applying on said inner annular layer at least one reinforcing layer comprising metal threads and / or synthetic fibers;

c) subjecting said annular inner layer and said at least one reinforcing layer to vulcanization to vulcanize said elastomeric material;

d) extruding an outer annular layer comprising at least one polyethylene grafted with silanes on said reinforcing layer;

e) crosslinking said polyethylene crimped with silanes to obtain the multilayer pipe.

Preferably, the vulcanization is carried out in an autoclave in the presence of steam.

The silane crosslinking of polyethylene can be carried out with the processes known to those skilled in the art, preferably with the process commonly referred to as Sioplast®. In accordance with the Sioplast® process, a polyethylene polymer grafted with a vinyl silane compound (e.g. vinyltrimethoxysilane), possibly pre-mixed with at least one hydrolysis catalyst and other additives (e.g. pigments, plasticizers, etc.) is extruded onto the layer reinforcement to form the outer layer. Crosslinking of polyethylene can take place in environmental conditions. Preferably, the crosslinking can be accelerated by immersing the tube comprising the polyethylene layer in hot water (e.g. 60-95 ° C).

Polyethylene crimped with vinyl silane compounds can be prepared according to the known art, for example by treating polyethylene with an alkoxy vinyl silane compound in a mixing unit (e.g. twin screw extruder or co-mixer), at a temperature of, for example, 50 - 150 ° C, in the presence of a peroxidic compound capable of promoting the anchoring of the alkoxyvinyl silane groups to the polyethylene chains (radical initiator).

The production process according to the present invention has the advantage of allowing the production of a multilayer pipe with a particularly favorable balance between performance and production costs, in particular with respect to processes which provide for the peroxide cross-linking of thermoplastic polymeric materials. In fact, these latter processes require expensive systems and strict control of operating conditions, in particular of the extrusion temperature in order not to trigger the decomposition of peroxides and therefore the initiation of crosslinking.

A further aspect of the present invention relates to the use of the multilayer pipe, as previously described, for the transport of a fluid under pressure, preferably at a temperature in the range from -60 ° C to 150 ° C.

Claims (11)

CLAIMS 1. Multilayer pipe for the transport of pressurized fluids which includes, from the inside to the outside: - an internal layer comprising a vulcanized elastomeric material; - at least one reinforcing layer comprising a plurality of metal threads and / or textile fibers; - an external extruded layer comprising silane cross-linked polyethylene. 2. Pipe according to claim 1, wherein the elastomeric material is selected from: natural rubber, nitrile rubber, styrene-butadiene rubber, butadiene-acrylonitrile copolymer, chlorobutadiene polymers. 3. A tube according to claim 2, wherein the elastomeric material is a butadiene acrylonitrile copolymer. 4. Tube according to any one of the preceding claims, in which the metal threads and / or the textile fibers are intertwined or spiraled. 5. Pipe according to any one of the preceding claims, in which the metal wires are steel wires. 6. Tube according to any one of claims 1 to 4, in which the textile fibers are selected from: aramid fibers, nylon fibers, polyvinyl alcohol fibers, polyester fibers and their combinations. 7. Pipe according to any one of the preceding claims, wherein the outer layer has a thickness of between 0.2 and 1.5 mm. 8. Pipe according to any one of the preceding claims, wherein the inner layer defines, internally with respect to the pipe, a cavity for conveying pressurized fluids with a diameter between 3/16 of an inch and 2 inches. 9. Process for producing a multilayer pipe according to claim 1 comprising the steps of: a) extruding an inner annular layer of elastomeric material; b) applying on said inner annular layer at least one reinforcing layer comprising metal threads and / or synthetic fibers; c) subjecting said annular inner layer and said at least one reinforcing layer to vulcanization to vulcanize said elastomeric material; d) extruding an outer annular layer comprising at least one polyethylene grafted with silanes on said reinforcing layer; e) crosslinking said polyethylene crimped with silanes to obtain said multilayer pipe. 10. Use of the multilayer pipe according to claim 1 for conveying a fluid under pressure. 11. Use according to claim 10 at a temperature in the range from -60 ° C to 150 ° C.