AU674519B2 - Composite material pipes - Google Patents

Description

AUSTRALIA

Patent Act COMPLETE SPECIFICATI ON

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: o* e Priority: Related Art: Names(s) of Applicant(s): LEHUNT ASSOCIATES PTY. LTD.

Actual Inventor(s): Robert J. LEHUNT Our Address for service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street MELBOURNE, Australia 3000 Complete Specification for the invention entitled: COMPOSITE MATERIAL PIPES The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 0804N 0804N 2 COMPOSITE MATERIAL PIPES This invention relates generally to composite material pipes, and in particular to rigid, thin walled pipes composed of multiple thermoplastic materials. The pipe is applicable in pipeline systems, particularly pressurised systems such as water mains, sewer lines, conduits and the like, where satisfactory long term performance is influenced by stress resistance within the pipe. It will convenient to hereinafter disclose the invention in relation to that exemplary application, although it is to be appreciated that the invention is not limited to that application.

Rigid thin walled thermoplastic material pipes have been made from a wide range of singular base materials. Those pipes are specified in terms of the base materials used, for example polyethylene polyvinyl chloride (PVC), etc, as S well as in documents such as Australian Standards AS 1477, AS 1159 and AS 2977 used by pipe purchasing authorities. The S materials are selected depending on the pipe application, and it is usual to modify the properties of those base materials *2 by the addition of agents, such as impact modifiers and ultraviolet light stabilizers, to improve performance characteristics of the pipe. These agents are added in relatively small quantities to the base material and mixed uniformly through the entire material prior to pipe manufacture, so that the modified properties are uniform throughout the material.

In the case of plastic material pressure pipes, their long term performance has traditionally been determined by hydrostatic testing of samples over extended periods and then establishing a long term design stress to fix the wall thickness of the pipe. Typically, the pipes are designed with a factor of safety in the order of 1.5 to 2.1 being applied.

However, this assumes that the properties of the plastic material remains either constant across the projected lifetime of the pipe, or changes in a predictable manner as established in accelerated tests. It does not take into account the affects of any damage to the pipe from such causes as mechanical damage, ultraviolet light degradation or thermal oxidation, all of which will result in reduction of long term performance and may cause premature pipe failure.

3 The performance characteristcs of these pipes during long term use in a pressurised fluid application is particularly influenced by stress resistance within the pipe.

Stress resistance is reduced by fatigue loading, and stress intensity raised by scratches or notches in the pipe surface caused during pipe handling and installation. To meet authority specifications, such as those contained in AS 1477 and AS 2977, PVC pipes have a crack resistance value of about -3/2 MNm and a long term (50 years) static stress resistance of 12.3 MPa.

Sharp cracks or notches up to about 2 mm deep can be encountered in practice, which reduces the lcng term pipe strength, especially under cyclic loading in pressurised pipe lines by a factor of 3 to 4. However, increases in the fracture toughness is limited because of the adverse affect on the pipe tensile strength. Thus, in practice a thicker, and S hence more costly, pipe is required to ensure compliance with the specifications. In the case of PVC pipes, this is S reflected in about a 60% increase in the wall thickness of o:o• IMP pipes having nominal internal diameters of 100 and 150 mm.

In an effort to avoid or alleviate these difficulties, several pipes have been developed with multiple layers of different materials. Typical of such developments, are the use of aluminium cores to increase the long term pressure strengths of pipes made from PE or XLPE.

A further development has been the coating of the outer surface of PE pipes with nylon in order to improve the termite resistant properties of the pipes.

Another development involves pipes, having a foamed plastic core with inner and outer surface skin coatings of PVC used for non-pressurised drainage applications, to reduce material costs.

These developments have not succeeded in achieving inexpensive replacements for rigid thin walled thermoplastic material pipes, particularly those used in pressurised pipeline systems.

An object of the present invention is to provide a pipe of thermoplastic materials which has improved performance characteristics when compared with prior pipes of such materials.

-3a- A further object is the provision of a thermoplastic material pipe that can achieve an improved fatigue performance and damage resistance with a thinner pipe wall, when compared with previous pipes of such materials.

Another object of the present invention is the provision of an economical thermoplastic material pipe for use in both pressurised and non-pressurised applications.

With these objects in mind, the present invention provides a rigid, thin walled pipe for pressurized fluid pipeline systems, the pipe having a pipe wall including an extruded core layer, and at least one extruded inner layer and/or at least one extruded outer layer respectively located inwardly and outwardly of the core layer, the layers each being solid and being composed of compatible thermoplastic material, the core layer being composed of a long term hydrostatic pressure resistant thermoplastic material and each inner and outer layer being composed of a fracture resistant thermoplastic material so that the pipe has improved resistance to long term fatigue and crack propagation when compared with a thermoplastic material, single layer, thin wall pipe of the same dimensions.

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o•: :o o o• 4 A further object i- thec proviSion- of a thermoplasti material pipe that can achieve an improved fatigue perfor ce and damage resistance with a thinner pipe wall, whe compared with previous pipes of such materials.

Another object of the present inventj is the provision of an economical thermoplastic materip pipe for use in both pressurised and non-pressurised ap{ ications.

With these objects r mind, the present invention provides a thin walled /ipe having a pipe wall including a core layer, and at east one inner layer and/or at least one outer layer r epectively located inwardly and outwardly of the core la r, the layers being composed of compatible ther plastic material selected to provide the pipe with >,'rdetermined performance charactortitic.- In at least one embodiment, the pipe wall includes a single inner layer defining an inner surface of the pipe, but no outer layer. In an alternative embodiment, there is a single outer layer defining an outer surface of the pipe, but no inner layer. In these embodiments, the core layer defines *2tU the remaining outer or inner surface of the pipe. In a further embodiment, the pipe wall has a single inner layer defining the inner surface of the pipe, and a single outer layer defining the outer surface of the pipe.

Preferably, the core layer is thicker than the inner and outer layers (where provided). Where both inner and outer layers are provided then preferably the core layer is the thickest layer and the inner layer is thicker than the outer layer.

Preferably the pipe wall layers are co-extruded to form the pipe wall. The core layer is preferably composed of a thermoplastic material different from the material of which the inner and outer layers (where provided) are composed.

The following description refers to preferred embodiments of the thin walled pipe of the present invention.

To facilitate an understanding of the invention, reference is made ir the description to the accompanying drawings where the pipe is illustrated in preferred embodiments. It is to be understood that the thin walled pipe is not limited to the preferred embodiments as hereinafter described and as illustrated in the drawings.

KW u 5 In the drawings: Fig. 1 is an end view of a thin walled pipe according to one embodiment of the present invention; Fig. 2 is an end view of a thin walled pipe according to another embodiment of the present invention; and, Fig. 3 is an end view of a thin walled pipe according to a further embodiment of the present invention.

Referring to the drawings, there is generally shown a thin walled cylindrical pipe 1 having an annular pipe wall 2.

The pipe wall 2 is formed of smooth faced, annular layers composed of thermoplastic material. Those layers comprise an annular core layer 3, and an annular inner layer 4 and/or an annular outer layer 5. Each of the layers 3,4,5 is solid and extends throughout the circumferential extent and along the length of the pipe i.

S" The provision of the inner and/or outer layers 4,5 will depend on intended applications of the pipe i.

••coo: te In the embodiment shown in Fig. 1, the pipe wall 2 has the core layer 3 and an inner layer 4, but no outer layer. In "2 that embodiment, the inner layer 4 defines a smooth inner surface 6 of the pipe 1, the core layer 3 defining a smooth outer surface 7 of the pipe 1.

In an alternative embodiment shown in Fig. 2, the pipe wall 2 has the core layer 3 and outer layer 5, but no inner layer. In that embodiment, the outer layer 5 defines the outer surface 7 of the pipe 1, the core layer 3 defining the inner surface 6 of the pipe i.

In yet another embodiment shown in Fig. 3, the pipe wall S 2 has the core layer 3 as well as both the inner and outer layers 4,5, the inner and outer layers 4,5 defining the smooth inner and outer surfaces 6,7 of the pipe 1, respectively.

In these embodiments, the core layer 3 is composed of a thermoplastic material that provides the pipe 1 with an acceptable long term (50 years plus) hydrostatic pressure resistance having regard to the intended application of the pipe i.

One or more of the layers 3,4,5 are composed of a thermoplastic material selected to provide the pipe 1 with one or more of the following performance characteristics: Fracture resistance so as to retard the propogation of 6 cracks initiated by mechanical or other damage on the inner and/or outer surface 6,7 of the pipe i.

Light stabilization to inhibit initiation of micro cracks which act as stress raisers.

Heat stabilization to inhibit initiation of micro cracks which act as stress raisers.

Oxidation stabilization to inhibit initiation of micro cracks which act as stress raisers.

Impermeability to fluid through the pipe wall 2 to prevent leakage or contamination either of the contents being conveyed by the pipe 1 or the surrounding environment.

Non-toxic or inert to the contents being conveyed by the pipe 1 or to the surrounding environment.

15 In these embodiments, the layers 3,4,5 defining the oeooe S inner and/or outer surfaces 6,7 provide the pipe 1 with one or S more of the above performance characteristics. Each layer S 3,4,5 is composed of a thermoplastic material that enables the S pipe 1 to achieve one or more of those characteristics.

o:o• Depending on the intended application of the pipe, the layers 3,4,5 are composed of materials having properties that achieve S the above characteristics either singly or in combination.

S Thus, in alternative embodiments, the core, inner and/or outer layers 3,4,5 are composed of materials with the appropriate properties. The pipe wall layers 3,4,5 may be composed of materials which individually may not be capable of meeting required performance characteristics for the pipe i, but when S combined result in improved pipe characteristics when compared S with similarly dimensioned thin walled pipes composed of a single layer thermoplastic material.

The pipe 1 is composed of at least two different thermoplastic materials. In one embodiment, the core layer 3 is composed of a thermoplastic material that is different from the material of which the inner and/or outer layer 4,5 is composed. The pipe 1 may be constructed with inner and outer layers 4,5 of the same thermoplastic material. In these embodiments, the layers 3,4,5 are composed of PVC.

The layers 3,4,5 are of the same or different thickness depending on various factors including the layer numbers, their materials of composition, and the required pipe 7 performance characteristics. The thickness of each layer 3,4,5, remains constant about the circumferential extent of the pipe 1 and along the length of the pipe i. In these embodiments, the core layer 3 is generally thicker than the inner and outer layers 4,5. By way of example, the core layer 3 may be two or more times thicker than the inner and/or outer layer 4,5. The inner and outer layers 4,5 may be of the same (not shown) or different (as shown) thicknesses. In the embodiment of Fig. 3, where both layers 4,5 are provided, the inner layer 4 is thicker than the outer layer In the embodiment of Fig. 3, of a pipe composed of the above materials and having a nominal internal diameter of about 100 mm, the pipe 1 has a core layer 3 of about 3 mm thick, an inner layer 4 of about 2 mm and an outer layer 5 of about 2 mm thick. In the embodiments of Figs. 1 and 2, of pipes 1 of that diameter and having only a core layer 3 and an S: inner or outer layer 4,5, the layers 3,4,5 may also have thicknesses as set out above.

The pipe 1 of the present invention is manufactured through any suitable manufacturing process. In these embodiments the pipe 1 is manufactured by co-extrusion of the pipe layers 3,4,5.

Pipes according to the present invention provide an improved fatigue performance and damage resistance with a 025" relatively thin wall, compared with pipes of single layer thermoplastic material composition. The thin wall nature of the pipe enables the use of less material compared with pipes of single layer composition having the same performance characteristics. Moreover, pipes of the same outside diameter may have a larger internal diameter when manufactured in accordance with the present invention, resulting in an improved flow performance.

Finally, it will be appreciated that various modifications and/or additions may be made to the pipe without departing from the ambit of the invention as defined in the claims appended hereto.

Claims (7)

1. A rigid, thin walled pipe for pressurized fluid pipeline systems, the pipe having a pipe wall including an extruded core layer, and at least one extruded inner layer and/or at least one extruded outer layer respectively located inwardly and outwardly of the core layer, the layers each being solid and being composed of compatible thermoplastic material, the core layer being composed of a long term hydrostatic pressure resistant thermoplastic material and each inner and outer layer being composed of a fracture resistant thermoplastic material so that the pipe has improved resistance to long term fatigue and crack propagation when compared with a thermoplastic material, single layer, thin wall pipe of the same dimensions.

2. A thin walled pipe as claimed in claim 1, wherein the pipe wall includes a single inner layer defining an inner surface of the pipe, but no outer layer, the core layer defining an outer surface of the pipe.

3. A thin walled pipe as claimed in claim 1, wherein the pipe wall includes a single outer layer defining an outer surface of the pipe, but no inner layer, the .oo..i core layer defining an inner surface of the pipe.

4. A thin walled pipe as claimed in any preceding clam, wherein the core layer is thicker than the inner and outer layers (where provided).

5. A thin walled pipe as claimed in claim 1, wherein the pipe wall includes a single inner layer defining an inner surface of the pipe, and a single outer layer defining an outer surface of the pipe.

6. A thin walled pipe as claimed in claim 5, wherein the core layer is the thickest layer and the inner layer is the thicker than the outer layer.

7. A thin walled pipe as claimed in any preceding claim, wherein one or more o. of the layers is composed of a thermoplastic material selected to provide the pipe with one or more of the following performance characteristics: light stabilisation inhibiting initiation of microcracks: heat stabilisation inhibiting initiation of microcracks; oxidisation stabilisation inhibiting initiation of microcracks; 9 fluid impermeability preventing leakage through pipe wall; and non toxic or inert to contents being conveyed by the pipe or to the surrounding environment. -9-7 A thin walled pipe as claimed in any preceding claim, wherein the pipe wall layers are co-extruded to form the pipe wall, the core layer being composed of a thermoplastic material different from the material of which the inner and outer layers (where provided) are composed. c kt. A thin walled pipe substantially as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings. DATED: 27 July, 1993 PHILLIPS ORMONDE FITZPATRICK Attorneys for: LEHUNT ASSOCIATES PTY. LTD. 6168E t w S:RA% x ABSTRACT A thin walled pipe having a pipe wall including a core layer and at least one inner layer and/or at least one outer layer respectively located inwardly and outwardly of the core layer The layers are composed of compatible thermoplastic material selected to provide the pipe with predetermined performance charactertistics. a *o a 9*