AU636672B2

AU636672B2 - Protection of pipelines

Info

Publication number: AU636672B2
Application number: AU64736/90A
Authority: AU
Inventors: Samuel P Costin
Original assignee: Vinidex Tubemakers Pty Ltd
Current assignee: Vinidex Pty Ltd
Priority date: 1989-10-19
Filing date: 1990-10-18
Publication date: 1993-05-06
Anticipated expiration: 2010-10-18
Also published as: AU6473690A

Description

COMMONWEALTH OF AUSTRALIA Patents Act 1952 6 7 COMPLETE SPECIFICATION (Original) FOR OFFICE USE Application Number: PJ6968 Lodged: 19/10/89 Complete Specification Lodged: Accepted: Published: Priority: Related Art: Class Int. Class TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: Address for Service:- VINIDEX TUBEMAKERS PTY LIMITED Sainsbury Road, O'Connor, in the State of Western Australia, Commonwealth of Australia.

SAMUEL P COSTIN Wray Associates Primary Industry House 239 Adelaide Terrace Perth Western Australia 6000.

4 i Complete Specification for the invention entitled: "PROTECTION OF PIPELINES" The following statement is a full description invention, including the best method of performing to me:of this it known 1 2 THIS INVENTION relates to fluid conduits and in particular fluid conduits formed of plastics material and which may be subjected to radiant heat in use.

Pipelines formed of plastics material are used for the transportation of water in agriculture, in mining, and industrial applications. Such pipelines are often laid above the ground and as a result are the subject of heating through solar radiation and conductive radiation as a result of ambient conditions. In addition, such installations are often exposed to conditions where in the summer the air temperature can exceed 50"C in the shade and below 0°C during the night in winter. The average temperature of water being conducted through such pipes is approximately Since the strength of most plastics material is reduced when subjected to increased temperature it is necessary to accommodate the effect of temperature variations upon the structure of the pipes which may occur in the pipeline when designing a pipeline system.

Furthermore the variation in temperature of the pipeline can result in considerable longitudinal expansion and contraction of the pipeline. For example pipes formed of polyethylene have a thermal expansion coefficient of 5 18 x 10 mm/m/'C. The resultant longitudinal expansion and contraction of the pipe as a result of fluctuations in temperature can result in mechanical damage to the IL pipeline.

In addition the elasticity of the plastics material which is subjected to repetitive expansion, contraction, heating and cooling, will reduce with age.

3 It is an object of this invention to provide a means for reducing the temperature variation in pipelines which are exposed to radiant heat sources such as solar radiation.

In one form the invention resides in an above ground fluid conduit comprising a pipe formed of a plastics material and a flexible sleeve formed of a membrane composed of a plastics material, said sleeve being loosely received over the pipe, said sleeve being coloured to be a substantial reflector of radiant heat, the plastics materials of which the pipe and sleeve are composed having the property of being electrical insulators whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

In another form the invention resides in a sleeve for an above ground plastics pipe said sleeve being formed of a flexible membrane, said membrane being composed of a plastics material, said sleeve being of a cross-section dimensioned to be loosely received over a length of above ground pipe, said sleeve being coloured to be a substantial reflector of radiant heat, said plastics material having a property of being an electrical insulator whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

In another form the invention resides in a method of protecting an above ground pipe formed of a plastics material comprising applying over the pipe a flexible sleeve which is loosely received over the pipe, said flexible sleeve being formed of a membrane composed of a plastics material, said sleeve being coloured to be a substantial reflector of heat, the plastics materials of which the pipe and sleeve are formed being electrical S

__M

3a insulators whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

In another form the invention resides in a sleeve when applied over an above ground plastics pipe said sleeve being formed of a flexible membrane, said membrane being composed of a plastics material, said sleeve being of a cross-section dimensioned to be loosely received over a length of above ground pipe, said sleeve being coloured to be a substantial reflector of radiant heat, said plastics material having a property of being an electrical insulator whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

The invention will be more fully understood in the light of the following description of several specific embodiments.

4 The description is made with reference to the accompanying drawings of which:- Figure 1 is a schematic isometric view of the embodiment; Figure 2 is a graphical representation indicating the thermal effect of solar radiation on the wall of a pipe without the embodiment; and Figure 3 is a graphical representation indicating the thermal effect of solar radiation on the wall of a pipe with the embodiment.

The embodiments are directed to the protection of polyethylene pipe which may be formed of Medium Density Polyethylene (MDPE) or High Density Polyethylene (HDPE).

As stated above, the design characteristics of pipelines incorporating polyethylene pipes must take into consideration the temperature variations that can occur in the pipeline as a result of incident solar radiation and ambient temperature conditions. Such pipelines are often laid over the surface of the ground and are subjected to the ambient solar and temperature conditions. In addition such pipelines tend to increase in temperature at a faster rate than that of the surrounding ground principally because the pipe is generally black in colour.

As a result of the increase in temperature the strength of the pipeline can be significantly reduced. Generally the temperature limit for such pipe is below approximately Furthermore the repetitive expansion and contraction of the pipe during its life which results from the cyclic 5 heating and cooling of the pipe places design constraints upon the pipe due to the mechanical movement of the pipe which is generated by such expansion and contraction. In addition as a result of the repetitive expansion and contraction of the pipe the modulus of elasticity of the pipe will degenerate with age.

Therefore the pipeline which is formed of polyethylene pipes must be designed to have a wall thickness far in excess of that which is normally required in pipes when operating at normal temperatures to accommodate for the anticipated reduction in its resilience and elasticity when in use in an open environment.

The embodiment comprises sleeving the plastic pipe with a sleeve formed of a white plastics film. The film is also formed of polyethylene and is formulated to offer high resistance to the transmission of solar energy, to be reflective of solar radiation to reduce the effect of ultra violet radiation. The thickness of the film is such as to offer the best compromise between the resistance to tearing, product life, opacity, cost and the ease of installation. The film is flexible and has a diameter which is greater than that of the external diameter of the pipe. The sleeve is supplied in the form of a flat continuous ribbon which can then be opened up to provide a circular sleeve. Figure 1 provides a schematic illustration of the first embodiment which comprises a pipe 11 having a sleeve 12 of continuous cross-section applied over the pipe.

According to a second embodiment the sleeve can be constructed on site from a ribbon of material which is wrapped around the pipe and the sides of the ribbon are bonded together to create a sleeve which fully encloses the pipe.

6 According to a third embodiment when it is not possible or convenient to fully surround the pipe the edges of the ribbon can be bonded or fixed to the pipe at least at spaced intervals along the pipe to create a protective sleeve around the exposed or upper portion of the pipe.

Alternatively the sleeve can be formed with the pipe during extrusion of the pipe by extruding the sleeve over the pipe.

In use the pipeline is installed by laying lengths of pipe along the proposed pipe route and then butt welding the pipe lengths together. The pipe lengths may be provided with the sleeve installed over them. In such an instance when the lengths of pipe are butt welded the ends of the sleeve adjacent the ends of the pipe are pushed away from the abutting ends to allow for the butt welding process and on completion of that process the sleeve is extended over the length of the pipe.

Where the pipe is not provided with the sleeve, it can be installed on the pipe during the butt welding of lengths of pipe. When the lengths of the pipe are butt welded it is necessary that they be lifted up into position onto a portable butt welding machine and in such an instance the first sleeve is initially installed onto the first pipe after the pipe is lifted onto the butt welding machine prior to the butt welding of the second length. During the cooling phase of the butt welding procedure the sleeve is then slid along the pipeline over the butt weld to the next junction in the pipe until the cooling phase of the next butt weld. It is preferable to Lot join the ends of the sleeve together such that the interior of the space between the pipe and the sleeve is open to the atmosphere.

I.•

7 As a result of the similar nature of the plastics material of which the pipe and sleeve are produced an electrostatic charge is established between the opposed faces of the sleeve and the pipe which causes a repulsion force between such faces, such that the sleeve is forced out of engagement with the surface of the pipe. Such repulsion serves to effect separation between the pipe and the sleeve except in the region where the pipe is in engagement with the ground and the weight of the pipe overcomes such repulsive forces. It has been found in practice that sufficient electrostatic charge has been established between the sleeve and the pipe during the sliding of the sleeve onto the pipe to create sufficient repulsive forces to maintain the sleeve out of engagement with the pipe. Such electrostatic forces are maintained due to the electrical insulating properties of the plastics material of which the sleeve and pipe are composed. Furthermore additional electrostatic charges are created as a result of relative movements between the pipe and the sleeve which result from a differential expansion between the pipe and the sleeve and environmental conditions such as wind.

As a result of the repulsion of the sleeve away from the surface of the pipe a blanket of air is created between the pipe and the sleeve. This blanket of air serves to prevent the conduction of heat between the sleeve and the pipe. In addition the white colouring of the sleeve serves to reflect a significant proportion of the radiant heat and light which is incident on the sleeve thus reducing heat that is available for conduction between the sleeve and the pipe. Furthermore during conditions of incident solar radiation, the solar radiation which is absorbed by the sleeve causes heating of the air in the

",I

8 blanket between the sleeve and pipe whereby the hotter less dense air is located at the upper portion of the space between the sleeve and the pipe which then reduces the evolution of convectional currents in that space and the resultant transfer of heat between the sleeve and the pipe as a result of such convection currents.

By leaving the ends of the lengths of sleeve open however it has been found that this allows for the escape of hot air on the space between the pipe and the sleeve and the flow of cooler air into that space. Alternatively, the sleeves of each of the embodiments may be continuous for the length of the pipe and a plurality of openings are provided in the sleeve at spaced intervals along its length.

As a result of the reduction in heat transfer from the sleeve to the pipe and reduction in the amount of radiation absorbed by pipe by the presence of the sleeve the increase in temperature of the pipe is significantly reduced. Furthermore where the sleeve and pipe are in contact, an intimate contact between the two surfaces is prevented because of the inherent rough texture of the surfaces even though the roughness of the texture is microscopic.

Figures 2 and 3 illustrate the temperatures of the wall of the pipe of varying length in both the unshielded and shielded pipe.

The advantages provided by the embodiment over conventionally exposed polyethylene pipes include:the capacity to use a lower pipe classification for any particular task; 9 extended pipe life, since the lower the operating temperature of the pipe the longer will be the life of the pipe; increased reliability since the pipe will have an improved capacity to cope with pressure fluctuations; reduction in thermal expansion and contraction and thus mechanical movement of the pipe with respect to its supporting surface; improved resistance to buckling since the Youngs Modulus of the material is significantly increased if the pipe temperature is reduced; the increase in the Youngs Modulus will result in a reduction in the number of pipe supports required in overhead process applications; reduced heating of water passing through the pipeline which is critical for potable water pipelines; a redu6t.ion in the amount of plastics material required, for the manufacture of pipes due to the possibility of being able to use a thinner pipe; an increase in the inner diameter of the pipe with respect to the outer diameter which can result in a reduced pump energy loss due to friction; a reduction in butt welding time due to the use of a thinner pipe wall which can accelerate the installation time of a pipeline; 10 reduction in the delivery time and delivery costs of the pipeline due to the reduced weight of the pipeline; reduced mechanical movement of the pipeline as a result of an expansion and contraction.

In addition the installation of the sleeve to the pipeline can be effected during the butt welding process of the pipeline and thus it is not anticipated that the installation of the sleeve will significantly increase installation costs.

It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiment described above.

4a* Q

Claims

1. An above ground fluid conduit comprising a pipe formed of a plastics material and a flexible sleeve formed of a membrane composed of a plastics material, said sleeve being loosely received over the pipe, said sleeve being coloured to be a substantial reflector of radiant heat, the plastics materials of which the pipe and sleeve are composed having the property of being electrical insulators whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

2. A fluid conduit as claimed at claim 1 wherein the sleeve has a continuous cross-section.

3. A fluid conduit as claimed at claim 1 wherein the sleeve is formed from a spirally wound ribbon with the adjacent edges being bonded together.

4. A fluid conduit as claimed at Claim 1 wherein the sleeve is formed of a ribbon extending along the conduit and the side edges of the ribbon are bonded to the pipe at least at spaced intervals along the length of the pipe.

A fluid conduit as claimed at any one of the preceding claims wherein the sleeve comprises several lengths applied over the pipe in end to end relationship and whereas said ends are not sealed.

6. A fluid conduit as claimed at any one of claims 1, 2, 3 or 4 wherein apertures are provided in the sleeve at locations along its length.

7. A fluid conduit substantially as herein described.

8. A sleeve for an above ground plastics pipe said sleeve being formed of a flexible membrane, said membrane being I 12 composed of a plastics material, said sleeve being of a cross- section dimensioned to be loosely received over a length of above ground pipe, said sleeve being coloured to be a substantial reflector of radiant heat, said plastics material having a property of being an electrical insulator whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

9. A sleeve as claimed at claim 8 wherein apertures are provided in the sleeve at locations along its length.

A sleeve substantially as herein described.

11. A method of protecting an above ground pipe formed of a plastics material comprising applying over the pipe a flexible sleeve which is loosely received over the pipe, said flexible sleeve being formed of a membrane composed of a plastics material, said sleeve being coloured to be a substantial reflector of heat, the plastics materials of which the pipe and sleeve are formed being electrical insulators whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween.

12. A method of protecting a pipe substantially as herein described.

13. A sleeve when applied over an above ground plastics pipe said sleeve being formed of a flexible membrane, said membrane being composed of a plastics material, said sleeve being of a cross-section dimensioned to be loosely received over a length of above ground pipe, said sleeve being coloured to be a substantial reflector of radiant heat, said plastics material having a property of being an electrical insulator whereby an electrostatic charge is capable of being established between the sleeve and the pipe to generate repulsive forces therebetween. 13

14. A sleeve when applied over an above ground plastics pipe substantially as herein described with reference to the accompanying drawings. DATED this TWENTY EIGHTH day of JANUARY 1993 VINIDEX TUBEMAKERS PTY LIMITED Applicant WRAY ASSOCIATES Perth, Western Australia Patent Attorneys for the Applicant t