GB2377979A

GB2377979A - Improved pipe

Info

Publication number: GB2377979A
Application number: GB0118039A
Authority: GB
Inventors: John Alexandre Boudry
Original assignee: Petrotechnik Ltd
Current assignee: Petrotechnik Ltd
Priority date: 2001-07-24
Filing date: 2001-07-24
Publication date: 2003-01-29
Anticipated expiration: 2021-07-24
Also published as: GB0118039D0; WO2003010458A1; GB2377979B

Abstract

There is disclosed a pipe 10 constructed of plastics material and comprising an inner supply pipe 12 having an outer secondary pipe 13 tightly fitting over but not bonded to its outer surface; the construction characterised in that the inner surface of the secondary pipe contains one or more grooves 14, 15, 16, 17 running along the length of the pipe 10.

Description

Improved Pipe Field of the Invention The present invention relates to secondary containment systems and especially, although not exclusively, to a piping construction and a method for providing a secondary containment system for conveying organic fluids such as petroleum products. Such piping construction may be used to convey petrol/diesel from a reservoir to a dispensing pump at a filling station. The invention also relates to a system for dispensing petrol/diesel.

Background to the Invention The use of dual containment piping systems in which an inner supply pipe is coaxially placed within an outer secondary containment pipe is known and accepted commercial practice. Typically, such systems are found in the nuclear, oil and gas, petroleum refining and chemical processing industries. The supply pipe is used to transport hazardous or toxic fluid while the secondary containment pipe is used to contain leakage from the supply pipe should it occur. It is also known to provide leakage detectors and drainage systems within the annulus between the carrier and containment pipes.

In the design of petroleum forecourt installations, it is regarded as increasingly important to contain and detect any leaks of petrol or diesel fuel from subterranean pipes which connect one or more storage tanks to dispensing pumps in the installation. To that end, many current designs of forecourt installation utilise secondary containment. This involves containing each fuel supply pipeline in a respective secondary containment pipeline which is optionally sealed at its ends to the fuel supply pipeline. The secondary containment pipeline prevents leaks from

the fuel supply pipeline from being discharged into the environment, and also can convey leaked petrol to a remote-sensing device. Typically, the pipes forming the secondary containment pipeline are initially separate from the fuel pipes and are sleeved over the latter as the fuel pipes are installed between the fuel storage tanks and dispensing pumps.

Today there is great public concern because chemicals are penetrating into underground water supplies contaminating public drinking water and making some of the food supply unusable, amongst other things. The entire environment is being downgraded to a serious level which tends to cast doubt on the future availability of safe water. Therefore, many government agencies around the world have enacted and continue to enact laws which require a secondary containment system designed to capture and contain any spilled gasoline or other liquid materials thus preventing it from leaking into the surrounding earth. The captured gasoline or other liquid materials may then be pumped out of the secondary container for proper disposal. This eliminates the possibility of gasoline spillage contaminating underground water supply.

Manufacturers of containment systems have responded by developing and producing a variety of secondary containment systems for conventional underground piping which are designed to contain and prevent any leakage from escaping into the environment. Many of these systems have proven to be effective containment systems but have been found to be difficult and costly to manufacture and install.

One known approach is described in W093/20372 (Advanced Polymer Technology Inc.). This document describes a secondary containment piping system comprising

an inner supply pipe and a flexible outer secondary containment pipe having a plurality of radially inwardly projecting flanges adapted to engage the outer surface of the inner supply pipe to provide a locking engagement of the pipes with respect to each other and to provide for a flow passage between. The inner supply pipe IS a loose fit within the outer pipe and the two pipes are generally manufactured separately then inserted one within the other. The outer pipe is sized to permit the inner pipe to be inserted or removed with little or no resistance. It follows, therefore, that the secondary pipe contributes little or nothing to the strength or bursting pressure of the inner supply pipe. Furthermore, joining a pipe of this type in an endto-end fashion requires a double coupling, one outside the other, and this is bulky.

Similar features have been adopted in US5343738 (Furon Company) and W09512779. These systems have in common a ribbed structure formed on the inner surface of the secondary pipe or the outer surface of the supply pipe. This ribbed structure increases the overall diameter of the pipe and either weakens or makes no positive contribution to the overall strength of the combined piping system.

A different approach has been taken by PetroTechnik Limited in W099/26007. This describes inter alia, a foamed region between the inner supply pipe and the outer protective layer of the secondary pipe. This foam layer can contain passageways to conduct any leaked fluid to the end of the pipe. This system offers several advantages in that it is compact and strong but the manufacture of such a pipe is not straightforward and generally results in a cost premium over conventional coextrusion techniques.

Accordingly, it is an object of the present invention to provide a secondary containment system which overcomes or mitigates some or all of the above disadvantages.

Summary of the Invention According to the present invention there is provided a flexible piping system for conveying a fluid, said piping system being constructed from plastics materials and comprising :- (i) an inner supply pipe having an inner surface and an outer surface: (ii) an outer secondary pipe having an inner surface and an outer surface, the inner surface of the secondary pipe being a tight fit over but not bonded to the outer surface of the inner supply pipe ; characterised in that the inner surface of the secondary pipe contains one or more grooves running substantially the length of the pipe.

This construction has the advantage that the pipe system is strong yet flexible whilst occupying a smaller volume than known types of secondary contained pipes. The fact that the secondary pipe is in intimate, tight contact with the primary pipe adds greatly to the strength of the piping system.

Preferably said groove (s) extend substantially along the longitudinal axis of the pipe. This form of construction, where the grooves run in substantially straight lines along the pipe incurs minimum production cost and equipment.

In an alternative embodiment the groove (s) spiral helically around the pipe.

Preferably 3 and more preferably 4 grooves are formed in the inner surface of the outer secondary pipe.

Preferably said piping system further comprising an inner barrier layer which lines the internal surface of the inner supply pipe.

Preferably the profile of the bottom of said groove is formed in the shape of an arc of a circle to avoid angular indentations in the inner surface of the outer secondary pipe.

Preferably the inner barrier layer may comprise a plastics material selected from the group comprising :Nylon 612 Polyamides Polyamides 6, 11 or 12 Polyethylene terphthalate Polyvinyl chloride Polyvinylidene chloride or fluonde Polypropylene Ethylene/vinyl alcohol copolymers the selection being based on the nature of the fluid being conveyed.

Preferably the inner pipe layer and the outer protective pipe layer may comprise a plastics material selected from the group comprising :Polyethylene Polypropylene Polyvinyl chloride

According to a second aspect of the present invention there is provided a petroleum forecourt installation comprising a fuel storage tank connected to a dispensing pump through one or more pipes, said pipes being constructed according to a piping system made from plastics material and comprising :- (i) an inner supply pipe having an inner surface and an enter surface: (ii) an outer secondary pipe having an inner surface and an outer surface, the inner surface of the secondary pipe being tightly fitted over but not bounded to the outer surface of the inner supply pipe; characterised in that the inner surface of the secondary pipe contains one or more grooves running substantially the length of the pipe.

Brief Description of the Drawinos The present invention will now be described, by way of example only, with reference to the accompanying drawings wherein :Figure 1 shows a cross-sectional view of a pipe according to the present invention; Figure 2 shows a piece of pipe of the type shown in figure 1 being formed ; Figure 3 shows a section of pipe with a section of pipe coupling in place ; Figure 4 shows a diagrammatic cut-away view of part of a petroleum forecourt installation which includes a pipeline formed from a series of pipes.

Description of the Preferred Embodiments Embodiments of the present invention will now be described by way of example only. They are currently the best ways known to the applicant of putting the invention into practice but they are not the only ways in which this can be achieved. Figure 1 illustrates a cross-sectional view of a pipe 10 consisting of an inner barrier layer 11, an inner supply pipe 12 and an outer secondary pipe 13. The inner barrier layer 11, which is optional, comprises a cylindrical skin or coating of nylon or a nylon

derivative which is supported on the inner surface of the inner supply pipe 12. The supply pipe is typically constructed form polyethylene having a modulus in the range 100 to 4,000 MPa. Alternative construction materials are discussed below. The skin or coating 11 lines the central passage of the pipe 10 through which petrol/diesel is to be conveyed. The layer 11 is constructed from material which is substantially impervious to petrol and thus presents a barrier to the diffusion of petrol through the inner supply pipe. It is advantageous to have an inner barrier layer because a polyethylene pipe, although showing some resistance towards the diffusion of petrol, does exhibit some permeability thereto.

The inner supply pipe 12 is of conventional construction and takes the form of a regular thick-walled pipe of substantially uniform cross-section.

In prior art pipes there is usually a discreet air gap between the outer surface of the primary, inner supply pipe and the inner surface of the outer secondary pipe. As can be seen from figure 1, in this embodiment, there is no appreciable air gap. Any gap shown in Figure 1 is purely for illustrative purposes only, to show that pipes 12 and 13 are separate entities and not bonded together. Rather the outer pipe fits tightly and snugly over the outside of the inner supply pipe. In this example the two pipes are not stuck or welded together for a number of reasons. Firstly, the pipe would be much more rigid if the inner pipe and the secondary pipe were stuck together. Improved flexibility, rather rigidity, is a preferred feature because the complete pipe has to pass around tightly radiused bends during installation and replacement.

Secondly, the almost imperceptible gap between the two layers is permeable to fluid and forms an interstitial space between the two pipes to enable monitoring and

testing to take place. This interstitial space is infinitesimally thin and difficult to measure. Nonetheless it is fluid permeable.

This interstitial space is supplemented by one or more grooves 14,15, 16,17 or channels formed in the inner-surface of the outer secondary pipe. These grooves or channels run the length of the pipe. They may be substantially straight, following the longitudinal axis of the pipe, or they may be spiral, helicoidal or otherwise curvilinear.

The number, shape and configuration of these grooves is variable within certain limits. One groove around the circumference may be sufficient but more normally three or four grooves are formed, spaced equally around the inner circumference of the secondary pipe. A groove with a gently radiused profile, as shown in figure 1, is preferred since this limits any weakness in the secondary pipe which results from the presence of grooves.

It will be appreciated that with the exception of the grooved region (s), the inner surface of the secondary pipe follows substantially exactly the contour of the inner supply pipe. The two pipes are thus as one, and as such, this arrangement could be considered unitary construction.

A pipe as shown in figure 1 can be formed using convention extrusion techniques. The inner supply pipe is formed around an inner barrier layer, if required. An adhesive is typically used to bond the barrier layer to the inside of the inner supply pipe. Once the inner supply pipe has cooled below the temperature at which adhesion would occur, the secondary pipe is extruded over the outer surface of the inner supply pipe. This is illustrated diagrammatically in Figure 2. At time"o"the

inner and outer pipes are still separate and after time"t", when the inner pipe has cooled sufficiently the secondary pipe is formed tightly around it. Deliberately, no adhesive is applied between the two outer layers but may be applied between the inner barrier layer and the inner supply pipe as described above.

It will be appreciated that this form of construction has inherent strength and flexibility. As a result, the thickness of the two outer pipe layers maybe considerably less than in a conventional pipe.

The relative thicknesses of the various layers can vary according to particular application. The example given below is for the case where petroleum products are to be conveyed by the pipe. In this case, the preferred inner barrier material must have very low permeability to petroleum spirit and the various chemicals found in petrol and diesel fuels. Nylon 612 is one of the preferred materials. However, other materials can be used and these include polyamides, polyamides 6,11 or 12, polyethylene terphthalate, polyvinyl chloride, polyvinylidene chloride or fluoride, polypropylene, ethylene/vinyl alcohol copolymers, or mixtures thereof, the selection being based on the nature of the fluid being conveyed.

This selection is not intended to be limiting but rather demonstrates the flexibility and breadth of the invention. The plastics material with the lowest permeability to the fluid in question will usually be chosen by the materials specialist. Furthermore, it is known to use blends of two or more polymers and this invention extends to cover known and yet to be developed blends of plastics material.

Preferably the outer protective layer comprises a plastics material selected from the group comprising :-

Polyethylene Polypropylene Polyvinyl chloride or variations and combinations of plastics material specified for the inner barrier layer.

In a particularly preferred embodiment the inner layer comprises Nylon 612 or polyvinylidene fluoride and the outer layer comprises linear low density polyethylene. The choice would be made on the basis of the permeability through the polymer of the material to be conveyed.

The relative proportions and thicknesses of the two layers are important to the performance of the pipe. For petroleum based products, permeability should preferably be zero. However, as all plastics are permeable to a degree, a suitable commercially applicable range is 0. 2-4g/m2/day.

In the example where a pipe of 110mm diameter is intended for petroleum applications, then the thickness of the wall of the supply pipe is typically in the order of 7mm. Of this the inner nylon layer can be from 0.01 mm to 6.99mm. Conversely, the outer polyethylene layer could be of a thickness of 0.01 to 6.99mm.

Pipe according to the present invention can be used to carry a wide variety of fluids, which term includes both gases and liquids.

Referring to Figure 4, the pipes shown in F 1 is one of a plurality of identical pipes which form a pipeline 20 connecting a subterranean fuel storage tank 21 to dispensers 22 and 23 which include suction pumps (not shown). The pipeline 20 is

inclined so that the end adjacent to the dispensers 22 and 23 is higher than the end adjacent to the tank 21. The pipes are contiguously arrange and, where necessary, maybe joined together by a process of electro-fusion jointing which provides leakproof joints between adjacent pipes. However, joints other than at a manhole or in chambers are to be avoided. At the upstream end of the pipeline 20, at or near the lowest point, in a manhole chamber 24 above the tank 21, there is provided a leak detection sensor 25 which is situated downstream of a suction line 26 which extend into the tank 21 to allow the pumps 22 and 23 to draw fuel from the tank 21 and along the pipeline 20.

Figure 2 also depicts a pressure line 27 which forms part of an alternative form of fuel supply system. That system is known as a pressure system and uses a pump 28 at the top of the line 27 to supply fuel along the pipeline 20. In a pressure system the pump such as the pump 28 replaces the suction pumps in the dispensers 22 and 23.

In the example the detector comprises a reservoir (not shown) which communicates with the interstitial layer of the pipeline 20 and contains a float level switch (not shown).

The pipeline 20 can be fitted with an alternative form of leak detection system, for example one which pumps an inert gas such nitrogen through the interstitial layer of the pipeline 20, so as to displace petroleum vapour from any leaks to a suitable gas detector at the end of the pipeline 20.

The present invention extends to include a petroleum forecourt installation comprising a fuel storage tank connected to one or more dispensing pumps through

one or more pipes constructed according to the invention as described above and as defined by claim 1 and its dependent claims.

A typical pipe connector 30 is shown in figure 3, in this case in the form of a flange connector. The outer secondary pipe 13 has been cut back to expose a length of the inner pipe, such that an electro fusion weld joint can be formed around the inner supply pipe. A similar joint is formed around the outer secondary pipe in region 31.

In the intermediate region 32 the inner part of the connector is chamfered to form a cavity 33 extending around the circumference of the pipe. This connects the whole of the interstitial space, including any grooves, at the end of the secondary containment region.

The connector comprises two substantially coaxial sleeves 34 and 35 joined by an intermediate region 36. The annular sleeves are a tight sliding fit with the respective pipe portions and contain electrofusion heating wires and terminal connectors (not shown). A salable test port 40 of a type well known in the field is provided in the intermediate region (36) to connect with the interstitial region 33 formed once the joint is complete. Other forms of connector can be similarly constructed.

Claims

CLAIMS 1. A flexible piping system for conveying a fluid, said piping system being constructed from plastics materials and comprising :- (i) an inner supply pipe having an inner surface and an outer surface: (ii) an outer secondary pipe having an inner surface and an outer surface, the inner surface of the secondary pipe being a tight fit over but not bonded to the outer surface of the inner supply pipe; characterised in that the inner surface of the secondary pipe contains one or more grooves running substantially the length of the pipe.
2. A flexible piping system as claimed in Claim 1 wherein said groove (s) extend substantially along the longitudinal axis of the pipe.
3. A flexible piping system as claimed in Claim 1 wherein the groove (s) spiral helically around the pipe.
4. A flexible piping system as claimed in any preceding claim wherein 3 grooves are formed in the inner surface of the outer secondary pipe.
5. A flexible piping system as claimed in any of Claims 1 to 3 inclusive wherein 4 grooves are formed in the inner surface of the outer secondary pipe.
6. A flexible piping system as claimed in any preceding claim, said piping system further comprising an inner barrier layer which lines the internal surface of the inner supply pipe.

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7. A flexible piping system as claimed in any preceding claim wherein the profile of the bottom of said groove is formed in the shape of an arc of a circle to avoid angular indentations in the inner surface of the outer secondary pipe.
8. A flexible piping system as claimed in any preceding claim wherein the inner barrier layer may comprise a plastics material selected from the group comprising :Nylon 612 Polyamides Polyamides 6, 11 or 12 Polyethylene terphthalate Polyvinyl chloride Polyvinylidene chloride or fluoride Polypropylene Ethylene/vinyl alcohol copolymers the selection being based on the nature of the fluid being conveyed.
9. A flexible piping system as claimed in any preceding claim wherein the inner pipe layer and the outer protective pipe layer may comprise a plastics material selected from the group comprising :Polyethylene Polypropylene Polyvinyl chloride
10. A flexible piping system substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.

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11. A petroleum forecourt installation comprising a fuel storage tank connected to a dispensing pump through one or more pipes, said pipes being constructed according to a piping system made from plastics material and comprising :- (i) an inner supply pipe having an inner surface and an enter surface : (ii) an outer secondary pipe having an inner surface and an outer surface, the inner surface of the secondary pipe being tightly fitted over but not bounded to the outer surface of the inner supply pipe; characterised in that the inner surface of the secondary pipe contains one or more grooves running substantially the length of the pipe.