GB2306609A - Jetting resistant pipe - Google Patents

Abstract

A thin-walled plastics-based sewer pipe offers resistance to puncturing during jetting procedures. The pipe is of PVC or olefin of maximum thickness 8 mm, or of ABS of maximum thickness 6 mm. A variety of materials including UPVC, UPVC modified with ABS or MBS, highly filled UPVC, extremely highly filled UPVC, foamed UPVC, ABS and polyolefins. The extremely highly filled UPVC comprises filler to a level as high as 200 phr or even greater. Coarse grained fillers having an average particle size of 100-200m are also disclosed for use. The pipe structures all have the advantage of providing strength and durability in combination with relatively thin walls. Consequently the pipe can be manufactured economically and efficiently in a single line extrusion process.

Description

JETTING RESISTANT PIPE The present invention relates to a pipe which can be cleaned by jetting without detrimental effect. More particularly, the invention relates to such a pipe for use in a sewage network.

In recent years, water jetting has become increasingly employed as a means of both clearing blockages and cleaning pipes in sewage systems. This has been brought about by real technological improvements in water jetting equipment and high pressure pumps.

A large diversity of high pressure jetting equipment is presently in use. Pumps with delivery pressures of up to 30,000 psi are known to be in use. Although there is a large variation in the equipment in use, most contractors will use the pressures they have available and different types of blockage will require different pressures to clear them.

In the United Kingdom, research has shown that: i) The average starting pressure for jetting operation is 2,350 psi; ii) The most commonly used pressures are between 4,000 and 5,000 psi; iii) 30% of operators frequently exceed these pressures.

The maximum pressures used for clearing different types of blockage are detailed below.

TABLE 1 Pressure Under 3000 to Over (psi) 3000 7500 7500 Tree roots 25% 61% 14% Solids 6% 39% 55% Silt 40% 56% 4% Sewage 29% 69% 2% General 34% 66% 0% Grease 14% 75% 11% Total 25% 61% 14% From this it can be concluded that: a) Pressures of up to 3,000 psi clear only 25% of all kinds of blockage; b) Pressures of 3,000 psi or more are needed to clear the majority of all types of blockage; c) 95% of all sewer blockages (excluding solids) are cleared by pressures of up to 7,500 psi.

The above-discussed jetting pressures do not represent a serious problem when used in conjunction with traditional clayware sewage networks. However, in recent years there has been a significant move towards the use of plastics pipes. Conventional plastics pipes do not cope with such jetting pressures at all well and it is not uncommon for the jets simply to penetrate the pipe walls. Such leaks are obviously highly undesirable as effluent can leak into the surrounding area causing contamination.

Most commonly used pipes can be made tolerant to the demands of water jetting by increasing the wall thickness. Table 2 shows the minimum wall thicknesses required to provide a jetting time (period of time before failure occurs due to jetting pressure) of greater than 5 minutes for different typical pipe materials.The jetting specification is as follows: Pump delivery pressure: 7,500 psi (517 bar) Orifice flow rate: 3 gals/min (0.23 I/s) Orifice shape: straight Orifice length: 3 x diameter of Imm Stand-off distance: 20mm Jet angle: 450 Ambient temp: 1 40C+20 TABLE 2 Material Class Minimum Wall Thickness, mm UPVC 9-10 MDPE 10-11 PP 10-11 NYLON 8-9 HDPE 10-11 (UPVC FOAMED CORE 8-10) ABS 7-8 (ABS FOAMED CORE 6-7) Pipe products made with such high wall thicknesses are economically unattractive, particularly at smaller diameters. Attempts have been made to overcome this problem by providing pipes having structured walls.In one known example, the pipe wall thickness is relatively thin, but the pipe wall is provided with radially outwardly projecting annular flanges at regular axial intervals. In an alternative arrangement, the pipe wall is corrugated. This requires the provision of a liner so as to remove interruptions to the flow. It has been found that each of these pipes is unsuccessful because the jetting water merely penetrates the pipe wall between the flanges in the case of the former and at the radially narrower sections in the case of the latter.

The present invention sets out to provide a tough, robust and economical sewer pipe which is resistant to typical jetting operating practices, which can be efficiently manufactured in a single in-line extrusion process and which does not require any secondary process stage, and which can show acceptable levels of stiffness and resistance to impact damage. Naturally, the pipe structure must be capable of satisfying all other demands of the sewer industry.

According to the present invention there is provided a pipe for the conveyance of sewage comprising a wall formed from PVC and having a thickness of 8mm or less.

Preferably, the wall thickness is 5mm or greater.

The PVC may be UPVC. The UPVC may be highly filled. The level of filler may be 30 phr or greater. The term "phr" is used throughout this specification and means parts per hundred of resin" The associated value is the number of parts of filler that are added to 100 parts of the basic polymer.

The pipe wall may comprise a plurality of coaxial layers. One or more of the layers may be formed from UPVC. The UPVC may be filled UPVC. The UPVC in one or more layers may have a level of filler of 1-20 phr.

The filler may be calcium carbonate, talc, barium sulphate, wood flour, or silica.

One or more of the layers may comprise modified PVC. The PVC may be modified by MBS to the level of 10-20 phr. The PVC may be modified by ABS to the level of 10-20 phr.

One or more of the layers may be formed from ABS.

One or more of the layers may be formed from impact-modified PVC.

The pipe wall may comprise three coaxial layers. The radially innermost layer may be formed from UPVC. The UPVC may be mixed with filler to the level of 1-20 phr.

The UPVC may be impact modified.

The radially intermediate layer may be formed from PVC modified with MBS or ABS to the level of 10-20 phr. The radially intermediate layer may be formed from ABS. The radially intermediate layer may be formed from PVC filled to the level of 30 phr or greater.

Preferably the PVC is filled to the level of 50 phr or greater. Even more preferably, the PVC is filled to the level of 100 phr or greater. Still more preferably, the level of filler is 150 phr or greater.

The filler may have an average particle size of 75 Am or greater. Preferably, the filler has an average particle size in the range of 100-200Clm. The range of particle size may be 0-5001lm.

The filler may have an average particle size of 2.0 > m or greater. Preferably, the average particle size will be 2.51lem. The range of particle size may be 0-1 5Rm.

The radially outermost layer may be formed from UPVC or impact-modified PVC.

The radially innermost layer may have a thickness of from 0.5mm to 5mm. The radially intermediate layer may have a thickness of from 0.5mm to 4mm. The radially outermost layer may have a thickness of 3.5mm or less.

The pipe may comprise a first tie layer between the radially inner layer and the radially intermediate layer and a second tie layer between the radially intermediate layer and the radially outer layer. In such a construction the tie layers ensure good bonding between a highly filled intermediate layer and the inner and outer layers.

Consequently the pipe has a high impact strength, good resistance to erosion and is robust for handling and rigidity.

The tie layers may contain one or more of the following: resin, viscosity modifier, flow modifier and temperature modifier.

The radially inner layer have a thickness in the range of 0.5 to 2.5mm; the radially inner tie layer may have a thickness in the range of 0.5 to 2.Smm; the intermediate layer may have a thickness in the range of 0.5 to 3.5mm; the radially outer tie layer may have a thickness in the range of 0.5 to 2.5mm; the radially outermost layer may have a thickness in the range of 0.5 to 2.5mm.

Preferably, the radially innermost layer has a thickness in the range of 0.5 to 1.5mm; the radially inner tie layer has a thickness in the range of 0.5 to 2.5mm; the intermediate layer has a thickness in the range of 0.5 to 2.5mm; the radially outer tie layer has a thickness in the range of 0.5 to 1.Omm; and the radially outermost layer has a thickness in the range of 0.5 to 1.5mm.

Preferably, the minimum overall thickness of the pipe is 2.5 to 5.5mum.

The filler may be calcium carbonate, talc, barium sulphate, wood flour, or silica.

The intermediate layer may comprise UPVC foam. The foam density may be 0.5 g/cc or greater. Preferably the foam density will be 1.2 g/cc or less. The foam may have a pore size in the range of 100-500CLm. In such a case, the radially innermost layer may have a thickness of from 0.5 to 2.5mm; the radially intermediate layer may have a thickness of from 2.5 to 4.5mm; and the radially outermost layer may have a thickness of from 1 to 4.0mm. Preferably the layer thicknesses are 0.5 to 1 .5mm, 3 to 4mm; and 1.25 to 2.25mm respectively.

The pipe may comprise an additional two layers between the radially intermediate layer and the radially outermost layer. The radially inner additional layer may have the same composition as the said radially outermost layer. The radially outer additional layer may have the same composition as the radially intermediate layer.

The radially innermost layer may have a thickness in the range of 0.5 to 2.0mm; the radially intermediate layer may have a thickness in the range of 0.5 to 3.0mm; the radially inner additional layer may have a thickness in the range of 0.5 to 2.0mm; the radially outer additional layer may have a thickness in the range of 0.5 to 3.0mm and the radially outermost layer may have a thickness in the range of 0.5 to 2.0mm.

Preferably, the layer thicknesses are 0.5 to 1.5mm, 2 to 3mm, 0.5 to 1.5mm, 2 to 3mm and 0.5 to 1.5mm respectively.

These and other preferred features of this aspect of the invention are set out in claims 2 to 64.

According to a second aspect of the invention, there is provided a pipe for the conveyance of sewage comprising a wall formed from ABS and having a thickness of 6mm or less.

Preferably, the pipe wall has a thickness of 4mm or greater.

The wall may comprise a plurality of layers. The wall may comprise three layers which may include a radially innermost layer having a thickness in the range of 0.5 to 1.5mm; a radially intermediate layer having a thickness in the range of 1 to 3.5mm; and a radially outermost layer having a thickness in the range of 0.5 to 3.5mm. The wall may comprise 5 layers. Each layer may have a thickness in the range of 0.5 to 1.Smm.

One or more of the layers may be foamed. The foam may have a density of 0.3 g/cc or greater. Preferably the density is 0.9 g/cc or less. Preferably the foam has a pore size in the range of 100 to 500cm.

One or more of the layers may comprise a filler. The filler may be calcium carbonate, talc, barium sulphate, wood flour, or silica. The level of filler may be 20 phr or greater.

These and other preferred features of this aspect of the invention are set out in Claims 66 to 78.

According to a third aspect of the invention there is provided a pipe for the conveyance of sewage comprising a wall formed from polyolefin and having a thickness of 8mm or less. Preferably the wall has a thickness of 3mm or greater.

The pipe wall may comprise a plurality of layers. One or more of the layers may comprise a filler. The filler may be included to the level of 20 phr or greater. The filler may be chalk, talc, wood flour, glass spheres, or glass fibre.

One or more of the layers may be foamed.

The wall may comprise three, four or five layers.

Each layer may have a thickness in the range of 0.5 to 2.5mm.

These and other preferred features of this aspect of the invention are set out in Claims 80 to 87.

According to the present invention there is also provided a pipe for the conveyance of sewage, comprising a radially inner layer for resistance to erosion and to penetration by an incident jet of fluid; a radially intermediate layer for absorbing energy of a jet of fluid incident on the radially inner layer and a radially outer layer for supporting the intermediate layer and preventing failure due to yield under transmitted stresses resulting from a jet of fluid incident on the radially inner layer.

Preferably, any of the above described pipes according to the present invention will be able to resist ajetting pressure of at least 7,500 psi for at least 5 minutes. This will preferably be at an orifice flow rate of 0.2 elms. Preferably the stand-off distance will be 20mm or less. Preferably the jet angle will be 45" Preferably the ambient temperature will be in the range of 12"C to 16"C. Preferably, the orifice length will be 3 times the orifice diameter. The nozzle orifice shape will preferably be straight.

A more complete appreciation of the invention and its attendant advantages will be readily obtained by reference to the following detailed description, which is given by way of example only.

Due to the nature of the invention, appropriate materials and types of materials for use therein and appropriate physical parameters therefor will be discussed along with preferred physical configurations thereof. Specific examples will be described and discussed, as appropriate, for better understanding.

ASPECT 1 According to a first aspect of the invention, the pipe structure is based upon UPVC materials in combination with others that are mutually compatible.

The pipe wall is made from highly filled PVC (greater than 30 phr), having a minimum wall thickness of 5-8mm. The particles of filler have an average size of 2.Sum.

It is common within the rigid PVC industry to incorporate fine particles of low cost filler for a range of reasons. These include cost reduction, processing enhancement, opacity increase and density increase. The most commonly used fillers are various chemical and particle distribution forms of calcium carbonate and typically are incorporated in pressure pipe at 1-2 phr, window profiles at 4-6 phr, and non pressure products at 4-25 phr.

In the present case, the level of filler is significantly higher. It has been found that levels of filler of 30 phr greatly enhance jetting resistance. In terms of mechanisms, the filler particles are not chemically bound to the PVC and provide a multitude of fissures, micro-cracks and hard particles through which the jetting energy is absorbed.

Calcium carbonate is preferably used as the filler for economic reasons. However, other fillers are technically feasible - such as talc, barium sulphate, wood flour, and silica. The level of filler will still preferably be in the range 30-100 phr.

Example 1 A pipe incorporated calcium carbonate filler at a level of 50 phr. Ajetting time of over 20 minutes was achieved for a wall thickness of 6.5mm.

The inclusion of filler materials increases the tendency to long term creep in the material. Thus the use of highly filled materials will be dependent upon the severity of the product application and any local market demands.

As stated, highly filled PVC can be used as an individual material in the production of jet-resistant pipe. this class of material can also be used in some of the structures described later in this specification.

ASPECT 2 According to a second aspect of the invention, pipe is formed from a combination of compact materials based on PVC and materials which are compatible with PVC. In this case, combinations of solid material produce jet-resistant properties which are greater than those of the equivalent thickness of the individual materials.

In a first configuration, the pipe comprises three layers. Each layer plays a different and specific role most suited to the particular properties of the layer. The structure operates as follows.

The inner layer has good resistance to the initial jet penetration and provides good protection against long term erosion of the sewer in service. The inner layer is also tough and provides an adequate level of impact strength and contributes greatly to the overall stiffness of the structure.

The central layer absorbs the bulk of the energy from the jet. Several alternative material types may be used, each having a different mechanism of energy absorption.

Such mechanisms include: ductile tearing (with high toughness materials); multisurface generation and jet dispersion (with foamed or filled materials); and multicrack generation (with other high toughness materials as ABS). Nevertheless, whichever mechanism is operative, the overall contribution of the central layer is the same, i.e. jet energy absorption.

The outer layer supports the middle layer and prevents failure by the material yielding under the transmitted stresses from the water jet. The outer layer also makes a large contribution to the overall pipe stiffness and the impact resistance.

The inner layer is preferably formed from UPVC. As is common practice with this material, the material formulation may be extended to incorporate limited amounts of filler for cost reduction (1-20 phr is typical) or to incorporate limited amounts of modifier either to improve the impact strength or the heat resistance of the product.

Other materials providing the requisite above-described characteristics may, of course, be used.

The middle layer is preferably formulated from one of the following materials: a) PVC modified with highly effective modifiers which enhance the toughness as measured in a notch charpy test. Typical of such modifiers are MBS or ABS based PVC copolymers.

The tough materials may be specified and characterised by properties as shown in the following table.

TABLE 3 Formulation Yield Strength, Mpa Impact Strength, Gc, kgIm2 UPVC 40-50 2 ABS modifier 10-20 phr 3540 40-60 b) Highly filled PVC such as described above in relation to the first aspect of the invention, for example.

c) A tough material, which could be extruded in parallel with and is compatible with UPVC, such as ABS.

Of course, any other suitable material exhibiting the desired properties set out above could be used.

The outer layer is required to provide support to prevent premature punching through to the outer surface by ductile tearing. Thus, the outer layer is composed of a material which has an adequate thickness to resist yielding under the transmitted forces of the water jet.

Suitable materials for the outer layer are UPVC and UPVC containing relatively low amounts of impact modifier - such as CPE or acrylic based modifiers. Typical properties of such materials can be: Formulation Yield Strength, Mpa Impact Strength, Gc, kg/m2 UPVC 40-50 2 Impact Modified PVC 38-43 4-6 The minimum overall thickness of the triple layer pipe in accordance with this aspect of the invention is 6 to 8 mm. The thicknesses of the individual layers may be selected from the following ranges: Inner Layer: 2-5mm Middle Layer: 1-4mm Outer Layer: 0-3mm.

Example 2 A three-layered pipe has the following structure: Layer Material Thickness Inner Layer Modified PVC 3.6mm Middle layer Highly Modified PVC 2.6mm Outer Layer Modified PVC 1.1 mm The overall thickness is 7.3mm and the jet-resistant time is greater than 10 minutes. Further configurations of the second aspect of the invention include more than three layers in the pipe wall. With these structures an even more efficiently jet-resistant structure can be developed by increasing the number of separate layers in a given thickness section.For example, it has been found that by building structures of alternate layers of strong and jet-resistant materials over five layers, the resultant five layer material is more jet-resistant by a time factor of five than the same thickness of any of the individual layer materials at the standard test conditions specified above.

The addition of a central layer acts as a barrier to jet penetration, but at a location where the jet energy has already been drastically reduced. Thus, using solid materials, the overall minimum thickness of the wall will can be in the range of 47mm with typical thicknesses of the individual layers being in the range 0.5-2mm.

In the five layer construction, the inner layer may be formed from a similar material to the inner layer of the three layer pipe. The second and fourth layers from the inside of the pipe may be formed from a similar material to the middle layer of the three layer pipe. The third and fifth layers from the inside of the pipe may be formed from a similar material to the outer layer of the three layer construction.

Alternative embodiments include four layer configurations.

Further embodiments of the second aspect of the invention are formed from combinations of solid and foamed materials which are based on UPVC and materials which are compatible with UPVC.

By combining solid and foamed materials, it is possible to develop structures which, per unit of linear thickness, are more jet-resistant than single solid thicknesses or those of the foam core structures of the same thickness.

As with the above-described solid wall structures, two basic configurations will be described: A three layered configuration and 5-layered configuration. Other configurations may be employed.

In one three layered configuration, the inner layer consists of a material similar to those of the inner layer of the above-described three layer solid pipes.

The middle layer can consist of UPVC foam. The foam material will typically be UPVC together with those additives necessary for processing an adequate foam core structure. Such additives are widely known and used in the industry. The foam density may be 0.5 g/cc or greater and preferably 1 .2g/cc or less, with a typical pore size in the range of 100-500um.

The three layer foam/solid configuration operates in a similar way to the solid three layer form described above. However, the relative dimensions of the three layers differ with this configuration. The overall minimum thickness is in the range of 58mm, with the individual thicknesses as follows: Inner Layer 0.5-2.5mm Middle Layer 2.5-4.0mm Outer Layer 1.0-4.0mm.

Such configurations, as well as demonstrating enhanced jet resistant properties, also posses superior impact strength properties compared to the equivalent thickness of conventional foam core pipe.

Typical drop weight properties as measured by the impact test of British Standard 5481 and on 1 60mm outside-diameter pipe are compared below: Conventional Foam Core Jet Resistant Structure < 2kg from 2m 2-5kg from 2m (Conducted at 20C).

Example 3 By way of illustration one typical example of this pipe configuration is formed as follows.

Inner Layer 0.6mm Middle Layer 2.4mm Outer Layer 3.9mm.

This structure was found to withstand a jetting time exceeding 20 minutes and had an impact strength of greater than 4.5kg at 2m.

As with the above described compact solid layered pipe, structures using foam and solid layers are more jet resistant as the number of layers increases. Again as with the solid configuration, the material selection will follow the same pattern.

The overall thickness is in the range of 5-8mm, with the individual layers having thicknesses as follows: Inner Layer 0.5-2.0mm Second Layer 0.5-3.0mm Third Layer 0.5-2.0mm Fourth Layer 0.5-3.0mm Fifth Layer 0.5-2.0mm.

Example 4 By way of illustration, the properties of a particular configuration are as follows: Inner Layer 0.6mm Second Layer 2.4m Third Layer 1.3mm Fourth Layer 2.4mm Fifth Layer 0.7mm.

The jetting resistance time for this configuration was found to exceed 20 minutes.

The impact resistance is classified by a level of 3kg from 2m at 20C.

ASPECT 3 The structures of the pipe according to this aspect of the invention have some similarity to those of Aspect 2. The structures according to this aspect of the invention have multiple layers. At least one energy absorbing layer is formed from UPVC to which extremely high levels of filler have been added. The fillers may be conventional (fine) fillers having an average particle size of the order of 2.5 > m.

Alternatively, the fillers may be coarse, that is to say the average particle size may be considerably larger at greater than 75 m, or preferably 100 or 200clam, for example. The level of filler employed in the energy absorbing layer is preferably at least 30 phr, but better results are achieved at 50, 100 or even 200 phr.

It is not conventional with rigid UPVC to use such high level fillers or particles of such large sizes, as the surface finish will not be sufficiently smooth and the mechanical properties (impact and tensile strength) would be very poor. It is not conventional to use such high levels of fine fillers, as PVC and filler are difficult to process (both in terms of moving around a plant as a dry blend and in extrusion where the surface area to volume ratio becomes extremely high with a fine filler).

However, with high levels of coarse filler, lower K-value polymers than those typically associated with the extrusion of rigid PVC can be used. The high volume content of filler will increase the viscosity of the melt, and lower molecular weight resins have been found to offer advantages in processing.

Because the filler particles can be coarse, the formulation of this material is an ideal application for reclaimed/reprocessed PVC materials, as small levels of contaminant will not detrimentally affect the properties of the bulk materials.

To provide a pipe which takes advantage of the jetting properties of the highly filled material, but still provides good mechanical properties, the highly filled material is, in a preferred embodiment of this aspect of the invention, employed in a three-layer construction with either UPVC type materials or UPVC compatible materials, such as ABS. The inner and outer layers can be UPVC or UPVC combined with impact modifiers, as described above in relation to the second aspect of the invention. These materials may contain conventional amounts of conventional fillers as also described in relation to the second aspect of the invention.

Preferred embodiments of the invention are as follows: 1. Radially inner layer 0.5-3.5mm 2. Middle layer 0.5-3.5mm 3. Radially outer layer 0.5-3.5mm.

It has been found that particularly good results are achieved with three-layered constructions having layer thicknesses as follows: 1. Radially inner layer 0.5-1.5mm 2. Middle layer 1.5-3.0mm 3. Radially outer layer 0.5-1.Smm.

It has been found that the best results are achieved where the minimum overall thickness of the pipe wall is in the range 3.5-5.5mm.

Either the inner or the outer layer could be omitted, however this would lead to a reduction in performance.

Example 5 A pipe having a UPVC inner and outer layers and a middle layer formed from UPVC comprising 200 phr of chalk filler was formed. The filler had an average particle size of 100clam. The radially inner and outer layers each had a thickness of 1.5mm. The middle layers had a thickness of 2mm.

This structure was found to withstand a jetting time exceeding 5 minutes.

Further embodiments of this aspect of the invention include two additional layers.

Each of these layers is situated between the middle, highly filled layer and a respective one of the inner and outer layers. These additional layers are tie layers and ensure good mechanical contact between the highly filled material and the inner and outer layers. The inner and outer layers are formed from UPVC or UPVC compatible materials. These provide adequate impact strength, resistance to erosion, robustness for handling and product rigidity, as with previous embodiments.

When L'PVC is employed, the inner and outer layers are preferably formed using K65-K68 resins and appropriate additives, to ensure that the desired properties are achieved The formulation of the tie layers is adapted to be compatible with both the middle and the inner and outer layers. However, generally the formulation contains blends of resins, viscosity modifiers. flow modifiers and temperature modifiers, so as to ensure compatibility in terms of processing and bonding between all the layers.

The tie layers typically will be formed from materials having the following composition: Stabilizer/process lubricant: 2-5phr; Process aid: 1-6 phr; Pigment: 0.2-0.4 phr; Filler: 1-10 phr.

Embodiments of the invention incorporating such tie layers have been found to yield good results when given the following structure: Innermost layer 0. 5-2. 5mm Inner tie layer 0.5-2.Smm Middle layer 0. 5-3 . 5mm Outer tie layer 0.5-2.Smm Outermost layer 0.5-2.5mm.

Preferably, the structure is as follows: Innermost layer 0,5-l.Smm Inner tie layer 0.5-1.0mm Middle layer 0.5-2.5mm Outer tie layer 0.5-1.0mm Outermost layer 0.5-1.5mm.

Preferably, the minimum thickness for this construction is 3.5mm to 5.5mm.

Example 6 A pipe was formed which comprised the following structure: Inner layer 1.5mm Inner tie layer lmm Middle layer 2mm Outer tie layer 1 mum Outer layer 1.5mm.

The radially inner and radially outer layers were made from UPVC. The tie layers were formed from UPVC K-50 resin: 100 phr; stabilizer/process lubricant: 3 phr; process aid: 3 phr; process aid: 3 phr, pigment 0.3 phr; filler: 5 phr. The middle layer included filler to the level of 150 phr. The filler had an average particle size of 100 m.

It was found that this pipe construction resisted jetting at the above-described specification for a period in excess of 5 minutes.

Further embodiments of the invention that accord with this aspect of the invention include a five-layer construction similar to that employed in the second aspect of the invention. In this regard, the second and fourth layers from the centre of the pipe are formed from UPVC with a very high level of filler, such as the middle layer of the above-described three-layer structure.

It has been found that the best results are achieved where the pipe structure is as follows: Inner layer 0.5-2.5mm Second layer 0.6-2.5mm Third layer 0.5-2.Smm Fourth layer 0.6-2.5mm Fifth layer 0.5-2.Smm.

Preferably, the pipe structure is as follows: Inner layer 0.5-1.Omm Second layer 0.6-1.5mm Third layer 0.5-1.5mm Fourth layer 0.6-1.5mm Fifth layer 0.5-1.Omm.

Preferably, the minimum thickness for this construction is 3.5 to 5.5mm.

Example A pipe was formed which comprised the following structure: Inner layer lmm Second layer 1.3mm Third layer lmm Fourth layer 1.3mm Fifth layer lmm The inner, third and fifth layers are all formed from UPVC. The second and fourth layers are formed from UPVC with 200phr of filler. The average particle size was 1 00cm.

It was found that the pipe resisted a jet at the above specifications for a period exceeding five minutes.

Tables 4 to 6 below show jetting times for a 2. imam layer of UPVC comprising filler, such as might be used in a jet-energy absorbing layer in this aspect of the invention.

It can be seen that, for coarse fillers (Tables 5, 6) a significant effect can be seen at a filler level of 100phr. Excellent results are achieved at > lSOphr. For a more conventional, fine filler (Table 4) the results are less dramatic at lower filler levels.

However, very good results are still achieved at > 150phr.

TABLE 4 Filler Level, phr Time, secs 20 4 50 16 100 25 150 40 200 427 250 800 Average particle size 2.5 m Particle size range 0-15 m Below 2 m 40% TABLE 5 Filler Level, phr Time, secs 20 4 50 17 100 47 150 223 200 303 250 > 990 Average particle size 200Am Particle size range 0-500pm Below 75Am 7% TABLE 6 Filler Level, phr Time, secs 20 4 50 17 100 49 150 316 200 361 250 > 1200 Average particle size 100,um Particle size range 0400calm Below 75pm 70% UPVC such as is conventionally used in sewer pipes gives ajetting time of about 3 seconds at the same thickness and under the some conditions.

ASPECT 4 The structures according to this aspect of the invention are formed from materials which are not PVC based. As with the second aspect, multi-layered configurations are employed. These can be classified in two main groups.

The first group comprises multilayered foam/solid structures based on ABS instead of UPVC.

The structures operate via the same mechanisms as the above described UPVC structures. However, the overall dimensions differ as follows.

The minimum overall thickness of the three layer structure is in the range of 4-6mm with the thicknesses of the individual layers as follows; Inner Layer 0.5-1.5mm Middle Layer 1.0-3.5mm Outer Layer 1.5-3.5mm.

The foam density is in the range of 0.5-0.9g/cc and has a typical pore size in the range of 100-50011m.

One advantage of the ABS configurations is that jetting properties are available over a wider range of operating temperatures - both at the upper and lower limits. The ABS configurations also give higher levels of impact resistance.

Hybrid structures exist between the UPVC and ABS structures. For instance, each layer is interchangeable with the alternative material, to enhance particular properties rather than every attribute.

The minimum overall thickness of the five layer multilayered ABS structure is in the range of 4-6mm, with the thicknesses of each of the individual layers being in the range of 0.5- 1.5mm .

Again hybrid structures are possible, typically UPVC and ABS being interchangeable and compatible.

The second group of configuration comprise walls made from highly filled polyolefins.

The jetting resistance of polyolefins can be greatly increased by incorporating particulate and/or fibrous fillers.

This group of materials can be used in the same general way as the previous materials, either as single materials or preferably in multi-layer structures. The layers can be solid or foamed.

Typical examples include PP, as follows.

Example 8 The pipe wall was formed from PP with 65 phr of chalk and a wall thickness of 4mm.

The jetting resistance under the above described standard conditions is 21 minutes.

Example 9 The pipe wall was formed from PP with 25 phr of glass fibre and a wall thickness of 4mm. The jetting resistance was found to be greater than 6.5 minutes.

The reasons for the use of multi-layer structures using olefins are similar to those of the other materials, but with a greater emphasis on contributions to the product stiffness coming from the inside and outside layers in this construction.

Either PP or PE or combinations of these base materials can be used. Typically MDPE or HDPE and PP homo or co-polymer grades of material can be employed.

A wide range of fillers can also be combined with the olefin materials. Typically, the fillers will include chalk, talc, wood flour, glass spheres, fibres of glass, synthetic or naturally occurring materials.

The minimum thicknesses of the three and five layer structures are 3.5mm, with the dimensions of the individual layers being 0.5 to 2.5mm.

As described above, pipe designs for sewer applications are designed to give a combination of properties. Essentially, the design must provide an internal smooth layer, together with adequate impact strength and stiffness properties. There are a range of international standards and local market needs that are satisfied by changes in the overall dimensions of the wall thicknesses. The thicknesses described above are the minimum thickness of a single layer to meet the required jetting specification.

If this thickness does not provide adequately for other product properties for the local market needs, then the thickness would need to be increased or combined with another structure. For instance, the materials specified above could be combined in twin-wall corrugated sections to enhance the stiffness/weight ratio. In such structures, the internal layer could be the jetting resistant material, with the corrugated outer layer being formed from more conventional materials. This configuration is applicable to all the material classes, but in particular is very suitable for the polyolefin based materials. In such configurations, the inner layer would be of sufficient thickness to meet the jetting specification, with the corrugated layer contributing mostly to the product stiffness.

Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practised otherwise than as specifically described or exemplified herein.

Claims (88)

1. A pipe for the conveyance of sewage comprising a wall formed from PVC and having a thickness of 8 mm or less.

2. A pipe according to Claim 1, wherein the said wall comprises a plurality of coaxial layers.

3. A pipe according to Claim 1 or 2, wherein at least one layer is formed from UPVC.

4. A pipe according to Claim 3, wherein at least one layer formed from UPVC comprises a filler to a level in the range of 1-20 phr.

5. A pipe according to Claim 3 or 4, wherein at least one layer formed from UPVC comprises a filler to the level of 30 phr or greater.

6. A pipe according to Claim 5, wherein said at least one layer comprises a filler to the level of 50 phr or greater.

7. A pipe according to Claim 6, wherein said at least one layer comprises a filler to the level of 100 phr or greater.

8. A pipe according to Claim 7, wherein said at least one layer comprises a filler to the level of 150 phr or greater.

9. A pipe according to any one of Claims 5 to 8, wherein the filler has an average particle size of 75,um or greater.

10. A pipe according to Claim 7, wherein the filler has an average particle size in the range of 100zm to 200calm.

11. A pipe according to Claim 9, or 10, wherein the filler has a particle size range ofO - 500cm.

12. A pipe according to any one of Claims 4 to 11, wherein the filler comprises calcium carbonate, talc, barium sulphanate, wood flour or silica.

13. A pipe according to Claim 1, wherein the wall of the pipe comprises modified PVC.

14. A pipe according to Claim 2, or any claim dependent on Claim 2, wherein the wall of the pipe comprises at least one layer comprising modified PVC.

15. A pipe according to Claim 13 or 14, wherein the said modified PVC layer comprises PVC modified by MBS or ABS to the level of 10 - 20 phr.

16. A pipe according to Claim 2 or any claim dependent thereon, wherein the wall of the pipe comprises at least one layer formed from ABS.

17. A pipe according to Claim 1, wherein the wall of the pipe comprises impactmodified PVC.

18. A pipe according to Claim 2, or any claim dependent on Claim 2, wherein the wall at least one layer formed from impact-modified PVC.

19. A pipe according to Claim 1, wherein the wall comprises UPVC foam.

20. A pipe according to Claim 2, or any claim dependent thereon, wherein the wall comprises a layer formed from UPVC foam.

21. A pipe according to Claim 19 or 20, wherein the foam has a density of 0.3g/cc or greater.

22. A pipe according to Claim 21, wherein the foam has a density of 1.2g/cc or less.

23. A pipe according to any one of Claims 19 to 22, wherein the foam has an average pore size in the range of 100 to 500rim.

24. A pipe according to Claim 2, or any claim dependent thereon, wherein the pipe wall comprises a radially inner layer, a radially intermediate layer and a radially outer layer.

25. A pipe according to Claim 24, wherein the radially inner layer is formed from UPVC.

26. A pipe according to Claim 25, wherein the radially inner layer comprises filler to the level of 1-20 phr.

27. A pipe according to Claim 25, wherein the UPVC is impact modified.

28. A pipe according to any of Claims 24 to 27, wherein the radially intermediate layer is formed from UPVC modified with MBS or ABS to a level of 10-20 phr.

29. A pipe according to any of Claims 24 to 27, wherein the radially intermediate layer is formed from ABS.

30. A pipe according to any one of Claims 24 to 27, wherein the intermediate layer is formed from UPVC foam.

31. A pipe according to Claim 30, wherein the foam density is 0.3g/cc or greater.

32. A pipe according to Claim 31, wherein the foam density is 1.2g/cc or less.

33. A pipe according to any one of Claims 30 to 32, wherein the foam has an average pore size in the range of 100-500pm.

34. A pipe according to any one of Claims 30 to 33, wherein the radially inner layer has a thickness in the range of 0.5 to 2.5mm; the intermediate layer has a thickness in the range of 2.5 to 4.5mm and the radially outer layer has a thickness in the range of 1 to 4mm.

35. A pipe according to Claim 34, wherein the radially inner layer has a thickness in the range of 0.5 to 1.5mm; the intermediate layer has a thickness in the range of 3 to 4mm and the radially outer layer has a thickness in the range of 1.25 to 2.25mm.

36. A pipe according to any one of Claims 24 to 29, wherein the radially inner layer has a thickness in the range of 2 to 5mm; the radially intermediate layer has a thickness in the range of 1 to 4mm and the radially outer layer has a thickness of 3mm or less.

37. A pipe according to Claim 36, wherein the radially inner layer has a thickness in the range of 3 to 4mm; the radially intermediate layer has a thickness in the range of 2 to 3mm; and the radially outer layer has a thickness in the range of 0.5 to 1.5mm.

38. A pipe according to one of Claims 24 to 27, wherein the radially intermediate layer is formed from PVC comprising a filler to the level of 30 phr or greater.

39. A pipe according to Claim 38, wherein the radially intermediate layer comprises a filler to the level of 50 phr or greater.

40. A pipe according to Claim 39, wherein the radially intermediate layer comprises a filler to the level of 100 phr or greater.

41. A pipe according to Claim 40, wherein the radially intermediate layer comprises filler to the level of 150 phr or greater.

42. A pipe according to any one of Claims 38 to 41, wherein the filler has an average particle size of 75m or greater.

43. A pipe according to Claim 42, wherein the filler has an average particle size of 100 to 200cm.

44. A pipe according to Claim 42 or 43, wherein the filler has a particle size range of 0 to 5001lem.

45. A pipe according to any one of Claims 38 to 41, wherein the filler has an average particle size of 2pm or greater.

46. A pipe according to Claim 45, wherein the filler has an average particle size of 2.51lem.

47. A pipe according to Claim 46, wherein the particle size range of the filler is 0 to 151lem.

48. A pipe according to any one of Claims 38 to 47, wherein the radially inner layer has a thickness in the range of 0.5 to 3.5mm; the intermediate layer has a thickness in the range of 0.5 to 3.5mm; and the radially outermost layer has a thickness in the range of 0.5 to 3.5mm.

49. A pipe according to Claim 48, wherein the radially intermediate layer has a thickness in the range of 0.5 to 1.5mm; the radially intermediate layer has a thickness in the range of 1.5 to 3.0mm; and the radially outer layer has a thickness in the range of 0.5 to 1.Smm.

50. A pipe according to any one of Claims 38 to 48, further comprising an inner tie layer, situated between the radially inner layer and the intermediate layer, and an outer tie layer, situated between the intermediate layer and the radially outer layer.

51. A pipe according to Claim 50, wherein the tie layers comprise one or more of a resin, a viscosity modifier, a flow modifier and a temperature modifier.

52. A pipe according to Claim 50 or 51, wherein the inner layer has a thickness in the range of 0.5 to 2.5mm; the inner tie layer has a thickness in the range of 0.5 to 2.5mum, the intermediate layer has a thickness in the range of 0.5 to 3.5mm; the outer tie layer has a thickness in the range of 0.5 to 2.5mm and the outer layer has a thickness in the range of 0.5 to 2.5mm.

53. A pipe according to Claim 52, wherein the inner layer has a thickness in the range of 0.5 to 1.5mm; the inner tie layer has a thickness in the range of 0.5 to 1.0mum; the intermediate layer has a thickness in the range of 0.5 to 2.5mm; the outer tie layer has a thickness in the range of 0.5 to 1.Omm; and the outer layer has a thickness in the range of 0.5 to 1.5mm.

54. A pipe according to any one of Claims 38 to 48, further comprising a radially inner additional layer and a radially outer additional layer; the said additional layers being situated between the said intermediate layer and the said outer layer.

55. A pipe according to Claim 54, wherein the composition of the radially inner additional layer corresponds to that of the radially outer layer and the composition of the radially outer additional layer corresponds to that of the radially intermediate layer.

56. A pipe according to Claim 54 or 55, wherein the inner layer has a thickness in the range of 0.5 to 2.5mm; the intermediate layer has a thickness in the range of 0.6 to 2.5mm; the radially inner additional layer has a thickness in the range of 0.5 to 2.5mm; the radially outer additional layer has a thickness in the range of 0.6 to 2.5mm; and the radially outer layer has a thickness in the range of 0.5 to 2.5mm.

57. A pipe according to Claim 56, wherein the inner layer has a thickness in the range of 0.5 to 1.0mum; the inner layer has a thickness in the range of 0.6 to 1.5mum; the radially inner additional layer has a thickness in the range of 0.5 to 1.5mm; the radially outer additional layer has a thickness in the range of 0.6 to 1;smm and the radially outer layer has a thickness in the range of 0.5 to 1.5mum.

58. A pipe according to any one of Claims 24 to 33 further comprising a radially inner additional layer and a radially outer additional layer; the said additional layers being situated between the said intermediate layer and'the said outer layer.

59. A pipe according to Claim 58, wherein the composition of the radially inner additional layer corresponds to that of the radially outer layer and the composition of the radially outer additional layer corresponds to that of the radially intermediate layer.

60. A pipe according to Claim 58 or 59, wherein the radially inner layer has a thickness in the range of 0.5 to 2.0mm; the radially intermediate layer has a thickness in the range of 0.5 to 3.0mm; the radially inner additional layer has a thickness in the range of 0.5 to 2.0mm; the radially outer additional layer has a thickness in the range of 0.5 to 3.0mm and the radially outer layer has a thickness in the range of 0.5 to 2.0mm.

61. A pipe according to Claim 60, wherein the radially inner layer has a thickness in the range of 0.5 to 1.5mm; the radially intermediate layer has a thickness in the range of 2 to 3.0mm; the radially inner additional layer has a thickness in the range of 0.5 to 1 .Smm; the radially outer additional layer has a thickness in the range of 2 to 3.0mm and the radially outer layer has a thickness in the range of 0.5 to 1.5mm.

62. A pipe according to any preceding Claim, wherein the wall of the pipe has a thickness of 5mm or greater.

63. A pipe according to Claim 24, or any claim dependent thereon, wherein the outer layer is formed from UPVC or impact-modified UPVC.

64. A pipe according to Claim 24 or any Claim dependent thereon, wherein the radially inner layer is for providing resistance to erosion and to penetration by an incident fluid jet; the radially intermediate layer is for absorbing energy of a jet of fluid incident on the radially inner layer and the radially outer layer is for supporting the intermediate layer and preventing failure due to yield under transmitted stresses resulting from a jet of fluid incident on the radially inner layer.

65. A pipe for the conveyance of sewage comprising a wall formed from ABS and having a thickness of 6mm or less.

66. A pipe according to Claim 66, wherein the pipe wall has a thickness of 4mm or greater.

67. A pipe according to Claim 65 or 66, comprising a plurality of coaxial wall layers.

68. A pipe according to Claim 67, comprising a radially inner layer, a radially intermediate layer, and a radially outer layer.

69. A pipe according to Claim 68, wherein the radially inner layer has a thickness in the range of 0.5 to 1.5mum; the radially intermediate layer has a thickness in the range of 1 to 3.5mm; and the radially outer layer has a thickness in the range of 0.5 to 3.5mm.

70. A pipe according to Claim 68, comprising five coaxial wall layers.

71. A pipe according to Claim 70, wherein each said wall layer has a thickness in the range of 0.5 to 1.5mm.

72. A pipe according to any one of Claims 65 to 71, wherein at least one wall layer is foamed.

73. A pipe according to Claim 72, wherein the foam has a density of 0.3g/cc or greater.

74. A pipe according to Claim 73, wherein the density of the foam is 0.9g/cc or less.

75. A pipe according to any one of Claims 72 to 74, wherein the foam has a pore size in the range of 100 to 500vim.

76. A pipe according to any one of Claims 65 to 76, wherein at least one wall layer comprises a filler.

77. A pipe according to Claim 76, wherein the level of filler is 20 phr or greater.

78. A pipe according to Claim 77, wherein the filler comprises at least one of calcium carbonate, talc, barium sulphate, wood flour or silica.

79. A pipe for the conveyance of sewage comprising a wall formed from polyolefin and having a thickness of 8mm or less.

80. A pipe according to Claim 79, wherein the wall of the pipe has a thickness of 3mm or greater.

81. A pipe according to Claim 80, wherein the pipe wall is formed from a plurality of coaxial layers.

82. A pipe according to Claim 81, wherein the wall is formed from three, four or five layers.

83. A pipe according to Claim 82, wherein each layer has a thickness in the range of 0.5 to 2.5mum.

84. A pipe according to any one of Claims 79 to 83, wherein one of the layers is foamed.

85. A pipe according to any one of Claims 79 to 84, wherein one or more of the layers comprises a filler.

86. A pipe according to Claim 85, wherein the level of filler is 20 phr or greater.

87. A pipe according to Claim 86, wherein the filler comprises at least one of chalk, talc, wood flour, glass spheres or glass fibre.

88. A pipe substantially as hereinbefore described with reference to any one of the examples.