Drainage Services Department Specification For Gravity Sewer and Stormwater Drain Connections

Transcription

1 Drainage Services Department Specification For Gravity Sewer and Stormwater Drain Connections 1 Polyethylene Compounds 1.1 Polyethylene (PE) compounds used for the manufacture of PE pipe and fittings shall conform to BS EN Plastics piping systems for water supply, and for drainage and sewerage under pressure - Polyethylene (PE) 1.2 In addition to clause 1.1, PE compounds used for the manufacture of pipe shall meet the requirements of PE100-RC as defined in Clause 3.1 of PAS 1075: Pipes made from Polyethylene for alternative installation techniques. 1.3 Compounds shall be 100% virgin, pre-coloured compounds. All compounds used in pipe (including striping and co-extrusion colour compounds) shall have the same brand name and be the same base compound. No reprocessed, recycled or own reprocessed materials shall be used in the manufacture of any pipe or fittings; Clause 4.1 of BS EN shall not apply. 2 Polyethylene Pipes 2.1 PE pipes shall conform to BS EN : For pipes with a burial depth to the top of the pipe less than or equal to 4m, PE pipes with a Standard Dimension Ratio 1 (SDR) of 17 shall be used. If the burial depth is greater than 4m, PE pipes with lower SDR shall be used. In this case detailed design calculations shall be submitted to the Chief Engineer/Hong Kong & Islands, Chief Engineer/Mainland South or Chief Engineer/Mainland North for approval. Equivalent Size in nominal DN / ID PE (OD 3 ) Size PE pipes and fittings shall be black in colour and comply with the following additional requirements: Pipes shall have an internal co-extruded orange colour layer in accordance with BS EN Annex B. The internal colour shall be Orange with reference to BS 4800: 08 E 55 and thickness shall be 15% of the nominal pipe wall thickness 4 around the entire internal circumference, with a tolerance of +/-1.5%. No delamination shall occur during all tests of the co-extruded pipe. 1 Standard Dimension Ratio is the ratio of the pipe diameter to wall thickness (Pipe OD/SDR= min wall thickness). 2 Nominal DN / ID is the numerical designation of the size of a component, which is a convenient round number, approximately equal to the Internal manufacturing dimension in millimetres (mm). 3 OD is the outside diameter of the pipe. 4 Nominal pipe wall thickness is the numerical designation of the pipe wall thickness, which is a convenient round number, approximately equal to the manufacturing dimension in millimetres (mm).

2 2.3.2 It is preferred to have an external indication striping to identify gravity sewer and Stormwater drain. Striping compounds shall meet all the requirements of Section 1.1 and 1.3 of this specification and shall be pre compounded, Brown with reference to BS 4800: 06 C 39 for sewer and Green with reference to BS 4800: 12 D 45 for Stormwater drain There shall be six or more indication stripes equally spaced around the circumference, each stripe shall be between 6-24mm wide All pipes shall have permanent and legible marking complying with requirements specified in BS EN , Clause Polyethylene Fittings 3.1 PE Fittings, unless indicated otherwise in Sections 3.5 and 3.6 below, shall comply with BS EN :2011 and shall be manufactured from compounds complying with Section 1.1 and 1.3 of this specification. 3.2 All fittings shall have permanent and legible marking complying with requirements specified in BS EN , Clause Fabricated fitting welds shall be undertaken using butt fusion or side fusion following the principals of ISO Plastics pipes and fittings -- Butt fusion jointing procedures for polyethylene (PE) pipes and fittings used in the construction of gas and water distribution systems. Internal weld beads in all fabricated fittings shall be removed, leaving the surface smooth and uniform without marks, gouging or any reduction in the wall thickness resulting from the bead removal process. External weld beads shall not be removed. Extrusion welding or any form of hand or filler welding is not permitted to be used in the construction of any PE fittings. 3.4 Puddle Flanges shall be either moulded or machined from a single piece of PE. No welds or joints shall be permitted in the construction of the puddle flange. The OD of the restraint flange ring shall be at least 1.25 x OD of the connecting pipe. The width of the puddle flange ring shall be 1.25 x wall thickness of the connecting pipe. The puddle flange spigots shall match the connecting pipe s OD and SDR. The interface to the puddle flange ring shall be tapered at a length not less than 2 x puddle flange width. Puddle flange spigots shall match the connecting pipe s OD and SDR and spigot lengths shall be greater than or equal to L2 from BS EN Table Transition fittings that connect PE pipes to pipes of other materials by rubber ring joint shall comply with requirements and testing specified in Clause 10 of BS EN Plastics piping systems for non-pressure underground drainage and sewerage. Polyethylene (PE). Specifications for pipes, fittings and the system. Where the difference in the actual inside diameters between the two connecting pipes is greater than 5% of the pipe diameter, the transition shall be eccentric in design to maintain a level invert.

3 3.6 Manhole connectors Type A manhole connectors shall be made using two components; a PE ring for casting into the manhole and a matching push in PE spigot connecting to the PE pipe to provide a flexible connection. The flexible connection shall have two elastomeric sealing rings and a hydrophilic expansion ring, which shall comply with the requirements and testing specified in BS EN , clause 10. A typical detail is given in Appendix A Type B manhole connectors shall incorporate a puddle flange as specified in Section 3.4 above with the addition of a hydrophilic seal as indicated in Appendix A. 3.7 Electrofusion Couplers Electrofusion couplers shall comply with BS EN and have a SDR classification equal to, or less than the pipes that they are connecting to Fusion zone length L2 shall be a minimum of 1.5 x dimension L2 stated in BS EN : Table Electrofusion couplers 355 OD and above shall have an external reinforcement system either built in or supplied with each coupler and used to prevent the coupler from expanding during the fusion cycle. Such reinforcement shall be greater than the width of both fusion zones and the centre cold zone and shall be maintained in position throughout the welding & cooling process. 3.8 Bends may be used up to a maximum of 45º in gravity sewer and storm water drain, shall have a radius greater than or equal to 4x pipe OD and manufactured from pipe complying with Sections 1 and 2 above. Bends less than or equal to 500 OD shall be formed from pipe, bends greater than 500 OD may be fabricated with each compound angle no greater than 18º. Bends used for vertical drops may have a radius less than 4x pipe OD but shall include a rodding point. Pipe may be laid curved during installation using a radius greater than or equal to 27x pipe OD 4 Type & Batch Testing 4.1 Type & batch testing shall be carried out in accordance with CEN/TS Plastics piping systems for water supply, and for drainage and sewerage under pressure. Polyethylene (PE). Guidance for the assessment of conformity. Each test result shall be independently verified by a HOKLAS recognised independent authority 4.2 The initial type tests or subsequent process verification tests shall not be more than 36 months old. 4.3 Pipe batch test reports shall include all test results required in CEN/TS : 2014 Table 8 and in addition shall include; Geometrical characteristics provided for each pipe in the batch, these shall be linked to the compound certificate of analysis batch. Note b of table 8 shall also apply to the indication stripes. Note d of table 8 shall not apply, virgin materials shall be tested. Certificates of Analysis issued by the compound manufacturer for each compound used in each pipe batch shall be provided.

4 4.4 Fittings batch test reports shall include all test results required in CEN/TS : 2014 Table 9 and Table B.3. All test results shall then be submitted to the Chief Engineer/Hong Kong & Islands, Chief Engineer/Mainland South or Chief Engineer/Mainland North for record. 5 Employment of Qualified PE Pipe Layers 5.1 All connections or jointing of polyethylene pipe works must be carried out by qualified polyethylene pipe layers. 5.2 A qualified polyethylene pipe layer shall mean a worker who has successfully completed the courses Installation of Polyethylene Pipes or The Installation and Application of Polyethylene (PE) Pipes organized by the Hong Kong Institute of Vocational Education, or equivalent. 5.3 The records of the names and supporting documents of the qualified polyethylene pipe layers employed should be submitted to the Chief Engineer/Hong Kong & Islands, Chief Engineer/Mainland South or Chief Engineer/Mainland North for record.

5 REFERENCE DOCUMENT 1.O MATERIALS 1.1a What is a Polyethylene (PE) Compound? Compound is the PE material which all PE pipes & fittings are made from. It comes in a granule form and the granules are heated & compressed into a single shape by either extrusion into pipe or injection moulding into fittings. Compounds are pre coloured by the compound manufacturer, using identifying colours for different uses. (Red Brown / Fern Green for the Stripes, Orange CCTV for the inner layer, Black pipe body) Compounds include all the required anti-oxidants & stabilisers. BS EN clause defines a compound as: A homogenous extruded mixture of base polymer (PE) and additives, i.e. anti-oxidants, pigments, carbon black, UV stabilisers and others, at a dosage level necessary for the processing and use of components conforming to the requirements of this standard The quality and integrity of the compound is essential to the long-term performance of pipe and fittings. A compound means it has not been mixed or diluted with any other compounds or materials (refer to 1.3b below). Blending new & recycled PE together introduces different PE materials and potential contamination from the recycling process. Without testing there is no way to tell what has been mixed in (could be plastic bottles or bags for example) and while this significantly reduces the manufactures costs (up to a 60% reduction) it is diluting the performance of the virgin material that the owner is expecting to receive and is paying for. It is well proven that such dilution or mixing, (including the use of recycled materials) leads to premature pipe and fittings failures. HK has had several significant project failures as a result of such practices. 1.1b Why is BS EN12201, (pressure standard) being specified instead of BS EN for gravity pipes & fittings? DSD use both pressure and non-pressure pipes in the sewer system and therefore there are two relevant standards that could be used, BS EN for pressure systems and BS EN for gravity systems. However there are three reasons why only BS EN is being used for pipe & fitting applications; (refer sections 2.1 & 2.2) a. For gravity systems, DSD has specified SDR (Standard Dimension Ratio) 17 pipe which when manufactured from a PE100-RC compound with a E modulus of 1200Mpa the pipe will have a minimum SN (Nominal Stiffness) value of 24. This stiffness level is required to resist the expected external loads on pipe in HK applications. BS EN does not apply to pipes or fittings with an SDR less than 21, therefore it cannot be used to refer to SN values greater than SN8 so is not applicable for the pipe DSD are specifying in HK for gravity drainage. b. BS EN 12201:2011 cover PE pipes with SN ratings from SN 1 to SN 800, it also contains specific requirements for the control of material inputs, performance and materials testing not found in BS EN BS EN (-1) for raw materials, (-2) for pipes and (-3) for fittings covers both water & sewer. So referring to BS EN covers all PE pipe & fittings the DSD will use in HK for rising mains, gravity sewer and storm water systems. Harmonisation through the use of a single standard for DSD reduces any risk that gravity only BS EN fittings or pipe are mistakenly used in a pressure sewer system, potentially leading to a catastrophic failure.

6 c. BS EN standards are well proven in HK by WSD whom have specified BS EN since There is more than 1000km of PE pipe & fittings installed in HK under BS EN a What is PE 100-RC? PE 100-RC is the latest generation of high performance PE compounds. PE 100 indicates the strength of the material. PE 100 is a MRS (Minimum Required Strength) 10 material which means a PE100 compound in long term testing (extrapolated to 100 Years) has a minimum strength that does not fall below 10Mpa over time. RC indicates resistant to crack, which is explained in details below under slow crack growth. A PE 100 compound, which has been independently classified under ISO 9080 testing, will withstand up to 10Mpa hoop strength (the sum of constant internal pressure and / or applicable external loading forces) for the pipes whole operating life (>100 years). PE pipes have been on uninterrupted pressure test for more than 50 years at 20Deg C. The accelerated hot water testing used in classification testing (ISO 9080) matches the actual 50-year test results, So PE s long term performance claims of greater than 100 years are scientifically & independently proven. (As a comparison PE 80 is MRS 8 material). Important to note that this claim does not mean that PE pipes & fittings will not fail in less than 100 years, it means that a PE 100 has the strength to withstand it rated hoop stress from continuous loading for more than 100 years. However, the reason for a pipe failure may not be associated with hoop stress. Slow Crack Growth (SCG) is the typical medium to long-term failure mode of most plastic materials under such stress. This is where the plastic slowly tears itself apart due to the application of a constant excessive stress over months or years starting from an initiator or weak point in the pipe. PE is highly elastic; it has extremely good capacity to withstanding very high short-term (non constant) stress. As an example in a pressure situation, a PN 10 PE pipe can withstand a single instantaneous (short term) surge in pressure of up to 40Bar (4 x it s rated pressure) without failing. Generally speaking PE is unaffected by short term loads either external or internal such as a pressure spike or a short-term very heavy vehicle loading - even complete crushing as shown in the example below. PE being struck with force in Japan from a bucket tooth of an excavator, once removed the pipe reverts to its original state without damage and at operating pressure, the time to revert depends on internal pressure, but relatively quickly. This would be considered an instantaneous impact, as opposed to a constant stress. The pipe is undamaged and functions normally after such an impact. The gas industry uses a similar squeeze off technique to shut down PE gas pipes in emergencies. The typical failure mode for plastic pipes is almost always as a result of long-term constant stress that exceeds the design stress of the pipe. SCG failure can take several months or even years depending on a lot of factors most of them relating to the quality of the compound that the pipe is manufactured from and the type of constant stress the pipe is exposed to.

7 For example if pipes are made from a non-pipe grade compound (such as recycled PE plastic bottles), the pipe may easily pass a Hydrostatic test and function for weeks or months before failing in a brittle mode due to constant hydrostatic pressure in service (this was the case with 23/WSD/02 in Mong Kok). More often the failure is accelerated due to a point load applied by a rock constantly pressing on a pipe. Such impingement on a PE100-RC pipe made from Virgin compound would likely have no effect for the entire service life of the pipe. The most important focus in PE pipe systems is to ensure the quality of the compound used to make the pipe & fittings and that the compound has excellent crack resistant (SCG) properties - resistance to the tearing process. It s important to understand that not all PE s are alike; SCG resistance varies from very little in some PE materials compounds (like film grade PE) to more than 10,000 hours of accelerated testing at 80 Deg C in PE100-RC materials. Pipes made from poor quality, non-virgin or non pipe grade PE compounds can easily fail in just weeks or months after installation. SCG is the slow tearing of the plastic material over time as a result of constant stress being applied. This image shows a magnified view of the slow tearing of traditional PE100 materials as excessive stress is being constantly applied to the pipe over time. The tearing moves through the material at a very slow rate, the resistance to this tearing is the materials crack resistance RC materials are highly resistant to this failure mode. Meaning they can accommodate situations where the pipe is exposed to rocks pressing on the pipe surface and resist failure due to the material stopping initial cracks forming and propagating through the pipe wall. In this example, a traditional PE100 compound, with relatively low SCG performance (say 160 hours in accelerated testing) has failed in a brittle manner as a result of external rock point loading. This external load could be created from a rock pressing on the pipe, or damage combined with poor side wall support and the pipe deflecting. This situation creates stress on the pipe wall where the wall is stretched due to the load and this is where the crack starts (Crack initiator), slowly working it s way through the pipe wall until failure. This is a pressure pipe but the concept is the same for a non-pressure pipe where the same stresses can be created through rock impingement with external loads or lack of sidewall support leading to excessive stress. PE100-RC refers to Resistance to Crack the definition of an RC compound is contained in PAS 1075: the German Publically Available Standard. These compounds are used for alternative installation methods which means the pipes can be installed without sand bedding. Such pipes will be generally unaffected if damaged and the bedding materials around the pipe are lost due to secondary excavation at a later date. Unlike Concrete, Ductile Iron or Earthenware pipe, no typical flexible plastic pipes (PVC, GRP, PE, PP, ABS) should be installed without proper sand bedding around the pipe. Sand bedding and backfill prevent point loading created by rocks / sharp objects that apply a constant point loads to the pipe surface. In standard PE pipe materials (Non RC materials) a plastic pipe could fail (for example) in 10 years if it had a constant point load during service (ie: was not protected by sand bedding around the pipe).

8 In this example (image courtesy of Egeplast) two examples of PE pipe installation can be seen, the first with sand bedding, the second without. In HK it s almost impossible to achieve sand bedding due to site & trench width restrictions. RC compounds provide an alternative installation method to sand bedding. RC compounds have resistance to point loading approx. 10x traditional PE100 pipe grade materials. This resistance means the typical times to failure from point loadings increases from say 10 years to 100 years (in a typical example using PE100 vs. PE100-RC compound). While failure depends on the actual operating conditions (ground loading, external and internal pressures etc.) the performance benefits are significant, for no additional cost. In practical terms Hong Kong contractors are not accustomed to installing sand bedding around traditional pipe materials and generally speaking bedding is not required on Reinforced concrete pipe (RCP), Vitrified Clay Pipe (VCP) and Ductile Iron Pipes (DI) pipes. The use of PE100-RC materials limits the long-term risk of pipe failure where sand bedding surrounding the pipe cannot be installed and maintained around the pipe for the require pipe life. Irrespective of sand bedding being used, below ground services in cities like HK are always subject to secondary excavation where any bedding originally installed around the pipe is lost during excavation for other services at a later date and it is not replaced leaving Non PE100-RC plastic pipes exposed to failure. Photo above shows Secondary Excavation of a PE100 pipe installed beside a DI pipe. The excavation for a gas main has allowed the sand bedding material around the PE pipe to fall away into the new trench leaving the PE100 pipe unprotected. External Point loading (Rock Impingement) can be seen on the inside of the pipe in this example. For a traditional PE100 material, the time to failure in this situation will be relatively short. PE100 is not an RC material, therefore is at risk of future point loading when the excavation is backfilled by the gas contractor. This is an example (courtesy of Hessel) of what happens on the inside of a pipe with point loading tension is created on the inside surface of the pipe wall, first micro cracks form and over time the crack sizes increase, eventually propagating through the pipe wall, to the point of failure.

9 Testing a pipe sample selected from site for Slow Crack Growth performance; SCG can be easily tested from any pipe supplied to site by sending it to an approved lab. A small coupon is cut from the sample (as shown above) and tested to a correlated 3300 hour FNCT test, such as the ACT Test by Hessel in Germany. This test confirms if the material meets the requirements of PAS Results take ~10 days, the sample cut and then machined from pipe must not fail in less than 160 hours of accelerated testing which represents 3,300 hour of standard testing. 1.2b Why refer to a German Publically available standard and not a BE / EN / ISO standard? Until such time as the ISO body releases a standard for RC compounds, PAS 1075 is the only currently accepted standard used in the gas & water industry globally for this type of high crack resistant compound. An ISO committee has been formed in association with the major compound manufacturers to develop an ISO standard, however they all have to agree on the performance & testing parameters. The English translation is part of the PAS standard, starts on page 20. Growth testing are in addition to those required in BS EN The requirements in PAS 1075 for slow Crack

10 1.3a What is a 100% Virgin, pre-coloured compound 100% Virgin compound is described in BS EN clause as material in a form such as granules that has not been subjected to use or processing other than that required for its manufacture and to which no reprocessable or recyclable materials have been added This means the compound being used to make pipe or fittings is exactly as the compound manufacturer supplied, in its unaltered form. Pre coloured means the compound is supplied by the compound manufacture in the correct colour and is supplied with a Certificate of Analysis or batch certification, detailing the properties of the batch, the colour of the compound and the quantity supplied to the manufacturer. Above are images of Borouge HE 3492 LS pre compounded granules. It is possible to make a black, orange, brown or green compounds used in making PE pipes by master batching this is where the pipe or fittings manufacture buys natural (opaque) resin and they colour it themselves to save cost, this process is specifically banned in the BS EN standard, it leads to loss of control over quality and traceability of the compounds and is NOT recommended. WSD banned this practice in b Why must compounds that are combined (CCTV layer, brown & green stripes) have the same brand name? In this specification the Black pipe body, Orange inner CCTV layer and Brown/Green striping compounds are all pre coloured compounds and are combined in the die under heat & pressure as the pipe is made. This is called co-extruded pipe meaning the compounds are all extruded simultaneously. Correctly manufactured these three compounds form a single homogenous pipe, where the colours cannot be separated in any way. However, if the compounds are different brands from different manufacturers there is some risk that they may not combine together and form a single homogenous material. As different PE materials may not be completely compatible with each other, this may lead to a pipe failure. There is no practical reason for manufacturers to need to combine different materials and the practice must be avoided. Below is an image of a pipe extrusion line, the three compounds are combined into a single pipe inside the die head at 220Deg C and about 100 Bar pressure.

11 A typical line for 1000 OD pipe Below shows a cut away of the pipe die head, the three colours are combined under very high pressures & high temperatures to produce pipe. It s essential that these three compounds are clean and free of oils & dirt (found in some recycled materials) and of the same compound type or brand so they combine completely into a single homogenous pipe structure. Below are the typical data sheets for PE100-RC compounds for a drainage or pressure pipe all these share the same Borstar PE technology and their properties are listed. These are all the same base compound, they share the same brand name / Manufacturer, and use the same model number HE34XX, Borsafe HE3490 LS-H for black pipe body Borsafe HE3492 LS-H for Orange CCTV inner Borstar HE3497 LS for the brown stripe

12 These three compounds are extruded into a single homogenous pipe they cannot be separated in any way. However each manufacture of PE compounds uses different technologies to create their own PE, it is NOT like steel or ductile where the base material is the same. Each manufacturer s method of creating their own PE compounds varies according to their technology. Each method creates different PE chemistry (Rheology). Each manufacture may achieve the minimum performance requirements of PE 100-RC and it should be noted that they are usually compatible, however they may not always be. Therefore to avoid the risk in mixing different compounds where the colours could separate or be incompatible and could lead to a failure in the joints or pipe, the specification requires the use of a single brand of compound for the three coloured compounds in the pipe - the inner colour, main pipe and stripes. This avoids the risk of incompatibility in electrofusion. In this third example for a sewer pipe, the cream stripes were master batched by the pipe manufacture on the PE extrusion line using a different PE compound brand and adding in colour and a carrier base material. The cream stripes were not compatible with the base black compound pipe or the electrofusion couplers. In the end the pipe could not be welded on site by electrofusion because after welding the couplers failed in testing along the stripe path.

13 1.3 No Reprocessed or Recycled materials shall be used what are these materials? BS EN clause 4.3 specifically allows own recyclable materials to be used by the manufacturers in making pipes. However there are examples showing that if manufactures do not take care of the reject materials, they are not clean and they are re-mixed with other non-pipe grade materials, this simply dilutes the properties of the original virgin compound. Whilst PE pipe & fittings are 100% recyclable, it serves no benefit for a pipeline owner to allow the use of recycled materials in a 100 year asset, as it can significantly degrades the pipes performance for no cost benefit to the owner. The images below show the typical processes unethical manufactures can use to reduce their costs. They blend non-pipe grade materials with cheap recycled materials and colour it. Looking at the final pipe product, it s impossible to tell this has occurred however the pipe will fail relatively quickly depending on the stresses it is subjected to in service. Pipe made using this process does not meet the standard and could fail typically in 1 month or 6+ years depending entirely on what the manufacture used and the in ground conditions for the pipe.

14 2.0 PIPES 2.1 PE pipes shall conform to BS EN : For reference to why this standard is used refer to section 1.1b above SDR 17 pipe in the specification has a nominal stiffness SN24, the relationship between SN, SDR and the compound E-modulus can be found in Appendix D, Table D1 of BS EN For the main PE100-RC materials, the E modulus is typically given in the data sheets between values of Mpa. Using the formula provided in Appendix D a material with a Elastic (E) modulus of MPa gives an SN rating where SDR 17 = SN24 Appendix D refers to vacuum sewers, however the condition of a vacuum and external loading on a flexible pipe are both considered the same for the purposes of design calculations.

15 2.2 What is SDR?. PE pipes & fittings are often referred to by SDR Standard Dimensional Raito SDR s are cross-referenced to PN ratings for pressure pipes and to SN ratings for gravity applications in the standard. SN ratings are dependent on the Elastic Modulus properties of the particular compound the pipe is being made from. The PN rating is dependent on the MRS of the particular compound the pipe is made from. The SDR - PN relationship is in BS EN Annex A, the SDR SN relationship is BS EN Annex D Example: DN 300 is a 355 OD, SDR 17 pipe = 355mm/SDR17 = 20.9mm rounded up, plus 0.1 = 21.1 mm wall thickness SDR 17 pipes made from PE100 are all rated PN10 (maximum operating pressure PN10) - regardless of pipe size, however the SN is a stiffness rating that relates to each compound s Elastic Modulus properties. It is a reasonable assumption to say that all currently available PE100-RC materials complying to PAS 1075 have an E-modulus of 1100Mpa. This will provide an initial stiffness of SN24 based on mean wall thickness from the standard. OD Wall thickness SDR Standard Dimension Raito SDR = OD (mm) / Wall thickness (mm) 355 OD / 21mm = 16.9 or SDR 17 The Pipe wall gets THICKER as the SDR number DECREASES, so SDR11 is a thicker and stronger pipe than SDR a Why is SDR17 (SN24 pipe) being used for a burial depth only up to 4m to the pipe crown (non highway loads)? Firstly, background - Ductile Iron, Earthenware and reinforced concrete pipes all have medium to high Young s Modulus values but equally have almost no flexibility (>2% deflection to failure), classing them as rigid pipes. Ductile Iron 170 Gpa (Note: In some designs ductile iron is considered semi rigid ) Reinforced Concrete 200 Gpa Earthenware (VCP) 50 Gpa These are relatively strong stiff materials, they are typically installed without bedding and they do not require side support to resist pipe flexing when being installed, as they do not flex, they are rigid pipes and flexing or over load in service causes cracking and collapse (This frequently occurs with earthenware pipe) Installation design for rigid pipe design does not require the pipes to have interaction with the soil. Their burial design

16 philosophy is completely different to flexible plastic pipes, which typically interact with the soil. Meaning PE pipes flex as the soil strains during changes in soil or vehicle loads (Obviously within limits - EN 805-8% design deflection for Plastic pipes is acceptable). For this reason RCP & VCP pipes in Hong Kong are typically encased in concrete post installation to provide additional support and help to prevent deflection a leading cause of failure in VCP pipes. It is important to note that Concrete encasement of PE pipes is NOT required under BS 9295: 2010 Guide to the structural design for buried pipelines, specifically Clause A.14.3 Concrete surround to flexible pipes. Concrete encasement is not recommended for PE pipes unless such encasement is completely around the pipe and of sufficient thickness and uses steel reinforced concrete. This would only be required in extreme design situations such as highway loading where there is limited cover over the pipe for example (<0.6m cover). Partially encasing a flexible PE pipe with unreinforced concrete is not recommended as it prevents the whole PE pipe from acting in concert as it was designed by allowing the pipe to react with soil movement and flex as it comes under load. Insufficient or partial encasement creates a Hybrid pipe design (the part of the pipe supported by the concrete is rigid and the remainder is flexible) and this prevents the stresses in the pipe from being evenly distributed throughout the pipe wall allowing the pipe to self relax as operating conditions change. Unlike rigid pipes, Plastic pipes have very low young s modulus but have a much higher level of flexibility, short term PE can accept 100% deflection (complete flattening) and <20% long term deflection vs. <2% deflection on a rigid pipe. Plastic materials are designed to interact with soil movement. Refer to BS 9295:2010 Guide to the structural design of buried pipelines Figure 2 below (from BS 9295) explains the difference between rigid & flexible pipelines as they come under load, rigid pipes maintain their circular shape (do not deflect) and the pipe is forced downwards by the soil and surcharge loads, the ground below it compresses which directs the forces onto the pipe until it ultimately fails. In a flexible pipe, the pipe changes it s shape to accommodate the ground movement, as it deflects, the soil loads are dispersed away from the pipe into the surrounding ground. To understand that PE can accept 100% deflection, the image shown is an example of a PE gas pipe being shut off using the squeeze off method, the PE pipe is squashed completely flat by rollers until the gas supply is stopped and repairs can be made. The PE is then released and the pipe will return to its original circular shape due to the internal pressure (over time) this is short-term deflection. However, the long-term deflection must be limited to prevent the sides of the pipe cracking and falling over time due to this stress (explained in SCG 1.2a above). Deflection in EN 805:2001 limits the long-term maximum design deflection in flexible pipes to 8%. It should be noted that PE pipes are considered to have failed once long-term deflection exceeds 20%. Therefore, there is a significant factor of safety (2.5x) in a design limit of 8% maximum deflection. Deflection is limited in flexible pipes typically by providing side support to resist the pipe becoming oval and giving support to the sidewalls of the pipe. Pipe deflection = soil strain (refer to Figure 3 from BS 9295 excerpt below)

17 Side support is provided to flexible pipes during installation by the soil at the sides of the pipe being compacted progressively as it is being backfilled. However, in Hong Kong we know this does not always happen as the installation conditions are typically highly congested with other services and access to simply replace bedding material can be difficult, let alone compact it to native soil strength levels which is almost impossible to achieve on smaller pipes (DN 800 and less) Lack of bedding on a pipe with say a SN rating less than 12 would lead to the pipe failing in the medium term, therefore we need a pipe design that can accommodate Hong Kong installation conditions where compacted side support cannot always be provided. The conservative approach is to design the pipe with enough inherent rigidity within itself that the pipe can support the loads above it with little soil side support (from compaction) to prevent the pipe deflecting beyond the 8% given in EN 805. In reality there will be some un-compacted soil on the sides of the pipe, which will provide approximately 1Mpa of side support dependant of the backfill material (according to WIS IGN ). However, even if there is no soil at all, a SN24 pipe will function over its design life with non-roadway loading with a maximum soil cover of 4m. Example: PE 100-RC SDR 17 / SN 24 pipe (SN is linked to E-modulus & SDR regardless of pipe size) Hong Kong soil load assume 2000kg/m 3 (BS 1295) = 19.6kN/m 2 soil load Assume 1 Mpa side support is provided to the pipe. (un-compacted soil touching the sides of the pipe) Assume the long-term creep modulus for PE is 270MPa (22.5% of the short term modulus) Assume no vehicle loadings (surcharge pressures) based on BS 9295 Table A1 The maximum pipe deflection for a SN24 pipe with 4 meters cover to the crown of the pipe would be 7.48%. (max 8%) Conversely with only 1m of cover to the crown of the pipe, including full highway loading (+63.2Kpa) the deflection of a SN 24 pipe, would be 7.89%. (max 8%) Both these examples are within the maximum allowable deflection for a PE pipe in the EN 805 standard of 8.0% for flexible pipeline designs. Therefore, based on the table below, a conservative approach is to select a SDR 17 pipe for applications up to and including 4m of cover over the crown of the pipe. Vehicle loadings are technically in addition to this depth; if highway loadings are included it could reduce the maximum cover by 0.6m to 3.4m maximum. In this way the design of the pipe is fully self-supporting without side soil interaction and well within the maximum 20% deflection failure. This means the pipe is capable of resisting external loads without failure, to a maximum depth indicated (SDR 17 / SN24 = 4m) WITHOUT the requirement for compacted side support during installation.

18 The reason for this highly conservative approach is that the performance of the pipe long term is NOT solely dependent on the contractor bedding the pipe with progressive compaction on the sides of the pipe to provide support. Table for burial depths Assumptions for the table above CONCLUSION ON 4.0M BURIAL DEPTH RECOMMENDATION FOR SHORT SPEC Assume that PE100-RC pipes of SDR 17 ( SN24) in accordance with BS EN Annex D are installed Assume PE100-RC has a short term Modulus of 1200Mpa & Long term Modulus of 270Mpa (22.5%) Assume either Side support cannot be guaranteed, worse case excavated materials will be replaced loose & uncompacted (recommended) Or assume extreme case that NO backfilled materials exist at all on the sides of the pipe at all (which is impractical) Assume the PE pipe will be subjected to earth & traffic surcharge loads in accordance with BS 9295 Table A1 / BS EN Fig NA.6 Assume long term pipe deflection limited to 8.0% in accordance with BS EN 805, section 9.4 (PE fails at 20%) Assume buckling FOS 2.0x In accordance with BS EN Fig N.A5 (Buckling almost always exceeds both crushing and deflection*) Assume traffic surcharge loads (BS EN Fig NA.6) have the FOS included (Ref Clause B ) Assume HK earth loads are 19.6Kn/m2 in accordance with BS EN clause N.A Assume uncompacted soil provides 1Mpa side support in accordance with WIS IGN Table A.3 * Crushing FOS only needs to be considered In cases of extremely high side support or extreme depths, * Deflection is the limiting factor above 4.0m cover SDR 17 or lower APPLICATIONS WHERE THE USE OF SDR 17/SN 24 PIPE MAY NOT BE APPROPRIATE (CALCS MUST BE CHECKED) Where cover depths to the pipe crown exceed 4.0m cover. SOLUTION - Use pipe SDR 13.6 /SN 50 pipe Where cover depths are less than 0.60m - SOLUTION - A specific design is required, would need to be encased in reinforced concrete Where additional static load occurs (buildings built directly above or in close proximity to the installed pipe) It should be noted that higher SDR pipes (lower SN rating) can also be used, however appropriate attention needs to be given to providing side support during installation and achieving the required compaction levels. Typically, in larger diameter PE pipes (>800mm) burial conditions allow access for achieving proper compaction. 2.2b Why the linkage table between OD & DN? PE pipe is manufactured in a wide range of standard sizes as given in BS EN However, for interconnection purposes, PE s ID s should line up as closely as possible with existing pipe materials (VCP, DI, RCP) to avoid special level invert transition fittings being required when connecting to other materials. The table in clause 2.2 provides this alignment. Typically, PE would be run in batches not less than m, so for small jobs (building to boundary) the pipe needs to be specified standard stock sizes (matching VCP / RCP). The table below gives typical stock sizes available in HK. NOTE: that a full range of PE OD & SDR sizes are available, however manufacturers would need m of pipe for it to be economical to make a production run in a special size.

19 2.3.1a Why is the internal layer orange in colour? Orange is available as a pre compounded 100% virgin material, it requires no additives or mixing and the colour provides good CCTV performance. Orange is also the standard colour for PE100-RC gas pipe, it is available from all the major PE manufacturers, and it is completely compatible with the same manufacturers matching black PE100-RC compound (refer section 1.3b 2.3.1a Why do the Pipes need to have an internal light colour layer? Two main reasons: CCTV assistance layer & wear indication. For CCTV black absorbs light, the CCTV inspection of black pipe is very challenging and damage or defects in construction may go unnoticed during CCTV inspections. It can be difficult to get contrast at joints and connection points to inspect workmanship quality of fittings & joint welding. A light colour layer dramatically improves the CCTV performance (Yellow, orange, grey), however a completely white layer is also not ideal as it s the direct opposite of black and rather than absorb, it reflects light back into the camera lens. A light colour gives the best definition and Orange is the only available pre compounded colour (refer to section 1.1a).

20 In these examples of black, white & orange inner layers, the contrast benefits are obvious. In these close up examples the PE pipe electrofusion joint detail can be clearly seen along with surface scraping on the second image, this level of CCTV inspection is simply not possible with a black or white internal surface b. Wear indication layer Why the requirement for 15% inner CCTV layer with a tolerance of +/- 1.5%? This is so that the inner layer thickness is even inside the entire pipe surface providing an even colour and allows CCTV inspection to identify wear or physical damage over time. If black is showing then the pipe needs to be scheduled for maintenance along with the cause of the scouring understood. It s important to add that PE provides superior resistance to wear compared of any other plastic, DI, VCP or RCP pipe material when tested using the Darmstadt test as specified in BS EN Such wear where black pipe is exposed internally (more than 15% of the wall thickness has been consumed) would not typically occur in a normal sewerage pipe situation even with excessive jet cleaning over many years. However, 15% (+/- 1.5%) provides a constant reference point for wear in extreme applications such as: installed Bends and high velocity situations (>5m/s) or where physical damage has occurred.

21 2.3.1c. No Delamination of Coextruded pipe shall occur during testing In the left hand example below, a sample cut from a drainage pipe is subjected to >350% elongation testing (required under the standard), during this test, no separation of the colours is visible, this is a typical quality test performed on each batch of pipe and is a good indicator of compound compatibility (refer section 1.3b). In the second image a tapping tee (black) is electrofusion welded to the blue colour outer colour surface layer of a WSD water pipe, the welded fittings is then subjected to a destructive test where the items welded together are separated mechanically to the point of failure. This demonstrates that the compounds used in pipes & fittings cannot be separated in any way from each other after joining by electrofusion welding. NOTE: The tapping tee which is only fused to the external blue external colour, literally tears the whole black & blue pipe open with a force of 5.2Kn without separating in any way from the blue layer, equally the blue & black layers in the pipe do not separate. This indicates a 100% cohesive bond between the pipes blue & black compound and the fitting and pipe also External striping External colour stripes are used to indicate the pipes use: Red Brown is the BS EN Norm to indicate Sewerage pipe the colour is BS 4800: 06 C 39 The equivalent reference colour to this is RAL8012 Fern green indicates storm water drainage pipe the colour is BS 4800: 12 D 45 The equivalent reference colour to this is RAL6025 The stripes must be made from the same compound type as the black & Orange PE materials (refer section 1.3b). They are extruded as part of the pipe (they are NOT painted or marked on the pipe). They are generally 0.5-2mm thick and form a permanent part of the pipe, they will remain colourfast even when buried for the life of the pipe. They should never be able to be separated from the pipe body in anyway during testing or even using a knife blade, if they can it indicates that there is not proper cohesion and this can create a leak path past the coupler after electrofusion welding.

22 Stripe colours and size Six stripes evenly spaced ensure that regardless of future excavation, the pipe designations as either sewer or storm water will be clearly visible. Indicated stripe thickness range is 6-24mm. The actual width depends on each pipe manufacturers extrusion dies. Typically, the stripes get wider as the pipe diameter gets larger. The transition between black pie & the stripe is not always a definitive line, so it is impossible to measure accurately that is why the width range is broad for indication purposes Pipe marking Pipe marking is vitally important as it allows traceability of the pipe and batch numbers back to the manufacturers data records. These records hold information about the pipes dimensions at the time of manufacture and each pipe number is linked to the compound batches and their certificate of analysis (CoA). A typical example of a batch report is provided in Appendix 1 for reference. These should be issued and cover the pipe numbers of every pipe delivered to site. BS EN Clause 11, Table 6 - PIPE In this example below the BS EN standard requires the items listed above NOTE that under Manufacturers information (a) a batch number must be provided to allow traceability of the pipe and raw material inputs. Ideally marking which includes bar codes in accordance with ISO is preferable in order to provide complete traceability meter by meter of the installed pipe. In this example below the barcode identifies the manufacturer, Compound material and details, pipe size, SDR, Batch number, length and pipe meterage.

23 WSD have used this bar code system since 2011 in Hong Kong to record data about installed products, it is permanent marking, unlike stickers which can fall off, this is also a good method of ensuring the pipe is genuine product FITTINGS 3.1a Why are DSD specifying pressure fittings? For the same reasons explained in section 1.1b. The BS EN standard for fittings is far more prescriptive than and has greater controls on the material inputs and manufacturing tolerances required to ensure quality. 3.1b Why are fittings only required to be made from a PE100 material and not a PE100-RC required in clause 1.2? Many fitting manufacturers are converting their PE fittings to PE100-RC material, however this transition is slow for two reasons: 1. Fitting manufacturers have to make physical changes to their steel moulds to account for RC materials different shrinkage rates. Such changes are expensive and time consuming and will take many years for the market to change 2. Slow crack growth failures from point loadings are almost exclusively occur in pipe and not fittings, so a PE100 compound complying with BS EN with 1000Hrs SCG performance is perfectly acceptable for manufacturing fittings from. 3.1c How will I ensure that using a non PE100-RC compound for making fittings is OK? The BS EN standard has a National Annex Section E and it states: Note 5 to Clause 1 refers to the test for resistance to slow crack growth of the PE compound. The PE pipe compound in pipe form is tested in accordance with BS EN ISO 13479:2009, with a test period of 500 h in accordance with BS EN :2011, Table 2. It is UK practice to use a test period of h, which aligns with WIS (Issue 2) Polyethylene pressure pipes for pressurised water supply and sewerage duties. Requesting that all compounds meet the national Annex in BS EN of 1,000 hours will require a quality compound to be used. 3.2 Fittings Marking Fitting marking is important as it allows traceability of the fitting and batch numbers back to the manufacturers data records. These records hold information about the fittings test performance undertaken by the manufacturer and link to the compound batches (see a typical example in Appendix 1 of manufacturers records you should expect to receive)

24 In this example below the BS EN Section 11 Table 8 standard requires Material, PN (or SN) rating, SDR & use, size & wall thickness, manufacturers batch designation, manufacturers name or logo and the standard of manufacture. Example of the bar code from a 110mm OD SDR 11 Electrofusion coupler according to ISO The top bar code provides the electrofusion machine on site with the information required to fuse the fitting correctly. The fusion time, voltage, current, thermal compensation, fitting description. The bottom bar code is the traceability bar code for each fitting, it holds the batch number, the compound, information about the compound etc BS EN , Clause 11, Table 8 - FITTINGS 3.3a What is a Fabricated fitting? Fabricated or formed fittings are PE fittings that are not moulded. They could be machined from a solid piece of PE (air valve off take), welded up from various sections of pipe (fabricated bend or Y junction) or hot formed into a shape (formed bend). A moulded fitting is one that is formed in a steel die on an injection-moulding machine, using pressure heat and time. Generally moulded fittings can be identified because they have round surfaces unable to be machined and they have a mould finished surface finish. Moulded fittings are generally standard products such as bends, tee s, stub flanges, electrofusion fittings. Moulded fittings are normally only found up to OD 630 other than some special exceptions. Left: Five Axis CNC machine milling a stub flange from hollow bar Below: Large fittings (2500 OD) can be machined from hollow bar - a thick wall hollow section of solid PE. Used as a blank, almost any fitting type can be made this way.

25 Right: Sewer rising main, air valve Chamber with off takes, dismantling joint, knife gate & air valve fittings all in PE. Below: 1400 OD pressure tees, centre body is machined, pipe ends are welded on. Left: A standard DSD 225NB PE chamber trap, with a 150 rodding arm and screw cap. Fabricated from 3 x 90º moulded bends, intake flange, 3x straight pipes with a 45Deg intake, all butt welded together using butt fusion techniques. An expanding Hydrophilic sealing ring under the intake flange seals it into the concrete chamber. More expensive than CI or VC, however once cast in place it is 100% maintenance free for the life of the chamber and incredibly impact & damage resistant. Because it is fabricated from moulded fittings, it cannot have a CCTV layer or stripes The image right shows the components used In fabricating a 225 PE DSD trap Indicates butt welds to ISO Machined rodding eye cap end & cap Short pipe for rodding eye 45º Y Junction & butt weld Machined intake flange & Hydrophilic seal Pipe end for an Electrofusion Short pipe coupler to join Moulded 90º bends x 3

26 3.3b What is a butt fusion weld on a fabricated fitting? A Butt weld is formed by heating both weld surfaces to a specific temperature ( º C) using a hot plate designed specifically for the fitting shape required and then forcing the two melted surfaces together under specific pressure and time in accordance with the principals of ISO (refer 3.3c). In this case above (left) the weld operator has hot stamped his identification number for the purpose of traceability. Butt welds are easily identified by the hot weld melt that rolls over during the welding process, both inside & outside. A correctly formed butt weld is the same strength as the items they are connecting to, as it uses the full cross sectional area. This elbow below left is a moulded fitting that is fabricated into a chamber trap. Butt welds Butt welds

27 3.3c What does using the principals of ISO mean? There is no specific standard for welding fabricated fittings; however methods other than butt fusion have been proven highly unreliable, weak and frequently fail. Many markets insist on butt fusion joints only in all fittings to ensure that the weld has the same strength as the rest of the components being joined ISO is the standard covering the preparation, heating and forcing together under pressure two PE surfaces and holding them in this position until they have cooled and formed a single piece. Although you can see the weld bead (the melt which has rolled over as the surfaces were forced together) If correctly welded with compatible materials, a clean surface, the correct pressures, temperature and time, there is no actual joint below the bead. The two surfaces join cohesively using the full cross sectional area - exactly the same as making pipe with an inner CCTV layer and stripes, the separate items become a single piece after cooling and has the same strength as each individual item (ref 1.3b above). 3.3d What is the internal weld bead and how should it look after removal? The internal weld bead is the same hot melt which has rolled over as described above internally, in gravity pipes it has to be removed to ensure the pipe & fittings bore is smooth and will not obstruct the flows. The image below is the inside of a PE gravity sewer pipe undergoing CCTV inspection, the camera is rotating 360 Deg around a butt weld pipe-to-pipe joint that has been internally de-beaded after butt welding. This is how a de-beaded joint should look on inspection. Note: When viewing coextruded pipe with orange CCTV inner, a black line will be visible after de-beading, this is normal and expected as the black melt rolls out as part of the bead. 1. The weld seam is smooth and barely visible around the whole circumference. 2. There are no weld bead protrusions sticking that were not properly removed up that could create blockages 3. There is no gouging into the surface by the de-beading tool. Below a pipe weld de-beader removing the internal butt weld bead after welding of a pipe to pipe joint. The de-beader is on the end of a long pole and is manually rotated inside the pipe after the weld has cooled. For fittings, de-beading is done during manufacture by hand

28 3.3e Why are we not removing the external weld bead? The external weld bead should remain in place on all fittings & pipe for three reasons: 1. It enables site engineers to confirm that the welding of any parts in a fitting meet this specification and were actually completed using butt fusion techniques rather than by extrusion or another form of welding. 2. The weld bead does provide some minor reinforcement and there is no reason for it to be removed. 3. Butt welding in fittings requires skill and custom equipment but provides full strength welds, in all cases the pair of external butt weld seams should be visible at EVERY joint as shown in the images below. These joints are all fusion butt welded, if a pair of rolled over weld seams like this is not visible, then the joint is likely to have be extrusion welded and should be rejected. 3.3f What is extrusion welding? Extrusion welding uses a hot gun that has a heated tip and PE filler rod. The gun extrudes hot PE filler rod onto the cold PE surfaces to be joined, somewhat like you would join items using a silicone fillet. The cross sectional area of each component are not joined and even in the very best conditions the joint may have <50% of the parent materials strength. In the worst case they will fall apart when under any stress or impact. Extrusion welding gun Placing PE fillet between two items typical extrusion weld joint

29 For PE to join cohesively together and have a joint that is the same strength as the parent material, several requirements must be fulfilled: 1. The cross sectional area which is physically fused together, must have the same dimensions. Without the dimensions being the same, the heat and pressure requirements would be outside on the standard Correct butt weld jointing provides a joint as strong as the components being joined. 2. To weld PE successfully both components must be cleaned, heated to the correct temperature, that heat allowed to soak into each item and then pushed together before the surfaces can cool and maintained under pressure for the correct time and allowed to cool with the same pressure maintained throughout the process. This delivers a single homogenous component with no physical joint between them providing a full strength fitting. In these two examples above the Left one is extrusion welded and should NOT be accepted The one on the right is joined using butt-welding principals. Note: Fabricators may grind the extrusion weld back so no seam is visible, this is why the external weld beads should remain so that the welding process can be confirmed on site. 3.4 Why is a puddle flange required with PE pipe? A puddle flange is designed to anchor the PE pipe to prevent movement, the same as used for ductile iron pipe. PE Gravity pipes require anchoring because PE is designed as an end to end system where the forces from operations, ground movement and thermal change are transferred over the length of the pipe until the stress is transferred either into the soil or to the ends of the system. Unlike a rigid pipe (RCP, VCP, DI) PE provides a flexible, thermoplastic fully end restrained piping system. It moves with the soil and as it will expand and contract with temperature changes, must be restrained. The benefit of this end-to-end system is that bends can be used in PE sewers, eliminating a significant quantity of chambers in a system. Puddle flanges are designed to be encased in concrete and can take the entire tensile end load force until the pipe fails. For this reason they need to be fabricated (machined) from a solid hollow bar, without welds in the outer ring to enable transfer of the full forces. The dimensions of the ring are designed to interact with a minimum of 20Mpa concrete and limit tensile stress in the PE to 18Mpa (FOS = 1.25). For the purposes of simplification this means the width of the ring (w) must be 1.25x the wall thickness of the pipe (W=OD/SDRx1.25) and the outer diameter of the same ring needs to be 1.25x the pipe OD.

30 In order to transfer the stresses evenly from the ring into the chamber wall, a taper no less than (2xw) wide is required on each side of the ring, this taper must be completely embedded in the concrete chamber wall or by addition of an integrated corbel on larger diameters in order to provide sufficient thrust resistance in both directions to overcome thermal stresses. The taper provides a quick on site confirmation that the puddle flange is embedded with sufficient cover on both sides to resist pull out. The lengths of the spigot shall be long enough to use an electrofusion coupler to weld the puddle flange to the connecting pipe. These dimensions can be found in BS EN , table 3 Tubular Length for electrofusion L2 An optional hydrophilic sealing ring ( 6mm diameter) can be fitted into a machined groove on the outer ring to ensure there is no infiltration or exfiltration around a puddle flange encased in concrete. Unlike DI or VCP, PE and concrete are not a good match. Concrete does not adhere to PE and there is always a gap between the surfaces, thus a hydrophilic sealing ring is always required. 2 x W W L 2 For reference the dimensions from the image: t D4 is pipe OD x 1.25 DN/OD D 5 D5 refers to ISO 9624: Thermoplastics pipes for fluids under pressure - Mating dimensions of flange adapters and loose backing flanges D 4 W 1.25 x the pipe wall thickness (OD/SDR) DN/OD the OD of the pipe the fitting connects to L2 The tubular length for electrofusion from BS EN Table 3 spigot dimensions

31 3.5a What is transition fitting? A transition fitting connects other pipe materials to PE. This may be required for connecting to existing materials (VCP, RCP, DI, PVC) or making a repair in existing materials using PE. Transitions are typically made using a PE socket with a rubber ring or using a PE spigot sized to suit the other pipe material and push into a VC or RCP socket with it s own rubber ring sealing system. Because PE is viscos elastic material, unlike rigid pipes PE can pull out of a rubber ring socket due to soil movement and thermal changes. Therefore each transition fittings needs to either have an integrated puddle flange or is restrained after the connection by a puddle flange anchored in concrete. The puddle flange shall have the same dimensional requirements as specified in section 3.4, however no hydrophilic is necessary. The rubber ring connection needs to be type tested in accordance with BS EN clause 10, to ensure that the design & sizes seal correctly. BS EN is referred to for type testing requirements, as BS EN has no provision for rubber ring joints in pressure systems. 3.5b Eccentric design If the bore of the transitioned fitting does not line up with the invert of the SDR 17 pipe within 5% of nominal bore, (occurs in certain sizes of VCP - PE) then the transition fitting needs to be moulded or machined eccentrically to maintain a level invert in the gravity system. 3.6 Manhole connector A manhole connector connects PE pipe to precast or cast-insitu concrete chambers to form a leak tight connection. Unlike in rigid socket spigot pipe systems, PE pipes may need to be secured to the manhole, the selection of the connector type depends on several factors that need to be considered; Are the pipes and chamber installed aboveground (not buried)? If buried, is there a significant fall to the next chamber (Hillside installation) with a gradient of >1:10 Is the connection size greater than DN550 (630 OD)? Is the installation in a reclaimed area where significant settlement is expected? If the answer is yes to one or more of these items above, then either a Type B connector should be used or a Type A connector combined with a puddle flange to anchor the pipe to the chamber. When installing PE pipes above ground, the pipe is subject to a thermal change in length of ~0.18mm / ºC / meter of pipe. So consider an exposed gravity pipe falling 300m between two chambers, which is installed at 37ºC (summer time). At 10ºC (wintertime) the pipe will be [0.18mm x (37-10) x 300 = 1,458mm or 1.45m shorter if it is unrestrained along it s entire length. (NOTE: This pipe would not require restraint in buried applications, as the soil friction will overcome the stress from the thermal movement)

32 Type A Manhole Connector: Two components, a spigot and a cast in ring Making a flexible joint that allows up to 3º deflection between the spigot and the sleeve to accommodate pipe and or chamber settlement while providing a flexible leak tight connection. X Z Y W 8mm ØOD SDR Key features: 2 x O-ring seals allow lineal movement of the spigot to accommodate thermal movement Ød4 O-ring Waterstop Hydrophilic expanding seal (Waterstop) between O-Rings ensures no infill from ground water or exfiltration of sewerage from the chamber. The shoulder on the spigot is larger than the pipe OD to prevent the spigot being thermally forced or over inserted into the chamber during construction. L L ØDs 50mm The groove shape (w,x,y,z) when embedded in concrete create a water stop. To achieve this they must have a difference between dimensions z & y as indicated, this may also be achieved using a dovetail slot. Type A manhole Connector Typical connector dimensions Pipe DN Nom. Pipe OD Nom. Sleeve ID Spigot Stop OD Length of Sleeve * Nominal wall locking groove dimensions OD d4 Ds L W X Y Z * Nominal, designed to allow concrete to enter the grooves when casting in a structure to form a watertight anchor.

33 Type B Manhole Connector: A rigid joint that casts into the chamber, typically used: In larger sizes (typically greater than DN 550) In Non buried applications, where the thermal movement is not restrained by a puddle flange Where full end restraint must be provided (expected ground movement). In reclaimed land (Note: provision for the pipe to settle must be included in the design) Key features: For reference the dimensions from the image: D4 is pipe OD x 1.25 D5 refers to ISO 9624: Thermoplastics pipes for fluids under pressure - Mating dimensions of flange adapters and loose backing flanges W is 1.25 x the pipe wall thickness t (OD/SDR) DN/OD is the OD of the pipe the fitting connects to 2xW is the minimum taper & concrete encasement length to ensure the forces are transferred from the pipe into the chamber Tapers each side transfer stresses into the puddle and into the concrete chamber Tapers indicate minimum recommended concrete encasement length based on 20MPa concrete. Hydrophilic sealing ring on the outer diameter ensures the connection is water tight The spigot length is extra long to allow for electrofusion on site before or after concrete encasement 3.7 Electrofusion Couplers An Electrofusion coupler (EF Coupler) is a PE pipe-pipe or pipe-fitting joiner that has internal electrical wires embedded in it to heat and melt the external surfaces of the pipe and the inside of the coupler until they fuse together, forming a single homogenous joint. As with any welding of PE, the critical elements are cleanliness, heat, pressure and time Cleanliness of the joint during installation cannot be overstated. If a PE weld joint is subject to any dirt, moisture, dust, oil (even touching with hands) in the jointing area prior to welding, the joint will likely fail or leak. Refer joint prep instructions. Example of a electrofusion coupler OD 355

34 Outer Cold Zone (one each side prevents melt escaping during fusion) Hot zone x 2 (coils melt coupler & pipe together here) Inner cold zone x 2 (one each side of the coupler centre) Coupler thickness ( >Pipe OD/SDR) Permanent External Reinforcement to prevent the coupler expanding during fusing Fusion Parameters & coupler size and SDR ra ng informa on What is the SDR of the coupler? The SDR of the coupler is the thickness of the coupler - it must be the same or greater than the thickness of the pipe it is connecting to. All couplers must be rated minimum of SDR 17 (PN10) to meet this specification. (Note: the higher the SDR number, the lower SDR Rating ie: SDR 17=PN 10, SDR 11=PN16) In the case of couplers manufactured using a pressed on PE external ring to provide reinforcement, unless the two PE rings are fused together into a single composite piece (either during manufacture or in the fusion process) the inner ring which is fused to the pipes must have a cross sectional area greater than or equal to the pipes it is connecting. This is to ensure that the tensile strength of the coupler is not less than that of the pipe.

35 3.7.2 What is Fusion Zone length L2? Each coupler has 2 x hot zones (L2) with a cold zone each side (L3 on the outer edge & (L1 L2-L3) on the inner (see illustration above and below Fig 1). Each hot zone has a coil which heats the pipe & coupler surfaces at the same time, fusing them together, the width of EACH of these coils is the fusion Zone Length L2. The cold zones remain cooler and cool the expanding melt so it prevents the melt from escaping out of the hot zone, this containment creates pressure in the hot zone which is needed for a successful weld (successful PE weld requires: pressure, temperature & time). This specification requires a minimum fusion length of 1.5x L2 from BS EN to increase the factor of Safety in the weld. These coils must be visible on the inside surface of the coupler. They are measured from the first tightly adjacent circumferential coil until the last tightly adjacent coil in the same plane. Gaps between coils or where the coil separates away to the electrofusion pin are NOT included. Coils must be tightly wound side by side, If the coils are not visible to the naked eye the fitting should be rejected as they need to be exposed to achieve the highest transfer of heat. BS EN , Clause 6.2, Fig, 1 - DIMENSIONS OF ELECTROFUSION SOCKET BS EN , Table 1 - ELECTROFUSION SOCKET DIMENSIONS Minimum values required (1.5x L2) OD L2 (mm)

36 3.7.3a Why do we need external reinforcement on couplers OD 355? At the start of the fusion process, the inner coils heat up the coupler bore and the material expands contacting the pipe wall. This then heats the pipe wall, both expand in diameter due to the increase in temperature. Without external reinforcement of the coupler, the expanding coupler reducers the amount of pressure created within the fusion zone, resulting in a poor weld. As couplers get larger in size (>250 OD) the manufacturing tolerances on pipe diameters increases proportionally (0.09% x OD), however the couplers ability to close a larger gap does not increase with size. This means special technologies must to be employed in the design of large fittings (>OD 250) to help minimise the gap and create successful welds. External reinforcement is one of these technologies. Because circumferential expansion is controlled by the external reinforcement, close fits between coupler and spigot can be maintained throughout the fusion process. Additionally, quality couplers have a pre heating function on larger sizes ( OD 315), this applies a low voltage & current below the fusing temperature and warms up both components helping to close the gap before the actual fusion cycle take place; This is called a Pre Heat function b What is external reinforcement on couplers? External reinforcement can take many forms, as in the examples below: LEFT is a heavy wire ploughed into the external body of the coupler to resist it expanding as it heats up during fusing. This wire performs only a mechanical function and has no electrical connection. RIGHT is a factory fitted fabric band, which applies compressive force to the groves over the hot zones and resists expansion. There are other forms of external reinforcement used by other manufacturers. Permanent reinforcement is preferred, because the contractor can not forget to apply it during fusing.

37 3.8 Bends Horizontal bends can be used in a fully end restrained gravity sewer system - such as a PE welded system. Bends are used to smoothly change the direction of sewers without interrupting the pipeline with a manhole chamber. Bends have been widely & successfully used in PE gravity drainage systems for many years. Although there are limitations required on maximum bend angles, minimum bend radius and how the bend is manufactured. Countries that have year s experience in PE sewer systems have eliminated up to 75% of man-hole chambers by using bends. Using horizontal bends has significant cost & maintenance advantages whilst maintaining some chambers in the system allow access for CCTV and jetting equipment, or in the unlikely event, clearing blockages. The following is the reasoning behind the requirements of bends installed in gravity sewers; These are based on the specifications from several international markets: Bend Angle - Any angle up to max 45º, (typically 11.25º, 22.5º, 45º) which is the maximum angle to ensure rodding & cleaning can be achieved around corners Bend Radius - The radius of bends must not be less than; r = 4x OD, to ensure access can be provided around the bend and cannot be blocked. Spigot Lengths (le) Must be equal to or greater than the lengths given in BS EN Table 3 to allow electrofusion on site. OD & Ovality Spigot ends of formed and fabrication bends may be subject to distortion, poor material selection or manufacturing techniques. It is IMPORTANT TO CHECK that the OD & ovality of the spigot ends comply with BS EN Table 3 in order to achieve a successful weld. Bend Types Bends are either fabricated by welding mitred sections of pipe or formed by heating and bending a piece of pipe that complies with this specification (ie: the pipe includes a CCTV inner layer and all other requirements from section 1 & 2 above). Formed bends (below) are made by heating straight pipe and bending in a jig to the desired angle and radius. Formed bends are required to be used in sizes less than or equal to DN 450 (OD500). Formed bends ensure a smooth bore eliminating chance of blockages and allowing CCTV, rodding, jet cleaning to be easily performed on smaller sizes.

38 Fabricated bends (Below and above right) for sizes greater than DN450, are made by welding mitred sections of pipe with mitre angles not greater than 9º per cut (18º compound) In horizontal drainage, the maximum allowable angle of all polyethylene bends 45º. However each mitre weld is limited to a maximum angle of 18º to ensure a smooth change in direction. In the case of a 45º bend, it must have 3 x equal compound mitre joints at 15º to make the 45º bend shown (Below Right) Further explanations can be found in BS EN Annex B In this example (left), a single mitre joint is shown; each single mitre is limited to a 18º compound angle (9º cut angle). Fabricated bends shall have the internal weld beads removed during fabrication to prevent future blockages. In the case where a vertical drop is incorporated, the radius may be less than 4x OD because the change in direction is installed in the vertical plane, however a min DN 150 rodding eye must be included for cleaning & maintenance purposes. (example right) PE can be installed by naturally forming a curve during installation using the PE pipes inherent flexibility such as this syphon sewer system (Left). If cold bending pipe, the radius for SDR17 pipe shall not be less than 27x OD to maintain flows and avoid buckling in the pipe wall. At 27x OD the reduction in cross sectional area of the pipe bore is ~ 5%