PERFORMANCE AND SUSTAINABILITY ADVANTAGES OF PVC SEWER PIPES IN AUSTRALIA
by Alan Whittle, Nigel Jones and Mark Heathcote
Iplex Pipelines, Australian Vinyls and Plastics Industry Pipe Association
PVC has been used successfully for sewer and sanitary drainage pipes in Australia for over 40 years. It is the predominant material for these applications. The reason for this success is the superior, all round performance of PVC piping systems compared to the various alternatives. Equally important has been the ability and readiness of the PVC pipe and fittings industry to adopt new technology and design features relevant to the Australian environment, to invest in new production equipment and expand the product range. The use of material efficient pipe constructions and the ability to use the core of PVC sandwich construction pipes as a sink for the recycling of PVC from a variety of sources has led to an enhanced sustainability status of PVC sewer pipe. This, along with other environmental aspects such as low embodied energy, makes PVC the most sustainable material for sewer applications in Australia.
Poly (vinyl chloride) (PVC) was the first plastics material introduced into plumbing applications in Australia. PVC was initially adopted in above-ground drainage applications as a replacement for the then traditional metal products such as cast iron and copper. PVC has proven so successful that after some 40 years it is still the major material used in both above and below ground drainage. However, over the years a number of technical, commercial, regulatory and environmental issues have had to be resolved in order for PVC to retain its dominant position.
The first PVC plumbing product adopted in Australia in domestic applications was the toilet pan connector. This incorporated a rubber ‘O’ ring and was much less labour intensive to install than the traditional method of joining pans to VC or cast iron. Polypropylene waste traps for sinks and baths were also introduced about the same time. These products were quickly followed by PVC drainage systems.
The rate of acceptance of PVC drainage pipes varied within each regulatory jurisdiction, being dependent upon a number of factors.
The difficulties faced in the very early years by the PVC pipes and fittings industry included:
- Commercial. Difficulty in convincing merchants to stock the new products. PVC was first offered for use in above ground drainage applications and the plumbing merchants already stocked and sold an established product range. There was little incentive for them to stock a new product. This problem was addressed by various promotional schemes and ultimately by the demand of the plumbers. Note that PVC was only permitted in buried applications some time after above ground usage was established. The acceptance of PVC as a buried piping system was much more rapid to the extent that within 2 to 3 years there was about 80% market penetration. The rate at which PVC replaced vitreous clay (VC) piping was phenomenal. In the case of sewer systems (i.e. below ground) merchant support was much stronger because it represented new business to them. The VC pipe market was controlled at the time by the manufacturers and the merchants were largely excluded from the supply chain. The PVC pipe industry actively involved the merchants in the marketing of PVC. This meant that not only did PVC piping systems offer technical advantages over VC; the merchants actively supported the new material for commercial reasons. The cost of setting up extrusion plants to produce the range of pipes was much easier than establishing an injection moulding plant with the wide number of expensive moulding tools. It was therefore necessary to access a range of fittings from overseas until the market grew large enough to justify the investment in injection moulding tools for local production.
- Regulatory Australia is a Federation and plumbing regulation was managed by individual States or Territories or even municipalities in some areas. As a consequence, the manufacturing industry had to go through an approval process in each jurisdiction. Approval in one jurisdiction did not automatically mean acceptance in another. Whilst there was some progress over the years in achieving a common approach to product approval, it is only now that a uniform plumbing code has been adopted in Australia. One of the major problems to gaining acceptance by the plumbing trade was confusion in the interpretation of the installation codes by both plumbers and the inspection officers. The installation code was good, but there was a new set of rules to deal with, particularly in regard to expansion joints, support and pipe length restrictions. Misinterpretation occurred with both plumbers and inspectors.
- Training Installation and jointing practices for PVC are substantially different from the materials previously used and extensive education programs were necessary to ensure the systems were installed properly. Manufacturers took a lot of the responsibility for training by running trade nights and breakfasts for plumbers in the period leading up to formal, regulatory acceptance of PVC. In critical installations, the manufacturers actually provided site supervision. For example, during the construction of the first building over 2 stories that utilised PVC, the foreman plumber had no PVC experience and only his apprentice had been trained in solvent cement jointing. The apprentice was put in charge of the PVC installation, with a licensed plumber provided by the manufacturer, to oversee the work.
- Standards The plumbing industry in Australia is highly regulated and the publication of national Standards has been a very important feature in the successful introduction and continued use of PVC sewer and sanitary drainage pipes. The PVC manufacturing industry recognised this from the outset and has continued to actively participate in maintaining the Standards to reflect changes in products, application and installation. In fact this has become increasingly a responsibility of the manufacturers as the utilities and regulators have become less willing to devote resources to Standards activities. The first Australian Standard for PVC pipe was published in 1963 but it only addressed pressure pipes. The Standard was amended in 1967 to include non pressure products. In 1973/4, three separate Standards were published for Pressure (1), Soil Waste and Vent (SWV) (2) and Sewer (3). The publication of an installation Standard was also an important factor in the successful introduction of PVC systems. The first installation Standard (4) was published in 1972. The installation Standard has been progressively updated since 1972, but many of the fundamentals remain unchanged. Having a suite of Standards was an extremely important feature in the adoption of PVC pipes. As well as the product and installation Standards mentioned above, it was very important to have a design Standard to address soil – flexible pipe interactions. The first Standard for design of plastics pipes in buried applications was published in 1972 (5) and subsequently revised in 1982 and 1999. In the Australian context it was essential to have a comprehensive raft of Standards. The PVC industry recognised this and has, from its inception been very active in Standards activities.
- Professional Reluctance To some plumbers, the introduction of PVC was seen as down-skilling with a threat of do-it-yourself plumbing. The commercial implications of not adopting the new material were such that ultimately all plumbers started to use PVC.
Despite the issues and difficulties referred to above, PVC was rapidly and widely adopted in drainage applications for reasons including:
- Longer pipe lengths resulting in fewer joints to be made.
- Sufficient longitudinal rigidity to enable pipes to be accurately laid to line and grade without ponding.
- Lighter weight pipes which was an advantage in both manual handling and allowing plumbers to transport they pipes and fittings with their own motor vehicles. The plumbers could collect their product from the merchants with their work vehicles rather than rely on the merchants or manufacturers heavy trucks.
- Solvent cement joints resistant to tree root intrusions. The combination of a climate with very dry periods and vegetation with aggressive root systems created severe choke problems with VC pipe joints. This was particularly the case with mortar joints, but was also a problem with elastomeric seal joints whether the rolling ring type or plastic coupling.
- Lower installed cost.
Although it enjoyed earlier success, it has been necessary for the PVC pipe industry to address a wide range of issues and adapt to changing demands. This adaptation has been critical in PVC maintaining its dominant position in the market.
RESISTANCE TO TREE ROOT INTRUSIONS
Although the inherent resistance of PVC solvent cement joints and longer pipe lengths meant joint performance was much better than VC pipes, there are instances where flexible joints incorporating elastomeric seals are required. This is particularly the case where there is potential for subsidence or in reactive soils.
Initially this problem of tree root intrusions was addressed by specifying a minimum interface pressure of 0.55 MPa between the seal and the pipe, over a length of not less than 7 mm. This was firstly adopted by some of the regulators then introduced into the product Standards.
For a period in the 1980s and 1990s elastomeric seals used in non-drinking water applications contained a root growth inhibitor. A number of OH&S and environmental issues were associated with the additive and there was a concern that the treated seals might be inadvertently used in water supply. In consultation with the regulators and water agencies the industry discontinued the practice.
In 1999, arrangements were made to publish a combined Australian and New Zealand Standard. NZ had previously found an interface pressure of 0.4 MPa over 4 mm sufficient to prevent tree root causing chokes. In order to gain Australian regulatory acceptance of the apparently relaxed NZ requirements, the pipe industry undertook a comprehensive research program which determined that intrusion of roots past elastomeric seals is not just a function of interface pressure, but also the surface roughness of the material and permeability of the material to water. The results of this work was reported by Whittle (6) and Lu et al (7). As a consequence, the NZ interface pressure regime was adopted and an Australian Standard test developed (8) for directly assessing the resistance of pipe joints to plant roots including woody tree roots and fine rye grass roots.
As a result of the interface pressure requirements placed on elastomeric seal joints, the performance of all PVC pipe systems had been excellent with respect to resistance to root intrusions. Where chokes have occurred with PVC pipes, the cause has usually been incorrect assembly, such as seal displacement or intrusion from VC branch line.
INSTALLATION IN MINE SUBSIDENCE AREAS
Whilst elastomeric seal joints provide the flexibility needed to cope with ground movement some areas are subject to mining with the risk of significant ground strains. Long pipe lengths with normal socket depths do not readily accommodate the large soil movements. This has been addressed by providing pipes in 3 m lengths rather than 6 m and constructing pipe sockets with extended insertions depths so as to accommodate greater contractions or extension of a pipeline. In this application, PVC has been shown to be the most appropriate material and flexibility in manufacturing and design meant the industry could readily adapt to these special needs.
RESISTANCE TO UV RADIATION
PVC was first used in above ground sanitary drains. When the pipes were accepted for buried applications, a separate product range was introduced. Whilst this was partly for commercial reasons, it was also recognised that above ground pipes needed a higher degree of protection against UV radiation, especially in the Australian climate. Rather than apply a performance test, it agreed to adopt a prescriptive requirement with buried pipe having not less than 1 phr of rutile titanium dioxide and above ground pipes having 2 phr. This approach was supported by work carried out by LeHunt (9) and (10). In the 1980s and 1990s it became increasingly apparent that the plumbing industry would prefer to have one product for all PVC sanitary drains, whether the product was to be used above or below ground. Rationalisation would have the greatest impact on diameters DN110 and DN160 which were used in both applications. That is, the extrusion and moulding companies produced and stocked two ranges of DN110 and DN160 product and this duplication was also carried by the merchants and plumbers. The major differences being colour (cream below ground and grey above), the TiO2 content. In addition, the pipe in one range was supplied plain ended and the other pipe was socketed. Previously the industry had sponsored a major research project, undertaken by the Burn et al of the CSIRO (11), to determine the optimum level of TiO2 in PVC exposed to sunlight and weather. On the basis of this work it was determined that 1.5 phr of TiO2 would provide sufficient UV protection for pipe and fittings used in either above or below ground applications.
With the introduction of PVC waste pipes in multi-story dwellings, there was an interest as to whether PVC might transmit sound more than the copper alternative. Cast iron was not a preferred product because although it had good acoustic properties, it was heavy and required substantial support. Tests showed that copper and PVC pipes were similar with respect to sound transmission characteristics and in sensitive areas, acoustic insulation was needed for both pipe materials. In other words there was no disadvantage in using PVC in such applications. More recently, filled PP piping systems have been introduced for applications requiring reduced noise transmission.
Lead based thermal stabilisers were used in PVC pipes in Australia from the industry’s inception. From about 1989, non-lead stabilisers were adopted for water supply pipes as there was a concern that water pipes in new housing areas with initially very slow flow rates, might result in higher than acceptable lead levels in drinking water. Reliance could not be placed on the pipeline commissioning procedures to prevent this initial high lead content from occurring. Appropriate commissioning procedures had been shown to quickly reduce the lead extracted into the water, but provision and disposal of the water needed for flushing was an issue from a public relations and environmental point of view. Whilst, the same problem did not occur with sewer pipes the question was asked as to the impact of lead stabilised drainage pipes on the lead content of sewerage effluent ultimately used as fertiliser on pasture. The PVC industry commissioned Burn and Schafer (12) of the CSIRO to investigate the matter. They demonstrated that lead stabilised pipe was not a significant contributor to the lead content of sewerage effluent and therefore lead stabilisers continued to be used in this application.
In more recent times the concerns about lead have extended to exposure of personnel during stabiliser production, PVC compounding and the ultimate lead load on the environment. It was decided about 5 years ago in Australia that it was appropriate to completely remove lead from all PVC formulations. The pipe industry was the first sector to completely phase out lead. To ensure phase out was adopted across all of the industry the product Standards were amended in 2009 to explicitly exclude the use of added lead compounds. Plumbing regulations require pipes and fittings to not only comply with the Australian Standard, but to also be third party certified. It was therefore easy to ensure all manufacturers eliminated the use of lead. Whilst the addition of lead compounds to PVC pipe and fittings formulations is banned, lead stabilised PVC recyclate is permitted to be used in the core of sandwich construction pipes. This provides a practical application for such recyclate which is encapsulated within non-lead stabilised inner and outer skins.
Fire resistance is another issue that the PVC pipe industry has had to address over the years. Whilst inherently self extinguishing architects and regulators have been interested in the early fire hazard ratings of PVC expressed as, indices relating to ease of ignition, flame spread, heat evolved and smoke developed. The inherent flammability characteristics of PVC are usually viewed favourably compared to other materials.
As with all thermoplastics pipes PVC will melt in the event of a fire and in multi story buildings, wall, ceiling and floor penetrations could allow fire to pass through otherwise fire rated constructions. Fire stop devices have been developed to prevent this. These are required for all thermoplastic pipe penetrations of fire rated walls, ceilings and floors.
When first introduced, PVC drainage pipes were claimed to have a nominal service life of 50 years. However, as PVC piping systems approached service lives of 30 or more years it became apparent the utilities would either need to start to provide money for replacement or revise their service life expectations upwards. For some utilities, accounting methods meant substantial annual allocations had to be made for replacement even though the money was never needed to be spent. The PVC pipe industry undertook an evaluation of the condition of sewer pipes exhumed after periods of up to 26 years service. After demonstrating there was no deterioration in the bulk properties of the material and no measurable loss of wall thickness due to abrasion, Whittle and Tennekoon (13) service life expectations have been extended to beyond 100 years. It is likely that future evaluations will result in further extensions to the expected service life.
STRUCTURAL PERFORMANCE OF BURIED PVC SEWER PIPES
The first applications for PVC sanitary drains were all above ground, in part because of a lack of understanding of the interaction between soil and flexible pipes. There has been in some quarters confusion as to the difference between time dependent properties and a deterioration of properties with aging. This is an issue for all plastics pipes. One misapprehension being that under the influence of soil load, PVC pipes will continue to deflect for the full duration of their service life with the pipeline ultimately failing because insufficient hydraulic capacity or catastrophic collapse. The plastics pipes industry has addressed this at both a national and international level with the publication of numerous research papers and installation and design codes. Ultimately, flexible buried pipe design has been accepted and PVC pipes are used in all States and Territories.
Minimisation of the use of PVC products was a condition of the Sydney bid for the 2000 Olympics. This was interpreted by some as an exclusion of PVC from the Olympic site and the minimisation/exclusion of PVC was subsequently embraced by other specifiers. The PVC industry had to engage in a number of programs to address the genuine concerns about PVC and to refute the scientifically invalid ones. The PVC industry as adopted a Product Stewardship Program (PSP) which addresses issues such as:
- Lead stabilisers (no longer permitted),
- No cadmium or hexavalent chromium pigments,
- Chlorine and vinyl chloride monomer (VCM) produced using mercury free pathways,
- Limits on VCM emissions during production of PVC and restrictions on VCM content in the resin itself,
- Provisions for recycling.
Whilst the PSP is voluntary, once a company signs up to it, the program becomes legally binding. The PSP has been very successful in properly addressing the valid environmental concerns about PVC whilst countering the invalid ones.
For a period, PVC products incurred a penalty in the Green Star rating of buildings. Now a scheme is in place for pipes and conduits to be made according to the requirements of the Green Building Council of Australia’s Best Environmental Practice PVC (BEP PVC). These requirements are closely aligned with the PSP. BEP PVC products are branded as such and are being increasingly specified in Green Star accredited buildings.
The original specifications for PVC drainage pipes nominated not only the diameter for the purpose of compatibility, but also the minimum wall thickness for serviceability. With the introduction of material efficient structured wall designs wall thickness was no longer appropriate and minimum pipe stiffness was nominated. In the first instance, the Australian industry made an error in specifying pipe stiffness for structured wall pipes and retaining minimum wall thickness for plain wall products. This resulted in the anomaly whereby plain wall pipes were actually significantly stiffer than structured wall products. This was corrected be specifying a minimum pipe stiffness for all products ≥DN110. Smaller diameters used in internal drains continue to be specified by diameter and wall thickness. For pipes ≥DN110 two stiffness classes were introduced, SN4 and SN8. As these pipe stiffnesses were slightly lower than those associated with the superseded minimum wall thickness classification some materials savings resulted. Whilst not great in percentage terms, the savings were significant when taken over the total industry. It was quickly recognised that in practice often inadequate attention was given to the quality of installation of the DN110 drains commonly used in residential construction. As a consequence there were installation problems in this particular diameter. To eliminate this problem, the industry increased the pipe stiffness classifications for DN110 to SN6 and SN10. The additional robustness of the higher stiffness classes was found to compensate for the rougher handling and poorer installation practices. This was considered a pragmatic response to the problem and was considered to be quicker to implement than endeavouring to change the practices of plumbers and drainers. The higher stiffness classes for DN110 pipes have remained in place since 1999.
In the search for even greater material savings sandwich construction (SC) PVC pipes have been widely adopted. Whilst there are other material efficient constructions such as ribbed pipes, SC pipes have the advantage of appearing exactly the same as the original products and handling and installation techniques are not altered. Material efficiencies are gained by a combination of factors such as:-
- Foaming the core of the pipe,
- Eliminating pigment from the encapsulated core and
- Incorporating recyclate into the core. This can be particularly advantageous from an environmental point of view as can provide a sink for waste PVC material from other sources to be utilised in a long-life product.
When structured wall pipes were first introduced the utilities expressed concerns about the possibility of the integrity of the systems being compromised by abrasion or other damage to the inner wall. A pragmatic approach was taken to allay these fears by specifying a minimum thickness of the inner layer of SC pipes, 50% higher than required in ISO21138.2 (14).
The increasing focus on sustainability and climate change has generated a lot of interest in energy usage, not only in the operation of buildings and infrastructure, but also in the Embodied Energy (EE) of the products used to construct them. This applies equally to pipes as to other building components. There has not been a universally consistent approach to EE calculations. For example, calculations should, but do not always include the conversion of the material into the final form. Also, for pipes, embodied energy comparisons should be based on product length, not material mass. Transport costs should also be taken into account as well as the contribution of coatings and linings. To date, it has been demonstrated that in the most commonly used diameters PVC sanitary drainage and sewer pipes compare favourably with other materials, especially when recyclate and foam core constructions are used. This is an evolving science and it will be incumbent upon the Australian industry to keep abreast of developments. This is expected to be by collaboration with other interest groups.
For a variety of reasons PVC pipes enjoyed a rapid adoption in the Australian sewer and sanitary drainage market. These included ease of handling and installation, joint performance and commercial incentive. However, in addition to the advantages of the material itself, the industry contributed to the success by making a concerted effort to train and educate plumbers, inspectors and regulators. Also the industry devoted significant resources to establishing a comprehensive range of national Standards addressing product specifications together with performance, installation and design.
Although the initial uptake of PVC pipes and fittings was very rapid, the industry has continued to be presented with challenges. It has responded to these by contributing to research, actively keeping national standards up to date and addressing installation, environmental and commercial issues in a timely manner.
PVC sewer and drainage pipes have been used in Australia now for over 40 years and continue to be extremely successful. There are no performance or environmental reasons why PVC should not continue to be used in sewer and drainage applications. Commercially, PVC outperforms competitive materials.
The longitudinal stiffness of PVC pipes means they can be readily laid at low grades without low points that can lead to pooling of sewage. This is particularly important in Australia where cyclical drought conditions has resulted in the use of low flow rate appliances and low volume toilets cisterns.
There is no reason to doubt the PVC pipes already installed will not continue to provide many more years of satisfactory service. Neither is there any basis for assuming alternate materials provide any inherent, overall advantage.
Ostensibly it might appear that the PVC pipe industry is the same now as it was over 40 years ago. However, the industry has responded successfully to a number of challenges and will no doubt continue to do so in the future.
Acknowledgement: The contribution of Mr. John Bines in providing detail of the early introduction of PVC pipes in sanitary drains and sewers is appreciated.
1 Australian Standard AS1477, Unplasticised PVC (UPVC) pipes and fittings for pressure applications, 1973, Standards Australia, Sydney, Australia.
2 Australian Standard AS1415, Unplasticised PVC (UPVC) pipes and fittings for soil, waste and vent (SWV) applications, 1974, Standards Australia, Sydney, Australia.
3 Australian Standard AS1260, Unplasticised PVC (UPVC) pipes and fittings for sewerage applications, 1974, Standards Australia, Sydney, Australia.
4. Australian Standard CA67, Installation of PVC Pipe Systems, 1972, Standards Australia, Sydney, Australia.
5. Australian Standard CA68, Plastics Pipes Laying Design, 1972, Standards Australia, Sydney, Australia.
6. A. Whittle, APRI National Conference, Leura, Australia, 1997.
7. J. P. Lu, L. S. Burn and A. Whittle, Polymer Engineering and Science, 2000, 40 (10), 2217.
8. Australian Standard AS5055, Test method for the resistance of pipe joints to plant root intrusion, 2006, Standards Australia, Sydney, Australia.
9. R. J. LeHunt, Plastics Pipes V, 1982, York, UK, 21.1.
10. R. J. LeHunt, Plastics Pipes VI, 1985, York, UK, 9.1
11. L. S. Burn, K. G. Martin and S. D. Terrill, Effects of titanium dioxide on the weathering performance of UPVC pipe, 1987, DBR Report R87/3, CSIRO Highett, Australia.
12. L. S. Burn and B. L. Schafer, The environmental impact of lead leaching from uPVC sewerage waste and vent pipes, 1997, CSIRO, Highett, Australia.
13. A. J. Whittle and J. Tennekoon, Plastics, Rubber and Composites, 2005, 34 (7), 311.
14 ISO 21138.2, Plastics piping systems for non-pressure underground drainage and sewerage – structured-wall piping systems of unplasticized poly(vinyl chloride) (PVC-U), polypropylene (PP) and polyethylene (PE) – Part 2: Pipes and fittings with smooth external surface, Type A. 2007, ISO, Geneva, Switzerland.