Safe, durable & cost-efficient, sustainable and recyclable PVC

The durability of PVC pipes is related, as it is for all other thermoplastics materials, to the chemical degradation of the polymer used in the pipes. However unlike other thermoplastic pipes PVC pipes do not oxidise.

Stabilisers are used in PVC pipes to prevent degradation of the polymer during the extrusion process and storage of the pipes before they are buried in the ground. However, when the pipes are buried in the ground, no chemical degradation is expected to take place. For this reason the durability of the PVC material in buried pipes is expected to be very good (maybe even be more than 1000 years[1].

In standardised pipes for potable water (EN 1452) the expected lifetime of PVC pipes under pressure is extrapolated based on hoop stress testing of pipes for up to 20000 hours. This allows an estimation of the durability by extrapolation to a life expectancy under pressure of 50 to 100 years[2]. Real experience in Germany[3] has shown that buried PVC pressure pipes dug up after 70 years of active use were proven to be fit for purpose when analysed and likely to have a further life expectancy of 50 years.

Studies in the Netherlands have examined several potential degradation processes for PVC pipes and carried out tests on pipes up to 45 years old. These studies also concluded that the life of PVC drinking water systems could exceed 100 years[4].

References
[1]Janson, Lars Eric 1996 "Plastics Pipes - How Long Can They Last? KP Council, Nov. 1996
[2]EN-ISO 9080
[3]"70 years of experience with PVC pipes" by Thomas Hülsmann and Reinhard E. Nowack, 13th World Pipe Symposium, Milan, Italy, April 2004.
[4]"Long Term Performance of Existing PVC Water Distribution Systems" by A. Boersma and J. Breen, 9th International PVC Conference, Brighton, 26-28th April 2005, pp. 307-315

PVC-U piping systems belong to the category of so called "flexible designed pipes". This flexibility provides a great advantage compared to pipes made of traditional materials such as concrete or clay.

For flexible designed pipes: the soil supports all the stresses on the pipe (including soil weight) and the pipes deform slightly but do not break. For pipes made of traditional materials, the soil concentrates the stresses directly on to the crown of the pipe; these pipes do not deform but a failure mode results in a break in the pipe.

For most of the "good quality soils" (e.g. granular types of soil) the soil supports all the stresses and, as this type of soil can be easily compacted, the deformation of the PVC pipes is only 1 or 2% which does not affect the functional properties nor the tightness of the systems at all. In weak soils ("plastic soils") the PVC piping systems deform slightly more (in the range of 5 to 10%) but they still perform perfectly well.

For all piping materials very difficult soil conditions will need a thorough examination or calculation by qualified civil engineers and certain European or national standards ask for static calculation for the piping systems[1].

Reference
[1]EN 1295 being developed tries to make a compromise between the two more widely used methods in Europe:

• ATV 127 (Germany)
• Fascicule 70 (France)

PVC-U and C-PVC pipe systems are completely safe for drinking water applications and have been used in such applications throughout Europe (and elsewhere) for many decades.

In Europe, the safety of PVC-U and C-PVC pipe systems for the transportation of drinking water is currently regulated and assessed nationally, although significant effort is ongoing at European level for the harmonisation of regulations and test methods. Regulations are presently determined by national bodies and third party certification is carried out by accredited laboratories and institutes who subsequently also carry out regular audits to ensure continued compliance.

As part of the harmonisation activities, European (EN) standards are under development for a number of test methods designed to assess the suitability of plastics pipe systems for drinking water. These standards include tests for organoleptic assessment (odour and flavour), the migration & leaching of substances into the water and microbial growth.

Migration: Different methods are used to detect the migration of substances present in PVC-U and C-PVC formulations. Leaching behaviour is assessed by prolonged direct contact of the potable water with the products in very severe conditions. Then the "migration water" is checked using different techniques, including searches for traces of molecules below the level of a few µg/l. Virtually nothing leaches out: the leachates are very similar to the blanks used when analysing them with techniques such as gas chromatography combined with mass spectroscopy (GC-MS).

Lead is not used anymore in stabilisers and such stabilisers have never been a source of lead in drinking water, as the stabilisers are immobilised within the PVC pipe structure during the manufacturing process. New stabiliser systems being used as alternatives to lead are fully assessed ("positive listing") and do not affect the drinking water characteristics in any way.

Traces of vinyl chloride monomer, sometimes exceeding regulatory limit of 0.5 µg of VCM/l of water, have been detected in some cases. It is important to keep in mind that this 0.5 µg/l limit is based on a guideline from the World Health Organisation (WHO) where the value has been set in order to guarantee an acceptable health risk, even in case of exposure during an entire lifetime.

These cases are related to exceptional circumstances (small diameter pipes in thinly populated regions, hence with intermittent flow). Most importantly, these cases appeared only in pipes installed before the 1970s, when the health risks of VCM were identified. PVC resin produced before then, although meeting all standards applicable at that time, contained higher levels of residual monomer than presently. Under usual conditions of use, water transported in PVC pipes produced in those days does also comply today with the current drinking water regulation. However, model calculations show that in exceptional circumstances (small diameter pipes, infrequent use) the VCM level reached after a period without flow can exceed the limit. No measurement result above the limit has ever been found in water flowing in pipes made from PVC produced after 1980.

It is important to stress that no vinyl chloride monomer is produced by the degradation or incineration of PVC products.

In any case, VCM concentration can easily be reduced to below the WHO guidance limit by flushing the pipe or by boiling the water. The high volatility of VCM leads to a rapid transfer from water into the atmosphere, where VCM does degrade by reaction with photochemically produced substances naturally present in the atmosphere. This limits its half-life of VCM in the atmosphere to between a few hours and a few days. VCM is therefore not persistent in the environment.

Microbial growth: PVC-U and PVC-C pipes are known to perform very well indeed according to the different methods used in Europe for the assessment of microbial growth of products in contact with drinking water (Germany, United Kingdom and The Netherlands). Many field studies confirm this good behaviour, which is linked to the absence of migration and the very good surface properties of these piping systems.

Odour & Flavour: Owing to absence of migration and low bacterial growth in PVC & PVC-C, the organoleptic properties of pipes made from these materials are generally very good, which is confirmed by regular testing by different European institutes.

As part of the EU harmonisation process, EN standards include EN 1420 & EN 1622 for the assessment of organoleptic properties and water quality; CEN-TR 16364 for the prediction of migration using mathematical modelling; EN 16421 for assessing microbial growth and EN15768 for the GC-MS identification of water leachable organic substances. In addition, EN 14395-1 is used for organoleptic assessment of water in storage systems.

Apart from these standardisation initiatives, a European positive list for substances used in plastics materials in contact with drinking water is also under development. This harmonised EU positive list will eventually replace several existing national drinking water positive lists. Further guidance can be found in ISO TR 10358.

Across Europe, with some exceptions like the Netherlands and Denmark where ground water is exclusively used, chlorination of drinking water is a common way of avoiding the presence of pathogenic bacteria and to ensure that EU member states conform to the EU Drinking Water Directive.

Although chlorine can affect the taste and odour of water, it has long been considered as the best way to provide safe water at the tap. The concentrations used in Europe are calculated so that the remaining chlorine at the tap is in the order of 0.1 mg/l.

Even at levels of 1 mg/l, as used in several countries, there is virtually no interaction with the PVC piping system:

• The "chlorine demand" of the material is nil
• The chemical interaction with PVC is so low that the piping systems can withstand hundreds of years in such conditions (even at temperatures higher than 20°C which is the normal maximum "drinking water" temperature)

PVC pipes have excellent resistance to chemical attack which make them particularly suitable for a wide range of applications.

In normal civil engineering applications PVC push-fit pipes are not subject to chemical attack. In contaminated ground or specific foul water and industrial systems, they are highly resistant to strong acids, alkalis and surfactants. They can be used in the presence of sulphuric acid which often exists in abnormal conditions relating to sewerage systems.

PVC piping systems are used in industrial applications for their excellent chemical resistance. However, sealing rings are not recommended for these applications and solvent cemented joints are preferred.

PVC is resistant to most oils, fats, alcohols and petrol, but some petrol-based fuels containing benzene cause swelling.

PVC is suitable for use in contact with aliphatic hydrocarbons, but aromatic hydrocarbons can cause unacceptable swelling, even by absorption from the vapour phase[1].

PVC is resistant to all but the most severe oxidising conditions. Hydrogen peroxide at all concentrations has no effect, and even concentrated solutions of oxidising salts such as potassium permanganate cause only superficial attack.

PVC is generally unsuitable for use in contact with aromatic and chlorinated hydrocarbons, ketones, nitro compounds, esters and cyclic ethers, which penetrate the PVC causing marked swelling and softening. These penetrating solvents may be harmful to PVC even when diluted, but, when they are diluted, their effects fall off noticeably and, at very low concentrations such as are present in many effluents, can be handled safely.

Further guidance can be found in ISO TR 10358.

Reference
[1]Journal of Institute of Gas Engineers, 2, 3, March 1962, pp. 185-194

All plastic materials submitted to a constant load undergo a progressive deformation over time. This phenomenon, caused by the displacement of molecular chains among themselves, is commonly called creep. This phenomenon depends principally on the type of plastic, its molecular structure, the operating temperature and time (it can for example take several hundred years for PVC pressure pipes to fail as a result of creep). For non-pressure pipes, standards describe the relationship between short-term and long-term creep: this is called the Creep Ratio[1]. This ratio is also used in designing plastic pipes.

Among plastic pipes, PVC pipes have the lowest creep ratio. As an example, in the European project for structured wall pipe standards[2], the ratios demanded for different materials are:

PVC -U <2.5 and PP, PE <4

A lower creep ratio indicates that in the long term, the material maintains similar properties to those it initially had.

References
[1]ISO EN 9967
[2]prEN 13476
For further information: UK: Plastic Pipes Group: "PVC Pipe Systems", France: STR-PVC: "Livret Syndotec," Italy: "Le condotte in PVC", Spain: Asetub: "Manual Tecnico conducciones de PVC," etc…

As a result of the combination of the following characteristics, PVC is generally the most efficient, quick installing and cost-effective of all the spectrum of solutions for piping.

• Lightweight: PVC pipes are light and easy to handle (up to 6 m length), significantly reducing the need for mechanical support for placing and fixing the pipes together, leading to a cost efficient installation.
• Joints: PVC piping systems can be installed with different types of joints: solvent cement joints and push-fit joints. Across Europe , push-fit joints are usually preferred for municipal installations. The use of push-fit joints is a very important characteristic as it not only assures a watertight, safe and durable union, but permits a fast and simple mounting, an important cost saving during installation, as it avoids using complex welding operations and costly investments in sophisticated equipment and specialised skills.
• Fittings and special operations: PVC pipe systems are normally completed with the widest range of fittings and ancillary products, allowing a modular installation and high quality of the full network. When finishing work has to be done by hand (For example making holes, installing saddles and cuts in the pipes), rigid PVC is easy to work with, and does not need complex tools or special expertise.

Since the acceptance of the concept of Sustainable Development (SD) (world conferences of Rio de Janeiro 1992 and others) it became accepted that SD is based on three pillars, namely ecology, economy and society.

The environmental impact of PVC products has been investigated in numerous studies, quantified in many life cycle analyses and compared many times to products made from alternative materials. The latest and most comprehensive study was a Review commissioned by the EU[1]. It showed PVC products to be comparable to alternatives in their environmental impact. The strongest aspects of PVC products are performance and cost; PVC products are amongst the lowest cost products for a given performance. Low cost products can positively contribute to all areas of SD:

• Low cost products save scarce money, so they are favourable to a sustainable economic development.
• Low cost products are more affordable to socially disadvantaged people, not only in industrialised but more so in developing countries and the money saved can be used to optimise social development. Both points are favourable to sustainable social development.
• The money saved by low cost products can be used to optimise ecological development, so they are favourable to sustainable ecological development too.
• The huge potential impact of low cost products made from PVC can be shown easily: With only 0.5 % of the cost of PVC-products one can compensate the entire energy demand (100%!) and the entire Greenhouse Gas effect (100%!) caused by them. Investing this small amount of money into environmental improvements allows it to create products which are much better in these important environmental categories than all alternatives.
• The social aspect of products is not assessed well enough up to now, except for the positive economical/social points mentioned above in this chapter and the health impacts on workers in the PVC industry: After many years of sustained efforts, workers' safety has reached a very high standard in the chemical industry altogether compared to other industries.

Reference
[1]European Commission: "Life Cycle Assessment of PVC and of principal competing materials - Final report," July 2004