FAQ about PVC pipes

In our FAQ you can find answers to the most common questions about PVC in pipe systems.

Physical properties

1What is the life expectancy of PVC pipe?
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
2What effect does exposure to ultraviolet radiation have on PVC pipe?
Prolonged exposure of PVC pipes to direct sunlight may cause a thin film of degradation on the exposed surface of the pipe over time. This microscopic layer, with a thickness of about 0.05 mm, will gradually become visible as discolouration (so called bleaching) and it stops once the surface exposure ceases[1].

Experience has shown that this microscopic layer protects the underlying material from ultra-violet light ensuring that the rest of the pipe wall is unaffected by the sunlight[2]. If you make a gentle scratch on the outer pipe surface you will see that the normal colour is visible just under this very thin layer.

Extensive tests carried out on pipes exposed to sunlight over a period of up to 4 years demonstrate that there is a slight increase in tensile strength and modulus of elasticity and a minor decrease in impact strength. In practical terms the overall pipe properties are virtually unchanged, and pipes affected by this phenomenon may be used for normal installation.

References
[1]BPF Plastics Pipes Group, 2002: "PVC Pipe Systems for Water Supply" Version 01/02 (Revised)
[2]Uni-Bell: "UV Exposure has No Practical Effects on PVC Pipe Performance"
3What is a flexible pipe?
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)
4How do PVC pipes behave at sub-zero temperatures?
The performance of a pipe in service is not affected by low temperature as long as the fluid being conveyed is flowing freely. Several national organisations recommend best installation practices for PVC pipes[1],[2]. These manuals generally recommend installation at temperatures >0°C.

The minimum Impact resistance of a pipe is specified in the product standards (see EN 1401, EN 1452, etc.). For example, a sewage pipe with a diameter of 110 mm should withstand the impact of a striker of 1 kg mass falling from a height of 1.60 m at 0°C. In practice, the real resistance is generally much better than the minimum required value.

To highlight the strength of PVC pipes in cold conditions please look at the following video which shows how well PVC pipes perform.

Click to play

The video shows an impact test carried out on a solid wall PVC pipe of 110mm diameter with a striker of 8 kg mass being dropped from a height of 2 m at 0°C.

Impact resistance of modified PVC (PVC-M) or molecularly oriented PVC (PVC-O) is even higher than the resistance described above.

Reference
[1]UK: Plastics Pipes Group "PVC Pipes Systems", France: STR-PVC: livret Syndotec, Italy: 'le condotte in PVC", Spain: AseTUB: Manual Tecnico conduccionnes de PVC, etc.
[2]Uni-Bell PVC Pipes Association Technical Blog, March 13th 2013
5How do PVC pipes behave under constant stress?
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…
6Permeability of PVC pipes
Permeability is the ability of chemical substances to enter the pipe system through the pipe walls or joints.

The occurrence of this kind of event has been reviewed by various water distribution companies and no major problem has occurred with PVC piping systems.

As an example the intrinsic permeability of PVC is in the order of 10 times lower than for polyolefins.

There have been several studies concerning the permeability of plastic pipes and pipes of other materials[1],[2],[3]. The most recent study of plastics pipes was carried out by the Awwra Research Foundation on the "Impact of Hydrocarbons on PE/PVC pipes and Pipe Gaskets [Project #2946]"[4].

This concluded that either PVC or ductile iron (DI) water mains can be safely used in any level of gasoline contamination, even free product, as long as there is a minimal average water flow in the mains. Although benzene, toluene, ethylbenzene, and xylenes (BTEX) will permeate the gaskets, US EPA MCLs will not be exceeded. Similarly, PVC and DI pipes can be used with periods of stagnation (i.e., service connections) for any level of groundwater contamination by gasoline. PVC itself is impervious to gasoline, BTEX, and trichloroethylene (TCE) in groundwater at commonly encountered levels of contamination.

Berens[3] concluded that rigid PVC is an effective barrier against permeation of environmental pollutants.

In PVC pipe systems, the joint zone may be a weak point, but the exposed area of the elastomeric seal compared to the total area of the pipe surface is very small. Several of the studies mentioned below have also looked at the effect of hydrocarbons on the sealing rings; two of them concluded that NBR seals are more resistant than SBR seals.

References
[1]Vonk, "Permeation of Organic Compounds Through Pipe Materials," Pub. #85, KIWA, Neuwegein, Netherlands, 1985
[2]Cassaday, Cole, Bishop & Pfau, "Evaluation of the Permeation of Organic Solvents Through Gasketed Jointed Unjointed Poly (Vinyl Chloride), Asbestos Cement and Ductile Iron Water Pipes - Phase 1 Report," Battelle Columbus Laboratories, Columbus, OH, for the Vinyl Institute, Div. of Soc. of Plastics Indus, Inc. 1983 [3]Berens, "Prediction of Organic Chemical Permeation through PVC Pipe," JAWWA 77 (11), 57-64 (1985)
[4]Ong, Gaunt, Mao, Cheng, Esteve-Agelet, Hurburgh, "Impact of Hydrocarbons on PE/PVC Pipes and Pipes Gaskets [Project #2946]," Awwra Research Foundation, 2007
7Chemical resistance of PVC pipes
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
8Does chlorinated drinking water affect PVC pipes?
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)
9How do PVC pipes perform in fire?
PVC-U is inherently self-extinguishing and does not require any additional flame retardants to meet most flammability requirements.

Piping systems may have to withstand "resistance to fire" given in standards or regulations. In other cases, there are no national requirements or regulations for the fire behaviour of piping systems in relation to their function within the building structure.

The European system of classification of the reaction to fire test of construction products is described in EN 13501-1: "Reaction to fire classification of construction products and building elements" which includes optional requirements for smoke and burning droplets.

The Euroclass system is based on different tests depending on the level of fire protection that is required of the end product in its intended application. PVC piping systems are generally classified as Euroclass B and burning droplets are not a concern for them.

Some characteristics not covered by the EU classification system may be specified in national quality marks, for example intumescence in France.
10Safe drinking water in PVC pipes (migration and bacterial growth)
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.

Network characteristics

1What are the advantages of using push-fit PVC pipe systems?
The push fit joint with rubber seals on PVC-U pipes provides a number of advantages:

  • PVC pipes, fittings and ancillary parts are manufactured with tight tolerances on dimensions, which means that the elastomeric seal in the joint provides leak-free transportation of potable water as well as sewerage.
  • The push fit joint system makes PVC pipe systems easy to assemble.
  • The joints are superior to most other pipe connection systems due to quick and easy handling in the trench with no need for special tooling.
  • The pipes are easily cut and placed in the trench, making them a winner on installation cost.
  • Push-fit PVC pipes allow thermal expansion and contraction of the PVC pipelines.
  • In practise installation can be carried out with the minimum open length of trench enabling very limited transportation of excavation equipment.
  • Push-fit joints allow small changes of direction in a pipeline and for larger changes of direction there exists a huge range of PVC fittings which can provide the necessary solution.
2What is the choice of stiffness and maximum allowable depth of bury for PVC pipes?
Stiffness is the property of pipes that defines their resistance to deformation under exterior loads, mainly vertical loads associated with buried pipe conditions. In non-pressure applications, this is a basic property to ensure the right performance of the installation.

Stiffness depends mainly on two factors: E modulus, which is a physical property of every material, and the geometry of the profile of the pipe. The behaviour of the pipe, and the deformation it reaches over time, is not only dependant on stiffness, but on soil and installation conditions. A higher stiffness gives a better performance, but the following graph shows the behaviour and influence of both stiffness and installation conditions. Under a qualified installation, stiffness is not so relevant and all stiffness classes are suitable to be used.

Some organisations for plastic pipes have proposed or developed methods to rapidly evaluate the behaviour of buried pipes.

Stiffnes of PVC pipes - FAQ Figure 1: Design graph for determining the pipe deflections immediately after installation and after settlement of the soil

The diagram proposed by TEPPFA (The European Plastic Pipes and Fittings Association) clearly shows that SN4 or SN8 piping systems present very good behaviour when the level of workmanship is good or at least standard.

On the vertical axis, the pipe deflection is shown and on the horizontal the pipe stiffness classes. For each installation group an area is given in which the deflection after installation is expected. The upper edge of the area represents the maximum deflection to be expected. The lower edge of the area shows the average deflection to be expected.

The graph shows the deflections immediately after installation. It does not include the effect of traffic load, depth of cover or groundwater. The soil will further compact in the course of time. This further compaction is caused by the weight of the soil, the percolation of rain and ground water through the soil and by traffic load.

In order to obtain the final deflection including the effect of traffic, one shall add a consolidation value to the initial deflection. These consolidation values are listed in the table in the graph. Hence the final deflection becomes:

Final deflection = Initial deflection + C f

PVC4Pipes recommends SN 8 as a standard pipe that covers a depth of burial ranging from 0.6 to 6 metres in most soil conditions. Other depths of burial can be employed for PVC pipes (up to 15m) but, for these depths, specific conditions have to be studied on a case by case basis.

Many other calculation methods are listed in different European countries, but all of them agree on the wide versatility of PVC systems.
3What is the reason for selecting the correct pressure class?
The criteria for choosing the correct pressure class are established in the standard EN 805: "Water supply - Requirements for systems and components outside buildings."

The pipe system designer must calculate all the conditions that affect a water network, including static and transient effects, to obtain the basic parameters, as for example, the allowable operating pressure (PFA) and the allowable maximum operating pressure (PMA). After calculations, the designer will choose between the several classes that are possible in rigid PVC pipes.

The pressure classes for conventional rigid PVC pipes are defined in the standard EN 1452: "Plastic piping systems for water supply. PVC-U" and the pressure classes for molecular oriented (PVC-O) pipes are defined in ISO 16422: "Pipes and joints made of oriented unplasticised Polyvinyl chloride for the conveyance of water."

The following classes are available for PVC piping and; the most used in Europe are for PVC-U 10 and 16 and for PVC-O 16 and 25: Pressure classes for PVC pipes - FAQ
4Can PVC pipes withstand a vacuum? If so, what is the maximum vacuum that PVC pipes can withstand?
PVC pipe systems can withstand a vacuum and can operate under pressures as low as -0.9 bar in regard to the pressure class of the PVC-system PN 10. For non-pressure and vacuum to -0.3 bar, PVC sewer systems can be used.
5Length of pipes
It is conventional to use rigid PVC pipes of lengths between 3 m and 6 m in all applications although it is also possible to use pipes in lengths of up to 12 m on special projects. These relatively short lengths allow rigid PVC pipes to be stored and transported easily and also ensure that they are very easy to install. The short lengths also eliminate any problems associated with longitudinal bending.

Rigid PVC pipes are easy to handle manually as the weight of each section is relatively low. The assembly of rigid PVC pipe sections and their connections to other pipe fittings can be undertaken by using a sealing ring or, for some industrial applications, by the use of an adhesive; this depends for which application the pipes will be used, or on the different traditions country by country.

Short section lengths of rigid PVC pipes make it easy to install and to adjust the length at junctions etc. Rigid PVC pipes can also be repaired quickly and easily with only a short length of pipe needing to be removed.

In different countries when talking about the measurement of lengths of pipe there are two different measurements used and they are: "without socket" known as the working length, or "with socket" known as the overall length.
6What are the main advantages of installing PVC pipes compared with other solutions?
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.
7 What is the design coefficient for PVC-U pressure pipes?
The design coefficient (safety factor) is used in the design of all pressure systems using plastics pipes. It takes into consideration service conditions as well as properties of the components of a piping system.

This coefficient is illustrated by the following graph:.

Design Coefficient - PVC Pipes for Water Distribution design coefficient for PVC-U pressure pipes - FAQ

According to ISO 12162 the minimum value for design coefficients (C min ) are as follows:

  • PVC-U 1.6
  • PVC-A 1.4
  • PVC-O 1.4

Sustainability

1Why are Life Cycle Assessments (LCA) important?
To truly understand a product's environmental 'footprint', its entire life cycle needs to be evaluated. This is known as LCA. Through this form of assessment environmental effects associated with a product's manufacture may often be counterbalanced over time by a reduction in transportation and installation coasts and the benefit of a long, beneficial, low-impact life. For example, emissions associated with PVC window production compared to wooden windows are far outweighed by decades of energy-saving benefits and not having to replace them as quickly or apply preservative paints or chemicals.

PVC products perform favourably in terms of energy efficiency, thermal-insulating value, low contribution to greenhouse gases, low maintenance, and product durability.

Recent life-cycle studies show the health and environmental impacts of PVC building products are comparable to or less than the impacts of most alternatives.
2Why could PVC be good for sustainable development (environment, economy, society)?
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