FAQ - Chemical properties

Chemical 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. However, 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 phase1.

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.

References
  1. Journal of Institute of Gas Engineers , 2, 3, March 1962, pp185-194

Does 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 0.1mg/l.

Even at levels of 1mg/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)

How 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.
Currently some EU-countries have material specific national "reaction to fire" classifications such as the French M1, German B1, Italian Class 1 and the UK Class 1.

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 introduction of the new 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.

Safe drinking water in PVC pipes (migration and bacterial growth)

PVC-U and PVC-C 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 PVC-C 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 PVC-C 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 used less and less as a stabiliser 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.

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 under development include EN 1420 & EN 1622 for the assessment of organoleptic properties and water quality; CEN-TR 16364 for the estimation of migration by diffusion modelling; EN 16421 for assessing microbial growth and EN15768 for the GC-MS identification of water leachable organic substances.

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.