Plastic pipe performance
What different types of plastic are used in pipe manufacture?
Modern plastic piping is mainly manufactured from Polyvinyl Chloride (PVC), Polyethylene and Polypropylene. Different forms of these polymers are used depending on the performance characteristics required from the pipe system. Some typical examples of plastics used in pipes are:
· MDPE (Medium density polyethylene);
· HDPE (High Density polyethylene);
· PEX (Cross-linked polyethylene);
· PE-PEX/AI/PE-PEX (A multi-layer combination Cross-linked polyethylene and aluminium);
· PVC (Polyvinyl Chloride);
· CPVC (Chlorinated polyvinyl chloride);
· PVC-O (orientated polyvinyl chloride);
· PPR(Polypropylene Random Copolymer).
· PB (Polybutylene)
What do the various labels on plastic pipes mean?
The marking on pipes complies with relevant product standards. Plastic pipes and fittings are marked for the end-use application, e.g. Hot & Cold drinking water or floor heating, as prescribed in relevant product standards.
In general, the marking shows:
- Manufacturer’s name or logo;
- Application class including information about service pressure/temperature classes;
- The type of plastic material;
- Production data;
- European (EN), ISO and local standards;
- Approvals (if relevant).
In addition, Hot & Cold plastic pipe systems generally carry a number of national certifications.
The application class provides data on the system’s design. The EN product standards specify application classes (hot water at 60 or 70°C, under floor low-temperature and high temperature radiator heating). The marking reflects the basic characteristics of the product. For more specific explanation on hydraulic performance and heat conductivity for example, please refer to the technical documentation of the manufacturer.
For more information, please refer to the relevant European and ISO standards and the TEPPFA website.
What is the life expectancy of a plastic pipe?
The durability of plastic pipes is related to the chemical degradation of the polymer used in the pipes. Laboratory ageing tests indicate that the life expectancy of some types of plastic pipes could be in excess of 100 years. Real experience in Germany has shown that buried PVC pressure pipes dug up after 60 years of active use were proven to be fit for purpose when analysed and likely to have a further life expectancy of 50 years.
Hot & Cold water pipe systems are designed to have the same lifetime expectancy as a typical domestic building, i.e. more than 50 years. There have been plastic pipe systems for Hot & Cold application in service since the 1970s. Based on ISO and EN standards, the expected lifetime of a system is based on the following considerations: service temperatures; pressure; peak temperatures; malfunction of heating devices.
For more information, please refer to ISO and 21003 EN standards, as well as the technical documentation of the manufacturer.
Do plastic pipes require maintenance?
Plastic pipe systems are designed to deliver at least 50 years of technical performance, in most cases without the need for maintenance. However, specific applications (such as sanitary pipe work, floor heating and radiator supply) maintenance may be required due to the use of the system e.g. an oxygen inhibitor or a defrosting agent.
Please consult the technical catalogue of the manufacturer and/or instructions for use.
How is the hydraulic capacity of Hot & Cold plastic pipe systems designed?
All systems for Hot & Cold applications should be designed in compliance with EN 806. Plastic pipe systems do comply with this standard. Because plastic pipe systems do not corrode and are less subject to scaling than metallic pipes, they will maintain their hydraulic capacity during their entire lifetime. Pressure loss, due to the length and configuration of the plastic pipe network, is a parameter calculated according to EN 806.
For more information, please visit the building section of the TEPPFA website at www.teppfa.com/building.htm
Also consult the CEN standard EN 806 - Specifications for installations inside buildings conveying water for human consumption (part 2 “design” and part 3 “pipe sizing”).
What are the commonly used jointing techniques for plastic pipes?
The most commonly used jointing techniques in plastic pipe systems are: Press fit joints; Push fit joints; Heat socket welding; Butt fusion welding; Threaded compression fittings; Solvent cement welding.
The multiplicity of jointing technics offered by plastic pipe systems, associated to their light weight makes them quick and easy to handle, cut, lay and connect in the trench. Generally with no need for special tooling, making them a safer and more cost efficient solution compared to non-plastics solutions.
All jointing techniques are specified in product standards and therefore reliable in terms of durability and performance. For the specific jointing procedures and equipment requirements, manufacturer’s instructions should always be followed.
What support should be used for mounting and fixing plastic pipes?
Common brackets with soft clamping surfaces and sufficient spacing may be used. Pipe support spacing may vary according to the nature of the plastic pipe system; solid wall or composite (see manufacturers’ technical catalogue). When pipes are mounted and fixed to the wall, no further support is necessary. Where valves or taps are used, these should be firmly anchored as required for all piping systems.
For more information, please refer to the ENV 12108 and/or manufacturer’s instructions.
Are the different types of plastic piping systems used for Hot & Cold applications interchangeable?
Solid wall pipes of the same material are standardised, including connection dimensions, and are therefore interchangeable. This is the case for plastic pipe systems like U-PVC (cold water), CPVC or PP-R. Other plastic pipe systems, such as multilayer pipes, can be connected to other systems using transition fittings.
For renovation and repair, care should be taken to use the appropriate pipes and fittings, taking into consideration that special transition fittings may be required if the pipe systems are made out of different materials, or are from different manufacturers.
Every system contains transition fittings. Please refer to product standards; or if in doubt, contact the pipe manufacturer.
Does hard water show scaling in plastic water supply pipes?
Scaling effects can occur in plastic pipes, but it is much reduced in comparison with metallic pipes. Scaling is an aggravating factor of bacterial growth in drinking water pipes, This is another benefit offered by plastic pipes: less scaling means better quality drinking water.
Is there a difference in heat loss between pipe systems made out of plastics and metal in heating systems?
For non-insulated pipes, the heat loss will be intrinsically lower for plastic pipes than for metallic pipes. But the differences between plastic and metallic materials are marginal when considering water temperature at the tap of 60º Celsius. The low thermal diffusivity of plastic pipe systems makes them cooler than metallic pipes when touched and therefore ensure a lower risk of contact burns.
It is recommended to maintain a distance of at least 50 mm between the cold and hot pipe and/or to suitably insulate them.
When a piping network is properly designed - according to EN 806, and insulation specifications properly fulfilled, there is no difference in heat loss in pipe systems made out of non-plastic materials. In case of faulty insulation, the heat loss will be higher with a metallic pipe than with a plastic one.
For more information, please consult the study of Uneto-VNI on the heat loss of piping systems at different tap temperatures.
How do plastic pipe systems compare in the generation and transmission of noise compared to metallic pipe systems?
Plastic pipe systems may transmit some noise, but the level is significantly less than in metallic pipe systems. Plastic pipes’ acoustic properties, help to keep the sound generation and transmission significantly low. These benefits can be experienced during installation and in service (noise transport caused by water ‘hammer’, flow speed and thermal expansion).
For more information, please refer to the publication of “Installateur” (Technical Magazine in The Netherlands) HM: date 2009.
Can plastic pipes resist chemicals?
Plastic pipes systems generally have a high resistance to corrosion and are not corroded by soft drinking water. This is a great advantage as corroded surfaces are an aggravating factor for bacterial growth in drinking water pipes. In short, the absence of corrosion in plastic pipes offers a better water quality!
The chemical resistance of plastics pipes is established in the wide range of pH value 2 – 13; the chemical resistance of plastics pipes has been tested for most chemical substances;
Test methods are standardized in ISO 4433 (Thermoplastics pipes – Resistance to chemicals classification).
All investigations have established that plastic pipe systems are highly resistant to the most commonly used chemicals. But, as with metallic pipes, plastic pipes may be corroded by some specific chemicals, so manufacturer information needs to be consulted in specific situations.
Plastic pipe systems are not corroded by most chemicals used for frost protection of heating/ cooling systems and are not subject to galvanic corrosion.
More specific technical information can be found within the technical documents for the standard ISO 4433 and manufacturers’ product information.
Does chlorinated drinking water affect plastic pipes?
Pipe materials should always be selected to meet their specific performance requirements. Any material can be vulnerable to a particular weakness in operation (frost, crushing, fire, chemical degradation etc) it is therefore important to specify pipes that are designed for the purpose they are being installed for. Some plastics can be effected by disinfects such as chlorine used in drinking water systems, others remain completely unaffected and are perfectly reliable when exposed to chemicals like chlorine.
The advice of the manufacturer should be sought to check the compatibility with the disinfection treatments which could be used in the relevant network.
How do plastic pipe systems react to disinfection treatment?
Pipework within buildings, under certain conditions and regardless of the material used, may be exposed to the growth of micro-organisms which could ultimately present a hazard to health – particularly in drinking water installations. In this context, preventive and curative disinfection treatments may be applied to the piping network. Disinfection procedures may involve both thermal and chemical treatments.
Disinfection is typically carried out using chlorine and oxygen in different forms e.g. as hypochlorite, chlorine gas chloramine or chlorine dioxide, hydrogen peroxide, ozone. Sodium and potassium hypochlorite are the most commonly used.
Plastic pipe systems are resistant to the most commonly used chemicals for disinfection of drinking water networks. Studies with plastic pipes have resulted in clear recommendations concerning the concentration, time and temperature envelope for the safe use of these disinfectants in piping networks, without any detrimental effect on the plastic pipe networks in general.
Advice of the manufacturer should be sought to check the compatibility with the proposed treatment.
For more details, please consult DVGW guidance documents and the study from OFI – Österreichisches Forschungsinstitut: Legionella in Drinking Water Systems – An issue that does not depend on the materials used.
Please also consult the TEPPFA Guidance paper at http://www.teppfa.com/Industry-Studies-in-Building.asp
Do plastic pipe systems cause corrosion on the metal parts of heating systems?
No, the corrosion of metal parts in heating systems is primarily caused by oxygen.
Most plastic pipe systems designed for Hot & Cold applications are fully suitable for use in heating systems, either because they are non-permeable to oxygen (e.g. PVC-c) or contain an oxygen barrier layer (PEX pipes).
Corrosion of metals is a hazard in heating installations. Therefore it is essential that the water oxygen content is kept to an absolute minimum. Oxygen will almost always be present in any system as it can enter through a variety of points such as header tanks, threaded joints, valves and pumps. For heating systems, an oxygen inhibitor may alternatively be used. Please also refer to manufacturer’s information.
How do plastic pipe systems for Hot & Cold applications react to variations in temperatures?
All materials expand when temperatures rise. Plastic pipes expand more than metallic pipes but in most cases system design can cope with any expansion. In case of long length piping the installation of e.g. expansion absorbers, lyres, bends, loops etc may be necessary and should be done according to the manufacturer’s instructions.
For further questions on expansion, your plastic pipe manufacturer should be consulted.
How do plastic pipes behave at sub-zero temperatures?
Specific polymers are available that have particular resistance to extremely low temperatures in exposed above ground situations but the European standards for drinking water (EN1452) or on sewage pipes (EN1401) require a high impact resistance on standard plastic pipes at 0°C. This requirement allows for safe handling and installation at temperatures a few degrees below 0°C. Once in place, plastic pipe systems are able to withstand much lower temperatures without deterioration during their expected lifetime, but are in fact not exposed to extreme sub-zero temperatures.
What’s the failure rate of plastic pipes compared to non-plastic materials?
The reliability of plastic pipes over non-plastic materials like metal and concrete is undisputed. With less joints, flexibility to bend or flex under excessive loads or pressure, plastic pipes suffer from fewer cracks and breaks, thus minimising leaks and operating costs. Typically plastic pipes suffer from less than half the failure rate of steel, cast iron concrete or clay pipes. PVC pipes in particular are many times more reliable than similar pipes made of alternative materials.