Technical Feature
• The study will need to be extended to consider
cradle-to-grave.Doing this as described in EN15978, the main calculation standard for construction products’s impacts, will require construction products to use an expected service life in accordance with ISO15686 Service Life. Failing that, the design life would be used. Unlike concrete pipes, plastic pipes do not have a design life proven to exceed 100 years. EN13476 Plastics Piping Systems for Non-Pressure Underground Drainage and other plastic pipe standards refer to a range of test methods that indicate a 50 year design life. If EN 15978 rules on study period requirements are followed then a pipeline serving for 100 years will require two plastic pipe design lives (compared to a single concrete pipe design life), which will potentially almost double the carbon footprint of a plastic piping cradle to grave solution.
• End of life impacts should be included.EN15804 accounts for emissions occuring after hundreds of years (if significant): this means that the impact associated with degradation of thermoplastics after 100, 200 or 500 years or more must be included. The can be between 1.0 - 2.5 tonnes of CO2e per tonne of plastic left in the ground at the end of its working life. This can increase the carbon footprint of HDPE pipes by as much as 60%.
• Appropriate allocation of steam cracker
impacts.Ethylene (the main ingredient used in the production of HDPE), is produced by the steam cracking of naptha or ethane. This process results in a number of other by-products with much lower economic value than ethylene. The PlasticsEurope Eco-profile of HDPE pipe allocates the environmental impacts of this process by mass of each product produced. Given the significant variation in price of the products generated from cracking, the CPSA believe that it is highly unlikely that the mass-allocation process would be acceptable under EN15804,. The carbon footprint of HDPE pipe could increase by 25% to 170% if the carbon impact allocation was changed to a value-based system.
It is clear from the above that the PlasticsEurope Eco-profile study may be underestimating the carbon footprint impacts of some UK based plastic pipe manufacturers’ products by a factor of three.
To make it easier for specifiers, it would be helpful if plastic pipe manufacturers were to develop realistic and robust carbon footprints based on a recognised methodology and data sources in line with EN15804.
Of course, for asset owners and installers the carbon footprint of the manufactured pipeline product is only one part of the carbon footprint of an installation. Once on site another critical factor is the installation process and particularly the quantity of bedding material required.
One of the big advantages of using concrete for wastewater pipelines is that because concrete pipes are structural elements they contribute to the integrity of an installation. By contrast, plastic pipes are flexible and behave very differently with their installations more reliant on a high quality construction embedment to ensure they are structurally sound. As a result, plastic pipes can require significantly more imported granular bedding material compared to the equivalent concrete pipe leading to higher carbon emissions for the installation.
16 drain TRADER | December 2016 |
www.draintraderltd.com
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