Plotting A Plumbing System’s Lifespan

As the issue of sustainability continues to be seen near the top of the agenda in the construction industry, cost-effectiveness and low environmental impact are key elements in every specification process. However, in examining how a piping system can provide durability and performance throughout its lifetime, thus offering a sustainable solution, several criteria need to be considered. The most important are:

  • Internal pressure
  • Operating temperature
  • Water quality
  • Disinfectant additives (type and amount)
  • Material used for system

Wavin has developed a lifetime assessment tool in the form of software which can be used to determine the potential lifetime of a proposed piping system, considering a range of expected operating conditions. Below are two examples of how the tool can show the effect that changing the criteria for operating the system have on lifetime performance, each looking at one of the criteria. Two materials are considered in each of the examples: cross-linked polyethylene (PEXc) and polypropylene (PP-R).*

1: Impact of temperature on performance

Design criteria for system considered include:

  • No chlorine added to the public drinking water supply
  • No chlorine added to the water system by the carrier of the installation
  • 70°C backflow temperature
  • System operating continuously.

The life expectancy for this system, operating at 70°C, is 434 years using PEXc pipework and 117 years using PP-R. At 80°C, the life expectancy falls to 134 years for PEXc and 40 years for PP-R. Therefore lifetime assessment tool shows that a 10°C increase in operating temperature results in a greater than 65% reduction in lifetime performance.

2: Impact of chlorine disinfection on performance

The design criteria for the system in this example include the following:

  • Small amount of chlorine dioxide disinfectant added continuously to the water distribution (public and/or local)
  • 60°C backflow temperature
  • System operating continuously.

The life expectancy for this system, using 0.5ppm of chlorine dioxide, is 66 years for the PEXc pipework, and 23 years for the PP-R. At 2.5ppm of chlorine dioxide, the life expectancy falls to 40 years for PEXc and 12 years for PP-R. Therefore, a fivefold increase in chlorine dioxide results in a 40% reduction in lifetime performance.

The use of a lifetime assessment tool such as the one developed by Wavin, will enable the user to understand the impact of the piping material on the durability of a system. This is especially beneficial when considering the design of a continuously operated recirculating system, due to the demands placed on these kind of systems. When maintained at a constant high temperature to provide a constant source of hot water, the piping system is reliant upon the quality of the component parts and the installation.

*(It is important to note that recirculating systems are excluded from the scope of BS 7291:2010, the British standard covering thermoplastics pipe and fitting systems for hot and cold water for domestic purposes and heating installations in buildings. This covers solid-wall PEX and polybutylene, neither of which should be used in continuously operated recirculating systems.)

If you are interested in learning more about Wavin’s Tigris K1 press-fit plumbing system, information can be found here