Polyethylene of Raised Temperature Resistance (PE-RT) is a resin that builds on the traditional properties of polyethylene, combined with the latest technology (constrained geometry catalyst, solution process and ethylene-octene copolymer) to add extra performance characteristics such as enhanced strength at high temperatures. The family of DOWLEX™ PE-RT Resins has a proven track record of more than 25 years for delivering outstanding performance in pipe applications. MULTITUBO PE-RT/AL/PE-RT is manufactured in Germany and DOWLEXTM PE-RT resins and Dow adhesives are used in the production process.
In multilayer pipes, the separate layers are usually bonded using an adhesive with superior performance and excellent processing characteristics. For polyolefins, those adhesives typically consist of functionalized polyolefins which adhere well to the polyolefin layer and bond via their functionality to polar layers. It’s important that the adhesive is properly prequalified as the application characteristics, the possibility of extrusion and other properties can vary quite substantially. Some adhesives perform well at room temperature, for instance, but because of their chemical structure or molecular weight distribution, may suffer dramatic losses in peel adhesion values at higher temperatures. Depending on the technical demands the selection of the right adhesive to perform in an application can make the difference to whether the final product can meet the requirements or not. Another important aspect is the stabilization package of the adhesive. The application for hot and cold water is typically at higher temperatures. In order to prevent an early degradation of the adhesive, it needs to be properly stabilized and the components need to be compatible with the stabilization package of the PE resin. A good quality adhesive is not an optional extra – it is essential to the performance of the whole multilayer pipe, because unless the aluminium becomes one with the inner layer it cannot perform properly.
DOWLEX™ PE-RT resins which MULTITUBO uses in manufacturing, have been tested according to the ISO 9080 standard for long-term hydrostatic strength and fulfil the requirements for hot water applications according to ISO 10508 for all classes. However, defined by ISO 2578, there is an additional method available for the crucial outer layer that determines time-temperature limits after prolonged heat exposure. To meet its requirements, it must be proved in a heat aging oven test that the elongation at break of the material is more than 25% of the original value after a full year testing. Recent 12 month tests have confirmed that DOWLEXTM PE-RT resins outperform this minimum prerequisite by a considerable margin. This is an achievement which throws down a challenge to alternative outer-layer materials which cannot boast similar performance. Unlike MULTITUBO, some multilayer pipe manufacturers use another raw material for the outer layer in order to save, for example PEHD/HDPE, the so called alkathene or polythene pipe. In 2005, DOWLEX™ PE-RT resins systems were awarded a European Technical Approval – signified by the “CE” mark quality standard. This was the first time any pipe system had been awarded an ETA.
Combining the benefits of metal and plastic material, but avoiding the drawbacks of both, PE-RT/AL/PE-RT multilayer pipes are an ideal choice. This pipe is made up of a longitudinally welded aluminium layer that is surrounded on the inside and outside by layers of polyethylene of raised temperature resistance. The aluminium provides excellent resistance to pressure and temperature. The inner and outer PE-RT layers inhibit scaling and corrosion whilst the addition of aluminium gives the pipe a strength which makes it an excellent alternative to copper. With PE-RT, there is no need for additional cross-linking process as with PEX systems which has three main categories of PEX piping, grouped by the method in which they are manufactured. PEX pipes can be produced by using processes that employ peroxide (Type A), silane (Type B) or radiation (Type C) to cross-link the polyethylene. So the PE-RT pipe has greater innate flexibility meaning installers save time and money. Multilayer pipes combine the advantages of plastic pipes with the most important benefits of metal pipes, making them an ideal choice for all hot and cold water applications.
Because they are easy to bend, even at low temperatures, PE-RT multilayer pipes can be substantially cheaper to install than those made from metal and other plastic materials. Products made from DOWLEXTM PE-RT resins also offer greater flexibility in comparison with alternative plastic materials. PE-RT multilayer pipes combine the best characteristics of both plastic and metal, for instance improved shape memory and oxygen impermeability.
PE-RT layers protect the aluminium in multilayer pipes from corrosion. No chemicals or compounds are used during the production of the pipe so the system stays chemically inert during the application. Additionally, the pipe is cut from the coil which reduces the risk of waste.
PE-RT is more flexible than PEX, meaning real time savings for fitters with each installation. Pipes made from PE-RT have a surface smoothness than cannot be matched by other materials. This plays an important role in reducing both pressure loss and deposit formation. PE-RT resins provide excellent long-term hydrostatic strength without the cross-linking required for PEX. The avoidance of a chemical cross-linking process leads to a “purer” product which better meets drinking water requirements. PE-RT’s characteristics make it ideally suited for drinking water as its flexibility compared with other materials means that fewer linkages are needed during installation. PE-RT resins are easier to weld than other materials which help prevent leaks and contamination.
Because of its enhanced mechanical properties at elevated temperature, PE-RT resins can be used in all hot & cold water applications. (ISO 10508 Service Conditions including Class V). PE-RT Type I is the recommended choice for under floor heating applications, and PE-RT Type II is the material of choice for the more demanding applications like radiator heating, either monolithic or as a multilayer pipe combined with aluminium.