OPPORTUNITIES FOR PLASTICS IN FLEXIBLE INDOOR GAS PIPE SYSTEMS

摘要

Worldwide more and more buildings are connected to natural gas. Until recently the gas within the building was exclusively distributed through metal pipe systems, such as straight copper pipes, soldered together and straight steel pipes, screwed together. About six years ago some pilot projects with PEX (crosslinked polyethylene) piping systems in domestic buildings were started in the Netherlands. These projects are still in operation and no problems have occurred up to this moment. Subsequently other projects followed and nowadays the use of plastic (and multilayer) pipes in The Netherlands is common indoor installation practice. In this paper the suitability of PEX, PEX/Al/PEX and PE/Al/PE pipe systems for indoor gas installations with respect to technological aspects is discussed in more detail. Next to the technological suitability, the suitability of these systems also depends on other aspects, such as safety and economical aspects. These items are addressed as well. When it comes to the technological suitability of flexible pipe systems containing plastic, these can be divided into physical, chemical and mechanical aspects. The systems made of PEX, PEX/Al/PEX and PE/A1/PE are all suitable with respect to these aspects, as far as the system requirements are met. In The Netherlands these pipe systems have to meet the requirements written down in the relevant GASTEC QA Approval Requirements. A very important aspect to cover is the resistance against odorant permeation. Summarised, the following conclusions can be drawn from the results of the extensive research programme on the permeation of odorant, carried out by Gastec: In the case of multilayer pipes consisting of PEX-aluminium-PEX and PE-aluminium-PE the permeation of odorant through the pipe wall is zero. Pipe systems made of these pipes are therefore suited for use in indoor gas installations, as far as the resistance to odorant permeation concerns. In the case of PEX pipes containing an EvOH layer, present in or as a coating on the outside or inside of the pipe, the permeation of odorant through the pipe wall is negligible. Pipe systems made of these pipes are therefore suited for use in indoor gas installations, as far as the resistance to odorant permeation concerns. The permeation of odorant through pipes made of PEXa, PEXb or PEXc, without EvOH layer, show an inadmissible degree of permeation of odorant, when installed in a casing pipe (e.g. Corrugated PE pipe). Since the regulations for installation of PEX pipes for indoor gas installations prescribe the use of such casing pipes in certain situations, it is strongly recommended that PEX pipes without EvOH layer are not used for indoor gas installations. The safety of a flexible plastic indoor gas piping systems can be approached in different ways. One can build in extra safety devices, such as excess flow valves and thermal shut off valves, or one can install the system into the walls and floors, thus providing sufficient resistance against fire. The allowed options have to be described in the national installation regulations. The use of plastics in flexible indoor gas piping systems can reduce the total installation costs compared to traditional metal piping systems. The total reduction is strongly dependent on the layout of the pipework system as prescribed in the national installation regulations. The average reduction that can be achieved in a normal gas installation is about 30%. What opportunities exist for flexible plastic indoor gas pipe systems in the near future? A lot will depend on the ease of acceptance of these systems in different countries over the world. Next to the Netherlands also Germany allows the installation of multilayer pipe systems for gas indoors. Some other countries in Europe and other parts of the world are considering the application of flexible indoor gas pipe systems now as well. A final, very new development is to introduce plastic fittings to make the mechanical connection,