Material of soft water pipes

There should be no problem; many components of water softening systems use PVC or PE pipes

No problem, we use a steel framework with PE; it’s been a year now and it hasn’t had any impact on the quality of pure water. It’s much cheaper than stainless steel.

The people upstairs all said they had used it and there were no problems. I really haven’t seen it before; I suggest the original poster take another closer look. But I think as long as the quality of the PE material used for the steel framework is good, there should be no problem.

The external piping network is made of stainless steel, while PPH is used inside the ion exchange membrane unit.

No problem – outside our designated area, stainless steel is used; for the inlets and outlets of the pure water pumps, steel mesh combined with PE is utilized, while PPH is used for the distribution rings! I’ve been using it for 5 years, and there are no problems! This post was last edited by limingshuguang on 2009-2-7 13:34.]

What worries me most is the strength of steel-reinforced PE pipes – their capacity to withstand pressure isn’t high enough. Additionally, I’m concerned about their lifespan; I fear they might break after being used for a while. This post was last edited by limingshuguang on 2009-2-7 13:35.]

For the extremely cold regions in the north, it is recommended to use stainless steel insulated pipes for the outer tubes; once inside the room, PPR/H pipes can be used, as the pressure is not high.

　I. Scope of Application 　Since the 1990s, China’s synthetic resin industry has experienced rapid development, with production and consumption maintaining a strong growth trend. Currently, China’s synthetic resin production capacity has reached 10 million tons, placing it among the top five in the world behind the United States, Japan, Germany, and South Korea. However, there is still a significant shortage of various specialized resins required for plastic pipes. In China, although the production volume of PE and PP resins is high, there are not many resins suitable for use in pipe manufacturing. In particular, there is even less specialized PE material suitable for urban water supply and gas transmission, as well as PP-R material for building hot and cold water systems; therefore, a certain amount of specialized resins for plastic pipes still needs to be imported. 　　Plastic pipes in our country are developing rapidly, with their quality continuously improving. At present, a plastic pipe industry has initially taken shape, centered around PVC-U pipes, PE pipes, and PP-R pipes. Among them, polyethylene (PE) pipes are widely used in building water supply systems, building drainage systems, buried drainage pipes, building heating and gas transmission pipelines, electrical and telecommunications protection sleeves, industrial pipes, agricultural pipes, etc., thanks to their unique advantages. It is mainly used for urban water supply, urban gas supply, and farmland irrigation. 　　II. Analysis of PE Pipe Properties and Social Benefits We conduct our analysis using the table in the attachment, titled “Comparison of Properties of Common Water (Cold) Supply Pipes”. (1) Polyethylene boasts excellent corrosion resistance, good hygienic properties, and a long service life. As it is not an inert material, polyethylene can withstand the erosion of various chemicals, with the exception of a few strong oxidizing agents; moreover, it does not tend to support bacterial growth. It is well known that steel pipes and cast iron pipes have been replaced by plastic pipes, not only because plastic pipes require less energy for water transportation and household use, are lighter in weight, present less resistance to water flow, are easy and quick to install, are cheaper, have a longer lifespan, and offer insulation properties, but also because they possess advantages such as corrosion resistance and lower susceptibility to microbial growth over steel and cast iron pipes. 　　The service life of polyethylene pipes is over 50 years, a fact that has been confirmed not only by international standards and some advanced foreign standards but also by practical experience. 　　Another reason why polyethylene can be widely used is the increasing pressure on polyvinyl chloride due to environmental protection concerns. First is the issue of the hygienic properties of PVC itself: it is well known that PVC pipes produced under proper manufacturing conditions and with strict controls can ensure hygienic standards, allowing them to be used in drinking water applications. However, there are still concerns that problems may arise in areas with inadequate control: such as excessive levels of vinyl chloride monomer in polyvinyl chloride resin, or the misuse of toxic additives in the formulations for polyvinyl chloride pipes used for water supply. Drainage pipes and fittings, which do not guarantee toxicity, have been mistakenly used for water supply pipes and fittings. Next is the issue of recycling PVC pipes: Like polyethylene, PVC is a thermoplastic, and in theory it can be recycled. However, evidence from various countries shows that the proportion of old plastic products that can be recycled is limited. The main method of handling them is by burning them to generate energy. Since PVC contains chlorine, improper control during burning may result in the production of harmful substances, whereas polyethylene, which consists only of carbon and hydrogen, produces water and carbon dioxide when burned. Therefore, in countries such as Europe and the United States, the use of polyvinyl chloride is currently under increasing pressure from environmental protection organizations. 　　(2) Polyethylene possesses unique flexibility and excellent scratch resistance. The flexibility of polyethylene piping systems holds great technical and economic value. The flexibility of polyethylene is an important property that greatly enhances the value of this material for pipeline applications. Its good flexibility allows polyethylene pipes to be coiled and supplied in longer lengths, eliminating the need for numerous joints and fittings. For example, Nantong Water Supply Company, a national model unit for urban water supply improvement, made full use of the coiling property of PE small-diameter pipes when selecting materials for the installation of individual water meters; a single pipe was used from the water meter to the user’s end, eliminating the need for pipe fittings in between, which not only reduced costs but also improved work efficiency. These characteristics of PE small-diameter pipes have been recognized by water supply companies in cities across the country that are carrying out projects to install water meters outside households, making them the preferred choice for such water supply improvement tasks. At the same time, its flexibility, light weight, and excellent scratch resistance enable the use of various cost-effective installation methods that reduce the impact on the environment and daily life, such as trenchless construction techniques. Trenchless construction technology refers to the construction method that uses various rock and soil drilling techniques to lay, replace, or repair various underground pipelines without digging trenches on the surface. Various trenchless construction techniques are highly suitable for polyethylene pipes, such as horizontal directional drilling and guided drilling methods for laying new pipelines, the expansion method for replacing old pipelines in place, the cased replacement method for repairing old pipelines, as well as various improved lining methods (folded deformation method, hot drawing method, and cold rolling method). 　　PE’s unique flexibility also enables it to effectively resist ground movements and end loads. On the surface, in terms of strength and rigidity, plastic buried pipes are inferior to cement pipes and metal pipes. However, in practical applications, plastic buried pipes are considered \"flexible pipes\"; with proper design and installation, they share the loads with the surrounding soil. Therefore, plastic buried pipes do not need to possess the same strength and stiffness as \"rigid pipes\" in order to meet the mechanical requirements for use underground. At the same time, polyethylene’s pressure relaxation properties allow it to dissipate stress through deformation; its actual axial stress level is much lower than the values calculated theoretically. Its elongation at break is generally greater than 500%, and its bending radius can be as low as 20–25 times the diameter of the pipe. It is a highly ductile material with excellent resistance to uneven settlement of the foundation. These characteristics make it the ideal pipe for withstanding earthquakes, foundation settlement, and thermal expansion and contraction. For example, during the Great Kobe Earthquake in Japan in 1995, PE water supply pipes and gas pipes were the only pipe systems that remained unaffected. 　　(3) Polyethylene boasts excellent low-temperature resistance. The low-temperature embrittlement temperature of PE pipes is -70°C, which is better than that of other types of pipes. During outdoor construction in winter, PVC-U pipes are prone to cracking. An experience gained from pilot projects for installing PVC-U buried water supply pipes in Beijing, China, is that it is not suitable to carry out such installations when the temperature is below zero degrees. Another clear piece of evidence is that, in order to improve the toughness and low-temperature impact resistance of PP, ethylene and propylene monomers can be copolymerized to produce random copolymerized polypropylene (PP-R). The iPP production process and methods are generally used for this purpose, whereby a mixture of propylene and ethylene gases is copolymerized to yield a copolymer in which propylene and ethylene segments are distributed randomly along the main chain – this is the material used for PP-R pipes. The ethylene content in PP-R pipe materials is usually around 3%. However, the improved low-temperature resistance of PP-R is still not satisfactory; its embrittlement temperature is around -15°C, which is much higher than that of polyethylene pipes, which is -70°C. 　　(4) Polyethylene possesses good fracture toughness for rapid crack growth. When rapid crack growth failure occurs, the cracks can expand at a speed of 100–45 m/s over distances of several hundred meters to over ten kilometers, resulting in damage to long-distance pipelines, large-scale leakage incidents, and subsequent fires and explosions (in the case of natural gas transportation) or floods (in the case of water transportation). The probability of such an incident occurring is low, but once it happens, the consequences are severe. Over the past decade or so, this type of failure has been considered the most dangerous accident that must be absolutely prevented in plastic gas transmission pipes. For the continued development of plastic pressure pipes, the importance of preventing rapid crack growth and failure has surpassed that of requirements regarding long-term strength performance. The reason is that, for the same SDR (the ratio of pipe diameter to its thickness), the calculated long-term life and long-term strength are independent of the increase in pipe diameter (in fact, larger-diameter pipes may be safer than smaller ones), but the risk of rapid crack growth increases as the pipe diameter increases. In existing large-diameter plastic piping materials such as polyethylene, polypropylene, and polyvinyl chloride pipes, when a certain pipe diameter is reached, the allowable pressure determined by the need to prevent rapid crack growth and resulting failure is always lower than the allowable pressure determined by long-term strength considerations. In other words, once the allowable pressure is determined based on the requirement to prevent rapid crack growth and failure, the requirements for long-term service life (such as at 20°C for 50 years) can be met automatically ； Materials with poor fracture toughness due to rapid crack growth will be eliminated, regardless of their long-term strength properties. For example, polyvinyl chloride (PVC-U) gas pipes have been almost entirely replaced by polyethylene (PE) gas pipes. The trend of European PVC-U water supply pipes being replaced by polyethylene (PE) pipes is clear. 　　Our country has not yet established a testing apparatus for monitoring the failure caused by rapid crack growth. China’s standards for plastic pressure pipes do not address this issue, which indicates that the level of such pipes in China is at least one development stage behind the global average. 　　(5) Polyethylene pipes are easy and reliable to install and connect. Polyethylene pipes can be joined in a reliable manner using convenient heat fusion welding or socketing techniques, resulting in strong connections whose inner surface is close to that of the original pipe (with a small welded protrusion ring at the joint), or specialized electrofusion fittings can be used to connect polyethylene pipes. For small-diameter pipes, our company’s crimp-type connection method can also be used; it is convenient and reliable. (This product utilizes patented technology introduced by our company, and it is widely used in the ‘one meter per household’ projects carried out by many water supply companies in our country.) The welded joints of polyethylene pipes can withstand axial loads without leakage or separation. 　　Today, the joining techniques for polyethylene have become highly mature and reliable. Statistics show that the leakage rate of polyethylene pipes is less than two per hundred thousand, which is far lower than 2-3% for ductile iron pipes; this significantly improves the safety and economic efficiency of the pipelines. This is also a very important reason why polyethylene pipes are widely used in gas pipelines. It is generally used for buried pipes; if installed above ground, pipe supports must be added, as well as expansion joints. I am ignorant and inexperienced; I have heard of using steel frameworks with PE for saline water, acidic or alkaline wastewater, etc., but I have never heard of its use in pure water. Please refer to this information.

Steel-reinforced PE can be used; for long pipelines, steel-reinforced PE requires fewer joints compared to PE with a steel lining, and it is more reliable. Heat welding of steel-reinforced PE necessitates the use of special tools, and there are not many manufacturers offering this option, but it remains relatively convenient.

Will PE hot-melt joints age when exposed to sunlight?