Generally speaking, the low temperature floor radiant heating system with building life (more than 50 years), and the hidden part in 50 years is free maintenance (except for man-made factors), but that the service life of 50 years mainly depends on the service life of heating tube. At present, plastic tube material type, quality is various, the performance is different, whether all plastic tube material can guarantee this point? This has become a matter of great academic concern.
Due to the low temperature floor radiant heating engineering belong to take cover engineering, combined with the is 60 degrees Celsius hot water in the system, which means that when there is tube heating pipe due to quality problems, the structure of the ground goes broken, huge losses. Therefore, used in low temperature floor radiant heating system of heating tube is larger than that of ordinary building plastic pipe has a higher requirement: system of heating tube type, quality, manufacturing technology, selection of quality should be stricter. Only this low temperature floor radiant heating system can be realized in 50 years.
At present, the market can be used in the low temperature floor radiant heating tubes are mainly PE - X tube (cross-linked polyethylene pipe), pp-r pipe (three random copolymerization polypropylene pipe), PERT pipe, high temperature resistant polyethylene pipe, PB pipe (polybutylene pipe), aluminum pipe and so on, these pipes are used in the low temperature floor radiant heating system, and have their own characteristics. Other plastic pipe materials such as CPVC, PPH, ABS, PE, etc. cannot be applied due to the failure of performance to meet the requirements of low-temperature floor radiant heating system. Although aluminous model multiple tube in the low temperature hot water floor radiant heating technology regulations have also been included in the available pipes, but because of the aluminous model multiple tube compound - anti-aging performance of hot melt adhesive is an open question, unable to determine its service life, therefore, best not to.
Performance of the heat pipe is a complete index system, not just the one indicator to determine whether can be used in the low temperature floor radiant heating engineering, can guarantee its 50 years of life. Some companies only do some short-term physical testing of their products, which they claim can be used for 50 years, which is unscientific. Some companies don't make sense to say how long a product can withstand without specifying how long it will last. It is scientific and meaningful to evaluate the pressure index, temperature index and use time of pipe. In fact, under the same pressure, the working temperature of plastic pipe is different, and its life span is different. At the same temperature, pressure is different, life is different. However, 50 years of life can not be verified by actual experimental methods. Therefore, in international ISO9080 standard put forward "the equivalent transformation method" wen validation method to prove the point, the method is: by improving the experiment temperature and pressure for life under the condition of low temperature using pipes according to the actual life. By testing the temperature and the temperature difference between the actual use temperature ⊿ T determine the extrapolation factor Ke, Tmax experiment to get the biggest test of time and the product of Ke is permissible extrapolation calculations can achieve the longest life expectancy.
According to the principle of the performance evaluation of plastic pipes, China's chemical building materials testing center and some large plastic pipe manufacturers in China began to conduct 8760 experiments on plastic tubes from 2001. This experiment is an important method for the comprehensive evaluation of the service life of plastic pipes. As a heating tube for low-temperature floor radiant heating system, the test should be carried out in the first place.
The experiment need to chose the experiment temperature is 110 degrees Celsius, according to the equivalent transformation method, the experiment time is set to 8760 hours, because for 8760 hours a year, when the temperature is 70 degrees Celsius, difference in temperature of 40 degrees Celsius, extrapolation factor of 50, which can be calculated at 70 degrees Celsius for service life: under the condition of 50 * 8760 = 438000 (h), for 50 years.
Relevant data show that PE-X tube has the best heat resistance. In this sense, it is scientific to choose PE-X tube as heating tube in low temperature floor heating system. At the same time, PE-X pipe is also cheaper in the above-mentioned pipes, so it is also the most economical to choose PE-X tube as heating tube in low temperature floor heating system.
We can also see from the creep characteristic curves of several pipes. The creep characteristic curve is the comprehensive embodiment of the long-term stress and high temperature resistance of the pipe, which is the most practical reflection of the service life of the pipe. From the creep characteristic curves of the four pipes, it can be concluded that there is no turning point in PE-X tube from high temperature to low temperature, from 1 year to 100 years. With the increase of time, the ring stress of PE-X tube at the same temperature decreases very little (compared with other pipe materials). At different temperatures, the decrease degree of cyclic stress is much smaller than that of other pipes. It can be concluded from this that PE-X tube can well adapt to high temperature and long - term use under high pressure. Several other pipes in more than 60 degrees Celsius, all in different time period (the longest only for more than ten years, the shortest in less than a year) ring stress sharply decline of inflection point, with the increase of temperature, point in time in advance greatly. In the high temperature, PERT had an inflection point in about 14 years. Although the PB has a high stress level, it has inflection points from high temperature to low temperature, such as the inflection point in 2000 hours (less than three months) at 90 degrees Celsius. When the PPR tube was above 70 degrees Celsius, the inflection point appeared earlier. The occurrence of inflection points is an important reflection of the resistance to creep performance and the important reflection of pipe life. Why does this happen? We know that polymer plastic is divided into thermoplastic and thermosetting plastic. Theoretically, thermoplastic is a melt that has no fixed melting point and can be melted after forming. Its creep period is shorter. The thermosetting plastic is a crystal that does not melt after forming. Its creep period is very long and its performance is almost constant in 100 years. Among the commonly used plastic pipes, pp-r, PERT and PB belong to thermoplastic plastic, while PE-X (crosslinked polyethylene) belongs to thermosetting plastics.
PE - X (cross-linked polyethylene) is composed of high density polyethylene (PE) added crosslinking agent or under the ray irradiation, macromolecular chain formation of free radicals under certain conditions interconnected forming plane or three-dimensional network structure. There are three methods, one is silane crosslinking method; The second is the peroxide crosslinking method; The third is radiation crosslinking.