Generally speaking, the life of the low-temperature floor radiant heating system mainly depends on the life of the heating pipe. At present, there are many kinds, qualities and performances of plastic pipes. PE pipes have become the ideal choice for floor heating pipes.
Since the low-temperature floor radiant heating project is a concealed project, and the system passes 60 ℃ hot water, this means that when the heating pipe bursts due to quality problems, the ground of the building will be damaged, with huge losses. Therefore, the heating pipes used in the low-temperature floor radiant heating system have higher requirements than the plastic pipes used in ordinary buildings. Only in this way can the 50 year life of the low-temperature floor radiant heating system be realized.
Heating pipe Ultra wear-resistant composite pipe The performance index of is a complete index system, and it is not possible to judge whether it can be used in the low-temperature floor radiant heating project or whether it can guarantee its 50 year life. It is scientific and meaningful to comprehensively evaluate the pressure index, temperature index, service time and other indicators of pipes. In fact, under the same pressure, the service life of plastic pipes is different with different working temperatures; At the same temperature, the pressure is different, and the life is different. However, it is impossible to verify the 50 year life span through actual experimental methods. Therefore, the verification method of "time temperature equivalent transformation method" is proposed in the international ISO9080 standard to prove this point. The method is to calculate the actual life of pipes under low temperature service conditions by increasing the experimental temperature and pressure to obtain the life. The extrapolation factor Ke is determined by the temperature difference △ T between the test temperature and the actual use temperature. The product of the large test time Tmax and Ke obtained from the experiment is the long life that can be achieved by the allowable extrapolation calculation.
Relevant data show that the super wear-resistant composite pipe has good heat resistance strength. In this sense, it is scientific to choose PE pipe as the heating pipe in the low-temperature floor heating system. At the same time, PE pipe is also cheaper among various pipes, so it is economical to choose PE pipe as heating pipe in low-temperature floor heating system.
The creep characteristic curve is the comprehensive embodiment of the long-term stress resistance and high temperature resistance of the pipe, and actually reflects the service life of the pipe. From the creep characteristic curves of four kinds of pipes, it can be concluded that there is no inflection point in the range of PE pipe from high temperature to low temperature, from 1 year to 100 years. With the increase of time, the ring stress of PE pipe at the same temperature decreases very little; At different temperatures, the decrease of ring stress is much smaller than that of other pipes. It can be concluded that PE pipe can well adapt to long-term use under high temperature and pressure. Among the commonly used plastic pipes at present, PP-R and PB belong to thermoplastics, while PE belongs to thermosetting plastics.
Under certain conditions, the super wear-resistant composite pipe is formed by connecting the macromolecular chains to form free radicals and forming a plane or three-dimensional network structure. There are three methods, one is silane crosslinking method; Peroxide crosslinking method; The third is radiation crosslinking method.
The realization conditions of the three cross-linking methods and the advantages and disadvantages of the products are analyzed as follows: 1. Silane cross-linking method is to add silane agent into polyethylene, and complete the three-dimensional network cross-linking process in the hydrolysis process after molding. This cross-linking method requires low conditions. It can be completed as long as there is water and a certain temperature. Even in use, it can continue to be cross-linked until it reaches saturation cross-linking, The PE formed is a three-dimensional network structure. Silane crosslinking is a process of forming before crosslinking, and the product formed by this method is called PEb.
2、 Peroxide crosslinking method is to add peroxide crosslinking agent into polyethylene, and gradually complete the cross-linking process of plane network under the action of a certain temperature. This crosslinking method requires high crosslinking conditions, and the crosslinking degree will not change once it is molded. It is a process of crosslinking before molding. The product is characterized by good surface finish, good flexibility, but poor acid resistance. The product formed by this method is called PEa.
3、 Irradiation cross-linking is a physical cross-linking method. It is a physical cross-linking method that is used to transfer the pipe products formed by high-density polyethylene αβγ After irradiation by X - ray or electron beam, new free radicals are formed in the main chain of polyethylene macromolecule, and cross-linking is formed when the free radicals are recombined. This crosslinking method requires very high conditions, and the crosslinking is very stable. It has one feature: the product skin has a high degree of crosslinking, and the degree of crosslinking becomes lower and lower as the depth increases. This method is not suitable for producing products with too thick wall thickness, and the resulting product is called PEc.
