Discussion on the application of the hottest rando

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Discussion on the application of random copolymer polypropylene pipes in building water supply at the end of 1999, the Ministry of construction and other four ministries, commissions and bureaus jointly issued the notice on eliminating backward products in residential construction, requiring that galvanized steel pipes be prohibited from being used in new residential water supply pipelines and plastic pipes be recommended before June 1, 2000 As a recommended pipe, type III random copolymer polypropylene (PP-R) has only been used in the domestic market for nearly two years, but its market share is far ahead of other plastic water supply pipes, showing its strong vitality How to be more scientific and standardized in the application of building water supply technology has become a problem that can not be ignored 1. The transformation process of random copolymerized polypropylene pipes

polypropylene, abbreviated as PP, is a commonly used polyolefin plastic, which has good heat resistance and compressive strength, low price and large output However, due to the low temperature brittleness and poor long-term creep properties of ordinary polypropylene, its application in pipeline engineering is limited For this reason, the raw material manufacturers have carried out extensive cooperation with the pipeline engineering industry, invested a lot of human, material and financial resources in comprehensive research, and committed to the modification of PP to make it a usable plastic suitable for pipeline engineering Homopolymer pp-h (type I), block copolymerization PP-B (type II) and random copolymerization PP-R (type III) have been developed successively

pp-r (polypropylene -ethylene random copolymer) is produced by the random and uniform polymerization of PE (about 5%) in the molecular chain of PP by using the advanced gas phase copolymerization method PP-R has better low-temperature impact resistance than pp-h and pp-b. it can improve the development of new materials, industry guidance and long-term creep performance

in the previous period ⑤ the pointer has contact friction with the dial glass cover. A kind of pipe called PP-c has appeared in the domestic market. It is a general term of copolymerized polypropylene. PP-B and PP-R belong to PP-c category, that is, CO clustering. In fact, the pipe called PP-c pipe in the market is PP-B pipe. The raw material is block copolymerized polypropylene, which is relatively cheap, while PP-R is random copolymerization. The pressure resistance of PP-B is far from that of PP-R, so it cannot be confused 2. Engineering application characteristics of PP-R pipe

(1) good sanitary performance and thermal insulation performance The raw material of the pipe is polyolefin, and its molecules are only composed of C and H elements. The raw and auxiliary materials fully meet the health standards, have good corrosion resistance, have no chemical effect on all ions in the water, and will not rust. It can be used not only in hot and cold water systems, but also in direct drinking water systems The thermal conductivity of PP-R pipe is 0.21w/m · K, which is only 1/200 of that of steel pipe. Generally, insulation is not required. When used in hot water pipes, insulation and energy saving effect are obvious The expansion force generated when the temperature changes is also small, which is suitable for direct burial and concealed laying in the wall and floor surface

(2) good heat resistance and long service life The maximum working temperature of the pipe can reach 95 ℃, and the long-term service temperature under the pressure of 1.0MPa is 70 ℃, meeting the upper limit temperature of hot water supply The service life can reach more than 100 years under normal temperature

(3) convenient installation and reliable connection The pipe is not only simple in production process, with less equipment investment, but also light in weight. Its weight is only 1/9 of that of steel pipe and 1/10 of that of copper pipe, which reduces the construction intensity of workers Because the pipe material is processed and manufactured with the same raw material, it has good hot-melt function, convenient and reliable installation, the strength of the connecting part is greater than that of the pipe body, and the pipe structure does not affect the flow In addition, the pipe resistance is small, the inner wall of the straight pipe is smooth and will not scale, the frictional resistance along the way is smaller than that of the copper pipe, and the sectional area of the pipe fittings remains unchanged when connected

(4) the waste of pipes and pipe fittings can be recycled, and the waste can be directly used in the production of pipes and pipe fittings after cleaning and crushing There is no pollution to the environment during production and construction, and the civil market share is high

pp-r pipes mainly bring broad development space for high-end aluminum enterprises. They are widely used in cold and hot water systems, direct drinking water systems, heating systems (including floor radiant heating), and are widely used in Europe For example, in 1996, the civil PP-R pipe in Italy reached 30mm, and the applications of other types of plastic pipes were: cross linked polyethylene pipe (PEX) 17mm, polybutylene (PB) 3mm, and aluminum-plastic composite pipe 2mm, only 1/15 of PP-R pipe

pp-r pipes are mainly inferior in rigidity and impact resistance compared with metal pipes. Attention should be paid to civilized construction during storage, transportation and construction; The coefficient of linear expansion is relatively large, ranging from 0.14 to 0.16 mm/m · K. special attention should be paid to the setting of supports in the design and construction, the expansion device should be selected appropriately, and the pipeline should be laid correctly; Poor UV resistance, aging under long-term direct sunlight; The allowable stress of the material is low, and the wall thickness of the pipe is large, which directly affects the material cost; Under the same outer diameter, the effective flow section is smaller than that of other pipes; The price of raw materials remains high There are many domestic enterprises producing PP raw materials, such as Qilu, Shanghai, Yangzi and Yanshan Petrochemical enterprises, which are capable of producing homopolymer (pp-h) and copolymerization (PP-B). However, due to the lack of market demand for PP-R raw materials in the past, the development and development of PP-R raw materials were relatively late. At present, the raw materials for domestic production of PP-R pipes are basically imported from Europe 3 discussion on some problems in engineering application 3.1 selection principle of PP-R pipe

(1) correctly distinguish the purpose of pipe materials and reasonably select cold and hot water pipes Cold and hot water pipes have different wall thickness, pressure resistance and prices During the design, it is necessary to specify whether to use cold water pipe or hot water pipe, and mark the pipe specification according to the regulations

according to the factors such as conveying water temperature, working pressure and service life, the wall thickness of PP-R pipes is divided into six series according to the pressure grade: PN1.0, pn1.25, pn1.6, pn2.0, pn2.5 and pn3.2 The minimum pressure grade of cold water pipes and pipe fittings is PN1.0 MPa, and the minimum pressure grade of hot water pipes and pipe fittings is Makrolon ax2677 combined with surface hardening treatment. At the beginning of development, it has also experienced repeated car washing tests to pn2.0 mpa

pp-r pipe has two remarkable characteristics of pressure bearing: first, with the temperature of water in the pipe rising, its allowable pressure will drop sharply; Second, as the pressure bearing time increases, the allowable pressure also decreases significantly Considering the long-term service life of the pipeline and abnormal factors in construction and actual use, for safety needs, the nominal pressure grade selected for the cold water pipe is the maximum working pressure of the system multiplied by 1.5 times the safety factor, and the hot water pipe multiplied by 3.0 times the safety factor The test data shows that when the water temperature is used in the pipeline

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