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PPR tube rupture prevention measures in winter

Source: Date:2015-6-8
Low temperature brittleness
1. Why is there low temperature brittleness in PPR pipes?
Answer: PP-R is random copolymer polypropylene, which is what we call type III polypropylene. It is obtained by random copolymerization of propylene monomer and a small amount of ethylene monomer under the action of heat, pressure and catalyst. Ethylene monomers are randomly distributed into long propylene chains, where ethylene monomers are generally controlled between 3-5%. The ethylene content and the polymerization mode of ethylene and propylene determine its characteristics of cold brittleness. In the case of low temperature, especially during the construction in winter, the flexibility of the pipe is reduced at low temperatures, the rigidity is enhanced, and the pipe is brittle. Under the impact of external force or excessive accidental load, the pipe may crack straightly. Inconvenience to construction. For this reason, relevant national regulations have made clear requirements for this issue. During construction in winter, attention should be paid to the characteristics of low-temperature brittleness of polypropylene (PP-R) pipelines for building water supply, and corresponding construction plans should be formulated. GB / T50349-2005 has detailed regulations on this.
2, the expression of cold brittleness of PPR pipe in practical applications
Answer: When the ambient temperature is low, the toughness of the PPR pipe decreases and it is brittle. When the pipe is impacted or pressed by an external force, a linear cracking phenomenon occurs. The cracking situation starts from the inner pipe and extends to the outer pipe. After the pipe is cracked by a point force, in a moment, this crack will grow rapidly along the axis of the pipe. This characteristic is called rapid crack growth. In addition, during the winter, the pipe is injured during transportation, construction site and installation due to external forces, and it will be brittle and tough (when hot water is transported) during the use of the pipe.
3.The misunderstanding that everyone often goes into-the PPR water pipe that can crack is the poor water pipe
Answer: This method of judgment is wrong. Whether the PPR tube can be cracked is a misunderstanding of whether the PPR is good or bad. This does not test whether the PPR is good or not, because the performance of the PP-R material itself varies with the ambient temperature A certain degree of change has taken place. In the case of low temperature, especially in winter, the flexibility of the pipe is reduced at low temperatures, the rigidity is enhanced, and it is brittle. Under the impact of external force or excessive accidental load, pipe fracture may occur. Inconvenience to construction. For this reason, relevant national regulations have made clear requirements for this issue. During construction in winter, attention should be paid to the characteristics of low-temperature brittleness of polypropylene (PP-R) pipelines for building water supply, and corresponding construction plans should be formulated. GB / T50349-2005 has detailed regulations on this. On the contrary, some fake and inferior PPR tubes with other raw materials are not easy to break! PP-R, which can transport both hot water and cold water for 50 years, can be cracked, especially at lower temperatures. This is the low-temperature brittleness of PP-R. If the PP-R water pipe cannot be broken, it can basically be concluded that it is not a true PP-R material. The advantages of PP-R pipes are mainly reflected in higher creep resistance. Good pipes made of pure PP-R material have low temperature brittleness, especially in the environment below 5 ℃, so good pipes can be cracked. It is not PP-R pipes that are not broken, but PP-R for cold water B may be mixed with other materials.
4.How to avoid cold brittle fracture of PPR pipe in practical application
Answer: 1) It is strictly forbidden to throw, drop, roll, or drag the PPR pipe during the transportation;
2) The pipes are required to be stored in the warehouse and simple shed, and the stacking height cannot exceed 1.5m.
3) During the construction process, it is necessary to:
① PPR pipe has lower hardness and less rigidity than metal pipe. It should be protected during handling and construction to avoid mechanical damage caused by inappropriate external force. Mark the location of the pipe after the dark lay to prevent secondary decoration from damaging the pipe.
② PPR pipe has a certain low temperature brittleness below 5 ℃. Be careful in winter construction, and use a sharp knife to cut slowly when cutting the pipe. Do not apply heavy pressure or knock to the installed pipeline. If necessary, cover the parts that are susceptible to external forces.
③ Before cutting the pipe, if it is found that the pipe becomes white due to stress caused by external forces, the pipe cannot be used.
④Before the pipe is hot-melted, carefully check whether the pipe has been damaged. Especially the inner wall, because when the pipe is subjected to external force, the inner wall ruptures first and then goes outside. Avoid using pipes with cracked inner walls but unbroken outer pipes.
⑤ After installation, pressure test must be carried out before direct buried or non-direct buried buried. The test pressure of the cold water pipe is 1.5 times the working pressure of the system, but it must not be less than 0.9MPa; the test pressure of the hot water pipe is twice the working pressure, but it must not be less than 1.2MPa.
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