Why PPR pipes and fittings are brittle at low temperature?
PPR pipes and pipe fittings are brittle at low temperature, and will break under external impact or heavy pressure. So what are the causes of this and how can we prevent it?
1. What is low temperature brittleness? The impact absorption energy of materials (all materials, including metal materials and non-metal materials) decreases with the decrease of temperature. When the test temperature is lower than TK (critical transition temperature of toughness and brittleness), the impact absorption energy decreases obviously, and the material changes from toughness to brittleness. This phenomenon is called low temperature brittleness.
2. Why are PP-R pipes and fittings brittle at low temperature?
PP-R is random copolymerized polypropylene, which is called type III polypropylene. It is obtained by random copolymerization of propylene monomer and a small amount of ethylene monomer under the action of heating, pressure and catalyst. Ethylene monomers are randomly distributed in the long chain of propylene, and ethylene monomers are generally controlled between 3-5%. The characteristics of cold brittleness are determined by the ethylene content and the polymerization mode of ethylene and propylene.
3. We often go into the mistake that the PPR water pipe that can crack is the poor water pipe
This kind of judgment method is wrong. Whether to crack the PPR pipe or not is a mistake to judge the quality of PPR. The real PP-R that can deliver both high temperature hot water and cold water for 50 years can crack, especially in the case of low temperature, which is the low temperature brittleness of pp-r. On the contrary, some fake PPR pipes with other raw materials are not easy to be broken! If PP-R water pipe can not crack, it can be concluded that it is not a real PP-R material. The PP-R pipeline system of toule, Italy, adopts 100% raw material PP-R (Basel, USA) with a higher level of original ecology, which is ppr100 (currently the highest level), far higher than other ppr80 raw materials.
In the case of low temperature, especially in the winter construction process, the flexibility of the pipe is reduced, the rigidity is enhanced, and the pipe is brittle. Under the impact of external force or excessive accidental load, straight-line cracking of pipes may occur, which brings inconvenience to construction. For this reason, relevant national standards have made clear requirements for this issue. In winter construction, attention should be paid to the characteristics of low temperature brittleness of PP-R pipes for building water supply, and the corresponding construction scheme should be formulated. GB / t50349-2005 has detailed regulations on this.
How to avoid the cold brittle fracture of PPR pipes and fittings in practical application
1) It is strictly prohibited to throw, drop, roll or drag PPR pipes and pipe fittings in the process of handling;
2) PPR pipes and pipe fittings shall be stored in warehouse and simple shed, and the stacking height shall not exceed 1.5m.
3) In the process of construction, it is necessary to:
① The hardness and rigidity of PPR pipe are lower than that of metal pipe, so it should be protected during handling and construction to avoid mechanical damage caused by improper external force. After concealed laying, the position of pipeline shall be marked to avoid damage of pipeline by secondary decoration.
② There is a certain low temperature brittleness below 10 ℃ of PPR pipe. Be careful in winter construction. Use sharp knife to cut pipe slowly. The installed pipes shall not be pressed or knocked, and the vulnerable parts shall be covered with protective objects if necessary.
③ Before hot-melt connection of PPR pipes and pipe fittings, carefully check whether the pipes have been damaged. Especially the inner wall, because when the pipe is under external force, the inner wall first breaks and then goes out. Avoid using pipes whose inner wall has been broken but whose outer pipe has not been broken.
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