How to avoid cold brittle fracture of PPR pipe?

1. Why is PPR tube 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.

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, the straight-line cracking of pipes may occur. It brings inconvenience to the 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.

2. The manifestation of cold brittleness of PPR pipe in practical application

When the ambient temperature is low, the toughness of PPR pipe decreases, which shows brittleness. When the pipe is impacted by external force or heavy pressure, there will be linear cracking, and the cracking starts from the inner pipe and extends to the outer pipe.

After the pipe is cracked by the force of a point, in an instant, the crack will grow rapidly along the axis direction of the pipe, which is called rapid crack growth.

In addition, in winter, due to external force injury in transportation, construction site and installation process, brittle and ductile (when conveying hot water) pipe burst will occur during use.

3. The mistake that we often go into -- the PPR water pipe that can crack is the poor water pipe

This method is wrong. It is a mistake to judge whether the PPR pipe can be broken. It can't test whether the PPR is good or not, because the performance of PP-R material changes with the environment temperature to a certain extent.

In the case of low temperature, especially in winter, 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, pipe fracture may occur. It brings inconvenience to the 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.

Instead, it's something that adds other ingredients

Fake PPR pipes are not easy to be broken

The PP-R, which can transport 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.

4. How to avoid cold brittle fracture of PPR pipe in practical application

1) It is strictly prohibited to throw, drop, roll or drag PPR pipes during handling;

2) The pipes shall be stored in the 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 5 ℃ 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 cutting, if the pipe with white stress caused by external force is found, the pipe cannot be used.

④ Before hot-melt connection of pipes, it is necessary to 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.

⑤ After installation, pressure test must be carried out before direct and non direct buried concealed laying. The test pressure of cold water pipe is 1.5 times of the system working pressure, but not less than 0.9mpa; the test pressure of hot water pipe is 2 times of the working pressure, but not less than 1.2MPa.

5. Phenomena associated with it

1) Cracks were found in the pipes during home decoration.

2) When PPR pipe was embedded, it was found that the pipe broke.

3) The linear crack of PPR pipe occurs during pressure test or after a period of use.

4) After PP-R is used for a period of time, the pipe welded in the pipe fittings has cracks.