Water pipe winter lesson 1: how to effectively avoid PP-R pipe embrittlement?

With the arrival of winter, it will be found that the installation accidents of PP-R water pipe increase correspondingly. PP-R's material properties determine that it is easy to crack and fracture pipes and fittings in different degrees in the process of construction, loading and unloading, transportation and so on when the temperature is low in winter.

Rapid crack growth

When the pipe is impacted or pressed by external force, it will appear straight-line cracking, which starts from the inner pipe and extends to the outer pipe.

Why is cold brittleness in PP-R pipe?

PP-R is the abbreviation of polypropylene random. The chemical name is called random copolypolypropylene, which is generally called type III polypropylene. It is formed by random copolymerization of propylene monomer and a small amount of ethylene monomer (3% - 5%) under heating, pressure and catalyst.

Temperature deformation curves of amorphous polymers

Therefore, in the case of low temperature, especially in winter, the flexibility of the pipe is reduced, and the rigidity is enhanced, showing brittleness. Under the impact of external force or excessive accidental load, pipe fracture may occur, which brings inconvenience to the construction. For this reason, relevant national codes have made clear requirements for this problem, and corresponding technical specifications for pipeline engineering are formulated according to the characteristics of low temperature brittleness of PP-R pipeline (see the figure below).

What can't be broken is a good pipe?

Cold brittleness is the inherent property of PPR water pipe raw materials, that is, under the action of external force, when the external force is greater than its bearing limit, it may cause fracture and other phenomena. This kind of fracture is mainly caused by strong impact of external force during transportation or construction.

Therefore, it can be concluded that the water pipe that can not be damaged must not be the authentic PP-R water pipe. The low temperature toughness of PE is stronger than that of pp-r. if PE pipe is used as PP-R pipe, the water pipe must be resistant to smashing. However, PE pipe can not transport hot water and is generally only used as cold water pipe. For details, please refer to the national standard GB / t13663-2000.

In fact, the national standard GB / t50349-2005 has already made clear requirements on how to prevent the cold brittle fracture of PPR pipe

It is strictly forbidden to throw, drop, roll or drag PP-R pipes in the process of transportation. After concealed laying, the position of pipes should be marked to avoid the damage of secondary decoration;

The pipes shall be stored in the warehouse and simple shed, and the stacking height shall not exceed 1.5m;

There is a certain cold brittleness below 5 ℃ of PP-R pipe. Pay attention to the construction in winter and cut the pipe slowly with sharp knife. It is not allowed to press and knock the installed pipes, and cover the parts easily subject to external force with protective materials when necessary.

Before cutting the pipe, if the stress whitening phenomenon is found due to external factors, it should be avoided to use.

Before hot-melt connection, check whether the pipe has been damaged. When the pipe is subjected to external force, the fracture is from the inside to the outside, so as to avoid the use of the pipe with the inner wall broken.

After the pipeline is installed, pressure test must be carried out before directly buried and non directly buried concealed laying. The pressure test pressure of cold water pipe shall be 1.5 times of system working pressure, and shall not be less than 0.9 MPa; the test pressure of hot water pipe shall be 2 times of working pressure, and shall not be less than 1.2 MPa.

-Special reminder-

The PP-R is a kind of plastic pipe. There is no open fire on the storage and construction site. It is strictly prohibited to bake the pipe with open fire.

When there is possibility of freezing in the room, anti freezing measures should be taken. In winter, after the pipes are moved from the outdoor low-temperature environment into the indoor environment, the construction should not be carried out immediately. The temperature of the pipe should be raised to the temperature close to the warmer indoor temperature before construction, so as to obtain better construction quality.