PP-R is a random copolymer of polypropylene, also known as Type III polypropylene. It is produced by the random copolymerization of propylene monomer and a small amount of ethylene monomer under heating, pressure, and catalyst action.
Ethylene monomers are randomly distributed along the polyene chain, with ethylene content typically ranging from 3-5%. The ethylene content and the polymerization method of ethylene with polyene determine the material's cold-cracking properties.
In low-temperature conditions, especially during winter construction, the pipe material exhibits reduced flexibility and increased rigidity, resulting in brittleness.
Under the action of external impacts or excessive loads, pipe materials may experience linear cracking. This can cause inconvenience during construction. To address this, relevant national standards have specified clear requirements.
When working in winter, it is important to pay attention to the low-temperature brittleness of building PP-R (polypropylene-random copolymer) pipes and to develop appropriate construction plans. GB/T 50349-2005 provides detailed specifications on this matter.
The cold brittleness of PPR pipe materials is evident in their performance during actual applications.
When the ambient temperature is low, the ductility of PPR pipe decreases, resulting in brittleness. When the pipe is subjected to external impact or pressure, it will exhibit linear cracking, and the cracking starts from the inner pipe and extends outwards.
After a pipe is subjected to a localized force, the resulting crack will rapidly propagate along the pipe's axis within a short period. This phenomenon is known as rapid crack propagation.
Additionally, in winter, pipes can be damaged during transportation, on-site handling, and installation due to external forces, leading to brittleness and reduced impact resistance (e.g., during hot water transport), which can result in bursts.
Can PPR pipes that can be easily broken be considered as "damaged water pipes"?
This method of judgment is fundamentally flawed. The ability to crush a PPR pipe is a completely misleading indicator of its quality. This method cannot determine whether a PPR pipe is of good quality, as the properties of PPR materials change with environmental temperature.
Under low temperatures, especially in winter, the flexibility of pipes decreases and they become more rigid, exhibiting brittleness. This can lead to pipe breakage due to external impacts or excessive loads. This poses challenges for construction work.
Relevant national standards have specified clear requirements for this issue. During winter construction, it is important to pay attention to the low-temperature brittleness of building PP-R (polypropylene-random copolymer) pipes and to develop appropriate construction plans. GB/T 50349-2005 provides detailed regulations on this.
However, counterfeit and substandard PPR pipes containing added materials are relatively difficult to damage. Genuine PPR pipes, which can transport both hot and cold water and have a lifespan of up to 50 years, are more susceptible to damage, especially at lower temperatures. This is due to the low-temperature brittleness of PP-R.
If the PP-R pipe cannot be broken, it can generally be concluded that it is not genuine PP-R material. The main advantages of PP-R pipes lie in their high creep resistance.
Pure PP-R material has excellent cold-temperature brittleness, which is particularly noticeable at temperatures below 5°C. Therefore, good PP-R pipes are prone to cracking. Pipes that do not crack are often made of PP-B or contain other materials, rather than pure PP-R.
How can PPR pipe materials be prevented from cold-weather cracking during actual application?
1) PPR pipe materials must not be dropped, thrown, rolled, or dragged during transportation.
2) Pipe materials should be stored in warehouses and temporary shelters, and the maximum stacking height should not exceed 1.5m.
3) During construction, the following should be ensured:
PPR pipes are generally softer and less rigid than metal pipes. During transportation and construction, they should be protected to prevent mechanical damage from improper external forces. After installation, the location of the pipes should be clearly marked to prevent damage during subsequent renovations.
----PPR pipes exhibit certain brittleness at temperatures below 5°C. Exercise caution during winter construction and use sharp cutting tools to slowly cut the pipes. Do not apply pressure or strike existing pipes, and cover vulnerable areas with protective materials as needed.
- If, before cutting a pipe, any pipe material exhibiting whitening due to stress caused by external factors is found, that pipe material should not be used.
Before performing a hot-melt connection on the pipes, carefully inspect the pipe material for any existing damage. Pay particular attention to the inner surface, as pipes are most likely to crack on the inner surface first, followed by the outer surface. Avoid using pipe materials where the inner surface is already damaged but the outer surface is intact.
----After pipe installation, pressure testing is required before burying the pipes either in direct or indirect applications. The pressure test for cold water pipes should be 1.5 times the system working pressure, but not less than 0.9 MPa. The pressure test for hot water pipes should be twice the working pressure, but not less than 1.2 MPa.