What is PPR Pipe?
PPR pipe, also known as type III polypropylene pipe or random copolymer polypropylene, can be extruded into pipes or injection molded into fittings. Random copolymer polypropylene is a type of polypropylene. Its basic polymer chain structure is modified by the addition of different monomers. Ethylene is the most commonly used monomer, which modifies the physical properties of polypropylene. Compared to PP homopolymer, random copolymers offer improved optical properties (increased clarity and reduced haze), enhanced impact resistance, increased flexibility, and lower melting temperatures, which in turn lower heat-sealing temperatures. At the same time, they are essentially equivalent to homopolymers in terms of chemical stability, water vapor barrier properties, and organoleptic properties (low odor and taste). They are used in blow molding, injection molding, film, and sheet extrusion processes for food and pharmaceutical packaging, as well as for consumer goods.
Why does PPR pipe exhibit low-temperature brittleness?
PPR 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 heat, pressure, and a catalyst.
The ethylene monomer is randomly distributed throughout the propylene chain, typically containing between 3 and 5% ethylene. The ethylene content and the polymerization method of ethylene and propylene determine its cold brittleness.
In low temperatures, especially during winter construction, the pipe's flexibility decreases and its rigidity increases, resulting in brittleness.
External impact or excessive, unexpected loads can cause linear cracking in the pipe, creating inconveniences in construction. Relevant national standards have established clear requirements to address this issue.
During winter construction, attention should be paid to the low-temperature brittleness of polypropylene (PPR) pipes for building water supply, and appropriate construction plans should be developed. GB/T50349-2005 provides detailed regulations on this.
PPR pipe cold brittleness manifests in practical applications
When ambient temperatures are low, the PPR pipe's toughness decreases, resulting in brittleness. When subjected to external impact or heavy pressure, linear cracking occurs, starting from the inner pipe and extending toward the outer pipe.
After a crack is caused by a single point of force, it rapidly grows along the pipe's axis within a short period of time. This characteristic is called rapid crack growth.
In addition, in winter, pipes can be damaged by external forces during transportation, on-site installation, and installation, leading to brittleness and bursting during use (e.g., when conveying hot water).
Misconception: PPR pipes that can be cracked are inferior.
This judgment is incorrect. Whether PPR pipes can be cracked is a misconception. It doesn't truly determine the quality of PPR pipes, as the properties of the PPR material itself change to a certain extent with ambient temperature.
In low temperatures, especially in winter, pipes lose flexibility and increase rigidity, resulting in brittleness. External impacts or excessive, unexpected loads can cause pipe fractures, causing inconvenience during construction.
Relevant national standards have clear requirements for this issue. During winter construction, attention should be paid to the low-temperature brittleness of polypropylene (PPR) pipes for building water supply, and corresponding construction plans should be developed. GB/T50349-2005 provides detailed regulations.
Conversely, some counterfeit and inferior PPR pipes containing other raw materials are not easily cracked! Genuine PPR pipes that can transport both high-temperature hot and cold water and last for 50 years can crack, especially in low temperatures. This is due to PPR's low-temperature brittleness. If a PPR water pipe doesn't crack when broken, it's generally considered not genuine PPR. The main advantage of PPR pipe lies in its high creep resistance.
High-quality pure PPR pipes exhibit low-temperature brittleness, particularly at temperatures below 5°C. Therefore, if a good pipe cracks when broken, those that don't are often not PPR pipes, but rather PP-B pipes used to transport cold water or pipes mixed with other materials.