HDPE Pipe Pn25 represents its nominal pressure (PN) of 25bar (about 2.5MPa), which indicates the maximum working pressure that the pipe can sustain under 20℃ water temperature conditions. The pressure grade standard follows the ISO 4065 international specification, where the PN value is calculated by the following formula:
PN = 2×MRS/(C×SDR)
(MRS: minimum required strength, C: design factor, SDR: standard dimension ratio)
For PN25 grade HDPE pipes, PE100 raw materials (MRS≥10MPa) are usually used, and high-strength pressure bearing capacity is achieved by optimizing the wall thickness design (common SDR11). It is worth noting that as the medium temperature increases, its maximum allowable working pressure needs to be adjusted by a reduction factor according to the ISO 12162 standard.
The core advantages of modern PN25 grade HDPE pipes come from three major technological innovations:
Molecular structure optimization: Using bimodal polyethylene technology, the molecular chain branching degree is precisely controlled through copolymerization monomers, so that the material has both high crystallinity (improving rigidity) and an appropriate amount of amorphous region (maintaining toughness).
Nano-enhancement technology: Some manufacturers add layered silicate nanoparticles to the PE100+ formula to increase the ring stiffness of the pipe by more than 15%.
Extrusion process innovation: The melt gear pump is used to stabilize the extrusion pressure, and the laser diameter gauge is used to achieve a wall thickness control accuracy of ±0.3mm.
These technological advances have enabled the hydraulic bursting pressure of PN25 pipes to reach more than 4.0MPa, and the axial tensile strength exceeds 22MPa, which is significantly higher than traditional PE80 materials.
1. Fluid dynamics
The inner wall roughness is only 0.007mm (1/10 of the new steel pipe), the Hazen-Williams coefficient C=150, which can reduce the head loss by 30-40% compared with metal pipes
The microbial attachment rate is 60% lower than that of PVC pipes, and the biofilm formation rate is delayed by 2.5 times
2. Environmental adaptability
The working temperature range is -40℃ to 60℃, and the short-term heat resistance peak reaches 95℃ (pressure reduction is required)
The life decay rate of UV-resistant formula pipes under outdoor exposure conditions is less than 0.03%/year
3. Installation economy
The efficiency of hot-melt butt joints is 5 times higher than that of flange connections, and 300m pipelines can be laid in a single day
The density is only 0.95g/cm³, and the hoisting cost is 1/8 of the ductile iron pipe of the same diameter
1. Municipal water supply system: A city renovation project uses DN800 PN25 pipes to reduce the pipe network leakage rate from 28% to 12%
2. Industrial pressure transportation: Chemical plants use SDR7.4 PN25 pipes to transport 60℃ acid and alkali media, reducing annual maintenance costs by 75%
3. Deep-sea aquaculture: The HDPE pipe network system with a working pressure of 20 bar supports the construction of a salmon farm 5 kilometers offshore
Core certifications that meet the PN25 grade include:
ISO 4427:2019 (water supply pipes)
EN 12201:2011 (pressure piping systems)
GB/T 13663.2-2018 (China National Standard)
Certification tests must pass:
8760 hours of hydrostatic test (20℃/25bar)
Rapid crack propagation test (RCP) critical pressure ≥1.5×PN
Weld tensile strength ≥90% of parent material
With the advancement of materials science, the third-generation HDPE (PE100-RC) has achieved a breakthrough in the PN32 pressure level, which will further expand the application boundaries of high-pressure pipelines. Engineering practice shows that the actual service life of a correctly selected and designed PN25 HDPE pipeline system generally exceeds 50 years, which is 2-3 times that of traditional metal pipelines.
