HDPE pipe is also cross-linked polyethylene pipe, and HDPE corrugated pipe is commonly seen. It is obtained by cross-linking reaction of polyethylene powder, and can be divided into three types according to the different cross-linking agents, namely peroxide cross-linking agent, silane cross-linking agent and radiation cross-linking, which are produced by these three processes The cross-linked polyethylene uses HDPEXa, HDPEXb and HDPEXc respectively. The hygienic properties of HDPEXa and HDPEXc are close to PP-R, and HDPEXb has poor hygienic properties and has a slight odor. Among the three types of PEX, PEXb has the lowest processing cost. PEXb is sold instead of PEXa in the market. At present, HDPEXa should be more of them because the production cost of HDPEXc is too high and the process is difficult to control. There are some shortcomings in applying PEX to water supply pipelines:
The thermal conductivity of HDPEX is relatively high, 0.41, while PP-R is only 0.24. Therefore, from this point of view, PEX is more suitable as a floor heating pipe rather than a water supply pipe, and if an additional layer of insulation is added, it will increase significantly. cost.
HDPEX adopts mechanical compression seal, which requires the use of a large number of metal joints (mainly brass joints), and the overall cost of the pipeline increases more. In addition, this kind of mechanical compression joint is easy to cause leakage when used in high temperature occasions, mainly due to the fatigue reaction of thermal expansion and contraction of the plastic at the joint. In addition, the axial tension resistance of the connection is not high enough, and looseness will occur under the constraint of external force.
The material properties of HDPEX undergo a fundamental change after crosslinking, and it becomes impossible to recycle or weld. Therefore, in addition to increasing costs, it also has a great impact on the environment.
PEX pipes have high rigidity at room temperature and are not easy to bend or have a large bending radius. Correspondingly, it is difficult to bend at some small bends and takes up more space. In addition, the impact resistance is only half that of PE-RT, and the external pressure resistance is not as good as that of PP-R water supply pipes.
PEX has better creep resistance at room temperature, but as the temperature increases, its creep resistance will decrease, which will shorten the service life of the pipe.
To sum up, the performance of HDPE corrugated pipes in water supply is not as good as PP-R water supply pipes, and its performance in heating pipes is not as good as HDPE corrugated pipes. Sales in the European market can also reflect that HDPE corrugated pipes are gradually replacing PP-R has become the first choice for floor heating pipes
