Table of Contents

What is HDPE
High density polyethylene is a branch of polyethylene plastic. Different from LDPE, HDPE possesses a more crystalline structure. In addition, it does not have a branches which enables a more compressed molecular structure thus giving HDPE a higher density of 0.93-0.97 g/cm3 , making it more durable and rigid when compared with LDPE. HDPE also have a higher melting point of 120-140°C [1].
Figure 1: Polymer chain of polyethylene [2]

Advantages and Disadvantages
HDPE Advantages
HDPE Disadvantages
Very low water absorption [1]
Excellent electrical insulator
Good low temperature resistance
Higher tensile strength than LDPE
Low cost
High mold shrinkage [1]
Lower stiffness
Vulnerable to stress cracking

HDPE Chemical Compatibilities
A common HDPE pipes are capable of operating continuously at the temperature of -40°C to +60°C. It can withstand a maximum pressure of 20 bar depending on operation temperature and sizing [3].
Table of LDPE's chemical properties [1]
Element HDPE's corresponding resistance
Most Solvents Excellent
Alcohol Good
Acid Good
Oil Moderate
Aliphatic Poor
Aromatic Poor
Halogenated Hydrocarbons Poor

Applications of HDPE Pipes
When compared to LDPE pipes, HDPE pipes sees a lot more industrial use due to its larger size, abrasion and corrosion resistance. In additions, HDPE can be heat fused to produce a leak free joint that can transport hazardous chemicals without the need for thrust blocks or restraint harness.
Some industries currently using HDPE pipes include[4]:
Petrochemical
Power Plants
Mining
Liquefied Natural Gas
Fertilizer
Electrical and communications conduit
Hazardous Waste

HDPE Sizing
By industrial standard, the PN represent the Pressure Nominal, which is the pressure in bars the pipe can support with water at 20^oC. For instance, a PN 4 HDPE pipe can withstand a maximum pressure of 4 bars while operating with water at 20^oC.
The SDR stands for the Standard Dimension Ratio, which is the ratio of the pipe diameter to wall thickness. For instance, SDR 41 represent that that the outside diameter of the pip is 41 times the thickness of the wall [4].
Figure 2: A Sizing Chart of HDPE from Zeep Construction [5]

HDPE Recycling
HPDE cannot be recycled together with the other polyethylene. It is given the recycle number of 2.

Figure 3: Recycling symbol of HDPE [6]

References

Contributors:
User Last Update
Faculty Advisor: Mary Robinson

Element	HDPE's corresponding resistance
Most Solvents	Excellent
Alcohol	Good
Acid	Good
Oil	Moderate
Aliphatic	Poor
Aromatic	Poor
Halogenated Hydrocarbons	Poor

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