What Is the Difference Between HDPE and MDPE?
June 6, 2023
WL Plastics is North America’s largest manufacturer of solid wall polyethylene pressure pipe producing both high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) pipe. These two materials are versatile, high-performance plastics that differ in density, in how they are made, and in how they are used in piping applications. MDPE and HDPE have different physical properties due to their density differences and manufacturing process. MDPE pressure pipe is generally only used for natural gas distribution while HDPE pipe is used for all pressure pipe applications.
Both HDPE and MDPE are polyethylene pipe are:
- Ductile
- Flexible
- Resistance to corrosion
- Resistance to chemical damage, and
- Heat Fusible
Learn more about the similarities and differences between these two polyethylene materials in the following paragraphs.
What Is HDPE pipe?
HDPE pipe is black or black with colored stripes to identify its end use (e.g., yellow for natural gas, blue for potable water, green for wastewater, etc.). Well dispersed carbon black added to the natural PE4710 resin gives the pipe its black color and protection against UV degradation for a minimum of 10 years. PE4710 is a bimodal resin produced from two reactors in series which gives PE4710 a wide molecular weight distribution (MWD). A broad MWD improves processability and increases molecular side chain branching which increases the materials resistance to slow crack growth.
HDPE is the go-to choice for many applications including:
- Oil and gas gathering
- Potable water distribution and transmission
- Wastewater systems
- Mining and industrial systems
- Natural gas distribution
- Power and communication lines
What Is MDPE pipe?
MDPE pipe is solid yellow and is primarily used for natural gas distribution. Yellow color masterbatch added to the natural PE2708 resin the pipe its color and protection against UV degradation for a minimum of 3 years. PE2708 resin is made by either unimodal or bi-modal process. Unimodal resins are produced in a single reactor and have narrower MWD than bi-modal resins.
Differences Between HDPE and MDPE
PE4710 HDPE pipe offers higher tensile strength, higher operating pressures for a given wall thickness (DR), and better resistance to rapid crack propagation (RCP) than MDPE pipe made from bimodal or unimodal PE2708. Because of its higher tensile strength, PE4710 pipe can be pulled longer distances through no-dig installations such as horizontal directional drilling. The higher hydrostatic design basis (HDB) of PE4710 allows the design engineer to use a thinner wall pipe (higher DR) for a given maximum allowable operating pressure (MAOP). A thinner pipe wall increases pipe flow capacity and reduces material costs. The better resistance to RCP of PE4710 allows operators and contractors to feel more comfortable when installing or working on PE4710 pipe at low temperatures. Typical properties of PE2708 and PE4710 are shown in the Table below.
| Typical Values | |||||
|---|---|---|---|---|---|
| Property | Test Procedure | Units | Bi-Modal HDPE | Bi-Modal MDPE | Unimodal MDPE |
| Material Designation | PPI TR-4 | PE4710 | PE2708 | PE2708 | |
| Density, Natural (w/ UV stabilizer & color) | ASTM D1505 | gms / cm3 | 0.955 (0.960) | 0.94 (0.943) | 0.94 (0.943) |
| Tensile Strength at Yield | ASTM D638 (Type IV) | psi | >3500 | 2600 to 2800 | 2600 to 2800 |
| PENT (Slow Crack Growth) | ASTM F1473 | hrs | >2000 | >2000 | >500 |
| Hydrostatic Design Basis at 73°F | ASTM D2837 | psi | 1600 | 1,250 | 1,250 |
| Hydrostatic Design Basis at 140°F | ASTM D2837 | psi | 1000 | 1000 | 800 |
| Color; UV Stabilizer | ASTM D3350 | — | Black w/ yellow stripes & 2-3% carbon black | Colored Yellow w/ UV stabilizer | Colored Yellow w/ UV stabilizer |
| Rapid Crack Propagation Critical Pressure (Pc) @ 0°C (32°F) | ISO 13477 | psi | 174 | 123 – 145 | 15 – 90 |
| Rapid Crack Propagation Critical Temperature (Tc) @ 5bar | ISO 13477 | oF | <2 | 28 | 60 |
Choose HDPE and MDPE Pipes From WL Plastics
WL Plastics is North America’s largest manufacturer of solid wall polyethylene pressure pipe producing both high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) pipe. WL Plastics has nine ISO 9001:2015 certified facilities strategically located across the US manufacturing pipe in compliance with industry standards such as API (15LE), AWWA (C901 & C906), and ASTM (D3035, F714, D2513, F2619) under strict quality control. WL Plastics also carries several third party certifications such as UL, NSF, FM, and UPC.
Contact us today to learn more about HDPE and MDPE pipe options.
