Installing PE pipelines delivers outstanding advantages over other pipe materials. From corrosion resistance and weight savings in transport to the less obvious ability for PE to withstand ground movement. But PE is a plastic and, in our increasingly environmentally aware world, that can take some of the shine off the benefits.
As a manufacturer, PLASSON is very mindful of waste streams, both for their value and impacts on our planet. We currently recycle 97% of materials in the waste stream from our factories and work to improve that figure everyday.
HDPE can be recycled at least 10 times
High-Density Polyethylene, the material most common poly pipe is made from, happens to be one of the easiest materials to recycle.
Testing shows it can be recycled at least 10 times and injection molding and shredding does not alter properties, like strength, over the entire period of reuse. With PE pipelines having an expected life-span of around 100 years, there is the potential to recycle the material and for it to be repurposed for centuries.
High-Density Polyethylene, usually shortened to HDPE, is a plastic polymer with flexible properties that make it ideal for a wide range of applications including water and waste water pipe.
HDPE, as the name suggests, has a higher specific density than low-density polyethylene. What really makes the difference in the physical properties of HDPE is the lack of branching, meaning it is light with high tensile strength. As there is no branching, the structure is more closely packed, making HDPE a linear polymer. The branching can be controlled and reduced by using specific catalysts during production.
HDPE is relatively hard and resistant to impact and can be subjected to temperatures of up to 120 °C without being affected.
HDPE also does not absorb liquid readily and it is extremely resistant to many chemicals. It is resistant to many acids, alcohols, aldehydes, esters, bases and oils.
HDPE & PE Pipelines
The most common water, waste water and gas PE pipe is PE100. This third generation pipe grade has an optimum balance of three key things:
Minimum Required Strength (MRS) – this provides long-term strength and creep resistance.
Stress crack resistance (sometimes referred to as slow crack growth resistance).
Rapid crack propagation resistance.
HDPE PE100 pipe is easy to install, light, flexible, corrosion-free and has a service life of up to 100 years. It can be jointed using butt fusion or electrofusion to create a leak-free pressure network for gas or water.
HDPE & PE100 Pipe Properties
Minimum Required Strength (MRS): 10.0 MPa (1450 psi)
Hydrostatic Design Basis (HDB) Pressure: 1600 psi (11 MPa)
Allowable Compressive Strength: 7.93 MPa
Tensile Strength at Yield: 23 MPa
Elongation at Break: >600%
Modulus of Elasticity (50 years): 200 MPa
Flexural Modulus: 1000 MPa
Poisson’s Ratio: 0.45
Thermal Expansion Co-efficient: 1.3 x 10-4 °C-1
Manning: 0.009 (water); 0.010 (sewage)
Temperature Resistance of PE pipe
The properties of HDPE PE100 pipe are determined at temperatures of 20°C – 23°C. These properties can be significantly affected by temperature, so at higher temperature the properties, including MRS, decrease.
This is a consideration in wastewater rising mains in which there are solids transported with the water and pump operation sequences can result in solids rubbing along the pipe invert.
PE100 has the best abrasion resistance of the commonly used pressure pipe types. To resist abrasion, the piping system must be harder than the material being conveyed. There are different types of wear experienced in piping systems. The straight sections most commonly experience abrasive erosion. Size transitions and directional changes experience both abrasive erosion and impact abrasion.
In addition to conventional HDPE PE100 pipe there are several variants that have been developed for specific use.
RC indicates resistance to cracking. PE100 RC is a resin that has an increased stress crack resistance while maintaining the same MRS and rapid crack propagation resistance as conventional PE100. It is intended for use in more severe conditions.
There are three different types of RC pipe:
Type 1: Single-layer solid wall pipes made of PE 100 RC
Type 2: Pipes with dimensionally integrated protective layers of PE 100 RC
Type 3: Pipes with dimensions conforming to ISO 4065 with an outer protective casing. Inner pipe made of PE 100 RC.
Generally Types 1 & 2 are used for open trench applications where no sand bedding is used. Type 3 is more commonly used for trenchless applications.
RT indicates resistance to temperature. PE100 RT is a resin that has an increased resistance to higher temperatures while maintaining the same mechanical properties as conventional PE100.
It is intended for use when ambient or fluid temperatures are consistently above 50°C. This material is more commonly used in hot water and industrial applications and relatively seldom in buried water or gas networks.
Barrier PE Pipe
Certain gases and liquids can permeate through PE. Therefore when HDPE PE100 pipe is laid in contaminated ground and the fluid in the pipe must be protected from contamination, for example when potable water is carried, then a barrier pipe is necessary.
Barrier pipe is co-extruded with a barrier layer sandwiched between layers of PE100. The barrier layer is most commonly an aluminium foil but may also be a polymer such as EVOH.
Co-extruded PE Pipe
Co-extrusion of PE100 enables several additional pipe variants to be manufactured, often with several layers each offering different benefits. These include internal coatings, internal and external coatings, and conducting layers or strips for leak monitoring or pipe detection.