Description

HDPE Pipe physical properties & structure

HDPE is a type of polyethylene and accounts for over 34% of the global plastic market. It is a polymer made up of a huge number of repeating units (known as monomers), and its chemical formula can be generalized as (C2H4)n. The branching in high density polyethylene is of a relatively low degree (when compared to other categories of polyethylene).

High density polyethylene is a hydrocarbon polymer that can be prepared from ethylene via a catalytic process. Some common catalysts used here include Ziegler–Natta catalysts, chromium/silica catalysts (Phillips catalyst), and metallocene catalysts. The general structure of HDPE is illustrated below.

High Density Polyethylene (HDPE) is usually supplied by the manufacturer in a ‘ready to use’ pelletised form to make HDPE pipe products. There are several different grades available. The particular grades suitable for pipe manufacture are referred to as PE 63, PE 80 and PE100. The pipe manufacturer simply converts this material into pressure pipe.

The first SABS specification (SABS 533) made use of a design stress of 5 mPa. This specification has now been superceded by SABS ISO 4427 which covers 3 different material grades viz: PE63, PE80 and PE100. These three material grades have different properties which enable them to be classified with minimum required strengths (MRS) of 6.3 MPa, 8.0 MPa and 10.0 MPa respectively. Applying a design coefficient of 1.25 (safety factor) to the MRS gives the design stress used by SABS ISO 4427 for these materials (5.0 MPa, 6.3 MPa and 8.0 MPa respectively) with the result that the wall thickness for a particular size and class becomes progressively less as the change is made to a material with a higher MRS.

HDPE Pipe applications

HDPE pipe is a type of flexible plastic pipe used for fluid and gas transfer and is often used to replace ageing concrete or steel mains pipelines. Made from the thermoplastic HDPE (high-density polyethylene), its high level of impermeability and strong molecular bond make it suitable for high pressure pipelines. HDPE pipe is used across the globe for applications such as water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire system supply lines, electrical and communications conduit, and stormwater and drainage pipes.

An example of the durability of HDPE pipe is the 600 m (1,969 ft) long HDPE boom used for the Ocean Cleanup project. The HDPE pipeline is being released into the ocean to clean up the Great Pacific Garbage Patch.

HDPE pipe has been used in rural and mining environments all over the world for over 50 years, proving to be a very durable and effective means of fluid and gas transfer.

HDPE Pipe specifications

The HDPE pipes supplied by Rendifield are manufactured to, and carry the SABS mark for, SANS ISO 4427. These pipes are manufactured from three different designated materials viz: PE 63, PE 80 and PE 100.

It can be seen that SANS ISO 4427 have grouped together the different pressure classes, produced from different material designations, under a common heading known as the Standard Diameter (Dimension) Ratio or SDR. The minimum wall thicknesses specified are not exactly that which would be derived from a calculation using Barlow’s formula or the SDR but are the rounded up values of the highest minimum wall thickness calculated for any size and class in the SDR group.

HDPE Pipe dimensions (industrial use)

In these tables it can be seen that SABS ISO 4427 have grouped together the different pressure classes, produced from different material designations, under a common heading known as the Standard Diameter (Dimension) Ratio or SDR.

The minimum wall thicknesses specified are not exactly that which would be derived from a calculation using Barlow’s formula or the SDR but are the rounded up values of the highest minimum wall thickness calculated for any size and class in the SDR group.

(The tables are best viewed on devices with a wide view (laptop/tablet/desktop) )

Dimensions of PE 100 HDPE Pipes ISO / SANS 4427-2:2008 – SDR 7.4 to SDR 17

Dimensions of PE 100 HDPE Pipes ISO / SANS 4427-2:2008 – SDR 21 to SDR 41