Polyethylene Pipe

The structure and the mechanical properties of a butt weld in a polyethylene pipe were examined and contrasted to non-welded PE pipe. X-ray diffraction, differential scanning calorimeter and Fourier transform infrared spectrometer measurements revealed details of axial amorphous and crystal orientation in the original pipe. Contrary to expectations considering the squeeze, flow nature of butt-welding, formation of randomly oriented crystal structure was determined in the weld region. Tensile and notched impact tests at ambient and sub-ambient temperatures and varying rates of impact showed that welding consistently reduced resistance to failure. Microscopic evaluation of the brittle fracture surfaces revealed the surface morphology of the welded zone to be coarser than the non-welded PE material.

Polyethylene (PE) pipes have been produced in Australia and New Zealand since the mid 1950s, initially in small diameters for industrial and agricultural applications. The first Australian Standard was released in 1962 and Iplex Pipelines (then Hardie Iplex) commenced production in the early seventies. Usage has grown rapidly with over 40,000 tones of PE pipes being produced annually in Australasia. Polyethylene has become one of the most widely used of all plastic polymers.

Terms frequently used to describe this material when used for engineering applications are high density (HDPE), medium density (MDPE) and most recently high performance (HPPE) polyethylene. Others such as low density (LDPE) and linear low density (LLDPE) are sometimes used for irrigation pipelines.

The Type 50 PE of AS1159, which was in common use until 1994, is an HDPE with a long-term design stress of 5.0 MPa. However, with the introduction of new Standards, terminology relating to density alone is no longer recommended. AS/NZS4130 and AS/NZS 4131 recognized this, allow for three specific classifications by material strengths, and sub classifications by performance at elevated temperatures. The higher strength PE 80 and PE100 compounds are sometimes referred to as second and third generation materials. They were introduced into general service in the late seventies and early nineties respectively.

POLI plex polyethylene is an integrated family of PE pipes produced by Iplex , based on PE 80B, PE 80C and PE100 materials. These are manufactured to AS/NZS 4130 from polyethylene complying with AS/NZS 4131. Diameters range from DN 16 to DN 1000 with pressure ratings of up to 2.0 MP a. Pipes up to DN 110 can be supplied in coils lengths of up to 300 meters in some diameters. Larger diameters are typically 12 m long although 15 m and longer are occasionally manufactured by arrangement. Note that the nominal diameter of PE pipes refers to the outside diameter in accordance with international practice.

Iplex THERMAPIPE is a white co-extruded PE developed by Iplex, designed for above ground pipelines in hot climates to significantly reduce the heating effect due to exposure to solar radiation, which occurs with the normal black pigmented PE. This allows the use of lower class pipes to give reduced purchase and operating costs.

 

POLI plex PE pipes may be joined economically using thermal butt welding equipment. However, diameters of up to DN 110 are more commonly joined using the Iplex Metric compression couplings. These provide an easy system for making joints quickly which can be undone and reused when altering the system layout. An alternative form of welding PE is the electro fusion system where heating elements are embedded in PE sockets. These sockets form part of a coupling or other fitting and require an electrical input to produce a welded joint. For pipes, which are, constantly being uncoupled and moved, shouldered ends can be provided to suit proprietary metal clamps. For bends and tees a range of both injection molded and fabricated fittings