Polyethylene pipes and Steel pipes with 3LPE coatings are integral part of a citygas distribution network. These are being used in India since late 80’s. Standard MDPE and HDPE materials are Butene copolymers of Ethylene, where Butene (C4) is added as comonomer to form the side branches of linear Polyethylene (C2) chains. The research on PE materials have improved various attributes of the polymer, providing them with higher durability, pressure resistance and service life.
One such development is use of Hexene (C6) as a copolymer replacing Butene (C4) to make an Ethylene Hexene copolymer providing superior resistance to mechanical damages and slow crack growth during installation and service. For PE100 Orange pipe materials for low / medium pressure distribution system, the new hexene PE copolymer, offers much superior resistance to slow crack growth. Hence it is ideal for Trenchless installations like HDD or pipe bursting, where pulling the pipe through the bore in the ground may substantially notch and scratch the pipe or coating. Using a Hexene PE service life of the pipe is not affected despite the demanding installation techniques due to higher entanglement of polymer chains. These types of PE materials are already being used by Indian CGD Industry for past 2–3 years.
For 3LPE coated steel pipes for high pressure gas mains as well as trunk lines, Hexene based Black PE top coat has been adopted by several Gas companies. This is mainly due to two advantages. They offer a higher upper design temperature limit of +90 C (compared to +80 C as per international specification (ISO21809-1). They also offer material savings as 10% lower thickness compared to standard PE top coat is able to meet and exceed all system requirements. The paper deals with the mechanism of these new polymers that helps to offer these superior properties.