ACTUAL EXAMPLE 1

Type of Polymer : Thermoplastics

Name of Material : Unplasticised polyvinyl chloride (UPVC)

Location of Use : Water pipes

Properties :

Unplasticised polyvinyl chloride is a stiff, hard, tough but lightweight material. It has good strength while having low softening point (at about 70C). Also, it has good weather resistance as well as water resistance. It has good chemical resistance so as to be unaffected by dilute or concentrated acids and alkalis. Besides, it is non-flammable and self-extinguishing. It can be produced with wide ranges of colours and grades --- transparent, translucent or pigmented. It also has good abrasion resistance. As for welding, it is easily jointed by solvents. It is low in cost.

Why is this material used ?

Comparing with cast iron water pipes, unplasticised polyvinyl chloride water pipes are cheaper in cost. Its lighter weight can make easier to transport and handle. Moreover, there is no corrosion occurring to make a better maintenance.

1. Unplasticised polyvinyl chloride is not suitable for hot water pipe where the operating temperature closing to the boiling point of water because of low softening point. Instead, Chlorinated polyvinyl chloride (CPVC) is used but the problem of accommodating thermal movement remains.

2. Unplasticised polyvinyl chloride would collapse in case of fire owing to low softening point. Moreover, if an unplasticised polyvinyl chloride pipe penetrating a compartment wall or floor, it would leave a hole through which the fire could break out. There are three solutions to the above problem : I) allowing the use of a proprietary sealing system to maintain the fire resistance of the floor or wall. The way is that using a metal sleeve fits round the pipe where it passes through the structure. An intumescent material contained by the sleeve can swell in a fire and so close the hole left by the collapsed pipe. II) Using cement mortar, gypsum plaster or similar inert material round the pipe to stop the fire in case of pipes not exceeding 40 mm diameter. III) In case of unplasticised polyvinyl chloride pipe with a maximum diameter of 160 mm, using a non-combustible sleeve pipe to contact with the unplasticised polyvinyl chloride pipe and project at least 1 m from each wall surface or floor. As a result, fire will be stopped at its junction with the structure.

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