Polyethylene extrusión in the prehistory
Every time I see this vignette, I think, perhaps because of professional deformation, which perfectly represents the fundamental parameters of PE pipe manufacturing, ie, pressure (clubbed), temperature (fire) and time (depending on the bone length). These parameters are the ones we have to control during the PE extrusion.
Talking about the PE pipes butt welding, we also have these three parameter. Pressure in the butt welding is 1.5kg/ cm2, the plate temperature should be between 210º and 23º C and the tabulated time, is according to the pipe dimensions to be welded, diameter and thickness.
Obviously, manufacturing systems of plastic pipes in general and the PE in particular, have greatly evolved since they began to be manufactured for over 50 years.
1.- Low weight
They are extremely light with a density between 0.93 and 0.96 g/cm3, therefore, they float on water and are easy to transport and handle. For installation fewer mechanic resources are needed than for other heavier pipes or at least powerless, which cheapens installation.
2.- They do not get rusted
PE pipes are high molecular polyolefins, therefore, they have nonpolar structure, which provides excellent resistance to chemicals. Thanks to their chemical inertia, they are resistant to organic acids (hydrochloric, sulfuric, etc.), alkalis, detergents, tension depressants, mineral oils and fermentation products.
3.- They do not corrode
PE pipes properties are not altered in the presence of corrosive soils, acid soil with low pH level and high sulphate content. They don´t have problems of rot, rust, mold or mildew or rust, nor are they affected to algae, bacteria or fungi. The great weakness of metal pipes is corrosion, which is impossible to predict most of the time.
4.- Easy installation
PE pipes are supplied in rolls of 50 or 100 m with diameter up to 110mm. from which the 6 or 13m bars are supplied , its length is subjected just to transportation conditions. This means that we will have fewer joints than with other types of shorter length pipes. Although PE pipe installation is easy, we consider it necessary for installers to receive appropriate training, such as Specialist in Installation of Plastic Pipe Systems Certificate from AseTUB ( www.asetub.es ).
5.- Economical installation
PE pipes are flexible. They allow to be bent in cold, which speeds up and cheapens installation, which otherwise is very simple, as it perfectly adapts to the irregularities that may arise in the field. It must, always be compared the price of different material pipes plus the installation cost. PE installation is generally cheaper.
6.- Long life (50 to 100 years)
PE pipes are designed to work underground at 20º C over a lifetime of at least 50 years, with a minimum safety factor of 1,25 for water pipelines and at least 2 for gas networks. Taking into account that from 0,8m. burial depth stop pipes influence on the pipes, the environment temperature conditions, we can say that the total period is still much higher, talking of up to 100 years.
7.- Low maintenance costs
PE pipes do not require any maintenance, the idea is that once they are installed we can forget about them. On the other hand, the pipe roughness is a very important issue as it has influence on the daily energy consumption on a drive, for example, since while the pipes and installation are just paid once, the energy is being paid the rest of the installation life.
8.- It does not allows inlaids
The inside mirror surface, which causes the pressure loss is significantly lower than in traditional pipes. This quality also prevents inlaids by the precipitation of carbonates or other products.
9.- Multiple joining systems
I usually say that the best joint is the one which does not exist. PE pipes joined by butt welding or electrofusion, allow us to say so since in a weld, both pipe´s material are closely joined at a molecular level. Other joining systems are through mechanical fittings or flanges. PE pipes should not be either screwed or glued.
10.- Plastics are recyclable
Plastic waste is a valuable resource to get rid of them without using them as (recycled) material source or energy source (energy recovery). Once their useful life is over, polyethylene pipes can be mechanically recycled by triage process, cleaning and pelletizing becoming a new raw material, which at the same time, can be used for other products´manufacturing, thus giving to material a new useful life. CICLOPLAST (www.cicloplast.com) is a non-profit society committed to the Environment, in plastic promoting and recycling at the end of its useful life, in all its applications.
– Polyethylene Pipes Technical Manual from AseTUB
– PE 100 Pipe Systems de Heiner Brömstrup
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