Polyethylene pipes (PE) have been used in Spain for water supply and wastewater since 1960. Since that time, advances and significant improvements have been made in the raw material itself, as well as in manufacturing equipment and methods. Rodolfo Vegas, Technical Engineer and Blogger, with 40 years of experience in plastic pipes presents practical applications.
PE pipes are being used at all stages of the water cycle, from collection in rivers, wells, reservoirs or seas until their return to the medium. In practice, we take water, which may be polluted, put it through the water treatment process to ensure that when it reaches the consumer it is pure and fit to drink. The cycle is constantly repeated.
For more than 20 years now, water coming from sewage treatment plants or storm tanks is being treated to enable it to be used in the agricultural sector or for watering gardens. PE pipes are eminently suited to this application and have the advantage that they can be colour-coded to identify at a glance the purpose for which they are being used, for example, pipes used for drinking water have blue bands, whilst purple or brown bands are used for non-potable water. Around the world large and long diameter pipes have been laid under the sea to drive pre-treated wastewater and salt water under pressure for onward purification treatment.
In the Spanish economy agriculture is an important sector and a major consumer of water. Currently about 70% of water supplied is for irrigation, some six times the amount used in the home. In many cases the irrigation network systems are obsolete, resulting in water leakages of up to 60%. Another important factor is the long dry spells which are now occurring more frequently. Large diameter PE pipes are proving useful in moving large volumes of water to areas where it is needed.
Rainfall in the Mediterranean tends to be short-lived but very intense, causing much localised flooding and an increase in accumulations of ground water. PE pipes are being used to pump both potable and non-potable water away from flooded areas.
Union for butt welding
The most common joining system for large diameter PE pipes (<630mm) is butt welding. To obtain a perfect weld, the welding parameters, pressure, plate temperature, time and cleaning have to be carefully controlled, and the welding equipment itself has to be strictly calibrated according to current regulations.
Perhaps the most important point about working with large diameter PE pipes is that operatives must be fully trained in welding techniques. It is highly recommended that welders obtain the AseTUB (Spanish Association of Manufacturers of Tubes and plastic Accessories) Carné facilities in plastic piping systems or similar qualification. ISO 21307 states that PE100 pipes can be welded that are manufactured from raw materials having a melt flow rate (MFR) between 0.3 and 1.7g/10min under the conditions of 190°C/5kg using welding equipment that complies with ISO 12176.
ISO 21307: Plastics pipes and fittings – butt fusion jointing routines for polyethylene (PE) pipes and fittings used in the construction of gas and water distribution systems. This is the standard that provides the following three butt fusion procedures, shown in the tables below:
As shown in the graphs of the various systems, the high pressure method of butt welding takes less time to make a weld than low pressure. This is a very important factor in lowering the cost of installation, since the cycle times necessary for butt welding large diameter pipes are long. Using the high pressure method means that daily productivity can be significantly increased.