Production and use of polypropylene pipes - Студенческий научный форум

XII Международная студенческая научная конференция Студенческий научный форум - 2020

Production and use of polypropylene pipes

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Production and use of polypropylene pipes: Polypropylene Pipes (PP) pipes and PPR pipes are manufactured by extrusion in the same way as PE pipes. Particularly in the case of PP pipes there are several different molecular structures available on the market. In the simplest case the molecular chain is built up of one and the same repeating unit often the same as the monomer shown within the brackets). The polymer is then called homo-polymer.

The stiffness of the PP pipe will decline in the order: PP-h-PP-b-PP-r and consequently the impact strength will increase simultaneousness. It has also been found that the long-term strength at elevated temperature: (600 C ) will increase when going from PP-h to PP-r most commonly used for PP sewer pipes and for cold water pipes id PP-b . Particularly for sewer pipe purpose new high molecular weight resins have been developed recently. The melt flow rate expressed as MFR 230/2 may be in the range of 0.3g/10min. This value corresponds approximately to 0.6 expressed as MFR 190/5 normally used for PE. The most significant property for these new PP grades from a practical point of view as far as buried pipes is concerned, is the rather high short term E- modulus; i.e. Approximately 50% above corresponding values for the most common PE grades. The density of the PP compound is lower than for corresponding PE resins, or approximately900kg/m3 as compared with 950-960kg/m3 for PE. The designation for these polyethylene resins is PP 80.

By improvement of PP-r grades high temperature resistant hot tap water pipes have been introduced recently. They can compete with PEX and PB for many hot water applications, but are easier to process than PEX and safer than PB as far as strength reproducibility is concerned. Furthermore, the PP pipes can be jointed by welding, which is not the case with PEX.

Manufacturing of Polyvinyl Chloride Pipes: Polyvinyl Chloride Pipes (PVC) and PPR pipes can be manufactured with or without plasticizers. Examples of the former are garden hose, floor tiling and household articles. The addition of plasticizers increases material flexibility, but leads to some deterioration in other physical properties. Furthermore, some plasticizers display a tendency to migrate, escaping in the course of time so that the plastics becomes brittle. For these reasons, no pastiches are used in the manufacturer of PVC pipes for water mains and sewers. In this respect, the material is characterized as rigid PVC and this variety is termed PVC-U ( unplasticized PVC) according to ISO.

As in the case of PE, where melt flow rate describes the molecular weight of the material, PVC makes use of what is termed the K- value, It may be determined in various ways , but in the following pages consideration is given to the value obtained in accordance with the Fikentscher method, based on 1% PVC in Cyclohexanone at 25 C. A K-value of 65 determined in accordance with this method corresponds to viscosity grade of 105 according to ISO/R 174, 1961. K-value increase with rising mean molecular weight of the polymers, i.e. With greater molecule length. As for PE, the strength of a PVC material then improves, but at the same time it becomes more difficult to process. The K-value of PVC pipes normally lies in the range of 65-70, another definitive characteristic of PVC is its softening temperature, as compressed as what is termed the softening point (Vicat Point). Normally this lies between 70 C and 80 C . A rise in softening point leads to improved distortion resistance to heat and as a rule, also improved strength properties.

Distinctions are made in raw materials between emulsion, suspension and bulk resins. Manufacturing processes based on this order of raw materials, ensure, among other things, increased purity and lower water absorption in the PVC material. The most common type is suspension PVC (S-PVC), although emulsion PVC (E-PVC) also exists.

Сonsider as an example the system SupraTherm.

Supratherm pipes and fittings are produced from polypropylene random copolymer, PP-R 80/ PP-R 100/ Type 3 as raw material having low melt flow rate, high molecular weight and good flexibility. This raw material is recommended for the production of pressure pipes including potable water transfer lines, hot and cold water transfer lines, floor heating and also for chemical industry applications. Good long term pressure resistance and easy processing and installation technique give cold and hot water systems made of PP-R pipes and advantage as alternative to the traditional systems.

Advantages of the system.

Corrosion resistant

The Random Polypropylene possesses a high level of electrical insulation, which prevent the appearance of corrosive phenomena caused by stray currents.

The low affinity of the system towards acid and alkaline substances makes it compatible with the materials which are used in civil construction on a daily basis (lime and cement), as wee as to the majority of the chemical substances which are sometimes present in water pipes.

Low Thermal Conductivity

Substantially reduces the traditional formation of thermal condensation common in metal pipes.

Reduced Pressure Loss

The pipes and accessories are characterized by low roughness of internal surfaces, avoiding the creation of calcium deposits, reducing pressure loss to the minimum.

Acoustic insulation – low noise

The characteristics of the raw material and the thicknesses used confer high acoustic insulation to the system.

Organoleptic properties

PP-R is an entirely nontoxic product, guaranteeing that the system transport clean water.

Adequate life cycle

According to the clearance curve it is possible to observe that for water installations with defined temperatures and pressures, the system will last more than 50 years.

Reduced installation time

The most relevant characteristics of the PP-R system is the union of all elements through thermal fusion. This method is safe and easy to work with when compared with traditional products.

Recommendations for the appropriate use for the Systems

PP-R, like all thermoplastics, should not be directly exposed to sunlight.

PP-R, material it's crystallizable, stocked not less then +5 °C

PPR, is made of thermoplastic material. High and heavy load shape / reap the disorder is caused. 1 meter higher than the pipe on top of your stocking.

Thermoplastic material is flammable. Do not allow direct contact with fire PPR products!

Please use thermoplastic heaters to give shape.

The pipe must be protected from powerful hitting.

Healthy for the resource, of the ambient temperature is at least +5 °C

Use Teflon tape or liquid to avoid leaks do not use accessories with conical bolts or non-calibrated, and tighten without excessive force.

Pressure test. Test control.

Acc. to the Technical Rules for Potable Water Installations DIN 1988 have to be (while still visible) hydraulically pressure tested all pipelines. The test pressure has to be 1.5 times of the operating pressure. Due to the material properties of SupraTherm pipes a pressurization causes an expansion of the pipe. Different temperatures of pipe and test medium lead to alterations of pressure. A temperature change of 10 K corresponds to a pressure difference of 0.5 to 1 bar.

The pressure test of SupraTherm pipe systems should be made with a constant temperature of the medium. The hydraulic pressure test requires a preliminary, principal and final test. In the preliminary test the system is pressurized with the 1.5 times of the maximum operating pressure. This test pressure has to be re-established twice within 30 minutes within an interval of 10 minutes. After a test time of a further 30 minutes the test pressure must not drop more than 0.6 bar. No leakage may appear.

The preliminary test is to be followed directly by the principal test. Test time is 2 hours. Now the test pressure taken from the preliminary test may not fall more than 0.2 bar. The final test is made with a changing pressure of 1 bar and 10 bars. The pipe system must be unpressurized between each test cycle. Between each test course the pressure has to be released. No leakage must appear at any point of the tested installation system.

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