Information about polyethylene

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Polyethylene is used to produce and cover various types of pipes in various applications such as drinking water, sewage, gas, heating and plumbing pipes for homes, solid material transfer pipes, drip irrigation, protective pipes (wire and cable and glass fiber passage, etc.).

Polyethylene pipes have been in use for about 40 years, and gradually, with the recognition of the advantages and functions of this pipe and the gradual improvement of the characteristics used in many applications, they replaced various types of concrete, steel, cast iron and PVC pipes.

The flexibility of polyethylene pipes has made the movement and installation of pipelines much easier and less expensive than steel pipelines. The flexibility of these pipes allows for the bypassing of obstacles and the reduction of joints and connections. These pipes are much more resistant to natural disasters such as earthquakes than other types of pipes.

Polyethylene pipes have a wide range of applications, the most common of which are as follows:

Drinking water networks
Urban water supply networks
Urban and rural sewage networks
Pressure irrigation
Urban and rural sewage
Cable coating, metal pipe
Industrial water supply

Advantages of polyethylene pipes:

High resistance to breakage and cracking
Very high chemical resistance
Resistance to corrosion
High flexibility
Function at temperatures from minus 40o c to 70o c
Ability to use on uneven terrain
Long life
Easy and fast execution
High hydraulic resistance
Sound insulation
Excellent earthquake resistance
Impact resistance
Resistance to abrasion and scratching:
Polyethylene pipes are very suitable for transporting liquids that are abrasive or scratch-resistant due to the following polymer properties:

Low modulus of elasticity
High impact resistance
Friction coefficient Low
High chemical inertia The lifespan of polyethylene pipes against liquids containing abrasive particles and scratches is up to 10 times higher than that of metal and clay pipes.
The resistance of polyethylene pipes to natural disasters such as earthquakes is much higher than that of other types of pipes. The figure below shows the damage rate in the 1995 Japanese earthquake for different types of pipes.

Types of polyethylene raw materials:

PE63

PE80

PE100

Pressure classification of pipes according to the ISO I2I62 standard:

In the production of polyethylene pipes, the higher the pressure classification (PE63 to PE100), in addition to saving on material consumption, it increases the cross-sectional area of ​​the pipe at a constant outer diameter, which increases the pipe’s transfer capacity. If we assume that the transfer capacity is constant, the transfer speed can be reduced and, as a result, smaller pumps can be used for transfer. This reduces costs. In addition, when repairing pipes and using Amster pipes in the previous pipe – the loss of transmission capacity will not be large.

PE100 has advantages in non-pressure pipes, apart from pressure pipes, as it has a higher internal strength than standard heavy polyethylene (1250MPA versus 950MP), a higher modulus, greater radial stiffness, which is a great advantage in pressure and non-pressure sewage networks.

The most important functional characteristics of pressure polyethylene pipes:

1- Long-term strength:

Long-term strength or the basis of the hydrostatic design of the pipe determines the life of a pipe at a given pressure and temperature and is usually carried out by a series of tests at different pressures and temperatures over a specified period of time. To check the 50-year life of the pipe, the pipe must be obtained without creep tension.

2- Rapid crack growth:

Rapid crack growth is a very important defect that is frequently seen in transmission lines. The largest crack reported for a steel pipe was 11 km long, and for polyethylene, the largest crack was observed in a gas pipeline in Hungary with a diameter of 315 mm and a length of 700 m. Resistance to rapid crack growth is a term used to examine impact strength. These tests are used at a specific temperature to determine the pressure above which rapid crack growth occurs. This pressure is called the critical pressure.
The probability of rapid crack growth in pipes increases with increasing diameter and thickness of the pipe at low temperature and high ambient pressure. The term crack growth is used when the crack length is 4.7 times greater than the nominal outside diameter of the pipe.

3- Slow crack growth:

The slow crack growth characteristic shows the long-term and environmental resistance of the pipe. The initiation of crack growth depends on the internal stress residual from the processing time in the pipe and the installation pressure of the pipe. The crack test examines the long-term creep properties of the material, these tests are known as ESCR.
If a crack grows and a crack forms in the pipe, it is said that the pipe is bent. Pipes made of first-generation polyethylene bend in 100 hours, but the next generation bends in 1000 hours and the current generation lasts nearly 100 years.

4- Permeability:

This is important for the transmission of natural gas. Because it is possible for it to penetrate through polyethylene. Of course, the measured leakage rate is so low that it does not affect the transmission of gas.

Gas leakage rate from polyethylene

5- Expansion coefficient of polyethylene pipes:

The expansion coefficient is necessary for calculations related to the specific diameter and the amount of pressure on the pipe joints and the surrounding soil.

6- Thermal conductivity:

The amount of heat that a plastic pipe can transfer through its wall depends on the thermal conductivity of the pipe. The thermal conductivity of polyethylene is 0.43     w/mok. ASTM C177

7- Hygiene issues

For the transport of beverages, the hygiene of the materials in the pipe is important. The hygiene standards related to polyethylene are:
1- FDA, CFR, Title 21 (1994) 177. 1520. Olefin polymers     (USA)
2- NS

Standard certificates

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Operating License:

After obtaining an operating license from the Industries and Mines Organization of Guilan Province, Ethylene Pipe Company increased its quota in several stages by increasing production lines and sizes and is currently continuing to produce polyethylene pipes with a nominal capacity of 14,000 tons per year.

Standard License in Iran:

After the polyethylene standard was made mandatory by the Standards Institute in 1976, Ethylene Pipe Company obtained the standard license and since then has been able to renew its license without any defects in the General Directorate of Standards of Guilan every year by observing the rules and regulations.

Quality Management System (ISO 9001:2008)

In 2006, Ethylene Pipe Company was able to obtain the aforementioned certificate from the IEC Institute of England by implementing the rules and regulations of the quality management system and has been able to pass the audits without any defects every year. In 2008, this company also obtained the 2008 edition by implementing the ISO9001 conditions.

Environmental Management System (ISO I4000: 2004):

In 2006, Pipe Ethylene Company was able to obtain the aforementioned certificate from the American ICR Institute by implementing the regulations and guidelines of the environmental management system and took the necessary measures to preserve and maintain the environment on its own behalf.

Quality Model Unit of Guilan Province:

In 2007, 2008, Pipe Ethylene Company was selected as a model unit of the province by the General Directorate of Standards of Guilan after reviewing the company’s documents and conditions in terms of quality improvements.

Partner Laboratory:

In 2007, Pipe Ethylene Company obtained the Partner Laboratory Certificate for single-wall polyethylene pipes from the General Directorate of Standards of Guilan on 14/01/90 after implementing the ISO 17025 documents.
After completing its laboratory, this company was able to obtain a partner laboratory certificate for P.V.C – u pipes, polypropylene pipes, single-wall polyethylene, and double-wall polyethylene from the General Directorate of Standards on 01/14/90.

Quality control and laboratory

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Pipe Ethylene Company’s laboratory is a reference for testing various types of polyethylene pipes using national and international standards, as one of the capable arms of the company, which operates in line with the major goals of this complex.

Aiming to increase the level of satisfaction of its customers, this laboratory has placed the following at the forefront of its performance through providing laboratory services:

Employing capable and qualified people in the laboratory to ensure correct and accurate testing

Creating motivation, improving the level of skill and efficiency of employees through systematic, planned and continuous training

Expanding the scope of activities related to testing, through conducting studies and purchasing necessary equipment

Continuous improvement in the laboratory’s activities and functions

Following up and dealing with complaints received from customers in a timely and appropriate manner

The most equipped polymer pipe laboratory in the north of the country belongs to Pipe Ethylene. Tests related to polyethylene, polypropylene, PVC and double-walled polyethylene materials and pipes are performed in the Pipe Ethylene Company’s laboratory.

The tests performed in the company’s laboratory are as follows:

Melt flow index test This test is performed on both raw materials and polymer products based on ISIRI 7175-7 and ISIRI 6980 standards.

Density determination test This spear test is performed on raw materials and polymer products based on ISIRI 7175-5 standard for (PE).

Heat recovery test This test is specific to polymer pipes. For PE, it is performed based on ISIRI 7175-3 standard.
The test to determine the percentage of the cycle is performed based on ISIRI 7175-2 standard on both the final product and the raw materials of the paint itself.
The test to determine the distribution and dispersion of the cycle is performed based on ISIRI 7175-5 standard on both the product and the gravities of the raw materials of the paint itself.
The raisin test is performed on the product sample after preparing a furniture-shaped sample from the pipe based on ISO 6259 standard.
Thermal stability test is performed on the manufactured product according to ISIRI 7175-8 standard.
Resistance test in dimicromethane solvent This part is specific to PVC pipes (based on ISIRI9117 and ISIRI10609 standards)
Pressure test is performed according to the standard for all polymer pipes.
Vicat softening temperature test is performed according to ISIRI 2616 standard for PV pipes.
Impact test is performed according to ISIRI 9117 and ISIRI 11438 standards for PV and according to ISO 9856 standard for PP.
Internal pressure measurement

This test itself includes two types of tests, which are:

Burst test:
In this test, the pipe is placed under internal pressure at a fluid temperature of 22-250oc after isothermalization in the laboratory and the fluid environment. In this test, the ultimate pressure tolerance limit in the pipe and the type of material behavior and its processing are examined.

Static test:
This test is different from the burst test. In this test, based on the outer diameter, wall thickness and type of raw material, the pressure that must be applied to the pipe is calculated and placed under that pressure for the time specified by the standard, and ultimately no physical changes, including breakage or bursting, are observed.

Dimensional controls

Calipers:
The laboratory of Pipe Ethylene Company is equipped with two digital calipers from Mitotoyo, Japan, which measure the width and wall thickness of the pipes.

Circummeter:
The outer diameter of the pipes is measured by 4 circummeters from 20 mm to 1600 mm in size.

Appearance and marking controls will also be performed.