Quality control tests on raw materials and polyethylene pipes

The raw materials for polyethylene pipe production, whether polyethylene or masterbatch, are tested before use and after approval, are used in pipe production:

1- Raw material tests

1-1- MFR test

Polyethylene granules in accordance with ISO 9680-1 must be tested at a temperature of 190 degrees Celsius and a weight of 5 kg. After filling the device with about 3 grams of material, the material is preheated for 4 minutes and then the test is started. The device automatically cuts every two minutes. Since the MFR test result is reported as (gr/10min), the weight of 5 cuts from the device output will indicate the MFR value.

The permissible value in the INSO 14427 standard is reported to be between 0.15 and 0.7 g/10 minutes, and no distinction is made between the values ​​of PE100 and PE80 materials, but this value is desirable when it is between 0.15 and 0.23 for PE100 materials.

1-2- OIT test

Polyethylene granules in accordance with the national standard 6-7186 must be tested at a temperature of 200 degrees Celsius for 20 minutes under the blowing of oxygen gas. During this period, polyethylene should not undergo thermal degradation and oxidation. Although the thermal stability value is reported to be 20 minutes, this test is performed for more than one hour in the Pasargad Pipe Laboratory to obtain more information about the quality of the raw materials.

1-3- Density test

The density of polyethylene granules is also examined in accordance with the national standard 1-7090. The permissible value according to the INSO 14427 standard is greater than 0.941 g/cm3.

1-4- Soot percentage test

If the raw materials are self-colored, a soot percentage test is performed on the raw materials in accordance with the ISO6964 standard. In this test, 1 gram of the material is burned inside the furnace at a temperature of 10 minutes at 350 degrees Celsius, 10 minutes at 450 degrees and 30 minutes at 550 degrees Celsius under high purity nitrogen gas to determine the percentage of black carbon (soot). The permissible value according to the INSO 14427 standard is between 2 and 2.5 percent.

1-5- Soot dispersion test

Similar to section 1-1-4, if self-colored materials enter the factory, the soot dispersion rate of the raw materials is measured in accordance with the ISO 18553 standard. In this test, the degree of dispersion is determined by preparing thin films of the material and examining it with a microscope. The permissible value according to the INSO14427 standard is reported to be less than or equal to 3.

1-6- ESCR test

This test must be performed by the raw material manufacturer and stated in the raw material datasheet.

2- Tests related to polyethylene pipes

2-1- MFR test

Polyethylene pipes according to the ISO 9680-1 standard must be tested at a temperature of 190 degrees Celsius and a weight of 5 kg. After filling the device with about 3 grams of material (the pipe is cut into cubes), the material is preheated for 4 minutes and then the test is started. The device automatically cuts every two minutes. Since the MFR test result is reported as (gr/10min), the weight of 5 cuts from the device output will indicate the MFR value.

It is noteworthy that the MFR value of the pipe should not differ from the MFR of the raw materials by more than 20%.

In accordance with the INSO14427 standard, in multilayer pipes, the MFR test must be performed on each layer separately and the results recorded for each layer.

2-2- OIT test

Polyethylene pipes in accordance with the national standard 7186-6 must be tested at a temperature of 200 degrees Celsius for 20 minutes under oxygen gas blowing. During this period, the pipe should not undergo thermal degradation and oxidation.

In accordance with the INSO14427 standard, in multilayer pipes, the OIT test must be performed on each layer separately and the results recorded for each layer.

2-3- Density test

The density of polyethylene granules is also examined in accordance with the national standard 7090-1. The permissible amount according to the INSO 14427 standard is greater than 0.941 g/cm3.

2-4- Soot percentage test

The permissible amount of soot in polyethylene pipes according to the INSO 1442 standard is between 2 and 2.5%. The test is carried out according to the method of paragraph 1-4. Currently, due to the lack of use of self-coloring materials and the use of masterbatches to provide soot in the pipe, this amount is highly dependent on the complete mixing of the materials by the fine materials.

2-5- Soot dispersion

According to the ISO 18553 standard, the amount of soot dispersion of the raw materials is measured. In this test, the degree of dispersion is determined by preparing thin films from 6 different points of the pipe and examining it with a microscope. The permissible amount according to the INSO14427 standard is reported to be less than or equal to 3.

2-6- Tensile test

To perform the tensile test, samples are first cut by CNC machine depending on the thickness.

Pipes with a thickness of up to 5 mm are called Type 2, samples with a thickness of more than 5 mm are called Type 1, and samples with a thickness of more than 12 mm are called Type 3.

After placing the samples in the two jaws of the tensile machine, the samples are stretched at a certain speed. According to the INSO 14427 standard, the elongation before rupture of the sample must be more than 350%.

2-7- Hydrostatic pressure test

Polyethylene pipes according to the national standard 1-12181 must withstand a certain pressure for a certain period of time and temperature.

This test is performed for either 100 hours at 20 degrees Celsius or 165 hours at 80 degrees Celsius or 1000 hours at 20 degrees Celsius and for each given pipe, the applied pressure is calculated according to the following formula.

emin  Minimum thickness

dem  Pipe diameter

σ  Stress value

Pipe type Test stress in MPa

100 hours at 20 degrees Celsius 165 hours at 80 degrees Celsius 1000 hours at 80 degrees Celsius

PE 100 12.4 5.5 5

PE 80 9 4.6 4

PE 63 8