EN ISO 9080 Plastic Pipe and Duct Systems - Determination of Long-Term Hydrostatic Strength of Thermoplastic Materials in Tubular Form by Extrapolation

The standard "EN ISO 9080 Plastic piping and ducting systems - Determination of long-term hydrostatic strength of thermoplastic materials in tubular form by extrapolation" published by the International Organization for Standardization (ISO) describes a method for estimating the long-term hydrostatic strength of thermoplastic materials by statistical extrapolation. This method is applicable to all types of thermoplastic pipes at applicable temperatures. This standard was developed based on test data from piping systems.

For the purposes of this standard, the following terms and definitions apply:

Internal pressure refers to the force per unit area exerted by the medium in the pipe.
Stress is the force per unit area in the circumferential direction on the wall of the pipe due to internal pressure.
The test temperature is the temperature at which the voltage breakdown data is determined.
The maximum test temperature is the maximum temperature at which the voltage breakdown data is determined.
Service temperature is the temperature at which the pipe will be used.
The downtime is the time until a leak occurs in the pipe.
The maximum test duration is the time obtained by averaging the logarithms of the five longest failure durations.
Extrapolation period is the time limit within which extrapolation is allowed.
Long-term hydrostatic strength is a quantity with stress dimensions representing the predicted average strength at temperature T and time t, in megapascals.

Pipe stress rupture data shall be determined in accordance with ISO 1167-1 and ISO 1167-2 standards. Determination of resistance to internal pressure shall be made using straight pipes. The average outer diameter and minimum wall thickness of each pipe test piece shall be determined in accordance with ISO 3126 standard.

For all calculations, the pipes tested must be of the same nominal size, made of the same batch of material and come from the same production batch.

For existing materials evaluated according to the ISO 9080 standard, the initial data set may be supplemented with additional data generated from other batches to meet the requirements of this standard. In this case, the additional data must be distributed uniformly at each temperature and documented in the test report.

For the distribution of internal pressure levels and time intervals, at least 30 observations spread over the test period should be obtained for each selected temperature. Internal pressure levels should be selected such that at least four observations occur over 7.000 hours and at least one observation occurs over 9.000 hours. In the case of second-branch estimation, at least 20 observations are required for the second branches and at least 5 observations per temperature.

For all temperatures, failure times up to 10 hours are ignored. At temperatures up to 40 degrees, failure times up to 1.000 hours may be ignored, provided that the remaining number of observations complies with this standard. In this case, all points below the selected time at the selected temperatures are discarded.

Test pieces that have not failed for more than 1 000 hours may be used as observations in multiple linear regression calculations and in determining the presence of an index. Otherwise, they shall be ignored as long as the remaining number of observations complies with this standard.

This method is based on multiple linear regression and calculation details given in the standard appendix (Appendix A). It requires testing at two or more temperatures and for 9.000 hours or more and can be applied regardless of whether there are signs of knee presence.

In accordance with certain conditions, test data are obtained using two or more temperature values:

Each adjacent temperature pair must be separated by at least 10 degrees and not more than 50 degrees.
One of the test temperatures should be 20 degrees or 23 degrees.
The highest test temperature should not exceed the Vicat softening temperature determined according to ISO 2507-1 for glassy amorphous polymers by minus 15 degrees, or the melting temperature determined according to ISO 11357-3 for semi-crystalline polymers by minus 15 degrees.
The number of observations and the distribution of internal pressure levels at each temperature must comply with this standard.
To obtain an optimum estimate of the lower confidence limit of the predicted hydrostatic strength, the range of test temperatures should be selected to include the service temperature or range of service temperatures.
Failures due to contamination may be ignored provided that the remaining number of observations complies with this standard.
All valid data points must be used in calculations.
For most materials, the test environment and test temperatures are specified in the relevant product standards.

Our organization has a strong staff that closely follows the developments in science and technology in the world and constantly improves itself. Among the numerous test, measurement, analysis and evaluation studies provided for businesses in various sectors, there are also test services in accordance with the standard “EN ISO 9080 Plastic pipe and duct systems - Determination of long-term hydrostatic strength of thermoplastic materials in tubular form by extrapolation”.