ISO 2505: Longitudinal reversion testing for plastic pipes

ISO 2505: Determining the Longitudinal Reversion of Plastics Pipes and Fittings

Overview of ISO 2505 standard

ISO 2505 specifies the method for determining the longitudinal reversion of thermoplastics pipes and tubing after exposure to heating. The standard applies to both unplasticized and plasticized polyvinyl chloride (PVC-U and PVC-P), as well as other thermoplastics such as polyethylene (PE), polypropylene (PP), and their copolymers. This test is important for assessing the dimensional stability of pipes and fittings under heat, which is critical for ensuring reliable installation and service life. Testing in accordance with ISO 2505 helps to ensure that pipes do not significantly change length when exposed to specific thermal conditions for a defined period.

The main goal is to measure any change in length (reversion) when a sample is subjected to elevated temperatures.
The procedure is relevant to product quality checks and production control in the plastics pipe industry.
ISO 2505 outlines the equipment, test conditions, and calculation methods for reporting reversion results as a percentage of the original length.

Scope and application

ISO 2505 is applicable to pipes, fittings, and sample strips taken from finished or semi-finished thermoplastic products. The standard can be used for all diameters and wall thicknesses, provided that the sample can be placed in the test oven. It may be specified as a requirement by customers, industry regulations, or product certifications to demonstrate thermal stability properties. The test method helps manufacturers and users assess the quality and consistency of pipes for applications like water supply, drainage, and gas transportation.

Method principle

The principle of the test involves cutting samples to a defined length, marking a measured distance, and placing them in an air-circulating oven at a specified temperature (typically 150°C). After a set period, samples are removed, cooled, and the change in length is determined with precision instruments. The percentage of longitudinal reversion is calculated from the measured values, providing a consistent benchmark for material performance assessment.

Takeaway

ISO 2505 is an internationally recognized method for evaluating the dimensional stability of plastic pipes under heat. Reliable use of this standard supports manufacturers in maintaining product quality and helps customers ensure compliance with industry requirements.

Applicable to a wide range of thermoplastic pipe materials
Mandatory for many industry compliance and certification schemes
Measures an important property affecting safe pipe installation and use
Results are expressed as a percentage change for clear specification compliance

ISO 2505 step-by-step: preparing, heating and measuring longitudinal reversion

Step-by-step procedure for ISO 2505

Conducting the ISO 2505 test involves a specific sequence of steps to ensure results are accurate and repeatable. The process begins with careful sampling and preparation of the pipe specimen, followed by heating in an oven, cooling, and measuring the change in length. The test results are expressed as the percentage of reversion (shrinkage or expansion) of the original length, which serves as a key indicator of the pipe’s thermal stability.

Sample preparation

Cut pipe or fitting samples according to the standard’s specifications, ensuring surfaces are smooth and free from irregularities. Mark the initial reference length precisely with a permanent marker or suitable scoring tool. The samples should be representative of the production batch and of adequate length to minimize measurement error.

Cut specimens to the required standard length (typically 150 mm min.)
Ensure pipe ends are clean and square to the axis
Mark initial measured length at ambient temperature

Heating procedure

Place samples loosely in a pre-heated air-circulating oven set to the required temperature—generally 150°C unless otherwise specified by material or customer requirements. Heat the specimens for the minimum time specified in ISO 2505, ensuring that air can circulate freely around each sample so that the temperature rise is consistent.

Measurement and calculation

After the heating phase, remove each sample and allow to cool to room temperature. Measure the final length between reference marks using an accurate measuring device such as a vernier caliper. Calculate the longitudinal reversion using the formula provided in the standard to express the percentage change with respect to the initial length.

Cool samples in still air to avoid distortion
Measure each sample’s length precisely after cooling
Apply the standard calculation to determine reversion percentage
Record all results for compliance and quality control records
Repeat for representative batch samples if required

Reporting the results

Document the results, including the specimen details, initial and final lengths, percentage reversion, oven temperature, heating time, and any deviations from standard procedure. This information ensures traceability and supports product compliance audits or customer requirements.

Summary

ISO 2505 offers a clear and reliable method for determining the longitudinal reversion of thermoplastic pipes and fittings under heat. Careful sample preparation, consistent heating, and precise measurement are essential for generating valid and useful results that guide quality assurance for pipe products.