Standards Development

Scope

This document specifies a test method to determine the slow crack growth (SCG) behaviour (also known as the stress crack resistance) of polyethylene (PE) and polypropylene (PP) materials, incorporating recyclates, used in structured-wall Type B corrugated pipe for non-pressure gravity flow drainage applications.

The test method is appropriate to post-consumer recyclates (PCR) of PE and PP materials, and postindustrial recyclates (PIR) of PE and PP materials and blends of such materials with virgin and/or reworked PE or PP, respectively.

The test method is not intended for reworked material, or blends of virgin materials with reworked materials, where the reworked material is sourced from the manufacturer’s own production and is of known composition.

The test method is conducted on un-notched specimens in deionized water and evaluates both the crack initiation and crack propagation phases of the SCG mechanism.

The test method utilizes standard testing equipment utilized for other stress crack tests in the drainage pipe industry. Specifically, test method utilizes a lever-arm loading mechanism, typically with a 5:1 mechanical advantage, to apply a constant load to a dog-bone shaped test specimen immersed in an elevated temperature water bath.

Purpose

The proposed test method is intended to provide means of evaluating materials with PE or PP recyclate content for resistance to slow crack growth failure under stress when used in non-pressure underground drainage and sewerage structured-wall Type B corrugated pipes made of PE or PP. Currently, there is no existing test method to evaluate stress crack resistance in polyolefin drainage pipe manufactured with recyclate. This is a critical test method given the importance of stress crack resistance to the long-term performance of drainage pipe.

These piping applications are already significant consumers of recyclate in certain regions (>300 million kg per annum) and the establishment of this test, and corresponding requirements based on this test, would greatly facilitate the expansion of this practice into other regions. This practice would reduce the environmental impact of consumer and industrial plastics waste by upcycling these materials into durable plastics products for infrastructure applications and contributing to a circular economy. As contaminants within recyclates can act to decrease the resistance to slow crack growth failures, it is important that that pipe manufacturers have a means to evaluate such materials to ensure ongoing quality when using recycled materials. This method applies to recycled materials sourced from consumers (post-consumer, PCR) or industry (post-industrial, PIR). The method provides a rapid test that provides the pipe manufacturer a means to make this evaluation within a manufacturing environment on raw material and/or finished product.

By referencing this method and establishing minimum requirements, product standard for non-pressure underground drainage and sewerage pipes will be able to ensure that PCR and PIR materials are used without compromising the in-service performance compared to the design life. Suppliers of PE and PP recyclates will be able to enhance the value of their products by characterizing the performance of their materials with this test.