New HDPE test shortens the pipeline to market
By Barry Copping
Posted 26 June 2012
Test requires neither a special notched specimen nor detergents and is much faster
Sabic has developed a new method to rapidly evaluate the slow crack growth resistance of high-density polyethylene (HDPE) used for pressure pipes.
The aim is to let processors benefit more quickly from developments in HDPE for pipes by cutting the time taken to bring a new material from the laboratory to the market.
Sabic is convinced that adoption of its strain hardening test method (SHTM) will accelerate adoption of its latest Sabic Vestolen A RELY grades of bimodal HDPE for high-pressure pipe.
Lada Kurelec, technical marketing manager for HDPE at Sabic reports that unlike traditional methods of obtaining data on long-term material performance in pipes, SHTM requires neither a special notched specimen nor detergents. It is easy to implement in laboratories, is suitable for the development of new grades by researchers, and is applicable as a batch release test for resin suppliers. SHTM saves time, money and energy.
Apeldoorn, The Netherlands-based gas technology specialist Kiwa has adopted the method. Materials testing expert Frans Scholten says “We have found that SHTM delivers reproducible results which correlate very well with those from traditional slow crack growth tests – but taking much less time. We use the test to quickly provide pipeline owners with a long-term quality prognosis for their existing polyethylene gas and water distribution networks. We also enable resin manufacturers to compare the performance of development resins with that of other products.”
Traditional methods for assessing long-term behaviour in pressure pipes such as the full notch creep test (FNCT) and notched pipe test take months or sometimes years. The tests are costly and their reliability is uncertain, according to Sabic. Using traditional notch tests, it would take many months to prove that a new material meets, for example, the demanding pipe installation requirements of Publically Accessible Standard PAS 1075. SHTM reduces that that time to a few hours, requiring a simple tensile test at 80°C. Further advantages cited for the method method are very low measurement variation and the small amount of test material required (<50g).
According to Kurelec, Sabic went back to basics to develop the new test. “SHTM is based on fundamental theories of crack propagation in terms of basic polymer properties.”
Increasingly rigorous pipe installation standards such as PAS 1075 result from greater use of new trenchless pipe installation methods such as guided boring and horizontal directional drilling. These methods may have a very positive impact on the environment, but they pose greater demands on pipe durability through potentially greater surface damage which can cause premature deterioration.
Sabic cites the new generation of pipe materials with enhanced slow crack growth resistance as a solution, and offers its Vestolen A RELY 5922 for typical applications. The company is involved in the initiatives to adopt SHTM as a standard test method for the pipe industry by test houses in Europe and around the world.
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