New Standard Fortifies Testing of Corrugated HDPE Pipe Materials

Measuring resistance to slow crack growth (SCG) is of utmost importance when seeking the highest durability of HDPE (high density polyethylene) materials for corrugated pipe used in highway and bridge construction.

“In long-term field applications, polyethylene pipe fails by a small crack that initiates on the inside of the pipe and slowly grows through the pipe wall until it reaches the outside of the pipe,” explained Gene F. Palermo, Ph.D., technical director, Plastics Pipe Institute, Washington, D.C. “If the PE [polyethylene] material has poor SCG resistance, failure could occur in a year or two. If the PE material has good SCG resistance, the pipe will probably not fail for hundreds or thousands of years.”

ASTM adds an established precision statement to their new measure of SCG resistance in F 2136, Standard Test Method for Notched Constant Ligament-Stress (NCLS) Test to Determine Slow-Crack Growth Resistance of HDPE Resins or HDPE Corrugated Pipe. Based on research conducted by the Plastics Pipe Institute and Drexel University, Philadelphia, Pa., an initial test method was drafted by PPI resin and corrugated pipe manufacturers. It was then reviewed by ASTM Committee F17 on Plastic Piping Systems and approved as an ASTM standard on Aug. 10.

In addition, F 2136 will be referenced in American Association of State Highway and Transportation Officials (AASHTO) Standards M 294 and MP 7 for corrugated polyethylene pipe, Palermo said.

Corrugated HDPE pipe is manufactured from polyethylene resin. According to Palermo, F 2136 “is a beneficial test method for the corrugated polyethylene pipe industry to determine slow crack growth resistance of the base resin and eventually the corrugated pipe.”

He described the NCLS test and ASTM D 1693, Standard Test Method for Environmental Stress-Cracking of Ethylene Plastics [2000]. “The original ASTM test to measure SCG resistance of PE materials in the AASHTO standard was the ESCR (environmental stress crack resistance) test—ASTM D 1693. The problem with this test method is the lab-to-lab reproducibility, which can be as high as 200 percent.

“A few years ago, PPI contracted Drexel University to conduct a research project to evaluate appropriate test methods to measure the SCG resistance of PE piping materials. PPI recommended the NCTL (now known as NCLS) test. AASHTO then hired Drexel to use this test method for PE materials used in corrugated pipe. Based on their report, AASHTO included the requirement in the standard, but there was no established ASTM test method. This NCLS test is now an officially recognized ASTM test method with a known precision that is considerably better than the ESCR test. With the minimum requirement established by AASHTO (based on the Drexel recommendation), PE materials now used for corrugated pipe must have a minimum SCG resistance, which assures good long-term performance of the corrugated pipe.”

Technical inquiries may be directed to Gene F. Palermo, Ph.D., technical director, Plastics Pipe Institute, Washington, D.C. (phone: 202/462-9607 ext. 11). Committee F17 meets Nov. 5-8 in Dallas, Texas. For meeting or membership details, contact Pat Picariello, manager, Technical Committee Operations, ASTM (phone: 610/ 832-9720). //

Copyright 2001, ASTM