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Poly Pipe Specifications

Poly, or polyethylene, pipe is ubiquitous in building and plumbing applications. It is important to use the right type of pipe for the application, including size, density and makeup. The standard in 2010 is the D 3350, "Standard Specifications for Polyethylene Plastics Pipe and Fittings Materials." This is the document outlining the limits and grade numbers for a variety of different properties for PE pipe. Each piece of polyethylene pipe will have a classification number describing these properties. The first letters in the classification number are PE to designate polyethylene pipe.


Density

Polyethylene pipe has different specifications for different uses.

Polyethylene pipe comes in both standard and high density formulations.  After PE, the next number in the ASTM grade number, an international standard, is the density.

There are several grades, shown as numbers from 0 to 8, although 0 is not used.  A density grade of 1 indicates 925 grams of material per square centimeter or lower, while a grade of five means 955 grams per square centimeter or less.

Higher grades will indicate exact density. 


Melt Index

The next number is the melt index.  This indicates the weight of a PE resin that would flow from a standard die for 10 minutes.

The melt index is important so that pipes will only be used for long-term exposure to heat if they are able to handle it. 


Flexural Modulus

This is the next number in the ASTM grade.  The flexural modulus number indicates the amount of stress necessary to put a 2 percent strain on the outer fiber of the pipe.

The higher density the pipe, the higher the flexural modulus number, generally speaking. 


Tensile Strength

The fourth number is the tensile strength of the pipe.  This indicates the point at which the PE pipe will become deformed beyond the point where it can snap back into place, or the plastic strain region.


Slow Crack Growth

Poly pipe in general is highly resistant to slow crack growth in its typical use in potable water systems.  High density PE pipes are particularly resistant.

The fifth number indicates the level of resistance, with many of the modern pipes ranking 6 or higher on this property. 


Hydrostatic Design Basis

To find the sixth number in the ASTM grading label, the PE pipe is tested at two temperatures: 73 and 140 degrees F.  This measure allows users to calculate the amount of water pressure the pipe can handle.


Color

The seventh space in a ASTM grade for PE pipe is a letter indicating the color and UV stabilizer found in the pipe.  A means natural poly pipe, B is colored, C is black with minimum 2 percent carbon black, D is natural with UV stabilizer, and E is colored with UV stabilizer.

About the Author

Rachel Murdock published her first article in "The Asheville Citizen Times" in 1982. Her work has been published in the "American Fork Citizen" and "Cincinnati Enquirer" as well as on corporate websites and in other online publications. She earned a Bachelor of Arts in journalism at Brigham Young University and a Master of Arts in mass communication at Miami University of Ohio.

Photo Credits

  • large plastic pipes image by Yali Shi from Fotolia.com