HDPE pipe terminology - everything you need to know

By Logan Bridges

Are you new to the HDPE piping world? No problem. Take a few minutes between projects to review the below collection of common HDPE pipe terminology and definitions. Once you have finished, please contact us for additional information and guidance or to discuss your company’s specific HDPE needs.


HDPE: High density polyethylene (HDPE) refers to the thermoplastic polymer produced from the monomer ethylene. HDPE piping has a high strength-to-density ratio and highly bendable, allowing for pipe to be coiled. HDPE is lightweight, flexible, inexpensive and corrosion resistant. In addition to piping, HDPE is used in the production of plastic bottles, geomembranes, grocery bags, toys, containers and plastic lumber.

IPS and DIPS: Iron Pipe Size or IPS represents the nominal diameter of the pipe. A 6-in. IPS pipe has an inside diameter of six inches. Ductile Iron Pipe Size or DIPS is used to specify the size of ductile iron pipe. Typically, IPS refers to black iron or carbon steel pipe while DIPS refers to cast/ductile iron pipe. IPS and DIPS are used in the HDPE market to replicate the familiar dimensions of these other IPS pipe is available in size ranging from ¾-in. to 65-in. diameters while DIPS is available from 4- in. to 36-in. diameters.

CTS: Copper Tube Size is specific to plumbing and potable water systems. In copper, the OD is always 1/8 inch larger that the nominal size of the pipe, and that has carried over to HPDE that is built to CTS sizes. As a replacement for traditional copper lines for water, a 2-in. HDPE pipe that follows CTS sizing standards would have an OD of 2 1/8 in. For water applications HDPE pipe can be sized as small as ¾ in OD.

Bend Radius: Bend radius, measured to the inside curvature, is the minimum radius one can bend a pipe, tube, sheet, cable or hose without kinking it, damaging it or shortening its life. The smaller the bend radius, the greater is the material flexibility. HDPE piping is more flexible than other competitive piping options, offering a smaller bend radius. However, exceeding minimum bend radiuses may result in mechanical failure and decreased longevity. And for HDPE-encased fiber-optic cabling, it is problematic, as exceeding minimum bend radius can cause light attenuation resulting in performance loss.  

Dimension Ratio (DR): The Dimension Ratio (DR) is the ratio of the pipe outside diameter to the pipe minimum wall thickness. As diameters change, the pressure rating remains the same for the same material, dimension ratio and application.

Standard Dimension Ratio (SDR):

Certain Dimension Rations (DRs) that meet an ASTM International specified number series (32.5, 26, 21, 17, 13.5) are referred to as Standard Dimension Ratios (SDRs). There is approximately 25% difference in minimum wall thickness between each SDR.

Calculating SDR: SDR is defined as the ratio of the nominal outside diameter to the nominal wall thickness.

SDR = dn/en

 Where dn is the nominal outside diameter of pipe and en is the nominal (minimum) wall thickness of the pipe.

Carbon Black (CB): Carbon Black products are additives used to improve the strength and performance of HDPE pipe. CBs are typically used to improve UV resistance and to reduce or lower moisture absorption in pipe

Coefficient of friction: Coefficient of friction measures the amount of friction existing between two surfaces. As this measurement relates to piping, a lower coefficient of friction typically means less friction damage in piping (example: outer layer wear). To find the coefficient of friction (fr) use this formula:

Fr/N = fr

Where Fr is the resistive friction force and N is the normal force pushing on objects.

Surge pressure - Recurring and occasional: American Water Works Association standard AWWA C901 defines two types of surge pressure, recurring and occasional. The safe peak pressure or allowed total pressure for HDPE pipe is 1.5 times the pipe’s pressure rating for recurring surge and 2.0 times the pipe’s pressure rating for occasional surge.

Temperature derating: Materials rated for operating pressures or tensions at a standard temperature, must be ‘derated’ when temperatures increase. Derating is usually expressed graphically or in terms of derating factors. HDPE piping loses its strength to pressure and tension as temperature is increased.

FM approved: FM Approvals is a third-party testing and certification service. FM Approved-HDPE pipe and fittings are subjected to more severe performance testing. The five-step certification process includes product review, testing, and manufacturing facility audits.

UL Rating: Underwriters Laboratories (UL) is a global safety science company and third-party certification company founded in 1894. The company tests products and technologies for safety. Beginning in 1965, UL published a series of standards for polymer raceway products, including rigid PVC conduit as well as HDPE conduit.

Seismic loading: Seismic loading is one of the basic concepts of earthquake engineering which includes application of a seismic oscillation to a structure. It happens at contact surfaces of a structure either with the ground or with adjacent structures.

According to an Electric Power Research Institute report Nondestructive Evaluation: Seismic Design Criteria for Polyethylene Pipe Replacement Code Case, there are two potential sources for seismic loads on the piping: loads from wave propagation in the soil and from seismic anchor motion of the buildings that form the boundary for the buried pipe.

Most of these definitions come from industry-recognized sources such as PPI. See below for a complete list of sources.

About United Poly Systems

United Poly Systems produces quality HDPE pipe in diameters from ¾-in. to 26-in. IPS, 4-in. to 24-in. DIPS, and ¾-in. to 2-in. CTS for use in many industries including telecommunications, power utility, water, electrical and oil and gas. The market for HDPE pipe continues to expand as initiatives to improve, repair and expand the country’s infrastructure are implemented. 

Our off-the-shelf HDPE conduit/pipe is available in a variety of sizes, colors, dimensions and lengths, with or without stripes. We also offer fully customizable HDPE conduit options. In addition, piping can be customized with a ribbed interior (to maximize the distance cable may be pulled or jetted), pull tape, or a lubricated interior (for easier installation).  

Success at UPS can be attributed to our vast experience, extensive client relationships, state-of-the-art manufacturing and quality processes.  Our agile business model that allows UPS to quickly meet customers’ needs without the overhead expenses that are incurred by many of the larger producers in the industry. 

Conveniently located in Springfield, Missouri and Albuquerque, New Mexico, United Poly Systems can provide quick delivery to a majority of the U.S. market.  



Tags: MicroPath, Conduit, Oil & Gas, Power & Communications