When building a custom home, the number of design choices are innumerable—from layout and size to fixtures and finishes. None technically more important than the other – although some are more fun. However, in the world of high-density polyethylene (HDPE) piping, the decisions are equally critical but often less visible.

A lion’s share of the “hidden” variables is addressed by the contractors and builders (see Federal and State regulations and zoning laws), before the process even begins.

If you are a piping project engineer, understanding these design considerations is key to ensuring a successful HDPE piping system.

And one blogger is going to try and explain just that.

Overview: HDPE Piping Design Considerations

HDPE piping systems require thoughtful planning and consideration. Just as in construction, where timing, supply and demand affect the process, selecting and installing HDPE piping demands a similar attention to detail.

The timing of HDPE piping projects is crucial, as delays can impact not just the schedule but also the overall success of installation.

Proper specification of HDPE parts and materials ensures that all components meet the necessary standards and perform as expected in the field.

Home design considerations are focused on function AND style. In HDPE piping, functionality takes precedence. A little less glamorous compared to home design, but we’re talking FUNCTION to seek maximum pipe performance.

HDPE Standards Every Engineer Should Know

HDPE piping systems are governed by a strict set of standards that ensure safety, quality, and performance. Engineers must be familiar with standards such as ASTM D3350 and ASTM F2206, which dictate everything from material properties to fitting dimensions.

Because they are so perfectly concise, this is directly from ASTM’s Wikipedia page:

“ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and services.”

Whether you’re designing for water distribution, gas lines, or industrial applications, adhering to these HDPE standards is crucial. The complexity of these standards can be daunting, but they ensure that your project meets industry benchmarks for durability and safety.

I mean – we laugh at jokes on “Big Bang Theory”.

But the top 0.3% on the intellect scale laugh at things we don’t understand.

There is a reason we let the experts handle the ASTM standards – they are the “Big Bang Theory” 0.3% joke of HDPE piping. 

Allow the experts to be the “Soft Kitty” song soothing your rattled nerves while this blogger goes on a tangent.

If I may insert a shameless plug – there is no shortage of smart folks at ISCO that can metaphorically sing “Soft Kitty” so smoothly that Sam Cooke would blush.

Now the tangent:

To illustrate the complexity – Thermoplastic Pipe Material Designation Code PE 4710 Cell Classification conforms to ASTM D3350 and is an improved high-performance polyethylene compound for pressure pipe.

Is it like Windows and this is the 4,710th iteration of the standard?

No. That would be awful.

But it isn’t without its intricacies.

Key Material Properties of HDPE Piping

Understanding the key material properties of HDPE pipes is essential for optimal system design.

• Density (PE 4710): The four in PE 4710 represents the density of the pipe at greater than 0.947-0.955 grams per centimeter cubed. (I am hearing this in Sheldon Cooper’s voice). The seven stands for 500 PENT (hours) Molded plaque, 80 degrees Celsius, 2.4 Mpa, Notch depth per F14732. I have literally never understood a sentence that I have typed less than that one.

• Hydrostatic Design Stress: The third and fourth digits (10) of PE 4710 represent Hydrostatic Design Stress in units of 100 psi based on service factor of 0.63 – in this case 11.03 (1,600 psi).

• Stress Cracking Resistance: The third property, stress cracking resistance measures the pipe’s durability against slow crack growth.

You see why we leave it to the experts.

It’s like trying to understand how to play Rock, Paper, Scissors, Lizard, Spock.

On to something easy.

Decoding HDPE Color Striping

HDPE color striping refers to piping identification, aiding engineers in quickly identifying the pipe’s function

The primary colors represent:

• Fire main (red)
• Natural gas (yellow)
• Potable/drinking water(blue)

Your secondary colors:

• Wastewater/sewer transmission(green)
• Reclaimed/raw/irrigation water (purple)
• Conduit/cable(orange)

If you didn’t know your color wheel you may have learned two things there.

Silver or grey striping represents polyethylene for raised temperature (PE-RT) piping for moving hot water or liquids up to 180 degrees.

If the pipeline requires camera inspection, the interior might be grey. And in some cases, special resins can be used to change the color of the pipe itself.

In mining and aggregate applications, the colored stripes distinguish the Dimension Ratio (DR) of the pipe–the ratio of the pipe’s outer diameter to its wall thickness (more on that later).

You’ll be happy to know that the color striping does not add any additional cost to your job. And, if you ask really nicely, stopping short of having a chain filled with a Crayola box of paint chips, they may be willing to place a new color on the pipe.

Maybe periwinkle piping stripes?

In addition to color striping, HDPE pipes are marked with print line on both sticks and coils to indicate their manufacturing specifications. Print lines vary between manufacturers and are repeated in regular intervals.

Understanding Dimension Ratio (DR) for HDPE Pipes

Previously mentioned, the Dimension Ratio (DR) is the ratio of the pipe’s outside diameter to the minimum wall thickness. It’s used to describe the pipe’s wall thickness relative to its diameter and helps in determining its strength and pressure rating.

The Dimension Ratio (DR) directly influences the pipe’s pressure rating and flexibility. Engineers must carefully select the appropriate DR to match the specific demands of their project, balancing factors like operating pressure, installation method and environmental conditions.

No two jobs are the same, proper DR selection is crucial for ensuring your HDPE piping system meets the required performance standards while remaining cost-effective and durable.

HDPE Fabricated Fittings

When designing an HDPE piping system, it is imperative the fittings match the pressure ratings of the pipe, which brings us to ASTM F2206 – Equivalent Dimension Ratio (EDR).

For example, when adding a mitered elbow to your system, be aware that the elbow’s pressure rating is reduced. To accommodate this change, you should use a fitting with a DR that is one step lower than the pipe’s DR rating. For example, if your pipe has a DR of 11, the fabricated fittings should have a DR of 9.

Like so many design considerations, here’s a chart that helps explain the crucial aspect of HDPE piping that is EDR.

Concerned about fusing dissimilar DRs? Per ASTM standard F2620 (another one), you can join DRs that are one step away in terms of the sizing.  Here is a comprehensive video that outlines how that works (https://www.youtube.com/watch?v=WmBeu6NqnCY).

Bazinga.

HDPE Thermal Expansion and Pipe Performance

HDPE naysayers and legacy piping aficionados love to critique the pipe and thermal expansion. HDPE piping’s flexibility is a double-edged sword—while it allows for thermal expansion, it also reduces the force needed to restrain it compared to materials like carbon steel.

For instance, a 200-foot length of HDPE pipe may expand by eight inches with a 40-degree temperature change. However, this expansion is easily managed by the surrounding soil or with restraint systems in above-ground applications. Proper installation methods can mitigate these concerns, ensuring long-term performance.

Reading that it seems like a lot.

But the force needed to restrain that eight inches of expansion is only 321 pounds. In contrast, if that same line is carbon steel pipe, the expansion is only three-fifths of an inch. But the force needed to restrain the steel is over eight THOUSAND pounds.

Understanding Bend Radius in HDPE Piping

The flexibility of HDPE pipe is one of its standout features, but this flexibility comes with some considerations, particularly when it comes to the bend radius.  HDPE gives you the luxury of following a curved path with fewer fittings, or in some cases—no fittings. Legacy pipe requires joints for subtle changes of direction.

Calculating Bend Radius: The bend radius is typically expressed as a function of the pipe’s DR. For example, an HDPE pipe with a DR of 11 will have a minimum bend radius of 25 times its outside diameter.  Therefore, a 20-inch, DR 11 pipe would be able to have a bend radius of 500 inches.  Math is fun.

Bending a pipe beyond its specified radius can cause stress, leading to potential cracking or failure over time. Properly calculating and adhering to the correct bend radius is essential to maintaining the integrity of the piping system, especially in applications where the pipes are installed underground or in tight spaces.

Best Practices for HDPE Pipe Installation

If you desire a general overview of trenchless installation methods for HDPE, you may want to sneak over here – https://isco-pipe.com/blog/hdpe-pipe-trenchless-installation-methods-who-you-gonna-call/

Proper installation is just as important as material selection in ensuring the longevity and performance of an HDPE piping system. Following best practices during installation can prevent common issues such as leaks, misalignment, and undue stress on the system.

Trenching and Bedding: The trench should be free of sharp objects and properly graded. A well-prepared bed of compacted soil or sand supports the pipe evenly along its length, reducing the risk of sagging or distortion.

Fusion and Joining Techniques: HDPE pipes are typically joined together using butt fusion or electrofusion. These methods create a seamless bond between MDPE and HDPE pipe segments, eliminating weak points that could lead to leaks.

If you’re connecting a new HDPE system to older legacy material, you have several options.

• Flange adapters are the most common choice, but if fusion is not possible, mechanical connections such as joint adapters, Victaulic connectors, and transition fittings (for connecting HDPE to other materials) are available.
• To address expansion and contraction issues, especially in legacy piping systems, restraint harnesses or thrust blocks—including wall anchors and flex restraints—can be used to protect weaker joints on the legacy pipe. When transitioning to a non-HDPE piping system, it’s important to manage the Poisson Effect, where internal pressure causes HDPE to expand outward and contract in length. This contraction requires that you protect the joints on the legacy pipe, which are more rigid and prone to stress.

Pressure Testing: After installation, pressure testing is essential to verify the system’s integrity per ASTM F2164. It ensures that all joints and fittings are secure, and that the system can withstand the operating pressure without failure.

HDPE Design Resources

There is no shortage of digital assets that give insight into HDPE design considerations.

Here is a list of a few of those resources:

PPI Handbook of PE Pipe – https://www.plasticpipe.org/MunicipalIndustrial/Shared_Content/Shop/PE-Handbook.aspx

• Material Properties
  • Inspections, Tests, and Standard Specifications
  • Installation Design and Guidance
  • Direct Burial and Above-Grade
  • Trenchless (HDD, Sliplining, Pipe Bursting)
  • Marine
  • Repair

PE Alliance – https://pepipe.org/

• Roadshow program – https://pepipe.org/events/
  • Case Studies – https://pepipe.org/case-studies-login/

ISCO – ISCO-pipe.com

• Catalog – https://isco-pipe.com/isco-catalog/
  • Fusion Manual – https://isco-pipe.com/wp-content/uploads/2023/08/Fusion-Manual_2024_spreads.pdf
  • Technical Hub – https://isco-pipe.com/technical-hub/

HDPE Pipe Calculator – https://plasticpipecalculator.com/

PPI Pace App – http://ppipace.com/

Conclusion: Navigating HDPE Design with Confidence

So that was a lot.

One truth is that no two jobs are the same.

The growth of the industry gives you a multitude of options when it comes to your design considerations.

But it doesn’t need to be intimidating.

A trusted source like ISCO will help you navigate what can be confusing waters, will have answers to all of your questions and guide you to a system that has maximum pipe performance.

Bang!