SDR 35 vs Schedule 40
SDR 35 and Schedule 40 are two of the most common types of plastic pipes used for plumbing and water supply applications. But what exactly are they, and how do they differ from each other?
This guide examines SDR 35 and Schedule 40 in detail, including their respective features, applications, pros and cons, and factors to consider when choosing between the two. Read on to gain a deeper understanding of these ubiquitous piping materials to determine the best option for your next project.
What are SDR 35 and Schedule 40 Pipes?
SDR and Schedule 40 refer to pipe dimension ratios and pressure ratings rather than specific materials. However, SDR 35 and Schedule 40 pipes are typically made from different types of plastic.
SDR 35
SDR stands for “Standard Dimension Ratio.” SDR 35 pipes have a wall thickness equal to 1/35 of their outside diameter. For example, a 4-inch SDR 35 pipe will have a minimum wall thickness of 0.113 inches (4/35 = 0.113).
SDR 35 pipes are predominantly made from polyethylene (PE) plastic. The PE used is typically HDPE (high-density polyethylene) or MDPE (medium-density polyethylene). Polyethylene offers flexibility, corrosion resistance, and leak-free joints.
SDR 35 pipes have a lower pressure rating and are designed for low-pressure applications like underground water service lines. They are commonly used for water mains, irrigation, and lateral lines.
Schedule 40
Schedule 40 refers to the pipe’s pressure rating rather than its wall thickness. Schedule 40 pipes can withstand higher pressures depending on size and material. Different varieties of Schedule 40 pipes can be found on the market
With their higher pressure capacity, Schedule 40 pipes are suitable for both underground and above-ground applications. They transport pressurized fluids in plumbing, HVAC, industrial, fire protection, and chemical delivery systems.
Side-by-Side Differences Between SDR 35 and Schedule 40 in Detail
SDR 35 and Schedule 40 vary substantially in their material composition, wall thickness, pressure ratings, applications, installation methods, cost, strength properties, diameter sizing, temperature ratings, and burial depth suitability. Here is an in-depth feature-by-feature comparison:
Material Composition
When it comes to material composition, SDR 35 pipes have a distinct makeup compared to Schedule 40. SDR 35 pipes are constructed out of polyethylene plastic, usually HDPE or MDPE. The polyethylene material provides these pipes with enhanced flexibility, chemical resistance, and abrasion resistance. It also enables strong leak-free fusion joints to be formed. Schedule 40 pipes, on the other hand, can be made from materials including PVC, CPVC, or low-carbon steel.
While these materials allow Schedule 40 pipes to withstand high pressures, they also decrease the pipe’s flexibility and make them more susceptible to cracking or fracturing during handling and installation. For example, a PVC Schedule 40 pipe is prone to developing cracks if bent too aggressively, whereas a polyethylene SDR 35 pipe can make tight bends without damage.
Wall Thickness
The wall thickness also differs considerably between SDR 35 and Schedule 40 piping. It has a thickness of 0.12 in to 0.437 in whereas Schedule 40’s thickness can be 0.133 in to 0.688 in.
A 4-inch SDR 35 pipe, for instance, will have a wall thickness of 0.12 inches. Schedule 40 pipes, on the other hand, have a thicker wall designed to withstand higher pressures. A 4-inch Schedule 40 steel pipe may have a wall thickness of 0.237 inches, over two times the thickness of the same diameter SDR 35 PE pipe. This thicker construction makes Schedule 40 pipes less flexible but enhances their pressure capacity.
Pressure Rating
When it comes to pressure ratings, SDR 35 PE pipe is only designed for low pressure installations of 46 psi or less. This precludes it from being used in pressurized plumbing systems above or below ground.
Schedule 40 pipes, however, can have pressure ratings ranging from a minimum of 120 psi for small diameter pipes up to over 800 psi for large diameter Schedule 40 steel pipes. This high-pressure tolerance enables Schedule 40 to be used in hot and cold potable water delivery systems, fire suppression piping, industrial compressed air lines, and more.
Applications
The applications permitted for SDR 35 and Schedule 40 pipes differ as well, owing to the differences in pressure rating and material performance. SDR 35 PE pipe cannot withstand sunlight exposure or temperature extremes and lacks the requisite pressure capacity for above ground use per code. As such, it is restricted to only underground use for water service lines. Schedule 40, on the other hand, can be installed both underground and above ground for hot and cold water plumbing, HVAC systems, chemical lines, fire sprinklers, and general industrial piping applications. Its diverse material options and pressure ratings allow it to transport myriad fluids both indoors and outdoors.
Installation and Handling
Installation and handling also sets SDR 35 and Schedule 40 pipes apart from one another. The flexible polyethylene makeup of SDR 35 allows it to be bent and snaked underground with relative ease. It requires minimal cutting or heat joining to route around obstacles, saving time and labor costs.
Schedule 40 PVC and steel pipes, however, are rigid and challenging to manipulate around bends and corners. This necessitates more extensive cutting and heating or mechanical bending equipment to install Schedule 40 pipe in anything but straight runs. The effort required to join and install Schedule 40 can be exponentially greater than flexible SDR 35.
Cost
Economically speaking, SDR 35 provides some of the most affordable plastic piping on the market, offering savings of 25% or more compared to Schedule 40 pipe options. The polyethylene material and thinner walls make it economical to manufacture and install. Schedule 40 steel, PVC, and other plastic pipes come at a notable premium in terms of upfront cost. In some cases, the costs could be 30-50% more per linear foot for Schedule 40 pipe supply and installation compared to SDR 35 PE pipe. However, Schedule 40 may pay off long-term thanks to greater pressure durability and longevity.
Strength Properties
Strength and durability also set these two pipe types apart. With its thin polyethylene walls, SDR 35 is prone to crushing, leakage, and deformation without proper burial support and bedding. It lacks the impact strength that Schedule 40’s thicker walls and stronger PVC, CPVC, and steel materials provide.
Schedule 40 is better equipped to withstand years of pressure fluctuations, vacuum service, and even accidental impacts. For example, an exposed Schedule 40 PVC pipe would be unlikely to leak or burst if struck, while SDR 35 PE would crack or fracture under the same impact.
Diameter Sizing
When it comes to properly sizing the diameters, SDR 35 offers an advantage owing to its thin walls. It provides full, standard inside diameters that maximize flow rate. But Schedule 40’s thicker walls slightly reduce the inner passage size, so a larger diameter may be required to achieve an equivalent flow to SDR 35. For a residential yard water line, a 3/4″ SDR 35 line might supply the needed 7 GPM, whereas Schedule 40 might need a 1″ line to supply the same flow due to its reduced ID.
Temperature Rating and Burial Depth
Both SDR 35 and Schedule 40 have a similar 140°F maximum temperature rating. This makes both suitable for cold and hot water delivery up to about 60°C before needing insulated protection.
In terms of burial depth, Schedule 40 has a clear advantage. While SDR 35 can only be buried around 14 feet deep safely, Schedule 40 can go 24 feet deep or greater to supply water to larger multi-story buildings via their underground mains.
In summary, while SDR 35 offers advantages like flexibility, cost savings, full diameters, and chemical resistance, Schedule 40 provides enhanced durability, pressure tolerance, and application diversity for above and below-ground installations across industries.
Summary
| Feature | SDR 35 | Schedule 40 |
| Material | Polyethylene (PE) | PVC, CPVC, low-carbon steel, etc. |
| Wall thickness | Thinner | Thicker |
| Pressure rating | 46 psi | 120 to 810 psi |
| Applications | Underground water service | Above and below ground |
| Installation | More flexible, easier | Less flexible |
| Cost | Less expensive | More expensive |
| Strength | Less strong | Stronger and more durable |
| Diameter sizing | Standard sizing | Smaller diameters for same flow |
| Temperature | 140°F | 140°F |
| Burial depth | 0-14 ft | >24 ft |
Which One to Choose Between SDR35 and Schedule 40
When selecting between SDR 35 and Schedule 40 pipe, consider your specific application and requirements.
For underground drainage lines that may experience soil movement or settling, SDR 35 may be the better choice thanks to its flexible polyethylene construction which can flex and bend with the surrounding soil. Schedule 40 is more rigid and could potentially crack under ground shifting or loads.
If you are conveying pressurized flows, dealing with heavy overhead loads, or installing pipe above ground, Schedule 40 is typically the stronger and more durable option. Its higher pressure rating and thick walls provide reserve strength to withstand pressures, impacts, and mechanical stresses over a long service life.
You should also evaluate whether your planned fittings and connections are compatible with SDR 35 or Schedule 40 pipe. Their differing diameters, materials, and wall thicknesses mean not all fittings work interchangeably between the two pipe types. Consult manufacturer specifications and plumbing codes to ensure your accessories are approved for use with either SDR 35 or Schedule 40.
Properly assessing the demands of your particular installation environment and application is crucial in determining which pipe type will perform safely and reliably. Contact a qualified plumbing professional for guidance on choosing between SDR 35 and Schedule 40 for your project’s unique needs.
Wrapping Up
I hope this guide gave you a helpful overview of the key differences between SDR 35 and Schedule 40 pipe. There’s a lot to consider when choosing between these two popular piping options. It really comes down to evaluating your specific needs in terms of pressure, flow rate, installation environment, and budget. For underground water lines, I’d probably go with SDR 35 polyethylene pipe since it’s flexible, corrosion-resistant, and more affordable. But for pressurized systems above ground, Schedule 40 is the safer bet thanks to its durability and pressure handling. Whichever you choose, be sure to refer to codes and manufacturer recommendations for proper installation. If you have any other questions, don’t hesitate to contact me in the comments below!
