ASTM D2729 vs SDR 35 [Comparing PVC Sewer & Pressure Pipe Standards]

Polyvinyl chloride, or PVC, is one of the most widely used plastic piping materials in the world. Within the many PVC piping standards, ASTM D2729 and SDR 35 are two of the most common specifications used in municipal and residential applications. But what exactly do they mean, and what are the differences between ASTM D2729 and SDR 35 PVC pipe?

ASTM D2729 is a standard that covers polyvinyl chloride (PVC) plastic sewer pipe and fittings, often referred to as DWV (drain, waste, vent) pipe. It is intended specifically for gravity-flow drainage applications like sewers, drains, and waste pipes.

SDR 35, on the other hand, refers to a standard dimension ratio (SDR) for polyvinyl chloride (PVC) pressure pipe. SDR 35 PVC pipe is rated for high pressure applications like municipal water and irrigation systems.

While both are made from PVC resin, ASTM D2729 and SDR 35 have very different performance specifications, dimensions, pressure ratings, and intended uses. This article will examine the key differences between these two widely used PVC piping standards.

Here is an in-depth comparison table between ASTM D2729 and SDR 35 PVC pipe standards:

ASTM D2729 – Poly(Vinyl Chloride) (PVC) Sewer Pipe and Fittings

ASTM D2729 covers the specifications, dimensions, requirements, and test methods for PVC and composite PVC-Aluminum gravity flow sewer pipe from 1.5 to 36 inches in diameter. It was first issued in 1971 but has been updated many times over the years to reflect industry developments.

History and Origins of ASTM D2729

PVC sewer pipe meeting ASTM D2729 replaced older materials like vitrified clay and concrete used in sewer systems. Compared to breakable clay and corroding concrete pipe, PVC provided a lightweight, durable, leak-free, and cost-effective material for underground drainage applications.

The success of PVC sewer pipe led to the creation of several dimensional standards in the 1960s, which were consolidated into ASTM D2729. This provided uniform specifications and testing procedures for the growing PVC sewer pipe market.

Specifications and Properties of ASTM D2729 Pipe

ASTM D2729 specifies important performance criteria like pipe stiffness, impact resistance, chemical resistance, and flammability. It also standardized sizing conventions based on nominal pipe diameter rather than actual inside/outside dimensions.

Key properties of ASTM D2729 PVC sewer pipe include:

• High stiffness and beam strength for buried applications
• Smooth interior walls for maximum flow capacity
• Good impact, abrasion, and corrosion resistance
• Joining systems like gaskets, solvent cement, and elastomeric seals

The standard also defines requirements for quality control, performance testing, and markings on the pipe. This ensures consistency across manufacturers and reliability in the field.

Manufacturing and Production of ASTM D2729 Pipe

ASTM D2729 PVC sewer pipe is extruded from Type 1, Grade 1 PVC compound with a Cell Classification of 12454. This is a general-purpose unplasticized PVC resin with high stiffness and tensile strength.

Pipe is produced in lengths up to 20 feet and uses bell-and-spigot or gasketed joints to form an aligned, leak-free pipeline when installed. Standard laying lengths and fittings make it easy to assemble long sewer lines above or below ground.

After production, all ASTM D2729 pipe must pass hydrostatic pressure, flattening, impact, pipe stiffness, and other qualification tests defined in the standard. This ensures quality control and reliability.

Applications and Uses of ASTM D2729 Sewer Pipe

The intended application of ASTM D2729 is underground gravity drainage and sewer conveyance, including:

• Municipal sanitary and storm sewers
• Residential drain, waste, and vent (DWV) systems
• Foundation drainage collection pipes
• Leachfield piping for septic systems
• Industrial process and wastewater piping

Its high stiffness, watertight joints, corrosion resistance, and flow capacity make ASTM D2729 well-suited for these underground applications. It provides durable service for decades when properly installed.

SDR 35 – Standard Dimension Ratio Polyvinyl Chloride (PVC) Pressure Pipe

Unlike ASTM D2729 sewer pipe, SDR 35 refers to PVC pipe engineered specifically for pressurized water and wastewater pipelines. SDR stands for “standard dimension ratio,” referring to the ratio between pipe diameter and wall thickness.

History and Development of SDR 35 Pipe

PVC pressure pipe was introduced in the 1950s as an alternative to traditional metal water pipes. Early PVC pressure pipe used thin walls prone to damage and failure. SDR dimension ratios were developed to standardize wall thicknesses for given pipe diameters that would withstand pressure over long service.

SDR 35 was introduced in the 1970s as a standard for residential and municipal pressure pipes up to 18″ in diameter. SDR 35 pipe provided cost-effective, corrosion-resistant, high pressure service compared to steel and copper pipes. Its success led to rapid adoption for water infrastructure.

Specifications and Properties of SDR 35 Pipe

SDR 35 pipe is defined by PVC material meeting cell class 12454 and a standard dimension ratio of 35. This means the pipe diameter is 35 times the minimum wall thickness. For example, 4″ SDR 35 pipe will have a minimum wall thickness of 4/35 = 0.113 inches.

Key properties include:

• Rated for continuous pressure up to 235 psi
• Surge allowance up to 470 psi
• Smooth interior for high flow rates
• Corrosion and abrasion resistant

SDR 35 also defines requirements for extrusion, sustained pressures testing, markings, gaskets, and fittings. Dimensions and tolerances are standardized for pipes from 1/2″ to 18″.

Manufacturing and Production of SDR 35 Pipe

SDR 35 PVC pressure pipe is extruded from the same PVC resin type as ASTM D2729 sewer pipe – Type 1, Grade 1 PVC meeting cell class 12454. This unplasticized PVC provides high tensile and burst strength.

The pipe is extruded to the proper SDR 35 dimensions and must pass sustained pressure testing defined in ASTM D2241. Standard lengths, diameters, and molded fittings are made for easy assembly into pressure pipelines using elastomeric gasket seals.

Applications and Uses of SDR 35 Pressure Pipe

The primary use of SDR 35 PVC pipe is pressurized water service including:

• Municipal water mains and distribution piping
• Residential water service lines from the main to the building
• Irrigation pipelines in farms, golf courses, and parks
• Industrial water lines
• Fire suppression pipelines and sprinkler systems

It is well suited for buried service under constant pressure up to 235 psi. Its combination of performance, corrosion resistance, and cost-effectiveness make SDR 35 ideal for many above and below ground pressure applications.

Key Differences Between ASTM D2729 and SDR 35

While both are made from PVC, there are many important differences between these two pipe standards:

Intended Applications

The most fundamental difference is intended use. ASTM D2729 is only for gravity flow drainage like sewers. SDR 35 is engineered for pressurized water and wastewater.

Material Composition

Both use basic PVC resin, but ASTM D2729 allows composite PVC-aluminum pipe. SDR 35 is PVC only.

Dimension Ratios and Sizing

ASTM D2729 uses nominal diameters, while SDR 35 specifies actual dimensions based on the standard pipe diameter-to-wall-thickness ratio.

Pressure Ratings

ASTM D2729 is not rated for internal pressure. SDR 35 has a standard pressure rating of 235 psi with a surge allowance of 470 psi.

Joining Methods

Sewer pipe uses push-together bell-and-spigot or compression joints, while SDR 35 uses elastomeric gasket seals to create aligned, flexible pressure joints.

Applicable Standards

They comply with different ASTM and industry standards for materials, testing, markings, and installation. This keeps them separated for their distinct applications.

In summary, while both are PVC, ASTM D2729 and SDR 35 have significant differences making them suitable for gravity flow sewers or pressurized water lines respectively, but not interchangeable. Choosing the right standard for your project’s needs is important.

The next sections will compare the performance, design considerations, and costs of these two popular PVC piping standards.

Performance and Design Considerations

PVC pipes meeting ASTM D2729 or SDR 35 provide exceptional corrosion resistance, flow capacity, and longevity. However, there are some important considerations when selecting between them:

Strength, Stiffness, and Flexibility

SDR 35 has greater tensile strength to withstand high pressures, but ASTM D2729 has greater ring stiffness for buried applications. SDR 35 is also more flexible for expansion and contraction.

Flow Capacity and Friction Loss

The smooth interior of both products provides high flow rates. SDR 35 can experience higher pressure friction losses.

Fatigue and Surge Pressure Resistance

SDR 35 is engineered to withstand ongoing pressures and pressure surges. ASTM D2729 is designed for intermittent gravity flows.

Chemical and Corrosion Resistance

Both offer broad chemical resistance for sewers and potable water. SDR 35 must meet more stringent VOC limits.

Considering these key performance factors will help determine which standard is optimal for your project requirements. Correctly installing either product per applicable standards is also critical.

Cost Comparison Between ASTM D2729 and SDR 35

When choosing between PVC sewer or pressure pipe, cost is often an important factor. Here is an overview of cost considerations:

Material Costs

In terms of raw PVC pipe cost per foot, SDR 35 is generally more expensive than ASTM D2729. The thicker walls required for pressure ratings add material cost. Exact costs depend on size, but 4″ SDR 35 may be 25-50% more per foot than 4″ ASTM D2729.

However, ASTM D2729 is produced in shorter lengths (typically 20 feet) compared to standard 40-50 foot lengths for SDR 35. This means more joints per linear foot for sewer pipe. The gaskets, fittings, primers, and solvents at each joint also add cost.

Finally, sewer pipe relies more on costly cast iron or PVC fittings like wyes, tees, elbows, and cleanouts compared to the molded and extruded fittings used with SDR 35.

In total installed cost per foot for complete pipelines, ASTM D2729 and SDR 35 are typically comparable for many applications. The thicker material cost for SDR 35 is balanced out by fewer joints and fittings.

Installation Costs

Installation costs are mainly labor dependent. However, some differences to consider include:

• Bell-and-spigot connections for ASTM D2729 may be simpler for do-it-yourselfers than SDR 35’s use of shielded elastomeric gaskets.
• SDR 35’s longer standard lengths and higher flexibility reduces the number of pipe joints to assemble.
• Pressure testing is more critical for SDR 35 water pipes than gravity ASTM D2729 installations.
• Trenching and embedment requirements may differ between the applications.

Overall, when done professionally, there is minimal difference in installation costs between the two pipe standards. Careful design, proper bedding, and following standard practices are more significant factors.

Lifecycle and Maintenance Costs

One of the biggest advantages of both ASTM D2729 and SDR 35 PVC pipe is their long service life compared to materials like steel or concrete. With proper installation, 50+ year lifespans are common.

Because ASTM D2729 is not pressurized, it experiences less stress and does not need pressure testing over time. However, sewer pipes are subject to buildup, root intrusion, and other blockage issues not shared by pressurized SDR 35 water mains.

SDR 35’s higher pressure capacity results in greater surge allowance and fatigue resistance. But higher working pressures and thinner walls also mean greater attention to damage prevention and leak detection.

Overall, both products provide low lifecycle costs compared to other piping materials. Given the buried nature of the pipes, replacement is expensive, so longevity is a primary benefit.

FAQs

Can SDR 35 pipe be used for sewers or drainage applications?

No, SDR 35 does not provide the stiffness needed to withstand crushing underground. Only use ASTM D2729 for gravity sewers and drains.

Can ASTM D2729 pipe be used for pressurized water lines?

No, ASTM D2729 is not engineered to withstand internal pressures. Use SDR 35 or other pressure pipe for water service.

Which PVC pipe is better in terms of durability?

Both products provide excellent longevity when used correctly. SDR 35 may last longer under pressure, but ASTM D2729 sees less stress in sewers.

Is SDR 35 more expensive than ASTM D2729?

The material cost per foot is higher for SDR 35. But with longer lengths and fewer fittings, total installed costs are generally comparable.

Can solvent welding be used to join SDR 35 pressure pipe?

No, SDR 35 requires elastomeric gasket seals. Solvent cement joints are only used on ASTM D2729 sewer pipe fittings.

Conclusion

ASTM D2729 and SDR 35 are both quality standards for PVC pipe used in municipal and residential applications. However, they are engineered for very different purposes.

ASTM D2729 covers PVC sewer pipe intended for gravity flow drainage, while SDR 35 defines thinner-walled PVC piping rated for high pressure water service.

Key differences include composition, sizing, pressure ratings, joining methods, and applicable standards. These reflect the specialized performance needs for pressurized service versus underground drainage.

When selecting piping, consider the application and operating conditions first. While costs are similar, only ASTM D2729 should be used for sewers, and only SDR 35 for pressurized water mains and service lines. Matching the right PVC pipe standard to your project ensures safe, long-lasting service life.