Answers to the top questions engineers are asking about PP-RCT

PP-RCT insights

• PP-RCT piping, a type of polypropylene random copolymer, is gaining popularity in commercial construction due to its durability, ease of installation and economic viability, offering several advantages over traditional metal pipes like resistance to corrosion, rust and scale buildup. This piping system is highly versatile, suitable for applications ranging from domestic hot and cold water to hydronic heating and cooling, and is designed to meet a variety of temperature, pressure and regulatory standards, making it a reliable choice for modern building projects.

The requirements for more efficient, sustainable, high-performing and cost-effective structures have brought several new building innovations to the market that help meet the needs of owners, developers, engineers, contractors and, ultimately, end users.

One such solution, polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) piping, is beginning to gain more traction in commercial building design and construction due to its durability, installation ease, economic viability and other important benefits.

Understanding the history, characteristics and design requirements of PP-RCT will help to ensure the product is specified, designed and installed properly for maximum performance in domestic water and hydronic heating and cooling applications.

The following information details key questions engineers may have about the piping system to gain a greater understanding of its properties for confidence in specifying and design.

What is PP-RCT?

According to industry standard ASTM F2389: Standard Specification for Pressure-Rated Polypropylene (PP) Piping Systems, the “R” (standing for random) means the material is made up of both long and short molecular chains scattered randomly throughout the material. This random pattern staggers the joints in the molecular bond and greatly increases the ability to withstand elevated temperatures and pressures while also making the material more ductile and resistant to shattering.

Figure 1: Polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) is the newest generation of polymer piping materials manufactured to provide greater durability and long-lasting service for domestic water and hydronic heating and cooling applications. Courtesy: Uponor

What are PP-RCT applications?

PP-RCT is pressure rated for water service lines, hot and cold domestic water, hydronic hot water heating, chilled water, condenser water, geothermal and distribution piping for radiant heating and cooling, snow and ice melting, turf conditioning and permafrost prevention (cold storage) applications.

Some manufacturers offer PP-RCT with a coextruded fiber layer for domestic hot water and hydronic hot water heating applications. This middle fiber layer helps minimize expansion and contraction of the piping system when transporting fluids with larger Delta Ts (temperature differences).

Because most polymer piping systems need to account for linear expansion, this “locked-in” fiber layer keeps the pipe expansion minimal — up to 80% less when compared to nonfiber plastic pipes.

Figure 2: The random pattern of the long and short molecular chains in polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) provide superiority over PP-R materials of years past. Courtesy: Uponor

Note that while PP-RCT fiber pipe will expand less than nonfiber polymer piping options, it is going to expand slightly more than steel (about 2.3 inches at a 100°F Delta T over 100 feet).

What pipe sizes are available?

PP-RCT is manufactured to metric sizes. Typical pipe sizes range from 16 mm to 630 mm (3/8 to 24 inches), depending on the manufacturer. The pipe is also available in various standard dimension ratios (SDRs, i.e., wall thicknesses), including 7.4, 9, 11 and 17.6. This provides many different design options when sizing for domestic water or hydronic heating and cooling applications.

Figure 3: The middle fiber layer in polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) pipe for domestic hot water and mechanical applications helps minimize expansion inherent in polymer materials. Courtesy: Uponor

What are PP-RCT temperature and pressure ratings?

Hydrostatic temperature and pressure ratings are typically 180°F (82°C) at 100 pounds per square inch (psi; 690 kilopascals, kPa). However, pressure ratings can vary depending on the pipe SDR, so it is important to refer to the specs for each individual product.

It is also important to keep in mind that domestic hot water operating temperatures should not exceed 140°F (60°C) at 80 psi (551 kPa) and a velocity of 8 feet per second (fps) or 2.4 meters per second (m/s) to align with industry best practices. For domestic hot water recirculation systems, operating temperatures should not exceed 140°F (60°C) at 80 psi (551 kPa) and a velocity of 2 fps (0.6 m/s).

What are PP-RCT regulatory requirements?

There are various codes, standards and listings for PP-RCT, including:

• ANSI/NSF 14 (Plastic Piping Systems Components and Related Materials).

• ANSI/NSF 61 (Drinking Water System Components — Health Effects).

• ASTM D2657 (Standard Practice for Heat Fusion Joining of Polyolefin Pipe and Fittings).

• ASTM E84 (Standard Test Method for Surface Burning Characteristics of Building Materials).

• ASTM E814 (Standard Test Method for Fire Tests of Penetration Firestop Systems).

• ASTM F2389 (Standard Specification for Pressure-rated Polypropylene Piping Systems).

• CAN/ULC S115 (Standard Method of Fire Tests of Firestop Systems).

• CSA B137.11 (Polypropylene Pipe and Fittings for Pressure Applications).

• IAPMO K-12775 (Research and Testing – Pressure Rated Polypropylene Piping Systems).

• IAPMO R&T Certificate, Listing 8358.

• ICC-ES-PMG 1106 (Polypropylene PP-R and PP-RCT Pipe and Fitting System).

• ICC-LC1004 (PP, PEX, PEX-AL-PEX and PP-AL-PP Piping, Tube and Fittings used in Radiant Heating and Water Supply).

• NSF/ANSI 51 (Food Equipment Materials).

• QAI P321-5 (Water Pipe Systems – PP-RCT Pipe and Fittings).

• UL 1479 (Standard for Through-penetration Firestops).

It is important to note that different PP-RCT manufacturers have their pipe tested and listed to various codes, standards and listings, so it is important to research the manufacturer and ensure the proper regulatory requirements for the project and application.

Figure 4: The various wall thicknesses of polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) provide many design options to meet most any application. Courtesy: Uponor

What are the joining methods?

There are two joining methods for PP-RCT: heat fusion and electrofusion. These processes eliminate open flame, glue, solvents and solders from the jobsite.

Heat fusion uses an iron heated to around 500°F (260°C) to melt the pipe and fitting before joining via socket, butt or outlet. Electrofusion uses fittings with metal coils to enable electric current to run through the coils, generating heat and melting the material to form a connection.

What are PP-RCT sizing considerations?

PP-RCT resists corrosion, rust and scale buildup, providing long-term consistent flow throughout the life of the system. This means there is no need to upsize the system to account for scale and corrosion.

And because PP-RCT is produced with a special manufacturing process that enhances the crystalline structure to produce a material with improved pressure ratings at elevated temperatures, it provides more than a 50% improvement in long-term strength compared to PP-R. This long-term strength improvement allows designers to achieve higher pressure ratings with the same wall thickness or potentially down gauge to a thinner-wall pipe with better hydraulic capacity and lower cost.

The first step in designing a project with PP-RCT is selecting the correct SDR. The increased temperature and pressure capabilities of PP-RCT may allow the ability to down gauge the wall thickness and still meet the performance requirements of the system. Down gauging may also allow the ability to choose the next pipe size down due to the higher hydraulic capacity of the pipe.

Downsizing the pipes — where possible — can potentially help save clients money while also helping save space in the install area as well as make pipe handling much easier for the contractor.

Figure 5: Fusion connections for polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) provide durable, reliable, monolithic joints throughout the piping system. Courtesy: Uponor

What are the design differences compared to metallic pipe?

PP-RCT is significantly smoother than metal piping systems. For example, it is more than 75 times smoother than carbon steel. Steel will corrode and lose performance over its lifetime, but PP-RCT resists corrosion, rust and scale buildup, so it remains clean and smooth throughout its service life.

Depending on the SDR, the flow rates may be very similar for PP-RCT and metallic pipes. For example, 6-inch Schedule 40 steel has flow rates around 450 gallons per minute at 5 fps. SDR 17.6 PP-RCT has the same flow rates at 6 fps. And pressure drop in feet of head per 100 feet of pipe is very similar between PP-RCT and carbon steel as well.

Note these are characteristics on Day One. It is important to remember what happens over time with metallic systems. Because PP-RCT will not corrode, rust or experience any scale buildup, the pipe will perform as expected throughout its service life. There is no need to upsize the system on the front end to account for scale buildup.

What are other benefits of PP-RCT over metals?

• The thermal conductivity of PP-RCT is 1.67 Btu x in / (hour x square feet x °F). This low conductivity value, combined with the thickness of the pipe and fitting wall, act as a natural insulator. Traditional metal piping systems have much higher thermal conductivity values. Under normal operating conditions, noninsulated PP-RCT pipes have less heat loss or gain and greater resistance to condensation compared to metal piping systems.

• Depending on the water conditions, the life expectancy of a metallic piping system can be as short as 20 years. PP-RCT, however, has an expected service life of more than 50 years.

• Even filled with water, PP-RCT is often half the weight of the same piping system in steel. This means lighter weight hanging systems and can also reduce the structural stress on a building.

• PP-RCT can also help lower installation costs. For example, installing a cooling tower on a building with carbon steel piping often requires structural shoring to the roof to account for the weight of the equipment and piping. PP-RCT can reduce that weight significantly and reduce or eliminate the need for additional structural shoring.

• Because it is not a traded commodity, PP-RCT has relatively stable pricing (unlike the price fluctuations of commodity metals).

• The smooth inner wall of PP-RCT makes it very difficult for bacteria to attach to the inside surface of the pipe. Hence, PP-RCT does not support the attachment of biofilms. However, the corroded interior surface of metallic pipes provides an ideal environment to catch and hold biofilms.

• The process of mining metals from the earth causes problems for the environment and damages ecosystems in the area while also promoting land degradation, deforestation, ground and surface water pollution and habitat destruction. Because PP-RCT is a byproduct of the natural gas industry, it requires no additional mining activity to produce, making it a far more sustainable material for piping systems.

Figure 6: Polypropylene random copolymer with modified crystallinity and temperature resistance (PP-RCT) is significantly smoother than metal piping and will continue to remain smooth throughout its service life. Courtesy: Uponor

What are some specification requirements?

In the “part 1 general” section, include ASTM F2389 (for polypropylene pressure pipes) along with ASTM D2657 (for the fusion connections) as well as the Canadian equivalent. In the “part 2” section, call out the mechanical or domestic hot water pipe with the fiber layer with all the various SDRs offered. For fittings, call out socket fusion fittings for pipe sizes ½ (20 mm) to 4 inch (125 mm) and butt fusion fittings for anything larger than 6 inches (160 mm).

For the “execution” section, there are a couple options for writing the hangers and supports. Either reference the PP-RCT manufacturer’s manual or list out the requirements as shown in the manual. When it comes to the connections portion of the execution section, be sure to reference the DVS 2207-11 Standard, which is currently in the 2017 edition.

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