Specifying pipe and piping materials
Piping is used within many building systems, including HVAC, plumbing, specialty chemicals and fluids, and fire protection. Knowing what type of piping to use in a specific application can help preserve the life of a system or avoid a catastrophic failure.
1. Understand the challenges of low- and high-rise piping systems.
2. Learn about three piping system types: HVAC (hydronic piping), plumbing (domestic water, and waste and vent piping), and specialty piping for chemicals and fluids (saltwater systems and hazardous chemicals).
Pipe and piping systems are found within many elements of buildings. Numerous people have seen a P-trap below a sink or refrigerant lines routing to and from their residential split system. Fewer have seen the main utility piping routing from a central plant or the chemical treatment systems within a pool equipment room. Each of these applications requires a specific type of pipe to meet the requirements of the codes, physical limitations, specifications, and best design practices.
There is no simple piping solution to meet all applications. Provided that specific design criteria are followed and the right questions are asked of the owner and operational staff, these systems can meet all of the physical and code requirements. In addition, they can maintain the proper cost and lead times to create a successfully implemented building system.
HVAC piping encompasses many different fluids, pressures, and temperatures. This piping can be located above or below ground and route through the interior or exterior of a building. These factors must be taken into consideration when specifying HVAC piping within a project. The term “hydronic” refers to the use of water as a heat transfer medium for cooling and heating. In each application, the water is supplied at a set flow rate and temperature. Typical space heat transfer is completed using an air-water coil designed to return the water at a defined temperature. This results in a specified quantity of heat delivered or removed from the space. Hydronic chilled and heating water are the dominant systems used to condition large commercial facilities.
For most low-rise building applications, the expected system working pressure is typically less than 150 pounds per square inch gauge (psig). Hydronic systems (both chilled and heating water) are closed-loop systems. This means that the total dynamic head of the pumps takes into account the friction losses within the piping system, associated coils, valves, and accessories. The static height of the system does not affect the pumping capacities, but it does affect the required working pressure of the system. A 150 psig working pressure rating for chillers, boilers, pumps, piping, and accessories is common for equipment and component manufacturers.This pressure rating should be maintained within system designs whenever possible. Many buildings that are considered as low- or medium-rise will fall into the 150 psig working pressure category.
Maintaining the piping system and equipment below the standard pressure of 150 psig becomes more difficult when designing high-rise buildings. A static piping height above approximately 350 ft (with no pump pressure added to the system) will exceed the standard working pressure rating for these systems (1 psig = 2.31 ft of head). This system would most likely employ a pressure break (in the form of heat exchangers) to isolate the higher pressure requirements of the tower from the rest of the connected piping and equipment. This system design would allow standard pressure chillers to be designed and installed, while specifying higher pressure piping and accessories within the tower component.
When specifying piping for a large campus project, designers/engineers must be intentional when editing the associated specifications sections (ARCOM MasterSpec sections 23 21 13.23 and 23 21 13.13, respectively, for above- and below-grade hydronic piping) to be certain that the piping specified for the tower and podium are reflective of their individual requirements (or collective requirements if heat exchangers are not used to isolate the pressure zones).
Another component of the closed-loop systems is water treatment and purging of any oxygen from the water. Most hydronic systems are fitted with water treatment systems composed of various chemicals and inhibitors to maintain the water flowing through the pipes at optimal pH (approximately 9.0) and microbiological levels to resist bio-film buildup and corrosion within the piping. Stabilizing water within the system and removing any air helps provide the full life expectancy of the piping, associated pumps, coils, and valves. Any air left within the piping can cause cavitation at the chilled and heating water pumps and reduce heat transfer within chillers, boilers, or hydronic coils.
Hydronic systems can use the following piping types:
Copper: Drawn-temper tubing, which complies with ASTM B88 and B88M with types L, B, K, M, or C, with ASME B16.22 wrought-copper fittings and unions joined with lead-free solder or brazing for underground applications.
Drawn-temper tubing, which complies with ASTM B88 and B88M with types L, B, K (normally only used below grade), or A, with ASME B16.22 wrought-copper fittings and unions joined with lead-free solder or brazing for aboveground applications.Pressure-seal fittings are allowed for this tubing as well.
Type K copper is manufactured with the highest tubing thickness and allows for working pressures from 1534 psig at 100 F for ½-in. piping, to 635 psig for 12 in. The working pressures of types L and M are less than K, but are still more than suitable for HVAC applications (pressures range from 1242 psig at 100F for ½-in. and 435 psig for 12-in. for type L, and 850 psig and 395 psig for type M, respectively. These values are taken from Tables 3a, 3b, and 3c of “The Copper Tube Handbook,” published by the Copper Development Assn.
These working pressures are taken for straight lengths of piping, which are not typically the pressure-limiting areas of the system. Fittings and unions, where two pieces of pipe are joined, are more likely to cause leaks or fail under the working pressures of some systems. The typical joining types for copper piping are soldering, brazing, or pressure seals. These joining types should be made with lead-free materials and be rated for the expected system pressures.
Each joining type is capable of maintaining a leak-free system when the joint is sealed properly, but these systems respond differently when a joint is not fully sealed or crimped. Solder and brazed connections will more likely fail and leak when the system is first filled and tested and the building is not yet occupied. In this scenario, the contractor and inspector can quickly identify where a joint has not been sealed, and remedy this problem before the system is fully operational and occupants and interior finish items are damaged. Pressure-seal joints can replicate this scenario as well, provided that they are specified with a leak detection ring or assembly. This allows water to leak out of the fitting if it is not fully pressed to identify problem areas in the same manner as solder or brazing. If the pressure-seal fittings are not specified with this item, they can sometimes hold pressure during the construction tests and may only fail after a period of operational time, thereby causing significantly more damage to the occupied space and potentially harming the occupants, especially if this piping is carrying heating hot water.
Sizing guidelines for copper piping are determined based upon code requirements, the recommendations of the manufacturer, and best practices. For chilled water applications (where the supply water temperature is typically 42 to 45 F),the recommended velocity limitations of copper pipe systems is 8 fps to maintain low system noise and reduce the possibility of erosion/corrosion. For heating water systems (where the supply water temperature is typically 140 to 180 F for space heating applications and up to 205 F when used to produce domestic hot water in a hybrid system),the recommended velocity limitations for copper pipe is much less. “The Copper Tube Handbook” lists these velocities at 2 to 3 fps when supply water temperatures are above 140 F.
Copper piping is typically available in certain sizes, the maximum of which is 12 in. This limits the use of copper within main campus utility piping systems, because these building designs typically require piping sizes in excess of 12 in. routing from the central plant to the associated heat exchange devices. Copper piping is more typically found within hydronic systems for sizes 3 in. and smaller. For sizes larger than 3 in.,grooved steel piping is more commonly used. This is due to cost differences between the steel and copper, the differences in labor requirements of grooved piping compared to solder or brazed piping (where pressure fittings are not allowed or recommended by the owner or engineer), as well as recommended water velocities and temperatures within each of these piping materials.
Steel: Black or galvanized steel piping, which complies with ASTM A 53/A 53M with malleable-iron (ASME B16.3), or wrought-steel (ASTM A 234/A 234M) fittings and malleable-iron (ASME B16.39) unions. Both class 150 and class 300 flanges, fittings, and unions may be used with threaded or flanged fittings. This piping may be joined by welding with welding filler metals which comply with AWS D10.12/D10.12M.
Grooved mechanical-joint fittings and couplings, which complies with ASTM A 536 for grade 65-45-12 ductile iron, ASTM A 47/A 47M for grade 32510 malleable iron, and ASTM A 53/A 53M for types F, E, or S, Grade B fabricated steel; or ASTM A106, Grade B steel fittings with grooves or shoulders constructed to accept grooved-end couplings.
Steel piping is more commonly used for larger piping sizes in hydronic systems as stated above. This system type allows for a variety of pressure, temperature, and sizing requirements to meet the demands of chilled and heating water systems. The class designation indicated for the flanges, fittings, and unions references the psig working pressure of saturated steam for the associated element. A class 150 fitting is intended to operate at a working pressure of 150 psig at 366 F, while a class 300 fitting will provide a working pressure of 300 psig at 550 F. A class 150 fitting will provide a water working pressure of 300 psig up to 150 F, while a class 300 fitting will provide a water working pressure up to 2000 psig at 150 F. Additional fitting classes are available for specific piping types. Class 125 or 250 is available for cast-iron pipe flanges and flanged fittings in compliance with ASME 16.1 as an example.
Grooved pipe and coupling systems use a cut or formed groove located on the ends of the piping, fittings, valves, etc., which is attached by a flexible or rigid coupling system between each length of pipe or fitting. These couplings contain two or more pieces that are bolted together and have a gasket within the waterway of the coupling. These systems work with class 150 and 300 flange types and with ethylene propylene dienemonomer (EPDM) gasket materials, and are able to operate with 230 to 250 F fluid temperatures (depending upon the piping size). The grooved piping information has been taken from Victaulic guide specifications and literature.
Schedule 40 and 80 steel piping is acceptable for HVAC applications. The piping schedule refers to the piping wall thickness, which increases as the schedule number increases. With the increase in piping wall thickness, there is also an increase in the working pressure allowed for straight pipe. Schedule 40 piping allows for working pressures from 1694psig for ½-in. piping, to 696psig for 12 in. (both from -20 to 650 F). Schedule 80 piping allows for working pressures from 3036psig for ½ in. and 1305psig for 12in.,respectively (both from -20 to 650 F). These values are taken from the Watson McDaniel engineering data section.
Plastic: CPVC plastic piping, which complies with ASTM F 441/F 441M for both schedule 40 and schedule 80 with socket-type fittings (ASTM F 438 for schedule 40 and ASTM F 439 for schedule 80) and solvent cements (ASTM F493).
PVC plastic piping, which complies with ASTM D 1785 for schedule 40 and schedule 80 with socket-type fittings (ASM D 2466 for schedule 40 and ASTM D 2467 for schedule 80) and solvent cements (ASTM D 2564). Include primer according to ASTM F 656.
Both CPVC and PVC piping are indicated for below-grade hydronic applications, though even in this environment one must exercise caution when installingthis piping within a project. Plastic piping has been widely used within waste and vent piping systems, specifically for underground applications where the uninsulated pipe is in direct contact with the surrounding soil. In this instance the corrosive resistance of CPVC and PVC piping is advantageous due to the corrosive nature of some soils. Hydronic piping is typically insulated and covered with a protectivePVC jacketing, which provides a buffer between the metallic piping and the surrounding soil. Plastic piping can be used in smaller chilled water systems where lower pressures are expected. The maximum working pressure for PVC piping is above 150 psig for all pipe sizes through 8 in., but this is only for temperatures of 73 F or below. Any temperature above 73F will result in a reduced working pressure within the piping system up to a maximum of 140 F. At this temperature the de-rating factor is 0.22, where it is 1.0 at 73 F. The maximum service temperature of 140 F is applicable to both schedule 40 and schedule 80 PVC piping. CPVC piping is capable of a greater range of service temperatures, allowing it to accommodate up to 200 F (at a 0.2 de-rating factor), but its pressure ratings are identical to PVC, which makes it acceptable for underground standard pressure chilled water systems up to 8 in. For heating water systems supporting higher temperature water up to 180 or 205 F,neitherPVC norCPVC piping is advisable. All data is from Harvel PVC piping specifications and CPVC piping specifications.
Plumbing piping is concerned with the flow of many different liquids, solids, and gases. Both potable and non-potable fluids flow within these systems. Due to the wide variety of fluids carried within plumbing systems, the associated piping is categorized as either domestic water or drainage and vent piping.
Domestic water: Soft copper tubing, which complies with ASTM B88 for types K and L, and ASTM B88M for types A and B with wrought copper solder-joint pressure fittings (ASME B16.22).
Hard copper tubing, which complies with ASTM B88 for types L and M, and ASTM B88M for types B and C with cast copper solder-joint fittings (ASME B16.18), wrought copper solder joint fittings (ASME B16.22), bronze flanges (ASME B16.24), and copper unions (MSS SP-123). Pressure-seal fittings are allowed for this tubing as well.
Copper piping types and associated standards have been taken from MasterSpec section 22 11 16. Copper domestic water piping design is limited by the code requirements for maximum flow rates. They are stated in the plumbing codes as follows:
2012 Uniform Plumbing Code section 610.12.1 states: Maximum velocities in copper and copper alloy tube and fitting systems shall not exceed 8 fps in cold water and 5 fps in hot water.These values are also reiterated in “The Copper Tube Handbook,” which uses these values as the recommended maximum velocities for these system types.
Stainless steel piping, which complies with ASTM A403 for type 316 with similar fittings using welded or grooved couplings is used for both larger domestic water piping and direct replacement of copper piping. As copper prices have increased, stainless steel piping has become more common within domestic water piping systems. Piping types and associated standards have been taken from the Veteran’s Administration (VA) MasterSpec Section 22 11 00.
A new development that will be brought into application and compliance in 2014 is the Federal Reduction of Lead in Drinking Water Act. This is a federal implementation of the current California and Vermont laws regarding lead content found within the waterway of any piping, valves, or accessories used within the domestic water system. The law states that all wetted surfaces of pipes, fittings, and fixtures must be “lead-free,” which translates to a maximum lead content of “not more than a weighted average of 0.25% (lead).” This requires that manufacturers produce “lead-free” cast products to meet the new letter of the law. UL outlines the details in “An Overview of Regulations for Lead Levels in Drinking Water System Components.”
Drainage and venting: Hubless cast iron soil pipe and fittings, which complies with ASTM A 888 or Cast Iron Soil Pipe Institute (CISPI) 301. Sovent stack fittings, which comply with ASME B16.45 or ASSE 1043, can be used with a hubless system.
Hub-and-spigot cast iron soil pipe and fittings must comply with ASTM A 74, with rubber gaskets (ASTM C 564), and pure lead and oakum or hemp fiber calking materials (ASTM B29).
Both of these piping construction types are acceptable for building use, but hubless piping and fittings are most commonly used above grade within commercial buildings. Cast iron piping with CISPI hubless piping couplings allows for a permanent installation that can be reconfigured or accessed by disassembling the band clamps, but still retains the metallic piping mass to reduce breakout noise from waste flow through the pipe. The drawback to castiron piping is deterioration of the pipe from acidic waste materials found in typical installations serving bathrooms.
Stainless steel piping and fittings with socket and spigot ends, which complies with ASME A112.3.1 are found in above-grade drainage systems in place of cast iron piping. Stainless steel piping is also used within the first segments of piping connecting to floor sinks where soda products are drained to reduce the damage due to corrosion.
Solid-wall PVC piping, which complies with ASTM D 2665 (drain, waste, and vent), and cellular-core PVC piping, which complies with ASTM F 891 (schedule 40), socket fittings (ASTM D 2665 made to ASTM D 3311, drain, waste, and vent patterns and to fit schedule 40 pipe), adhesive primer (ASTM F 656), and solvent cement (ASTM D 2564). PVC piping can be found above and below grade within commercial buildings, though it is more often specified below grade due to breakout noise from the piping and specific code requirements.
Within the Southern Nevada building jurisdiction, the code amendment to the 2009 International Building Code (IBC)states:
603.1.2.1 Equipment rooms. Combustible piping shall be permitted to be installed in an equipment room that is enclosed by 2-hour fire-resistance rated construction and protected throughout by automatic sprinklers. The combustible piping shall be permitted to be extended from the equipment room to other rooms provided the piping is encased in an approved, dedicated 2-hour fire-resistance rated assembly. Where such combustible piping penetrates a fire-resistance rated wall and/or floor/ceiling assembly, the penetration shall be protected by a through-penetration firestop system that is listed for the specific piping material and that has F and T ratings not less than the required fire resistance rating of the penetrated assembly. The combustible piping shall not penetrate more than a single floor.
This requires that all combustible piping (plastic or otherwise) be encased in 2-hour rated construction when present within a Type 1A building as defined by the IBC. There are some benefits to using PVC piping within a drainage system. PVC is more resistant to corrosion and oxidation caused by waste and soils from bathrooms than cast-iron piping. PVC piping also resists corrosion from the surrounding soils when installed underground (as indicated in the HVAC piping section). PVC piping used within drainage systems has the same limitations found within the HVAC hydronic systems with a maximum service temperature of 140 F. This temperature is further solidified by the Uniform Plumbing Code and International Plumbing Code requirements, which state that any discharge into a waste receptor must be below 140 F.
2012 Uniform Plumbing code section 810.1 states: No steam pipe shall be directly connected to a plumbing or drainage system, nor shall water having a temperature above 140 F (60 C) be discharged under pressure directly into a drainage system.
2012 International Plumbing Code section 803.1 states: Steam pipes shall not connect to any part of a drainage system or plumbing system and water above 140 F (60 C) shall not be discharged into any part of a drainage system.
Specialty piping systems are associated with conveying atypical fluids. These fluids can range from salt water aquarium piping applications to chemical feed piping for pool equipment systems. Aquarium piping systems are not commonly found within commercial buildings, but they are installed in some hospitality properties, with remote piping systems routing from a central pump room to various locations. Stainless steel would appear to be an appropriate piping type for saltwater systems due to its ability to inhibit corrosion with other water systems, but in actuality saltwater will pit and deteriorate stainless steel piping. For this type of application, CPVC plastic or copper-nickel marine-grade piping meets the corrosive requirements; when routing this piping within a large commercial property, the combustibility of the pipe must be taken into account. As indicated above, in Southern Nevada the use of combustible piping requires an alternate means request to show compliance with the intent of the code for the associated building types.
Pool piping conveying treated water for human immersion contains diluted quantities of chemicals (both 12.5% sodium hypochlorite bleach and muriatic acid can be used) to maintain a specific pH level and chemical balanceto meet health department requirements. In addition to the diluted chemical piping, full concentrations of chlorine bleach and other chemicals must be conveyed from bulk storage locations and specific equipment rooms. CPVC piping meets the chemical resistance to convey chlorine bleach, but high-silicon iron piping can be substituted for chemical piping applications when routing through noncombustible building types (example: Type 1A). It is durable, but more brittle than standard cast-iron piping and weighs more than similar piping types.
This article addresses only some of the multitude of possibilities within piping system designs. They represent the majority of installed system types for larger commercial buildings, but there will always be exceptions to the rules. General master specifications are an invaluable resource when determining piping types for a given system and the associated standards by which to judge each product. Standard specifications will meet the requirements of many projects, but when high-rise towers, high temperatures, hazardous chemicals, or changes in the law or jurisdiction are involved, designers and engineers must review. additional information about piping recommendations and limitations to make informed decisions about the products being installed in their projects. We, as design professionals, are trusted by our clients to provide them with an adequately sized, properly balanced, and reasonably priced design for their buildings—one where the piping systems reach their expected life span and a catastrophic failure is never encountered.
Matt Dolan is a project engineer with JBA Consulting Engineers. His expertise is in designing complex HVAC and plumbing systems for various building types, such as commercial offices, healthcare facilities, and hospitality complexes including high-rise guestroom towers and numerous restaurants.