Specifying pipe and piping materials
By Matt Dolan, PE, LEED AP BD+C, JBA Consulting Engineers, Las Vegas
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.
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