Hangers and Support of Sprinkler System Piping
With all of the hard work and effort that goes into designing and installing a sprinkler system, we want to make sure it’s going to stay in place for years to come. Designing the support of such a system is no easy task but if done right can help save lives and property. Hangers need to do three things: connect to the building itself, typically to structural members; be long enough to reach the pipe they are supporting; and securely attach to the sprinkler system piping. Some hangers accomplish this with one piece while other types of hangers require multiple components. There are requirements for the specific hanger components, for example threaded rods, u-hooks and eye rods all need to be a certain thickness based on the size of the pipe they are supporting. Likewise, there are specific requirements on the type of fasteners that are based on the pipe size and material that the fasteners go into (wood, concrete or steel). This image shows a typical hanger assembly. It consists of a C-clamp that secures the threaded rod onto the building, the rod itself that reaches down to the pipe and the adjustable swivel ring that secures the rod to the pipe. As an added bonus there is a retainer strap that will help the C-clamp stay on the building in the event of an earthquake. This blog will address general requirements that cover most installations but it’s important to note that this blog doesn’t contain all of the requirements for hanging and bracing. To see all of the requirements for hanging and bracing be sure to read chapter 17 of NFPA 13. There are several different types of sprinkler piping support, this blog will discuss hangers (including trapeze hangers) pipe stands and riser clamps. Trapeze Hangers Trapeze hangers are a type of sprinkler piping support that consists of a length of pipe or angle iron that serves as a trapeze bar between multiple structural members which then support the sprinkler system piping. This is usually used for larger pipe so the load can be shared between two structural members or when you need to support pipe that is not directly underneath a structural member. The requirements in NFPA 13 for trapeze give you a certain section modulus that the trapeze member needs to have, and this is based on the length of the trapeze and the size of the pipe it’s supporting. That section modulus is then translated into either a pipe or angle iron size that is needed for the trapeze member. Installation of Pipe Hangers Two main concepts to consider when it comes to the installation of pipe hangers is the location of hangers on branch lines and the maximum distance between hangers. Maximum distance between hangers needs to be in compliance with the table below. This is done to ensure that there are not long stretches of unsecured piping. Note that nonmetallic piping should follow the hanger spacing requirements located in the product listing. There is more to know about installing hangers than just placing them at their maximum intervals. The following requirements are in place to ensure hangers can properly support the sprinkler system before, during and after activation. Minimum number of hangers – there needs to be at least one hanger on each piece of pipe. Clearance to hangers – the distance between a hanger and an upright sprinkler needs to be at least 3 inches (75mm). This is done to prevent the hanger from becoming an obstruction to sprinkler discharge. Unsupported lengths – the maximum unsupported length between the end sprinkler and the last hanger in the line needs to comply with the table below. Keep in mind that there are different requirements for pendent sprinklers where the maximum static or flowing pressure exceeds 100 psi. Unsupported armover – the horizontal length of an unsupported armover can’t exceed 24 inches (600mm) for steel pipe and 12 in (300 mm) for copper tube. Once again, there are different requirements once the pressure exceeds 100 psi. Pipe Material Pipe Size Maximum Unsupported Length Steel 1 in (25 mm) 36 in (900 mm) 1 ¼ in (32 mm) 48 in (1200 mm) 1 ½ in (40 mm) or larger 60 (1500 mm) Copper 1 in (25 mm) 18 in (450 mm) 1 ¼ in (32 mm) 24 in (600 mm) 1 ½ in (40 mm) or larger 30 in (750 mm) Support of Risers Risers, which are the vertical supply pipes in a sprinkler system, typically consist of large heavy pipes that are filled with a great deal of water. Due to the weight and force of water flowing through the piping, it is essential to be able to secure them from moving. Typically, risers are supported by a friction-type clamp that rests on or is secured to the floor slab. However, risers can also be supported with riser clamps that are fastened to the building structure or with hangers that support the horizontal piping at the top of the riser. When risers are installed in multistory buildings, they need to be supported at the lowest level and at each alternative level above that, as long as the distance between the supports doesn’t exceed 25 ft (7.6 m). Riser supports also need to be provided at the top of the riser as well as above and below offsets. Pipe Stands Sometimes it is impractical or infeasible to support sprinkler piping from the ceiling. When that is the case, pipe stands can be used to secure piping from the ground, for example, when supporting a back flow prevention device. When pipe stands are supporting piping from the ground, there are maximum heights in which the stands can support. The table below lists these limitations. Most pipe stands are much shorter and usually only used to support large pipe closer to the ground. When the system piping is 10 inch (250 mm) schedule 40 or smaller, it can be supported by a 2 inch (50 mm) schedule 40 pipe as long as the pipe stand isn’t any longer than 4ft (1.2m) (see figure below). The distance between pipe stands follows the same rules as the distance between hangers. Also, similar to pipe hangers it’s important to properly attach the pipe stand to the ground as well as attach the pipe stand to the system piping. Performance Based Approach As an alternative to the prescriptive based requirements mentioned above you can follow the performance-based approach for installing hangers and pipe stands. With this method, hangers or pipe stands certified by a professional engineer to meet the five conditions listed below can be an acceptable alternative to the other requirements in the hanging and bracing chapter of NFPA 13. This approach is typically only used where listed hangers can not be used for a particular building arrangement or system configuration. Hangers need to be able to support five times the weight of the water filled pipe, plus 250 lbs (115kg) at each point of piping support. The points of support need to be able to support the system Hanger spacing needs to be in compliance with the table 18.104.22.168 (referenced earlier in the blog) Hanger components need to be either iron an iron alloy (such as steel) Engineering calculations need to be submitted to the AHJ as requested. Conclusion In addition to hangers, riser supports, pipe stands and other types of components that support the sprinklers against the pull of gravity, sprinkler systems sometimes also need to be able to be resistant to seismic activity. Check out our recent blog for information on seismic protection of sprinkler systems.