Hanging /Supporting Grooved Piping Systems
There are a variety of hangers and supports typically used on grooved piping systems, ranging from a simple band hanger to a clevis hanger, trapeze supports,to more intricate rack designs using structural steel or Power Strut. All of these are acceptable methods of hanging/supporting, but all of them depend on the type of project, project design, specification requirements and code requirements. Referral to the project and code requirements is a must when choosing the proper hanging or supporting method. This is the obvious first step to consider.
Project logistics, whether it be a grooved or welded system, is another consideration. Quite often hangers and supports are an "afterthought" on a project simply because the big-ticket items such as labor and materials or the project schedule are the focus of the project team. Hangers and supports, however, are one of the first components needed on a project since you cannot hang pipe without them.
In nearly every hanger or support assembly there are three components. They include an upper attachment (beam or structural attachment), intermediate attachment (rod, couplings, eye nuts, etc.) and the lower attachment (pipe clamps, U-bolts, trapezes). All three components should arrive on the project site together. To save costly field labor hours, consideration might be given to having the hangers or supports pre-assembled by the manufacturer, or in the contractor's shop, or simply having the hanger or support components bundled and tagged by system or area of the project. These components can then be easily located without looking all over the lay-down area trying to find what is needed.
The grooved coupling choice is the next consideration in choosing the correct hanger or support method. This also ties in with the proper hanger/support maximum spacing allowables governed by project specifications, the applicable code or the hanger manufacturer's recommendations. Flexible couplings used on horizontal runs of pipe need to be supported at every coupling and usually require intermediate supports to satisfy the maximum spacing allowable requirements, whereas rigid couplings can be hung/supported based on the maximum spacing requirements only. In addition, wherever there is a change in direction of the piping system a hanger or support is usually required immediately following that change in direction.
Coupling choice and system pressurization are also a consideration when choosing the proper hanging or support method. As the couplings are installed, the pipe ends can either be butted up tight to one another or a gap can exist. Once the system is pressurized those areas or joints where the pipe ends are butted up tight and held by a grooved coupling can "Pop" or grow to the maximum gap depending on the coupling chosen. The joint at a flexible grooved coupling can expand about 1/4 inch at each coupling, whereas the joint at a rigid grooved coupling can grow about 3/32 inch. If you have a long run of pipe (horizontal or vertical) with multiple joints, the overall length of the system will grow depending on which grooved coupling you have chosen.
For example: If you have a grooved piping system that is 400 ft. long there will be roughly 19 grooved joints (assuming 21 ft. lengths of pipe are used). If you multiply the number of joints by the growth of each joint you can determine the overall growth of the system due to pressurization. If it is a flexible system 19 joints x .25" = 4.75" of overall growth. A rigid system would be 19 joints x .0938" = 1.78" of overall growth. This growth due to pressurization can have a significant impact on the hangers or supports used, if it is not taken into consideration. One way to avoid this is to install the grooved joints at full gap so that pressurization has no impact at testing or start up. If this is not possible, then periodic air pressurization as the system is installed will expand the grooved joints to full gap and the hangers or supports can be adjusted accordingly.
Thermal expansion is another important consideration when choosing hangers or supports for a grooved system. This is especially important on hot systems vs. chilled systems, since the amount of thermal expansion will be greater on hot systems as opposed to the amount of thermal contraction that will occur on chilled systems. This is all due to the temperature variation from ambient, when the pipe is installed, vs. operating conditions.
For example: Again you have a grooved piping system that is 400 ft. long. Let's assume the system is heating hot water that will operate at 170 degrees Fahrenheit. The pipe is installed under ambient conditions assumed to be at 70 degrees F so you have a 100 degrees variation in temperature. At 70 degrees the pipe has a coefficient of thermal expansion of 0.0 inches/ft., but at 170 degrees the pipe has a coefficient of thermal expansion of 0.0076 inches/ft. To determine the total thermal expansion of the pipe from ambient temperature to operating temperature you multiply the length of pipe by the coefficient of thermal expansion. In this case 400 ft. x 0.0076 inches/ft. = 3.04 inches. In other words, the pipe has grown in length over 3 inches because of the thermal expansion.
This is significant growth, especially if there is a change of direction at the end of the 400-ft. pipe run, or there are branch lines coming off the main run. If this thermal growth exceeds the allowable deflection of a grooved joint, especially where a change of direction or a branch line connects, then problems could occur. Thermal growth cannot be stopped. it can only be controlled by the use of anchors and expansion joints or expansion loops. It is also important to hang or support the pipe with rolls or slides, and use guides to control the thermal expansion of the pipe into an expansion joint or expansion loop.
The use of static hangers, such as clevis hangers, should not be considered on pipe that is thermally expanding. When using trapeze hangers for multiple systems it is important to have "like" systems on the trapeze, that is, systems that are operating near the same temperature. If you combine hot systems with cold systems on a trapeze, the thermal expansion of the hot system will cause the trapeze to twist and failure of the trapeze could occur, or excessive stress could be induced on the grooved joints on all of the systems on the trapeze. Hot systems should be hung or supported independently of cold or ambient systems, or a means should be provided--such as pipe rolls or pipe slides--to allow the hot systems to thermally expand on the trapeze.
If the pipe is a vertical riser then consideration must be given to the use of spring hangers to allow the pipe to grow vertically up or down, depending on how the pipe is anchored. Vertical pipe thermally expands the same amount as horizontal pipe and this has to be taken into consideration relating to supports, expansion joints or expansion loops. If the vertical pipe is supported by friction/riser clamps only and the pipe expands vertically upward, the clamps will grow with the pipe off the penetration or supporting structure and no longer support the pipe. If the growth is downward, the friction clamps (resting on the penetration or supporting structure) can either fail or the pipe may overcome the friction force and push its way through the clamp as the pipe thermally expands downward. In either case, the clamps are no longer supporting the pipe as intended and this may induce excessive stress on the grooved joints.
Whether it is horizontal or vertical grooved pipe, growth of the piping system due to pressurization and thermal expansion must be considered. On hot systems both must be taken into account and added together to determine the overall growth of the system and the effect on the hangers/supports used. In the previous examples, pressurization expansion on the 400-ft. run of pipe was 4.75 inches for a flexible joint system and 1.78 inches for a rigid joint system, and the thermal expansion was 3.04 inches. Adding these combinations together you could have a total pipe growth of 7.79 inches for a flexible system or 4.82 inches of total pipe growth for a rigid system, regardless of the horizontal or vertical orientation of the pipe. Again, this is a significant amount of growth relating to hangers/supports and the resulting stresses induced on grooved joints.
Grooved systems in seismic zones perform extremely well. However, consideration should be given to how a grooved system is seismically restrained. If you have growth due to pressurization or thermal expansion or both, consideration should be given on how to restrain the system but let the growth occur. Seismic restraints in the longitudinal direction of a long pipe run may restrict the growth of the pipe inducing stresses into the grooved couplings. Seismic restraints in the lateral direction should have little impact on expansion except where the system has a change in direction. If the seismic restraints are placed laterally to the pipe after a change in direction at the end of a long run of pipe, the expansion of the long pipe run may be restricted and this could induce excessive stress into the grooved joints.