Consider Hanging or Supporting Grooved Piping Systems

Grooved piping products have a very good maintenance track record in the field. Whenever there are "perceived" problems with installed grooved product, a high percentage is often related to the hanging or supporting method or application chosen. Although supported very similarly to welded piping systems, a few considerations should be given to assure the proper selection and application of hangers and supports used on a grooved piping system.

Review requirements and logistics
A variety of hangers and supports are typically used on grooved piping systems, ranging from a simple band hanger, clevis hanger and trapeze supports to more intricate rack designs using structural steel or a mechanical framing/strut system. All of these are acceptable hanging or supporting methods, but they are dependent on the project's type, design and specification requirements. With this in mind, a vital first step is to refer to the project and code requirements when choosing the proper method.

Project logistics is another consideration, regardless of system type. Quite often hangers and supports are an afterthought on a project, simply because the big-ticket items, such as labor, major equipment and schedule, are the focus of the project team. However, hangers and supports are among the first components needed on a project, since you cannot hang pipe without them.

Nearly every hanger or support assembly has three components: 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 and early. To save costly field-labor hours, consideration might be given to having the hangers or supports pre-assembled by the manufacturer or fabricated in the contractor's shop. Components can also be bundled and tagged by system or area of the project so that they can be easily assembled and located onsite.

Match the hanger/support to the coupling used
The type of grooved coupling used on a project is the next consideration when choosing the correct hanger or support method. The proper maximum spacing allowable governed by project specifications, the applicable code and/or the hanger manufacturer's recommendations all must be reviewed. 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. Rigid couplings, on the other hand, can be hung or 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; then the system is hung or supported accordingly.

Pressure point
System pressurization should also be reviewed when choosing the proper hanging or support method. As the couplings are installed, the pipe ends can either be butted up tight against 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" at each coupling, whereas the joint at a rigid grooved coupling can grow about 3/32". If there is a long run of horizontal or vertical pipe with multiple joints, the overall length of the system will grow, depending upon 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.

As you can see, this growth due to pressurization can have a significant impact on the hangers or supports used on a project. One way to avoid this growth is to install the grooved joints at full gap so that pressurization has no impact at testing or startup. 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.

Hot and cold
Thermal expansion is another important consideration when choosing hangers or supports for a grooved system. This is especially important on hot systems, since the amount of thermal expansion will be greater on hot systems than on chilled systems. This is due to the temperature variation from ambient conditions when the pipe is installed to operating conditions.

For example, again suppose you have 400 ft. of grooved piping. Let us assume that the system is heating hot water that will operate at 170 F. The pipe is installed under ambient conditions, assumed to be at 70 F, so you have a 100 F variation in temperature. At 70 F, the pipe has a coefficient of thermal expansion of 0.0 in/ft, but at 170 F the pipe has a coefficient of thermal expansion of 0.0076 in/ft. To determine the total thermal expansion of the pipe from ambient temperature to operating temperature, multiply the length of pipe by the coefficient of thermal expansion. In this case 400 ft. x 0.0076 in/ft. = 3.04 in. In other words, the pipe has grown more than 3 inches in length 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 if 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 to 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 can cause the trapeze to possibly twist and fail, 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 upon how it is anchored. Vertical pipe thermally expands the same amount as horizontal pipe; 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 provide support. If the growth is downward, the friction clamps resting on the penetration or supporting structure may 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; 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 or supports that are used. In the previous examples, pressurization expansion on the 400-ft. run of pipe was 4.75" for a flexible joint system and 1.78" for a rigid joint system, and the thermal expansion was 3.04". Adding these combinations together would result in a total pipe growth of 7.79" for a flexible system or 4.82" 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 and supports and the resulting stresses induced on grooved joints.

Consider some restraint
Although grooved systems in seismic zones perform extremely well, consideration should be given to how a grooved system is seismically restrained. If you have growth due to pressurization and/or thermal expansion, consideration should be given as to how to restrain the system, while still allowing growth to 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 after a change in direction at the end of a long run of pipe, the expansion of the long pipe run may be restricted; this could induce excessive stress into the grooved joints.

By reviewing the couplings to be used on a project, pressurization, thermal expansion and seismic restraints, one can best determine the proper selection and application of hangers and supports for a grooved piping system. This will, in turn, help ensure that grooved piping systems will continue to enjoy a solid reputation in the areas of maintenance and downtime.

This article was compiled from information provided by Anvil International.