Hangers & Supports
Hanger Support Spacing
Proper support selection and spacing is critical to prevent stress concentration areas as the result of weight loading, bending stress, the effects of thermal expansion/contraction, and to limit pipe displacement (sag). As with all thermoplastic materials,proper pipe support spacing is dependent on pipe size, the location and magnitude of any concentrated weight loads, and the operating temperatures of the system due to the effects that temperature has on the tensile and compressive strength of the material. Increases in temperature require additional supports. Piping should not be exposed to excessive heat producing sources such as light fixtures, ballasts and steam lines that could negatively affect its tensile strength. When operating at or near maximum recommended temperature limits, it may be more economical to provide continuous support for the system via structural angle or channel that is free from rough or sharp edges. Local building codes should also be consulted for applicable requirements prior to installation. Proper support spacing can be calculated similarly to that of metallic systems by using simple and continuous beam calculations. This can be achieved using the maximum fiber stress of the material, or deflection based on the long-term modulus of the material at the temperature selected as the limiting factors.
Many hangers designed for metallic pipe are suitable for thermoplastics; however, hangers and supports used must provide an adequate load-bearing surface,which is smooth and free of rough or sharp edges that could damage the pipe. The use of improper supports can generate excessive sag resulting in failure. Movement caused by the effects of thermal expansion and contraction of the system due to temperature variations, as well as movement as the result of pressure fluctuations must be considered to ensure proper hanger selection and placement. Hangers and supports used must permit axial movement of the system; they should not compress the pipe or otherwise restrict this movement.
Common practice is to install suitable hangers within two feet (2 ft) of each side of a pipe joint; changes in direction should be supported as close as possible to the fitting to reduce tensional stress. Heavy system components such as valves, flanged assemblies, tees and other forms of concentrated stress loads must be independently supported. In addition, valves should be braced adequately to prevent movement/stress loads as the result of operational torque. Consideration should also be given for certain processes where solids accumulation within the line is a possibility.
The use of protective sleeves or pads between the pipe and the hanger may be desirable in certain applications, as their use will distribute stress loads over a greater surface area, particularly when using U-bolt or roller type hangers. Piping should not be permitted to contact abrasive surfaces that could cause damage during axial movement of the system. Protective sleeves or pads should be used when pipe is resting on concrete or other abrasive support structures. Contact with localized heat producing sources must also be avoided. Plastic piping systems shall not be installed in close proximity to steam lines or other high temperature equipment without providing appropriate protection to prevent damage from distortion and/or forces generated by the effects of thermal expansion or contraction.
Vertical lines (risers) must be supported properly at intervals that will prevent excessive loading on the fitting at the lower end of the riser (or other stress concentration areas). Hangers and clamps suitable for this purpose include riser clamps or double bolt type clamps installed in such a manner that will allow for movement of the pipe due to thermal expansion and contraction (i.e. floating system). Clamps and hangers used must not compress, distort, cut, or abrade the piping. Clamps used must not exert compressive stresses on the pipe; the use of riser clamps that utilize compression to support the pipe weight are not recommended. If possible, the riser clamps should be located just below a fitting so that the shoulder of the fitting rests against the clamp to support the weight of the vertical column. Horizontal take- offs from the riser should be independently supported, and located as close to the riser clamp as possible. Offset configurations utilizing at least one change in direction should be used to tie horizontal runs into the riser in close proximity to the riser clamp. Offset configurations used between the riser tee and the wall entry will minimize stress on the horizontal connection should movement of the riser occur. The use of a single horizontal run from the riser tee through the wall should not be used on systems conveying fluids at elevated temperatures (i.e.CPVC hot water lines).
Thermal Expansion of Vertical Risers: Compared to horizontal runs, the affects of thermal expansion on fluid filled vertical risers is typically minimized due to the weight of the fluid column, in combination with the restraint provided at horizontal take-offs. The rate of thermal expansion must be calculated based on the temperature change anticipated. Refer to Thermal Expansion and Contraction section for additional information. Vertical piping should be maintained in straight alignment with supports at proper intervals plus a mid story guide,as specified by the design engineer, to allow for movement caused by thermal expansion and contraction of the piping. Mid story guides should always be used on small diameter pipe (≤2" diameter), particularly on CPVC hot water lines, to minimize deflection caused by thermal expansion. The guidelines provided herein for vertical risers do not apply to horizontal runs. For horizontal runs, the use of expansion loops, offsets, bends, and other means are recommended to compensate for movement due to changes in temperature. Refer to Thermal Expansion and Contraction section for additional information. Contact GF Harvel Technical Services for additional information if necessary.
For vertical risers requiring support where horizontal take-offs may not be present; one common approach is to install clamps just below a modified coupling so that the shoulder of the coupling rests on the clamp. Fittings can be modified in the field to achieve this by cutting a coupling in two, just above the stop at the socket bottom, and then cutting this piece in half lengthwise to provide two halves which do not contain the stop. The two halves are then solvent cemented to the pipe at the proper location, so that the shoulder of the modified coupling rests on the clamp once the joint is allowed to cure properly. Note: A modified coupling must only be used to provide support to the riser, and must not be used to join two pieces of pipe. The load bearing strength of a modified coupling used for riser support is directly related to the surface area of the coupling and the integrity of the solvent weld (Lap Shear strength).
Anchors and Guides
Anchors are utilized to direct movement of the piping by providing restraint at key points in the system. Their use may be required to control the effects of movement caused by expansion and contraction, forces generated by pressure surges, vibration, and other transient conditions. Anchors and guides are typically installed on long straight runs, at changes in direction of the system, and where expansion joints and other methods of thermal compensation are utilized. Guides are necessary to help direct this movement between anchors by allowing longitudinal movement while restricting lateral movement. Since guides act as supports, they should have the same load bearing surface and other requirements of hangers designed for the system. Guides must be rigidly attached to the structure to prevent lateral movement, but should not restrict longitudinal movement of the pipe through the guide. Anchors and guides must be engineered and installed in such a manor to perform adequately without point loading the system. Reference should be made to the section concerning Thermal expansion and contraction for additional information.
Hanger Support Recommendations
Horizontal pipe system support spacing is greatly influenced by operating temperature. The charts show the recommended support spacing according to size, schedule, and operating temperatures. Do not clamp supports tightly — this restricts axial movement of the pipe. If short spacing is necessary, continuous supports may be more economical. Charts are based on liquids up to 1.00 specific gravity, but do not include concentrated loads, nor do they include allowance for aggressive reagents.
The following hanger support spacing recommendations are considered conservative in nature and are based on straight runs of un-insulated lines with fluids being conveyed that have a specific gravity of 1.00 or less. These values do not consider concentrated weight loads or aggressive reagents.