Thermal Expansion and Contraction
Thermal expansion must be designed and installed to compensate for movement as a result of thermal expansion and contraction. This is particularly true for above ground applications installed outdoors and within unoccupied buildings where ambient temperature swings can be significant. For example, a system installed in an unoccupied (i.e. un-heated) building during the winter months will expand considerably when temperatures rise. The direct opposite is true for systems installed at higher ambient temperatures may fall considerably after installation. This fact must be addressed with proper system designed to compensate for movement generated as the result of the effects of thermal expansion and/or contraction of the piping. Click here
for more information on thermal contraction and expansion information.
PVC and CPVC piping products have been used successfully in outdoor applications when proper recommendations are followed. As with any other piping, the system must be protected from freezing in applications subject to colder temperatures. Many standard cold weather piping design and installation practices can be used to protect the system from freezing such as use of pipe insulation, antifreeze solutions, and heat tracing tapes. The manufacturers of these products should be consulted for suitability and compatibility of their use with PVC and CPVC products prior to use.
Harvel recommends that PVC and CPVC piping products exposed to the effects of sunlight (UV radiation) be painted with light colored acrylic or latex paint that is chemically compatible with the PVC/CPVC products. Compatibility information should be confirmed with the paint manufacturer. The use of oil – based paints is not recommended. When painted the effects of exposure to sunlight are significantly reduced, however, consideration should be given to the effects of expansion/contraction of the system caused by heat absorption in outdoors applications, The use of a light colored, reflective paint coating will reduce this effect, however, the system must also be designed and installed in such a manner to reduce the effects of movement due to thermal expansion.
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 dependant on pipe size, the locations 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. 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 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 and 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 horizontal 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 generate by the effects of expansion or contraction.
Vertical lines must be supported properly at intervals that will prevent excessive loading on the fitting at the lower end. 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. Clamps and hangers used must not compress, distort, cut, or abrade the piping. Common practice is to install clamps just below a 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. Then two ends are then solvent cemented to the pipe at the proper location so that the shoulder of the modified coupling rests on the clamp. Clamps used must not exert compressive stresses on the pipe; the use of riser clamps that utilize compression to the support the pipe weight are not recommended.
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.
The information contained in this article is for general information purposes only. The information is provided by
United States Plastic Corp. and while we endeavor to keep the information up to date and correct, we make no representations or
warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with
respect to the website or the information, products, services, or related graphics contained on the website for any purpose.
Any reliance you place on such information is therefore strictly at your own risk.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss
or damage, or any loss or damage whatsoever arising from loss of materials, time or profits arising out of,
or in connection with, the use of this information.