Supporting of Resistoflex Plastic-Lined Piping Products A contributing factor for leaks in plastic-lined piping is excessive loading at flange connections due to improper piping support. To prevent such loading, Resistoflex recommends that a stress analysis be performed that includes all potential sources of loading on the piping system. The maximum calculated Bending Stress due to Dead Loads should not exceed the Design Allowable Stress. The Design Allowable Stress, due to pressure, weight and other sustained loading is determined by dividing the Basic Hot Allowable Stress (Sh) for the metal pipe by an appropriate Safety Factor (FS). For example, a value of 10,000 psi is obtained for A53 steel pipe when a Safety Factor of 2 is applied to the Basic Hot Allowable Stress value of 20,000 psi as listed in ASME B31.3. Similarly, a value of 8,750 psi is obtained for Swaged plastic-lined steel pipe when applying the same Safety Factor of 2 to a calculated Basic Hot Allowable Stress of 17,500 psi for the swaged A 513, C1010 Aluminum Killed Steel housing. Displacement stresses due to thermal expansion should also be limited to these same Design Allowable Stress values. However, when calculating piping spans using accepted engineering practices, the magnitude of pipe deflection is generally the limiting factor in determining span distance. An industry accepted practice is to limit pipe deflection to no more than 1/4 of an inch. Initially, pipe hangers should be positioned such that the piping does not exceed the Design Allowable Stress and the desired pipe deflection. Usually, hangers are located near each flange but not so close as to interfere with the pipe installation. Added support is also recommended where flow changes direction, and in areas of high load concentration, such as clusters of valves or fittings. Additional support and dampening is recommended where vibration can occur. The reason that we recommend having support at or near the flanges on conventional plastic-lined piping is that if the piping is not properly supported, one could overstress the flared or molded PTFE plastic sealing surface and hence cause a leak. Gasket stresses exceeding 5,000 psi for PTFE, 6500 psi for PP and 8,000 psi for PVDF, should be avoided. These are best avoided by support at or near flange, fitting and or valve concentrations located in the pipe run. Support spans for flanged piping are generally determined from accepted engineering formulas for single pipe spans with free ends. However, the Resistoflex Conquest piping can be treated as welded piping and thus the more liberal continuous support formulas can be applied. The required span distance is then determined by the lesser of either the maximum calculated Bending Stress due to Dead Loads not exceeding the Design Allowable Stress or the pipe Deflection not exceeding the desired value. An important part of supporting plastic lined piping is that the supports should allow the pipe to move freely in response to thermal expansion and contractions. The Manufacturers Standardization Society (MSS) specifications MSS SP 58 and 69 provide good references for supports and hangers for certain applications. Additional information is also listed in Chapter B5 of the McGraw Hill Piping Handbook, Seventh Edition, edited by Mohinder Nayyar.