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ASME B31.3-2016 <br /> A318.4 Flexible Elastomeric Sealed Joints may occur upon repeated thermal cycling or on pro- <br /> Flexible elastomeric seals conforming to the following longed exposure to elevated temperature. <br /> may be used in Normal Fluid Service,subject to material (b) In brittle piping(such as porcelain,glass,etc.)and <br /> limitations: some RTR and RPM piping, the materials show rigid <br /> (a) Seals for joints in thermoplastic piping shall con- behavior and develop high displacement stresses up to <br /> form to ASTM D3139. the point of sudden breakage due to overstrain. <br /> (b) Seals for joints in RTR and RPM piping shall con- A319.2.2 Displacement Stresses <br /> form to ASTM D4161. (a) Elastic Behavior. The assumption that displace- <br /> ment strains will produce proportional stress over a suf- <br /> PART 5 ficiently wide range to justify an elastic stress analysis <br /> FLEXIBILITY AND SUPPORT often is not valid for nonmetals.In brittle piping,strains <br /> A319 FLEXIBILITY OF NONMETALLIC PIPING initially will produce relatively large elastic stresses.The <br /> total displacement strain must be kept small, however, <br /> A319.1 Requirements since overstrain results in failure rather than plastic <br /> A319.1.1 Basic Requirements. Piping systems shall deformation. In thermoplastic and thermosetting resin <br /> be designed to prevent thermal expansion or contrac- piping, strains generally will produce stresses of the <br /> tion, pressure expansion, or movement of piping sup- overstrained (plastic)type,even at relatively low values <br /> ports and terminals from causing of total displacement strain. If a method of flexibility <br /> (a) failure of piping or supports from overstrain or analysis that assumes elastic behavior is selected, the <br /> fatigue designer must be able to demonstrate its validity for the <br /> (b) leakage at joints piping system under consideration, and shall establish <br /> (c) detrimental stresses or distortion in piping or in safe limits for computed stresses. <br /> connected equipment (pumps, for example), resulting (b) Overstrained Behavior. Stresses cannot be consid- <br /> ered proportional to displacement strains throughout a <br /> from excessive thrusts and moments in the piping piping system in which an excessive amount of strain <br /> A319.1.2 Specific Requirements may occur in localized portions of the piping[an unbal- <br /> (a) In para. A319, guidance, concepts, and data are anced system; see para. 319.2.2(b)] or in which elastic <br /> given to assist the designer in assuring adequate flexibil- behavior of the piping material cannot be assumed. <br /> ity in piping systems.No specific stress-limiting criteria Overstrain shall be minimized by system layout and <br /> or methods of stress analysis are presented since stress— excessive displacements shall be minimized by special <br /> strain behavior of most nonmetals differs considerably joints or expansion devices (see para. A319.7). <br /> from that of metals covered by para.319 and is less well A319.2.3 Cold Spring. Cold spring is the intentional <br /> defined for mathematical analysis. deformation of piping during assembly to produce a <br /> (b) Piping systems should be designed and laid out desired initial displacement or reaction.Cold spring may <br /> so that flexural stresses resulting from displacement due be beneficial in serving to balance the magnitude of the <br /> to expansion,contraction,and other movement are mini- reaction under initial and extreme displacement condi- <br /> mized. This concept requires special attention to sup- tions.When cold spring is properly applied,there is less <br /> ports, terminals, and other restraints, as well as to the likelihood of overstrain during initial operation.There is <br /> techniques outlined in para. A319.7. See also also less deviation from as-installed dimensions during <br /> para. A319.2.2(b). initial operation, so that hangers will not be displaced <br /> (c) Further information on design of thermoplastic as far from their original settings. No credit for cold <br /> piping can be found in PPI Technical Report TR-21. spring is permitted in stress range calculations, or in <br /> A319.2 Concepts calculating thrusts and moments. <br /> A319.2.1 Displacement Strains. The concepts of A319.3 Properties for Flexibility Analysis <br /> strain imposed by restraint of thermal expansion or con- A319.3.1 Thermal Expansion Data. Appendix C lists <br /> traction, and by external movement, described in <br /> para.319.2.1,apply in principle to nonmetals.Neverthe- coefficients of thermal expansion for several nonmetals. <br /> More precise values in some instances maybe obtainable <br /> less,the assumption that stresses throughout the piping <br /> system can be predicted from these strains because of from manufacturers of components. If these values are <br /> fully elastic behavior of the piping materials is not gener- to be used in stress analysis,the thermal displacements <br /> shall be determined as stated in para. 319.3.1. <br /> ally valid. <br /> (a) In thermoplastics and some RTR and RPM piping, A319.3.2 Modulus of Elasticity. Appendix C lists (16) <br /> displacement strains are not likely to produce immediate representative data on the tensile modulus of elasticity, <br /> failure but may result in detrimental distortion. Espe- E,for several nonmetals as obtained under typical labo- <br /> cially in thermoplastic piping,progressive deformation ratory rate of strain (loading) conditions. More precise <br />