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ASME B31.3-2016 <br /> conditions. The melting point of brazing alloys shall be (b) reaction forces computed in para. 319.5 shall not <br /> considered where possible exposure to fire is involved. be detrimental to supports or connected equipment <br /> (b) Fillet joints made with brazing filler metal are not (c) computed movement of the piping shall be within <br /> permitted. any prescribed limits,and properly accounted for in the <br /> flexibility calculations <br /> 318 SPECIAL JOINTS If it is determined that a piping system does not have <br /> adequate inherent flexibility,means for increasing flexi- <br /> bility shall be provided in accordance with para. 319.7. <br /> Chapter II, Part 4, such as bell type and packed gland <br /> type joints. 319.2 Concepts <br /> 318.1 General Concepts characteristic of piping flexibility analysis <br /> 318.1.1 Listed Joints. Joints using listed compo- are covered in the following paragraphs.Special consid- <br /> nents are suitable for Normal Fluid Service. eration is given to displacements (strains)in the piping <br /> 318.1.2 Unlisted Joints. For joints that utilize system, and to resultant axial, bending, and torsional <br /> unlisted components,pressure design shall be qualified displacement stress ranges. <br /> as required by para. 304.7.2. 319.2.1 Displacement Strains <br /> 318.2 Specific Requirements (a) Thermal Displacements. A piping system will <br /> undergo dimensional changes with any change in tem- <br /> 318.2.1 Joint Integrity. Separation of the joint shall perature.If it is constrained from free expansion or con- <br /> be prevented by a means that has sufficient strength to traction by connected equipment and restraints such <br /> withstand anticipated conditions of service. as guides and anchors, it will be displaced from its <br /> 318.2.2 Joint Interlocks. Either mechanical or unrestrained position. <br /> welded interlocks shall be provided to prevent separa- (b) Restraint Flexibility. If restraints are not considered <br /> tion of any joint used for a fluid service that is flammable, rigid,their flexibility may be considered in determining <br /> toxic, or damaging to human tissues, of any joint to be displacement stress range and reactions. <br /> used under severe cyclic conditions, and of any joint (c) Externally Imposed Displacements. Externally <br /> exposed to temperatures in the creep range. caused movement of restraints will impose displace- <br /> 318.2.3 Bell and Gland Type Joints. If not covered ments on the piping in addition to those related to ther- <br /> in para. 316,bell type and gland type joints used under mal effects. Movements may result from tidal changes <br /> severe cyclic conditions require safeguarding. (dock piping),wind sway(e.g.,piping supported from a <br /> tall slender tower),or temperature changes in connected <br /> PART 5 equipment. <br /> FLEXIBILITY AND SUPPORT Movement due to earth settlement,since it is a single <br /> cycle effect,will not significantly influence fatigue life. <br /> 319 PIPING FLEXIBILITY A displacement stress range greater than that permitted <br /> 319.1 Requirements by para.302.3.5(d)maybe allowable if due consideration <br /> 319.1.1 Basic Requirements. Piping systems shall is given to avoidance of excessive localized strain and <br /> have sufficient flexibility to prevent thermal expansion end reactions. <br /> or contraction or movements of piping supports and (d) Total Displacement Strains. Thermal displace- <br /> terminals from causing ments,reaction displacements, and externally imposed <br /> (a) failure of piping or supports from overstress or displacements all have equivalent effects on the piping <br /> fatigue system,and shall be considered together in determining <br /> (b) leakage at joints the total displacement strains (proportional deforma- <br /> (c) detrimental stresses or distortion in piping and tion) in various parts of the piping system. <br /> valves or in connected equipment(pumps and turbines, 319.2.2 Displacement Stresses <br /> for example), resulting from excessive thrusts and (a) Elastic Behavior. Stresses may be considered pro- <br /> moments in the piping portional to the total displacement strains in a piping <br /> 319.1.2 Specific Requirements. In para. 319, con- system in which the strains are well-distributed and not <br /> cepts, data,and methods are given for determining the excessive at any point (a balanced system). Layout of <br /> requirements for flexibility in a piping system and for systems should aim for such a condition, which is <br /> assuring that the system meets all of these requirements. assumed in flexibility analysis methods provided in this <br /> In brief, these requirements are that Code. <br /> (a) the computed stress range at any point due to (b) Overstrained Behavior. Stresses cannot be consid- <br /> displacements in the system shall not exceed the allow- ered proportional to displacement strains throughout a <br /> able stress range established in para. 302.3.5 piping system in which an excessive amount of strain <br />