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ASME B31.3-2016
<br /> restraints, the maximum instantaneous values of reac- point must be calculated or estimated for proper analysis
<br /> tion forces and moments maybe estimated from eqs.(21) of the branch.
<br /> and (22).
<br /> (a) For Extreme Displacement Conditions,R,. The tem- 319.7 Means of Increasing Flexibility
<br /> perature for this computation is the maximum or mini- The layout of piping often provides inherent flexibility
<br /> mum metal temperature defined in para. 319.3.1(b), through changes in direction,so that displacements pro-
<br /> whichever produces the larger reaction. duce chiefly bending and torsional strains within pre-
<br /> scribed limits. The amount of axial tension or
<br /> Rm = R(1-g)E (21) compression strain (which produces large reactions)
<br /> usually is small.
<br /> where Where the piping lacks built-in changes of direction,
<br /> C = cold-spring factor varying from zero for no or where it is unbalanced [see para. 319.2.2(b)], large
<br /> cold spring to 1.0 for 100% cold spring. (The reactions or detrimental overstrain maybe encountered.
<br /> factor two-thirds is based on experience show-
<br /> The designer should consider adding flexibility by one ing that specified cold spring cannot be fully or more of the following means:bends,loops,or offsets;
<br /> swivel joints; corrugated pipe; expansion joints of the
<br /> assured, even with elaborate precautions.) bellows or slip-joint type; or other devices permitting
<br /> EQ reference modulus of elasticity at 21°C (70°F) angular,rotational,or axial movement.Suitable anchors,
<br /> mum metal Em = modulus l elasticity at maximum or mini- ties, or other devices shall be provided as necessary to
<br /> temperature resist end forces produced by fluid pressure, frictional
<br /> R range of reaction forces or moments (derived resistance to movement,and other causes.When expan-
<br /> from flexibility analysis) corresponding to the sion joints or other similar devices are provided, the
<br /> full displacement stress range and based on EQ stiffness of the joint or device should be considered in
<br /> R„� estimated instantaneous maximum reaction any flexibility analysis of the piping.
<br /> force or moment at maximum or minimum
<br /> metal temperature
<br /> 320 ANALYSIS OF SUSTAINED LOADS
<br /> (b) For Original Condition,RQ. The temperature for this
<br /> computation is the expected temperature at which the 320.1 Basic Assumptions and Requirements
<br /> piping is to be assembled. Sustained conditions may be evaluated by detailed
<br /> RQ = CR or C1R,whichever is greater analysis, approximate methods, or simplified means
<br /> such as span tables. When detailed analysis is per-
<br /> where nomenclature is as in para. 319.5.1(a) and formed, the stress due to sustained loads, SL, shall be
<br /> computed and combined as described in this paragraph
<br /> Ci = 1- ShEQ (22) and shall not exceed the allowable described in
<br /> SEE para.302.3.5(c).See Appendix S,Example 2 for guidance
<br /> = estimated self-spring or relaxation factor; use on loading conditions and support scenarios that result
<br /> zero if value of Ci is negative in the greatest SL for each operating condition being
<br /> RQ = estimated instantaneous reaction force or considered.The loads due to weight should be based on
<br /> moment at installation temperature the nominal thickness of all system components unless
<br /> SL = computed displacement stress range (see otherwise justified in a more rigorous analysis. Section
<br /> para. 319.4.4) moduli used to compute the stresses in this paragraph
<br /> Sh = see definition in para. 302.3.5(d) shall be based on nominal pipe dimensions less allow-
<br /> ances, i.e., the sum of mechanical (thread or groove
<br /> 319.5.2 Maximum Reactions for Complex Systems. depth), internal and external corrosion, and erosion
<br /> For multianchor piping systems and for two-anchor sys- allowances. Areas used to compute the stresses in this
<br /> tems with intermediate restraints,eqs. (21) and (22) are paragraph assume nominal pipe dimensions less allow-
<br /> not applicable. Each case must be studied to estimate ances affecting the inside diameter of the pipe,i.e.,the
<br /> location, nature, and extent of local overstrain, and its sum of mechanical and internal corrosion and erosion
<br /> effect on stress distribution and reactions. allowances. It is the responsibility of the designer to
<br /> determine sustained stress indices,IQ,h,10,and It,when
<br /> 319.E Calculation of Movements a piping component is not explicitly addressed in
<br /> Calculations of displacements and rotations at specific Appendix D, e.g., base-ells, reducing elbows, crosses,
<br /> locations may be required where clearance problems close proximity findings, etc., as well as elbows, pipe
<br /> are involved. In cases where small-size branch pipes bends, or miters other than 90 deg or supported by a
<br /> attached to stiffer run pipes are to be calculated sepa- trunnion. Sustained stress indices shall not be lower
<br /> rately,the linear and angular movements of the junction than 1.00.
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