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ASME B31.3-2016 <br /> Fig. 302.3.5 Stress Range Factor,f <br /> 1.2 <br /> 1.1 , <br /> 1.0 <br /> 0.9 <br /> 0.8 <br /> 0.7 <br /> 0.6 <br /> 0.5 <br /> 0.4 <br /> 0.3 <br /> 0.2 <br /> 0.1 <br /> 0.0 <br /> 103 104 105 106 107 108 109 <br /> N(cycles) <br /> ----- Ferrous materials,specified minimum tensile strength ---517 MPa(75 ksi), <br /> and at design metal temperatures 371T(700T) <br /> All other materials <br /> temperature of the operating condition being fm = maximum value of stress range factor; 1.2 for <br /> considered. ferrous materials with specified minimum ten- <br /> (d) Allowable Displacement Stress Range,SA. The com- site strengths <- 517 MPa (75 ksi) and at metal <br /> puted displacement stress range,SE,in a piping system temperatures <- 371°C (700°F); otherwise <br /> (see para. 319.4.4) shall not exceed the allowable dis- f„' = 1.0 <br /> placement stress range, SA (see paras. 319.2.3 and N = equivalent number of full displacement cycles <br /> 319.3.4), calculated by eq. (1a) during the expected service life of the piping <br /> SA =f(1.25Sc+0.25Sh) (1a) systems <br /> Sc = basic allowable stress b at minimum metal tem- <br /> When Sh is greater than SE, the difference between perature expected during the displacement <br /> them may be added to the term 0.25Sh in eq. (1a). In cycle under analysis <br /> that case, the allowable stress range is calculated by = 138 MPa (20 ksi) maximum <br /> eq. (1b) Sh = basic allowable stress 6at maximum metal tem- <br /> perature expected during the displacement <br /> SA =f[1.25(Sc+Sh) -SE] (1b) cycle under analysis <br /> = 138 MPa (20 ksi) maximum <br /> For eqs. (1a) and (1b) SE = stress due to sustained loads;in systems where <br /> f = stress range factor,3 calculated by eq. (1c)4 supports may be active in some conditions and <br /> inactive in others, the maximum value of sus- <br /> f(see Fig. 302.3.5) = 6.0(N)-0.2 5 fm (1c) tained stress, considering all support condi- <br /> tions, shall be used <br /> Applies to essentially noncorroded piping. Corrosion can <br /> sharply decrease cyclic life;therefore,corrosion resistant materials 5 The designer is cautioned that the fatigue life of materials oper- <br /> should be considered where a large number of major stress cycles ated at elevated temperature may be reduced. <br /> is anticipated. 6 For castings, the basic allowable stress shall be multiplied by <br /> 4 The minimum value for f is 0.15,which results in an allowable the applicable casting quality factor, E, For longitudinal welds, <br /> displacement stress range, SA, for an indefinitely large number the basic allowable stress need not be multiplied by the weld <br /> of cycles. quality factor,Ep <br />