ASME B31J:2008 pdf download Standard Test Method for Determining Stress Intensification Factors (i-Factors) for Metallic Piping Components ASME Code for Pressure Piping, B31
(b) Paragraph 3.2. Markl’s tests specimens wereASTM A 106 Grade B material, or equivalent in the caseof forgings, castings,and plate.Use of different materialsrequires a new C constant to be developed , since materi-als such as copper,aluminum,or very high-strengthsteels exhibit different fatigue life from plain carbonsteel. The intent of the test is to develop an SIF that isgeometry dependent, not material dependent.
Identifying nominal dimensions and wall thicknessesis important, particularly in the case of branch connec-tions, to ensure extrapolation of results to other sizes isdone correctly. The importance of the weld profile isclearly shown in reference [6].
(c) Paragraph 3.3. Markl’s tests were based on lin-ear elastic equivalent moments, i.e., a constant displace-ment or rotation was applied and the moment at thefailure location was based on extrapolation of the M-0(or F-8)elastic curve. This allows agreement with theway linear elastic thermal expansion analyses are used,even though predicted stresses may be above yield.
(d) Paragraph 3.4.The use of a nominal pressureis to ensure a ready means of detecting a through-wallcrack.The use of 500 cycles as a minimum is to ensurecorrelation with the lower bounds of Markl’s work. Fromreference [4], it can be seen that the preponderance oftests lie above 1,000 cycles. The few that fall below showa fair amount of scatter off the proposed straight line.Until more work is done in the very low cycle range,the lower limit of 500 will remain.
(2) Section 4
(a)Paragraph 4.1.If forces are being applied, it isimportant to measure the distance from the point ofapplication to the point of failure in order to determinethe appropriate equivalent moment.
b) Paragraph 4.2.The section modulus is used inpiping analysis to convert the calculated moments tostresses.Thus, it is important that the section modulusused to calculate the stress in the test agrees with thatto be used in the analysis (and described in the Code).
(c)Paragraph 4.3.The equation in para. 4.3 istaken directly from the work by Markl [e.g., reference[4], eq. (4)]. Since Markl’s tests formed the basis of thecurrent i-factors and Code rules, use of Markl’s equationis appropriate for correlation.
(d) Paragraph 4.4.The factor for the number oftests is to provide for uncertainty.The basis for the fac-tors is engineering judgment.The basis is a reasonableestimate when compared to ASME BPVC,Section III,Appendix II, II-1520(f) for the statistical variation in testresults
Kss = 1.47 -0.044 x number of replicate tests
While Kss would produce slightly higher factors,thoseprovided in para. 4.4 are deemed acceptable based onthe scatter in Markl’s original testing-
(e)Paragraph 4.6.The equation for variable ampli-tude tests is the same basic equation as was incorporatedin ANSI B31.1-1955 and is still used by the piping Codesto convert different operating condition stress ranges,typically thermal stress ranges, to a single base stressrange.
3) Section 5
(a) Paragraph 5.1.Based on the work in “ThermalFatigue and Thermal Stress” by Manson,the materialexponent, n, for metals stays fairly constant at 0.2, andhas been set to that value in the Standard. Based onwork done by w. Koves, the material constant, C, canbe found from a ratio of the moduli of elasticity, i.e.,
C(other material) = 245,000 E(other materiall) /
E(carbon steel = 27.8E6 psi)
(b) Paragraph 5.2.Dimensional extrapolationsneed to be justified based on either elastic-stress theoryor tests of additional sizes. Elastic theory was the basisof Markl’s extrapolation work in elbows and straightpipe. It is important that extrapolation be justified.
(4)Section 6. The reason for the test report is toassure owners that the testing was carried out in compli-ance with B31J. Since the test report must also describeany weld profiles, the owner can also ensure that suchprofiles / procedures are incorporated into the weldingprogram for the installation.The basis for the i-factormust be able to be reviewed by the owner or his agent.
A-2 REFERENCES
[1] WRC Bulletin 392,”Standardized Method forDeveloping Stress Intensification Factors for PipingComponents,” E.C. Rodabaugh, June 1994.
[2]Markl, A. R.C.,”Fatigue Tests of Welding Elbowsand Comparable Double-Mitre Bends,”Trans. ASME,Volume 69,869-879 (1947).
[3]Markl,A.R.C. and George, H.H.,”Fatigue Testson Flanged Assemblies,”Trans.ASME,Volume 72,77-87 (1950).
[4]Markl，A.R.C.,”Fatigue Test of Piping Compo-nents,” Trans. ASME,Volume 74,287-303 (1952).
[5]Markl,A.R.C.,”Piping-Flexibility Analysis,”Trans. ASME, Volume 77 , 127-i49(1955).
[6] WRC Bulletin 392, “Effects of Weld Metal Profileon the Fatigue Life on Integrally Reinforced Weld-OnFittings,”G.E. Woods and E.C. Rodabaugh, June 1994.[7]WRC Bulletin 329,” Accuracy of Stress Intensifica-tion Factors for Branch Connections,”E.C. Rodabaugh,December 1987.
ASME B31J:2008 pdf download
