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The ASME 07-02 project was awarded to Tony Paulin of Paulin Research Group (the original author of CAESAR II® and developer of NozzlePRO™, FE/Pipe™ and PCL-Gold™)
This session will review the study results regarding the tee model that will, eventually, be included in B31J and then referenced by the B31 codes.
Late 40’s: A.R.C. Markl of Tube Turns leads the effort to develop geometry-based multipliers for component flexibility and stress “Fatigue Tests of Piping Components” –
Trans. ASME, Vol. 74, 1952, pp. 287-303
Limited number of tests on 4” size on size tees
1981: R.W. Schneider (formerly of BonneyForge) notifies ASME of the unconservative SIF for reduced outlet tees
WRC 329 Identifies Several Problems with Existing Codes
Welding Research Council Bulletin 329 –Accuracy of Stress Intensification Factors for Branch Connections by E.C. Rodabaugh p.9 “… using i = 1.0 for Mt on full size outlet branch connections
can lead to inaccuracies far greater than the Mob inconsistency.”
p.12 “We would rate the relative complexity of i-factors for pipe, elbows and branch connections by the ratios of 1:5:500. … [readers] will not find any simple answers in this report.”
p.13 “Extruded outlets are somewhat related to ANSI B16.9 tees in that extruded outlets, like B16.9 tees, may vary significantly between manufacturers.”
WRC 329 Identifies Several Problems with Existing Codes
p.21 “[B31.3 itb=1] may be nonconservative by a factor of 2.7 … and may be nonconservative by a factor of 12 or more.”
p. 22 “For run moments on branch connections with small r/R, both intuition and Ref. 26 data indicate that the B31.3 relationship ii = 0.75io + 0.25 is at best, reversed in relative magnitude of iir and ior, … and in effect, [the] Code requirements are obviously silly.”
p.28 “The Mob tests indicate that there is a peak somewhere around 0.75.” [d/D=0.75]
p.29 “.. we do not necessarily achieve greater accuracy in Code evaluations by using more accurate i-factors unless more accurate k-factors are also used.”
WRC 329 Identifies Several Problems with Existing Codes
p.32-33 “… delete the use of ii = 0.75io + 0.25 for branch connections/tees, … [it] gives the wrong relative magnitude for Mor versus Mir, [and] it underestimates the difference between Mob and Mib for r/R between about 0.3 and 0.95 and perhaps over-estimates the difference for r/R below 0.2 and for r/R = 1.0.”
p.33 “For branch connections with r2 (outer fillet radius) provided, use iib/2.”
p.37 “[limits on the inside radius of the branch connection are] dropped because moment fatigue tests and theory indicate that the inside corner radius is not a critical consideration.” … for external loads (not pressure)
Once you have an estimate for the flexibility factors (k-factor), you don’t even have to use them in an analysis, just decide as a designer if that many extra diameters of pipe will affect the solution:
Is 131 inches of “flexibility length” going to change the loads on the pump nozzle at 40? Yes
With current tee flexibilities (=1), there is no difference between an unreinforced fabricated tee and a pad reinforced fabricated tee. But wouldn’t you expect the padded tee to be stiffer?
Rodabaugh in 1987 gave the following Example in WRC 329 Fig. 15:
Without considering the branch connection flexibility of the 12x30” fabricated tee at point 15 the out-of-plane (Z) bending moment at point 15 is 372,000 in.lb. Including the branch connection flexibility reduces the bending moment to 41,832 in.lb., a reduction of 8.8. (880%)
A more complicated (3 anchor) system – Heater Piping• When flexibility is added at one
location, displacement in the vicinity of that intersection increases and moments are redistributed in the piping system causing some loads to go up while others go down
Run in-plane bending k=2.8439, stiffness applied (between 20-21 & 20-22) = 2K*(pi/180);K=(EI)/(k*D-mean)= 8.528E8 in-lbf2K*(pi/180)=2.977E7 in-lbf/degree == this is RY between 20-21(the conversion of flexibility factor to stiffness is specified in ASME 07-02 Appendix D)
Node 22 is not on a tee so no component plane is defined. With 22-41 in Z, CAESAR II will set the plane in Y-Z. So SIF(o), here, is in Y and that is the tee’s in-plane direction.