Re: SIF on elbow weldolet

From: <Christopher>
Date: Tue Mar 30 2004 - 16:59:00 EST

>User's of pipe stress programs can also enter
>SIF's of
>their own, which are applied after the solution. They really don't affect
>the element formulation, (although this may just be a matter of symantics).
I wasn't clear--The stress increases don't affect formulation; the stiffness corrections do.

>This is often true too, but in the olet case, the olet serves as a localized
>stiffener, and depending on the d/D ratio, can influence the high stress on
>the side of the bend due to ovalization.
Right. That imposes the additional problem of mixing primary and peak stresses. Without actually knowing I presumed the post addressed the usual classical piping strss analysis with pipes idealized as beams and SIF's incorporated to address departures fom the usual Mc/I and P/A stress, but ignoring peak stress--as customary in ordinary piping stress analysis where allowables and construction details are set to obviate fatigue analysis. The poster didn't mention fatigue calculations.

>I dont beleive that a beam element
>analysis is the right tool in this sort of situation.
Again--that depends on what y0u're doing. If you're looking at a failure analysis FEA is the only way to sort it out quantitatively. If you're doing piping design, peak stresses get in the way of the piping code methodology, which is based on uniaxial stresses. When you need to do fatigue calculation, as for nuclear piping, you may need to calculate peak stress at unusual details, but by and large, modelling a piping system explicityly is a waste of time. In that way it's like building design. People use beam elements because that's engineering practice. If only from a practical standpoint, doing a piping analysis of a chamical plant or refinery with each pipe and fitting modelled with solid elements is really overdoing it.

If the poster was looking for peak stress at the connection, you're right, but I don't think he was. I think he was looking for SIF's analogous to those associated with elbows and tee's.

>proved the efficacy
>and prediction accuracy of the tools when properly applied.
I'm not quibbling with the ability of FEA to predict test measurements. But the guy was doing a piping code job, not verifying lab results.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=n716rYsgRhb6-UGi-d_aMpFCllvlmSaFy1L1KxmThJWnaVkWi495iA_fWW0QJm5AmiTgRMopoDSb5pA">chrisw@skypoint.com</a> | this distance" (last words of Gen.

___________________________| John Sedgwick, Spotsylvania 1864)

<a href="http://www.skypoint.com/~chrisw">http://www.skypoint.com/~chrisw</a> Received on Tue Mar 30 16:59:00 2004