Regarding 107 & 297 Use:
For cylinder-to-cylinder intersections WRC 107 does not include the thickness of the nozzle in the calculation, the stress in the nozzle, or the fact that there is an opening in the shell. WRC 297 was written in part to improve upon these assumptions in 1984. When the t/T ratio is less than 1, for example, the high stress due to external loadings can move into the nozzle and WRC 107 can completely miss this stress. For certain geometries, however, WRC 297 tends to overestimate the nozzle stress by at least two times while still calculating a stress in the vessel such that it is approximately equal to the value from WRC 107. Often of more concern is the flexibility which WRC 297 provides. Since the stiffness curves 59 and 60 often require extrapolation, and guidelines for this extrapolation are not given, values of an order of magnitude on the low side can be obtained if care is not exercised. Large changes in stiffness can produce similar changes in forces, moments and stresses, and seldom do we want calculated stresses to be in error by an order of magnitude. High stiffnesses are generally considered conservative, although in systems where stiffnesses are coupled in parallel, conservative stiffnesses will increase loads in one branch while reducing it in the other, (and vice versa for low stiffnesses). In general, our goal is to try and estimate the stiffness as accurately as possible when it's magnitude is within some number of orders of magnitude of the piping stiffness. Our experience is that users should be more cautious when using WRC 297 as the vessel parameter, often called "lambda" is increased, where "lambda" is equal to (d/D)(D/T)^1/2. We would not venture to provide any hard rules, except to say that a value of lambda of one is small, and ten is big.
Regards,
A.Paulin
PRG-Houston
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=EVbTMLBf-oUL1lidohQxLBJ1ThQnTQcx7SZxdst3dp0dcbYVGhF91Uf90eQYCI1CdamrJb2oLTeQ2Ue2UvCFKA74f9UW">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=EVbTMLBf-oUL1lidohQxLBJ1ThQnTQcx7SZxdst3dp0dcbYVGhF91Uf90eQYCI1CdamrJb2oLTeQ2Ue2UvCFKA74f9UW">PipingDesign@yahoogroups.com</a>] On
Behalf Of Christopher Wright
Sent: Tuesday, December 06, 2005 3:40 PM
To: <a href="/group/PipingDesign/post?postID=EVbTMLBf-oUL1lidohQxLBJ1ThQnTQcx7SZxdst3dp0dcbYVGhF91Uf90eQYCI1CdamrJb2oLTeQ2Ue2UvCFKA74f9UW">PipingDesign@yahoogroups.com</a>
Subject: Re: [PipingDesign] Preliminary Nozzle Loads
On Dec 6, 2005, at 10:40 AM, Ken Nisly-Nagele wrote:
> I am thinking that using a WRC
> program to generate some allowable loads for vessels in the range of
> the
> project scope may be the best approach for now.
You can automate that to a degree with a spreadsheet. It'll help a
little--It'll help if you use the more up to date revs of the original
work. WRC-107 has been updated recently and WRC-297 is also more
current. Check <http://www.forengineers.org/index.html>
Christopher Wright P.E. |"They couldn't hit an elephant at
<a href="/group/PipingDesign/post?postID=z8CU1PeCzfBOkVRdeutSpTVRQhVTUAPe1VY0gI5hqmYVfRnWLSTBeJ5115YWt0GU-5v-GrFQZrztpg">chrisw@skypoint.com</a> | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania1864)
Yahoo! Groups Links Received on Tue Dec 06 17:19:00 2005
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