Re: Unsustained Loading -Flange Pressure Rating

From: <Christopher>
Date: Wed Aug 17 2005 - 11:57:00 EDT

On Aug 16, 2005, at 5:12 PM, Geoff Stone DD&D Australia wrote:

> I would be interested to know how many people actually do surge
> analysis on process plants?

I'm sure this depends on the designer and the particular plant, so 'common practice' varies all over the map. I think it'd be very unwise to assume that your situation allows you to ignore something just because someone else ignores it. If surging is an occasional load, probably some offices ignore it if they haven't had trouble in the past. I expect a lot of offices make it a practice to specify higher pressure flanges anyway just in case. If I were doing any sort of extraordinary load for the first time, I'd look into it, do the numbers and satisfy myself that something wasn't slipping through the cracks. At the very least I'd do a Google search to see if there are any references in the literature. The number of references usually varies directly with the importance of the problem.

This is one of those judgment calls covered in the pressure vessel codes by U-2(g). The designer is responsible for addressing all significant loading regardless of whether there's a specific Code routine to handle it. A lot of people take the approach that if it's not spelled out, it isn't important--that's a recipe for disaster, if someone doesn't know his business. ANSI flanges usually have a pretty good margin built into the design that's obvious if you do the Code numbers, so you'll ordinarily not get into much flange trouble, beyond leakage, unless they're grossly overloaded, but flanges do fail. And even a small leak in a line carrying a lethal substance is more significant than a complete failure of a low pressure chilled water line.
Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=Cqx9Lu11Y6yAIvyQh5Gn2fPrXFLbqRjoWDkQNGM4smx2vS6tN0VRC9HBSC4yZ1ad2dSBJsDs-DvmliOwg5c">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 Wed Aug 17 11:57:00 2005