Need Clarification on Kellogg Design of Piping Systems, Pipe Span Design - Chart C-18

[alegna]

Hello,

I am wondering if any one can clarify Chart C-18 (page 358) in the MW Kellogg Design of Piping Systems book?

I don't understand the case scenarios and how the maximum moment and maximum deflection formulas are arrived at.
Especially the difference between case 1 and 2.. they have the same max moment, but different deflection?

I am assuming that F_s and F_delta are strictly for the use of Charts C-16 and C-17?

Thanks!

 

[JdeJong]

Hi Alegna

I'm just looking through the Kellogg book. The difference between the first 3 cases is that different end conditions are being represented. Case 3 is a fully pinned end while case 1 and 2 are pinned ends with slight moments acting against the deflection of the span at each end of the span (this moment is developed from the pipe spans on the other side of the pinned end). The reason that all 3 cases are shown is that all 3 cases are simplifications of the actual deflections and stresses in a piping system under uniform weight. Case 3 is the most conservative case (as allowable spans for larger lines are generally deflection rather than stress limited).

Kannappan discusses this in an easily understandable format in chapter 3 of his book Piping Stress Analysis.

Hope this helps.
Jono

 

[alegna]

Thanks for the clarification Jono.
So is the main difference between case 1 and 2 is the amount of moment applied? how do I know when you use case 1, and case 2?

 

[JdeJong]

Hi

I don't come on this website very often so sorry for the slow reply.

As I understand it, yes. And the applied moment comes from piping on either sides of the supports (not shown in the picture).

As to choosing case 1 or 2. The information contained in this is better taken from your company standards which will give you further information on allowable overhangs for specific configurations.. The longer span is maybe applicable to racks where there is a straight run of pipe which are regularly supported.

But find a copy of Kanappan's book if you want to understand the background - he explains it well.