Hi Steve, Paul
A sloped line must start at one elevation and slope consistantly to it's end (usually with a minimum slope of 1:100). You might need to slope a line to drain it based on it's commodity (ie slurry)
A "no pocket" line is permitted to climb to an elevation, but not dip below it's liquid level (creating a pocket).
A free draining has to drain the line regardless of where it's draining to. So it can have on high point, and free drain to both the origin and destination.
Cheers!
Dave
Steve McKenzie <gyro-@hotmail.com> wrote:
Hi Paul
To me, "free draining" is a functional term in that it describes the desired outcome but not the means of achieving it. Slope and no pockets are construction details which go towards making a system free draining. I think "free draining" means just what it says. I would probably add the free draining requirement to a P&ID but not the slope or (no) pocket. This is because slope and absence of pockets are construction details, which might better belong on the layouts, isos or even the tech specs or standard drawings, depending on the job.
Cheers
Steve
>From: Paul Bowers <pbowers@pipingdesign.com>
>Reply-To: <a href="/group/PipingDesign/post?postID=g-UBZdrf7bE_83ZWoQiECiWKJVm00TYgRPzEpWh7ODcdasDtL7ZxmrQG2v9XAb1PIQoN0s8G-kiQfKJPWTMJUh7eOsNj">PipingDesign@yahoogroups.com</a>
>To: <a href="/group/PipingDesign/post?postID=g-UBZdrf7bE_83ZWoQiECiWKJVm00TYgRPzEpWh7ODcdasDtL7ZxmrQG2v9XAb1PIQoN0s8G-kiQfKJPWTMJUh7eOsNj">PipingDesign@yahoogroups.com</a>
>Subject: [PipingDesign] Free-Draining, No Pockets, Slope - PSV
>Discharges/Headers
>Date: Fri, 26 Jan 2007 21:50:53 -0700
>
>What is the difference between these terms on a P&ID:
>
>-Free draining
>-No pockets
>-Slope
>
>All of these refer to the concept of preventing (via piping
>configuration) liquid build-up (possibly due to condensation) downstream
>of the safety valve in order to avoid backpressure on the PSV spring,
>possible freezing of liquids or waterhammer effects. Typically the
>discharge piping is fairly short, so "powerlining" is not usually an issue.
>
>Of the three, sloping the discharge line is the best process design
>solution, but it is also the most labour-intensive for
>fabrication/construction due to elbow cut-backs/non-parallel butt welds
>and the sometimes need to trim pipe shoes progressively to maintain the
>slope. Also, Isogen tends to barf and do odd things with sloped piping,
>making isos sometimes really bizarre-looking.
>
>"No pockets" is pretty self-explanatory.
>
>"Free draining" is the ambiguous one. Does this imply that a slope is
>necessary or does it refer to no internal obstruction (say, a FOT
>reducer, flow orifice, etc.).
>
>Paul
[Non-text portions of this message have been removed] Received on Sat Feb 10 14:01:00 2007
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