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[Ghasem.Bashiri]

Dear All
I think this topic can be completed with different reply from your side as your experinces. Actually I status my question with this point: Definition of No Pocket (Liquid or Vapor), Free Drain,Sloped line and Necessity of this design. We know that No Pocket or Free Drain can have some piping cost during design. But when we should follow these design, Actually I try to gather some experince within this topic for other users. Also in reply to this topic explain how much should be percent of Slope and when we need slop?
I am going my experince also and share them for you soon.
But As I know there is not some written rule for this issue but you may have. Quantitative rule is very good (e.g. Dew Point in Design Pressure...)


I found following definition in google for terms that I asked about them:
1. Free Draining - Any such line with this note needs to "step" down from the high point to a lower point i.e: it would leave the origin point and then drop down then (possibly) run horizontal then maybe drop down then enter the destination point. The line does not need to be sloped but it must not be pocketed.

2. Sloped - Sloped means just that it must be sloped. However the Process Engineer must include the required slope angle.

3. No-Pocket - This is sometimes misunderstood and applies to almost every line in a process plant except lines in a pipe rack with loops. A "No-Pocket" or Do-Not-Pocket" line can leave vessel "A" and go up then horizontal then up again then horizontal then down to vessel "B" or to an exchanger. But it cannot go up then down then up then down, this would create pockets.

Ghasem.Bashiri@hotmail.com

[Ghasem.Bashiri]

API 520 Part II:

4.2.4 Configuration of Inlet Piping for Pressure-
Relief Valves
Avoid the installation of a pressure-relief valve at the end
of a long horizontal inlet pipe through which there is normally
no ßow. Foreign matter may accumulate, or liquid may
be trapped, creating interference with the valveÕs operation or
requiring more frequent valve maintenance.
The inlet piping system to pressure-relief devices should
be free-draining to prevent accumulation of liquid or foreign
matter in the piping.