Blind Vent / Drain for SS and Alloy Material

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This should not be a requirement associated with SS & AS to utilize vent and drain valve w/blind flange. The requirement is simply to have double isolation to atmosphere (e.g. double block valves or one block valve with plug or one block valve with blind flange). For small drain & vent connections, the choices is to go with valve & plug. For larger drain connection such as tank water draw off, 4 inch size, we use isolation valve and blind flange. There is no rational toward using blind flange in small drain vent assembly. I don’t believe myself that the mentioned plants decided to use threaded end blind flanges with the isolation valve in order to avoid losing them easily compared to small plug??

Khaled Mahmoud
Jeddah Refinery

--- On Sat, 3/19/11, Hafiz Ali Alvi <alima...@hotmail.com> wrote:

> From: Hafiz Ali Alvi <alima...@hotmail.com>
> Subject: [PipingDesign] Blind Vent / Drain for SS and Alloy Material
> To: "piping...@yahoogroups.com" <piping...@yahoogroups.com>
> Date: Saturday, March 19, 2011, 1:26 AM
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> Dear All,
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> My question is about vent/drain end type for SS and Alloy
> steel piping. In one of the company standard it is mentioned
> that" Vent and drain other then indicated in P&ID
> shall be in accordance with the following:
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> Vent /Drain : SS and Alloy steel piping : 3/4" NPS
> gate valve with blind flange.
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> : Carbon Steel piping : 3/4" NPS
> gate valve with plug.
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> Anybody knows the reason of this difference, that why we
> use blind flange for SS and AS piping. In my view this type
> of assembly will be more costly as compare to plugged
> drain/vent.
>
> I saw this arrangement on Petro Rabigh plant and also in
> PMS of Manifa Refinary in KSA.
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> Regards.
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> Hafiz Ali Alvi
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