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Add block valve between tank and breather valve

Add block valve between tank and breather valve

(OP)
Dear Sir,

I can't find wording about in case of add block valve between tank and breather valve on API 2000 , Can i add block valve full port for matenance purpose?(Block valve close when plant Shutdown)

Best regards,
SK

RE: Add block valve between tank and breather valve

songkarn,
I am not sure I completely understand what you are asking, but does this help?

API 2000 - 2009 Edition
4.7 Installation of venting devices
4.7.1 Installation of pressure- and vacuum-relief devices

Pressure- and vacuum-relief devices shall be installed to fulfil the following functions.

a) The devices shall provide direct communication with the vapour space and not be sealed off by the liquid contents of the tank.

b) Any block valve or isolating device fitted between the relief device and the tank, or the relief device and the discharge pipework shall be locked or sealed in the proper position. Where no spare relief devices are installed, this shall be done by locking or sealing these block valves open. Where spare relief devices are installed, then multiple-way valves, interlocked valves or sealed block valves and operating procedures shall be used so that isolating one pressure- or vacuum-relief device does not reduce the remaining relief capacity below the required relief capacity.

c) The design shall ensure that the inlet and outlet assemblies, including any block valves, permit the relief device to provide the required flow capacity. Inlet pressure losses developed during relief conditions shall be taken into account when sizing the pressure- and vacuum-relief devices. The inlet pipe penetration into the vessel, the pressure drop across any block valves used upstream of the venting device, and the inlet piping shall be considered when determining these losses.

RE: Add block valve between tank and breather valve

songkarn,
You should provide a sketch so we understand your question.

My assumption is that there is the top of the Tank, then there is a Nozzle, then there is the Breather Valve, direct connected to the Nozzle, then there is the clear blue sky.
No piping!

Why do you think you need a Valve?

Sometimes its possible to do all the right things and still get bad results

RE: Add block valve between tank and breather valve

DGrays, post says it all.

My initial thought was yes, but need to Lock Open or CSO.

All depends how good your lock open and work permit procedures are on site to then close it then forbid re-commissioning until it's open again.

If there's no valve then no one can close it when it's not supposed to be closed....

Failure to open it could have catastrophic consequences.

One of many root causes of the piper alpha disaster was that the work permit procedures were not followed and a pump was started which had its relief valve disconnected and should not have been started. Don't say it can't happen to you....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Add block valve between tank and breather valve

As requested by the O&M, we added the block valve between the tank nozzle and the PVRV for the valve maintenance. And, the block valve was included in the locked open valve list.

RE: Add block valve between tank and breather valve

The block valve cannot be closed for as long as you have some process liquid in the tank, which will be the case when the plant is shutdown. It can only be otherwise closed when

a) The tank is completely drained out during plant shutdown
OR
b) There is a spare identical breather valve fitted with a full port valve

RE: Add block valve between tank and breather valve

We know what you want to do, we just don't know why. As George says you can only close it when the tank is clean and empty and some other means of venting is available so why bother??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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