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TOPIC: Can we run Instrument Air in underground ??

Can we run Instrument Air in underground ?? 3 years 5 months ago #8979

  • rlpooniya
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Hi all,

I am working on a project in which 25/31.5 MVA transformers are supposed to be protected by fire water spray system and it will be controlled by Air operated deluge valve. Instrument air is not available in transformer surrounding area, so we have to plan AI supply from OSBL pipe rack, which is 300 meters far from deluge valve location.

My question is " can we run AI header underground? if not, why?"

Line size 2" / 3"
Pipe material - CS Galv
Design pressure - 10 Bar
Design temp. 65 Degree C
Operating pressure - 7 Bar

Pipe length required in UG = 200 / 250 Meters


If anyone has relevant experience, please share



Regards
Rameshwar

Can we run Instrument Air in underground ?? 3 years 5 months ago #8980

  • Jop
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rlpooniya,
Yes you can run an Instrument Air line underground. However there are some considerations to think about.
- Geographic location - If your plant is in an Arctic location you must deal with Permafrost.
- You will be creating a Low Point that will need to be drained. (Yes I know, Instrument Air is "Dry") There is still start-up and shutdown periods that need considerations.
Do it once and Do it Right
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Can we run Instrument Air in underground ?? 3 years 3 months ago #9026

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Thanks JOP

@11echo,
These transformers are installed in open area with three side firewalls and one side gates. Requirement of firewater deluge system has raised by client.

Can we run Instrument Air in underground ?? 3 years 5 months ago #8981

  • 11echo
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After re-reading this, a point of interest has popped out at me ...You have a water deluge system over the top of electrical transformers!!? ...I'm not an electrical guy, but this sounds like trouble waiting to happen! ...Ask your project engineer about using halon gas system. This might require the transformers to be in a building or shed, but it would be far better then electrocuting any first responders to any fires at this point! ...My $0.02
Last Edit: 3 years 5 months ago by 11echo.
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Can we run Instrument Air in underground ?? 3 years 3 months ago #9031

  • 11echo
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Since my last response, I have bounced this question off one of my electrical buddies and he has given me a more “refined” answer. He indicates that they can use fire water over transformers, but you need to be aware of the overall picture with this concept. The fire danger with transformer is they are filled with oil, and subject to explosions. So if there is a fire, the big problem is the oil is leaking out and feeding the fire. Transformers usually have a containment dike around them to hold this oil in the designated area (otherwise the flaming oil would run out in flat or sloped areas and cause an increase in the affected area). Now if the oil is contained, and still on fire, the water is sprayed on the oil to try to reduce the temp. to extinguish the flame. Problem there is water sinks in oil and is not as effective. Continuing the conversation with my electrical friend, he tells me the “best” way the deal with transformer fires is to use a float spray. This foam is generated with the water and is far more effective then with just plain water spray. The foam sits on top of the oil and eliminates the oil vapors the flame is feeding on.
So my advice on this subject is to talk with the engineer on this, ultimately he is responsible for the whole system! ...FYI, "if" your thinking of using threaded galvanized pipe, push to change that to H.D.P.E. pipe, at least in the buried section. ...Good Luck!
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Can we run Instrument Air in underground ?? 3 years 3 months ago #9033

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11echo,

Thanks for sharing educative conversation along with your own opinion.

Such efforts of senior members are highly appreciated....
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