ICE PLUGGING AIR LINES 3

[Bambie]

Is it possible to form an ice plug in a 1/2"nps steel pipe carrying air at 125 psig and 70 degF by installing a nitrogen freeze jacket and throttling the air flow as required to condense and freeze the water vapour?

Our instrument air system has a diaphragm vent valve with a body/bonnet gasket leak and we would like to isolate this valve to replace the gasket. I am looking for an alternative to installing a heavy encapsulating sealant injected valve enclosure or jury rigging a rubber patch with clamps.

 

[TD2K]

I don't think so.

I looked at using an ice plug on a water line we had to install a downstream isolation valve on. I talked to a couple of companies who do it, they said you need to have no flow, absolutely no flow through the line. If there was even a small water flow you couldn't get enough heat out of the system with the liquid N2 faster than the water was essentially bringing it in.

With your system, you have to have an air flow bringing in 'new' water vapor to build the plug. I think the air flow would be a problem in chilling it down (though the mass flow would be quite a bit less than for a water line) and I wonder if you did manage to freeze off most of the opening and then get the final freeze in place, how good of a plug you would have given the dynamics. I'd also be worried about cutting out and replacing a valve with 125 psig air pressure on the side of that plug.

Couldn't hurt though to talk to some companies, I can't remember who I used, likely just looked up someone using Google.

 

[SeanB]

And not to mention that your instrument air has been dried so that the water vapor is essentially non-existent.

 

[Bambie]

A typical psychometric chart marked with carburetor icing conditions indicates that ice will form with as little as 20% realtive humidity (see attached). The valve in question is off the pre-dryer header, so wouldn't vapour drifting by a pipe surface at -300 degF freeze? The operating pressure of 125 psig would put a shear load of only 25lbs on the ice plug.

 

[BigInch]

Sounds like you'll certainly make some snow.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[btrueblood]

You don't have an isolation valve in that line? Sounds like a d'oh moment.

 

[MintJulep]

From Furmanite

In order to establish an effective freeze plug, it is critical that the system has no flow and the freeze plug must be an established distance from any flowing pipe branches or headers

Seems that you can't establish the no-flow condition.

Mock it up an try it, then you'll know.

 

[KiwiMace]

The gas utility in the US has been known to heat up the pipe with a gas torch to a nice cherry and crimp it. Not sure i'd try this with 125 psi tho.

I can't understand how you have a pneumatic line to a control valve that you can't isolate. How do you operate it?

 

[Bambie]

Kiwimace& btrueblood, this is a manual vent valve with no downstream piping and a 6"long 1/2"nps steel pipe connection to the header upstream of the dryers.

BigInch, is it "snow" that causes aircraft engines to quit in flight?

 

[BigInch]

Carburator icing. Cold water vapor taken in with air is cooled slightly more with the reduction of pressure in the venturi where it condenses and becomes supercooled in the venturi. When it hits the butterfly valve in the carburator, instant ice blockage. A carburator heater is provided to prevent that, but it is normally only turned on when fuel flow is reduced for landing allowing longer residence time for freezing in the carburator, or when flying through visible moistures clouds at outside air temperatures near freezing, or when at cruise setting, at the first hint of carburator icing, coughing and sputtering and power drop of the engine. It is normally left in the off position, as running it all the time lowers efficiecy of combustion with the higher temperature, lesser air volume, created in the fuel-air mixture entering the engine.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Bambie]

MintJulep, the no flow condition could be achieved by plugging the leaking gasket, but without some air flow, I would think that ice accretion would be very slow.

 

[chicopee]

The famous Volkswagen Beetle with it rear, air cool, engine had it nemesis which was carburator icing on a damp cool day.