Use of ice to plug a pipe

From: <James>
Date: Thu Jul 29 2004 - 08:27:00 EDT

Hello guys and any other gals!

I have been away for a few days, it was nice to come back to find that I have been causing some minor controversy simply by being a female of the opposite gender! Anyway, I have a proper on-topic question:

I have been to survey an emergency feedwater system that requires some modifications. There are 3 pumps (two duty, one standby) that are fed from a manifold from a dedicated tank, the manifold also has a connection for a firehose in case the emergency lasts for so long that the tank is emptied. It is necessary to do some work on the tank and the outlet pipework, but the capability to use the pumps must not be compromised while the work is in progress. Obviously, the firehose can be connected to the alternative tanks some distance away to ensure a water supply but it is complicated by the lack of valves in the line between the primary tank and the firehose connection.

The client has proposed what to me is a novel solution: fill the main line with water, and then use cryogenic wraps to freeze a section of the pipe between the tank and the hose connection. The plug of ice thus formed to be used to seal the pipe while the section upstream is cut out and a modified section welded into place.

Has anybody used a similar method for temporarily plugging a pipe?

I can see that there are some problems with this: cutting the pipe will produce some heat, but it should be possible to position the cut sufficiently far from the ice plug to get round this, but I am not so sure that welding it all back together again will be possible without melting the ice. The only flange joint in the relevant section of pipework is at the tank outlet nozzle.

The pipe is 6" Sch 40 ASTM A312 Gr316L which has a min specified temp of
-425°F (-254°C) ASME B31.1 Table A-1. I have not been given a
temperature for the cryogenic wrap, but would not expect it to go below
-254°C.

Do you think the ice plug would be sufficiently air-tight to allow the pumps to work properly should they be required? The system is the emergency back-up to the main back-up feedwater system and to the best of my knowledge has never been used in its 30 year life other than its weekly test run.

I am sure there will be some interesting responses to this query ;->

Barbara +1

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For further information, visit us at WWW.MITSUIBABCOCK.COM Received on Thu Jul 29 08:27:00 2004