TECHMAIL: Pipefreezing

The following webpages are linked at
<http://www.PipingDesign.com/maintenance.html>

What is Pipefreezing ?

Pipefreezing is a means of isolating part of a pipework system by freezing the pipe contents over a short section, so that the contents form a solid plug.

This avoids having to drain the system down, and in many cases freezing can be carried out without shutting the system down.

Once a specific part of a system has been isolated with pipefreezing, it is possible to carry out repairs, modifications, maintenance, leak detection, pressure testing, etc.

How is pipefreezing carried out ?

A container (usually referred to as a jacket) is placed around the pipe, and then filled with liquid nitrogen. Liquid nitrogen boils at -196oC, and so boils very readily on the surface of the pipe within the jacket. This removes heat from the pipe and its contents, which will in time freeze solid. As the nitrogen boils off, it releases nitrogen vapour which is vented away to the atmosphere.
In certain situations, solid or gaseous carbon dioxide is used. This is not as cold as liquid nitrogen, and so freezing takes longer, but has the advantage of not exposing the pipe material to such low temperatures.

More about pipefreezing is available at the Bishop Engineering Home Page:
<http://www.bishop.co.uk/pf.htm>

Photographs of pipefreezing operations are viewable at Freeze Service, Inc.'s webpage:

<http://www.pipefreezing.com/casehist.html>

Some frequently-asked questions about pipefreezing:

Why doesn’t the pipe break?
Uncontrolled expansion of liquid within the pipe causes the pipe to rupture. Our technology affords us the ability to control the area of the pipe to be frozen. Once a small section of the pipe is sealed off the expansion is directed linearly away from the plug in both directions.

How long will it take to freeze pipe?

Freeze time is dependent upon many factors. Primarily it is the size of the pipe, although system conditions and ambient temperature are contributing factors. Once we know the particulars of your application, we can pinpoint the actual freezing time.

How long will it take for the pipe to thaw?

Thawing time is contingent on the same perimeters as listed above in the freezing time. However, if required by limited down time or other concerns, our technicians can safely thaw the plug using a controlled external heat source. Thaw time can be reduced in most incidences to within an hour.

Where does the freeze plug go?

The plug does not move down the pipe line as a complete solid. Rather it melts and is washed down the pipe line as a liquid.

What systems conditions are required for you to successfully freeze the pipe?

The system must be isolated so that flow does not exist in the area to be frozen. Any sources of heat or turbulence near the freeze area must be minimized. The system pressure is not a concern during the pipefreeze application.

More pipefreezing FAQs are at Freeze Seal, Inc.'s webpage:

<http://www.freezesealinc.com/support.htm>

Advantages of pipefreezing:

Time Saving

Safe

Cost Effective

Used in any environment

Used in the offshore oil & gas facilities

Used in the onshore petrochemical, nuclear power and water industries

Easy transfer of hazardous or toxic liquids to storage

Reduced loss of critical fluids from pipeline

Allows hydrotesting and pressure testing on difficult pipelines

No adverse reaction to most pipe materials

Can be used on all pipeline fluids

More info is available at Alfred McAlpine Pipeline Construction's webpage:

<http://www.amcivil.com/cryogenics.shtml>
Received on Thu Jun 29 18:34:00 2000