Cryogenic Pipefreezing is a method by which pressure resistant plugs are formed in liquid filled pipes by freezing the contents, using an externally applied coolant. It is similar to installing a temporary valve allowing sections of a piping system to be isolated for modification, maintenance, and repair.
The freezing is usually accomplished by bolting a lightweight insulated jacket around the pipe at the point at which it is to be frozen and filling the annuls between this jacket and the pipe with a coolant. For this application the coolant will be Liquid Nitrogen (LN2). The Liquid Nitrogen (LN2) is stored in portable vacuum insulated vessels, sometimes known as Dewars. The liquid is transferred to the freezing jacket by lengths of flexible corrugated stainless steel hose, which are usually foam insulated. The Liquid Nitrogen (LN2) boils on contact with the exterior pipe surface at a temperature of -320 Deg. F. (-196 Deg. C.) and the resultant removal of heat causes the liquid inside the pipe to begin freezing inwards in an annular fashion. Provided that conditions are suitable, the thickness of frozen material will increase until the pipe is completely sealed off.
Application of Pipefreezing
For a successful Pipefreezing application, two principal objectives must be met: firstly the conditions must allow a complete plug to form and secondly, once formed the plug must be capable of withstanding the required differential pressure.
A number of factors affect the ability to achieve these objectives. The prospect of forming a complete plug is mainly a function of the size of the pipe and the temperature, flowrate and nature of its contents. All these are interrelated, so it is not possible to state, for example, what the maximum pipe temperature is that can be frozen, since this is a function of the other three variables. For any given liquid, there is an envelope of diameter, temperature and flowrate outside which it is not possible to achieve a freeze. Unfortunately, these envelopes are not precisely defined and it is largely a matter of experience to judge whether a particular line can be frozen or not. Once frozen, the ability to maintain the seal is mainly a question of the magnitude of the pressure differential that will be imposed on the plug, although other factors do play some part.
Equipment and Clothing
The following equipment and clothing should be used when working with Liquid Nitrogen (LN2).
- Heavy gloves
- Safety glasses or face shield
- Leather boots
- Cuffless long sleeved shirts and cuffless pants
- Oxygen Monitor with alarm
- Emergency breathing apparatus
- Air mover (Fan)
Safe Handling Of Liquid Nitrogen (LN2)
There are two main risks associated with using Liquid Nitrogen (LN2) for Pipefreezing. The first is the risk of cold burns caused by contact with very cold gases, liquids or solids. The second is the danger of oxygen depletion in the atmosphere possibly leading to asphyxiation.
Treatment of Cold Burns
For skin contact from exposure to Liquid Nitrogen (LN2), immediately warm frostbite area with warm water not to exceed 105 Deg. F. (41 Deg. C). In case of massive exposure, remove clothing while showering with warm water. Call a physician immediately. Until physician arrives the casualty should be moved to a warm place, kept warm and calm and any clothing restricting the blood supply should be loosened, Smoking should not be allowed as this restricts blood flow.
This is similar to a cold burn, the difference being that frostbite is associated with longer exposure to less extreme temperatures. If the tissue becomes frozen, the effect and the required treatment will be as for cold burns.
It should be noted that prolonged inhalation of cold vapors and gases, may cause damage to the lungs.
Immediately flush eyes thoroughly with warm water for at least 15 minutes. Hold the eyelids open and away from the eyeballs to ensure that all surfaces are flushed thoroughly. See a physician, preferably an ophthalmologist, immediately.
Treatment of Asphyxia Victims
First the casualty must be removed to a safe atmosphere. In doing this it is vital that would be rescuers do not become victims themselves, so breathing apparatus and/or a rope and harness should be worn.
If the causality is not breathing, artificial respiration should be commenced without delay. If breathing is difficult, qualified personnel may give oxygen using resuscitation equipment. Call a physician immediately!
WARNING ! Extremely cold liquid and gas under pressure.
Can cause rapid suffocation.
Can cause severe frostbite.
May cause dizziness and drowsiness.
Self-contained breathing apparatus may
be required by rescue workers.
- nspect area for safety considerations.
- Inspection of the pipe to be frozen to check for visible defects of flaws.
- Mount an AFS jacket on pipe and follow AFS procedures for mounting jacket.
- Set up safety equipment, O2 Monitor and air movers when necessary.
- Introduce Liquid Nitrogen to freezing area.
- Monitor pipefreezing application during entire operation utilizing one of the following:
- Heat Flux monitoring.
- Allied Flow Specialists temperature monitoring equipment.
- Confirm freeze seal at test point.
- Maintain freeze seal during pipe repair or modification.
- Remove Pipefreezing equipment.
- Allow pipe to warm before defreezing process begins, according to Guide Lines For Safe Pipefreezing Practices.
- De-freeze pipe utilizing a plug defuser, to allow for disposal of the freeze plug.
- Clear and clean area
- Commercial Buildings
- Manufacturing Plants
- Power Plants
- Water Treatment Plants
- Carbon Steel
- Stainless Steel
- Cast Iron
- Coated and Lined Pipes
- Aluminium Alloys
- Nickel Alloys
- Chilled Water Lines
- Domestic Water Lines
- Condenser Lines
- Hydraulic Lines
- Heating Lines
- Sprinkler Lines
- Boiler Water