Automatic sprinkler systems are used more than any other fixed fire protection system and the global fire sprinkler market is expected to reach $11.04 billion by 2020. The annual market growth is estimated at 9.36% between 2015 and 2020 with over 40 million sprinklers fitted worldwide each year.
Maintenance plays an important role 1, 2, 3. Clearly any interruption in functional availability can be crucial with lives and property at risk. Minimising maintenance times therefore has to be a priority.
Replacement of control equipment such as valves and sensors, and repair of damaged or corroded pipework, has traditionally been undertaken by draining any affected section completely prior to commencement of the work.
This can be time consuming and costly.
The stored volume necessitated by possible sudden demand for sprinkler water in a large industrial system can easily exceed 1000 cubic metres (almost 250,000 gallons).
A better understanding coupled with recent advances in liquid freezing technology affords opportunities to apply this technique for routine maintenance.
Whereas extensive use has been made of freezing solutions for small bore pipework in domestic and commercial plumbing this has been limited largely to 50 mm diameter tubes, using small canister spray systems.
More recently techniques involving the use of bulk CO2 and liquid nitrogen have now extended the potential to pipes up to 900 mm diameter and beyond.
With Atlantis on the launch pad ready to go on mission ST-101 a last minute systems check revealed a fault in the power drive unit.
Repairing this sensitive system conventionally meant suspending the launch, rolling the shuttle back to the vehicle assembly building and draining out the hydraulic lines to undertake repairs. This would delay the launch for several weeks and be extremely costly.
The operation involved freezing six 16 mm hydraulic fluid lines. There were three demanding requirements:
- The lines were nested in the base of the tail of the shuttle and physical access was restricted.
- The freezing point of the hydraulic fluid was below -100ºC.
- Shuttle engineers needed to be able to continuously monitor and control the temperature of the pipes in order to ensure that the freeze was being safely and consistently undertaken.
The operation was a complete success, demonstrating how a novel approach to maintenance could significantly reduce both time and cost.
The application to fire sprinkler systems however has not yet been fully exploited despite the fact that the potential cost savings are very large.
An attractive and economical solution is to freeze the pipe contents either side of the repair or replacement zone. Only the volume between freezing points requires emptying. Two solutions are available, the first covering pipe diameters up to 200 mm for which solid carbon dioxide is a suitable freezing medium and the second diameters greater than 200 mm for which liquid nitrogen is more appropriate.
Carbon Dioxide Freezing
Pipes between 8 and 200mm diameter are commonly used for transport of liquids in virtually every processing industry. Petrochemical manufacturing plant in particular employs highly complex pipework, valves, pumps and monitoring equipment to control product manufacture. Lubrication and fuel systems on aircraft, marine vessels and power generating plant also are also major users of this range of pipework diameters.
A liquid CO2 technique now commonly used across the world is the Qwik-Freezer™ System4. A specially designed insulating jacket is wrapped around the pipe at the point where the freeze is required.
A nozzle in the jacket is then coupled to a cylinder of liquid carbon dioxide by means of a high-pressure hose. When the CO2 is injected into the space between the jacket and pipe at a temperature of -78ºC the pipe contents freeze and a secure “ice plug” is formed which seals the pipe. The ice plugs will easily withstand 100 bar pressure.
The plug forms only in a section of pipe covered by the jacket so the resulting rise in pressure is very small and there is no damage to the pipe.
The technique can be used safely on steel, lead, copper, brass and plastics.
Liquid Nitrogen Freezing
Liquids in pipes over 200mm diameter can be frozen using liquid nitrogen. Of the various products available the Accu-Freeze™ System5 is an example of a World leading system.
The procedure creates an in-line ice plug capable of withstanding 140 bar in pipes up to 300mm in diameter and can be modified using available options to handle even larger diameters.
Copper tubing is coiled around the pipe upstream of the item to be attended to (or on both sides) and a specially designed insulating jacket is wrapped around the frozen area and the coils.
An advanced temperature monitoring unit controls the surface wall temperature of the pipe to accurately and safely create an ice plug. The ice plug is formed in the section below the Accu-Freeze™ coil wrap and jacket, and does not extend outside the jacket.
The Accu-Freeze™ System is automatic and can be remotely operated. This makes it attractive for use in locations where engineer access is restricted.
Pipe freezer technology allows fluids to be frozen below -150ºC using liquid carbon dioxide or nitrogen (subject to actual temperature required).
Specially designed insulation and feeder hoses are used to deliver coolants and continuous temperature control during the freeze operation can be incorporated.
The use of freeze technology affords the opportunity to isolate sections of pipework for maintenance, repair and replacement of valves and instrumentation. There is no need to restrict fire prevention operations beyond the time needed to freeze and undertake changes.
- Inspection, Testing and Maintenance of Active Fire Protection Systems. June 2016. International Fire Protection Magazine.
- BS EN 12845. Loss Prevention Control Rules for Automatic Sprinkler Installations.
- Publication LPS 1048. Argus Fire Protection Co Ltd, Stourbridge.
- 4,5. Qwik-Freezer™ and Accu-Freeze™ are registered trademarks and products of Huntingdon Fusion Techniques HFT® in the UK.
Dr. Michael Fletcher is a qualified metallurgist with extensive experience in welding and non-destructive testing. He works as an independent consultant providing support to a wide range of manufacturing industry on a global basis.