WP-308 Liquid Nitrogen Freezing Solves Pipe Cutting Problems

02 AccuFreeze

Huntingdon Fusion Techniques HFT®”s USA Partner has recently helped solve a major environmental problem in a remote area of Oregon. Construction of a new access to the Willamette River was necessary, as part of a plan to replenish a salmon hatchery1 but this necessitated removal of part of a 10-inch (254 mm) pipeline that was causing an obstruction.

The pipeline had been isolated and abandoned previously and filled with water that had probably become polluted. Simply cutting the pipeline would release over 1 million 300 thousand gallons (5,000 m3) of contaminated water into surrounding land lying within a sensitive, environmentally protected area. A decision was made to use liquid nitrogen to create ice plugs and isolate the small section of pipe causing the obstruction. The pipe could then be cut, releasing only limited contaminated water and this could be contained and removed from the site.

Pits were excavated on either side of the access exposing the pipe and the anti- corrosion coating was removed. Freezing commenced in the early morning in record high temperatures combined with little to no shade in the area.


The pipe was cut on both sides and the remaining contaminated water drained to disposal containers for removal. Welders quickly capped the open ends. The freeze equipment was shut down and the ice plugs allowed to thaw naturally. The proposed river access refurbishment was allowed to continue the following week bringing life back to a vital natural habitat.



Excavation of pipe in progress
Excavation of pipe in progress.

The equipment employed for the freezing operation was an Accu-Freeze™ System. The procedure creates an in-line ice plug capable of withstanding 140 bar in pipes up to 12-inch (305 mm) diameter and can be modified using available options to handle even larger diameters.

A specially designed insulated aluminium jacket is placed around the required section of pipe to be frozen. An advanced temperature-monitoring unit controls the surface wall temperature of the pipe to accurately and safely create a short ice plug that does not extend outside the jacket.

Exposed pipe in readiness for freezing operation
Exposed pipe in readiness for freezing operation.

  automatic and can be remotely operated making it attractive for use in nuclear applications and other locations where engineer access has to be restricted. Freezing using liquid nitrogen is effective down to -184ºF (-120ºC) so is suitable for isolating sections of pipe carrying petrochemicals so that valves and other contr

ol devices can be removed without the expense and delays involved in draining the system.

The concept of isolation using liquid nitrogen had been used in the past to resolve major problems with a NASA launch vehicle and inside large chemical plant2.

With the space shuttle Atlantis on the launch pad ready to go on mission ST-101 a last-minute system check revealed a fault in the power drive unit. The PDU is an hydraulic power pump which controls the shuttles’ rear rudder or air brake so failure of this unit during flight could be catastrophic.

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 solution was to use liquid nitrogen to freeze six 16 mm hydraulic fluid lines either side of the faulty PDU and then remove and replace it. There were demanding requirements. The lines were nested in the base of the tail of the shuttle and physical access was restricted and Shuttle engineers needed to be able to monitor and control the temperature of the pipes in order to ensure that the freeze was being safely and consistently controlled.

50W Accu Freeze Pipe Freezing Systems
Accu-Freeze™ Clam Shell on Pipe.


Pipe freezer technology allows fluids to be frozen below -238ºF (-150ºC) using liquid nitrogen. 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, couplings and instrumentation and thus obviates any need to drain the system. There is no need to disrupt production beyond the time needed to freeze and undertake changes.


1. www.dfw.state.or.us/fish/HOP/Willamette%20HOP.pdf
2. White Paper from Huntingdon Fusion Techniques Ltd, reference HFT/WP 51.

Note for editor; The HFT® White Paper, referenced above, has been prepared for internal use and not previously published. It contains an extended version of the NASA project and a separate case study using liquid carbon dioxide as the freeze medium. We could submit this to you for possible future publication.

 By Dr. Michael J. Fletcher M.Sc. Metallurgy

Loughborough University
Delta Consultants  


Download White Paper Number 308 - Liquid Nitrogen Freezing Solves Pipe Cutting Problems


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