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| Metallic pipes.
Metallic pipes are generally all suitable for pipefreezing using liquid nitrogen. Care must be taken when freezing carbon steel and cast iron (ferritic BCC structures) pipes because they are embrittled at liquid nitrogen temperatures. Pipes in this condition should not be subjected to shock loading. Allowances must also be made for thermal contraction in cases where pipes are axially constrained. Nickel alloys, stainless steels (austenitic FCC structures), copper alloys, aluminium alloys, are all suitable for freezing. |
| Non-metallic pipes
GRP and polymer pipes. Extreme caution must be excercised when freezing these pipe materials: low conductivities and high thermal expansion coefficients can lead to very high thermal stresses on cooling. Our tests indicate that GRP pipes can be frozen using liquid nitrogen, but that some crazing of the outer surface is likely. Freezing un-reinforced polymer pipes using liquid nitrogen is best avoided: controlled temperature techniques using refrigerants or Carbon Dioxide are more appropriate in these cases. |
| Lined/coated pipes.
In our experience, concrete, bitumin, ceramic, glass, and rubber lined pipes can be frozen without any apparent damage to the lining. Allowances have to be made for the lining thickness, which may considerably slow the freezing process. There are of course risks associated with subjecting pipes made with components of differing expansion coefficients to very low temperatures, and the consequences of damage must be bourne in mind. |
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