Our technical experts answer your questions on Cryogenic Systems and their applications.
Flexible cryogenic transfer lines
No. For lines for Group 1 (hazardous) fluids, a CE mark must be applied starting with Type 30/58 (LOX, LNG, LH2). No CE mark shall be applied to lines for Group 2 (other) media; good engineering practice applies here.
Due to the manufacturing process of longitudinally welded and subsequently spirally formed stainless steel tubes, there are no length limitations in terms of production technology. The line systems can be coiled and uncoiled like a cable and are therefore logistically easy to handle. In addition, fewer couplings are required compared to rigid line systems. This saving in hardware also reduces the amount of heat that is lost and the cooling capacity. Lines can be routed through wall openings and easily moved to the desired position.
Practically, our vacuum insulated line systems are maintenance free. Only metal gaskets are used for the vacuum port. Since no elastomers are used, there is no diffusion in the seals and a long-lasting vacuum is guaranteed. The insulating vacuum is maintained for many years by built-in getter materials.
Directional changes in the pipe run can be realized by bending radii. This allows the use of rigid 90 degree bends to be avoided, with the result of ensuring a lower pressure drop. Any differences in length can be compensated for by the line routing and shaping of the bends. Bending radii can be significantly reduced with one-time bending during installation. Factors such as, flexibility in reuse or customization in application increase the attractiveness. Customized lengths and isometries are easy to realize.
For rigid piping, expansion joints are a flexible element to compensate for movement in piping, especially with thermal length changes. This component is not required for CRYOFLEX® piping; compensation for temperature-specific length changes is provided by the flexibility of the system.
System connections and accessories
In our delivery program, the appropriate gland types are available depending on the type. The standard cable gland types are 28/25 or 34/32. After consultation with the customer, we determine how the cable ends are to be fitted. The respective fitting counterpart is supplied if required. Our fittings, which correspond to the LINKUT fine thread as standard, are sealed with a graphite gasket. Alternatively, flanged couplings can be used by arrangement.
Johnston couplings allow completely ice-free connection of vacuum insulated transfer lines. They are suitable for extending or combining lines and are particularly recommended where effective consumption is essential and in environments where ice formation absolutely cannot be tolerated.
The vacuum-insulated coupling ensures low heat input and thus low nitrogen consumption. Quick and easy connection of the lines is made possible by a clamping chain that fixes the flanges of the male and female parts of the Johnston coupling (quick disconnect/quick connection), so that no welding work is required on site and quick installation is guaranteed. The integrated hot flange gasket and the cold PTFE gasket on the male part of the coupling ensure reliable sealing.
No. There is no standard that specifies the connection of Johnston couplings from different manufacturers. This means that a Nexans Johnston male coupling can only be connected to a Nexans Johnston female coupling. To enable a connection to other cable manufacturers, our customers can provide the required third-party couplings. These are then welded to Nexans line systems in our workshop.
Operation, maintenance and safety
For our CRYOFLEX® transfer lines starting with type 21/44 up to type 39/66 the test pressure is 1.43 * max. allowable working pressure = 1.43 * 20bar = 28.6bar. Regardless of how the customer wants to operate the line.
Yes. Nexans lines are delivered ready configured, leak tested and vacuum insulated 1 x 10-4 mbar. This ensures fast and cost-effective installation times at job sites. On-site welding is not necessary.
The vacuum of a Cryoflex line does not have to be generated laboriously at the point of use, quality-tested properties are immediately ready for use on site and enable efficient installation and commissioning.
All pipes are subjected to He leak testing with a sensitivity of 10-9 mbar l/sec. All welded joints are also helium leak tested.
In addition to the pump valve, a bursting disc is also integrated in the end pieces. Should a leak in the inner tube lead to a pressure increase in the vacuum chamber, the rupture disc provides a pressure safety device and protects the system from overpressure. Intelligent design thus ensures a high level of safety in the application, even in the event of a malfunction. The release pressure of a standard rupture disc is between 3 and 7 bar.
In these cases we recommend the use of our mechanical degassing system before the liquid nitrogen is discharged to the consumer. A maintenance-free, dirt-resistant deaerator made of stainless steel is used, which operates according to the proven float principle. The housing is completely welded, no seals are used. The exhaust valve is controlled by a free-swinging lever mechanism through the movement of the float and is located in the upper part. Air vents do not require adjustment and continuously vent gases that may be generated by evaporation when heat is applied. The deaerator can be integrated into the piping system via an uninsulated T-piece with two screwed halves.
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