Cryogenic Piping Makes 'Cents'
The three basic styles of insulated pipe used today include urethane-foam-insulated, dynamic vacuum-insulated and static vacuum-insulated.
Urethane-Foam-Insulated Piping. Also known as foam pipe, urethane-foam-insulated pipe requires the least amount of initial expense. This can be attributed to low material costs as well as a relatively simple manufacturing process. Also, foam pipe is produced in standardized lengths that lend itself to an automated manufacturing process. Standard sizes and components are typically available from stock with short lead times.
Despite the lower initial costs of foam pipe, liquid nitrogen operating costs are high due to the heat leak rate. Also, because of moisture intrusion into the foam, the heat leak rate will increase every year the pipe is in service. In general, foam pipe has a limited life expectancy of approximately five years.
Once installed, a dedicated vacuum pump must run continuously to maintain the vacuum in the piping. The drawbacks of a vacuum pump are the added operation costs due to additional electricity and maintenance requirements.
With dynamic vacuum-insulated piping, the heat leak rate is considerably lower than foam pipe. This allows for lower liquid nitrogen operating costs and a longer expected lifetime of 10 to 15 years. Dynamic vacuum-insulated piping and components typically are kept in stock at standardized lengths. This allows for short lead times and flexibility when designing and installing the systems.
Static Vacuum-Insulated Piping. The initial costs of static vacuum-insulated piping are slightly higher than that of dynamic vacuum-insulated piping. Static vacuum-insulated piping also employs an evacuated annular space, and has a stainless steel construction. Static vacuum-insulated piping typically requires a longer lead time as the individual spool sections are custom-built, thus requiring more detailed designs and site measurements, which add to the initial cost. Static vacuum-insulated piping systems are delivered with factory sealed vacuum sections and bayonet end connections. These male and female end connections are bolted together using flanges for quick assembly at the job site. The use of superinsulation and a gettering system eliminates the need for a vacuum pump and its subsequent operating costs.
Static vacuum-insulated piping has the least amount of heat leak (as much as 40 times less than foam pipe), resulting in the lowest liquid nitrogen operating costs. The expected lifetime is 20 years, with little or no required routine maintenance.
Calculating CostsAs any cryogenic piping system is a sizable investment, it makes sense to calculate the real costs rather than just consider the initial installed cost. To measure real costs, users must consider the following:
Initial investment. Cost of the entire piping system and components, including installation and production downtime.
Operating LN2 Costs. Expense of LN2 that is lost due to heat leak into the piping system.
Maintenance Costs. For urethane foam-insulated piping, you can expect to replace the piping in five years due to moisture intrusion. For dynamic vacuum-insulated piping, consider the electricity and maintenance costs to operate the mechanical vacuum pumps.
Lifetime of System.Calculate the expected lifetime of a cryogenic piping system before it needs to be repaired or replaced.
The impact of these costs should be assessed. A cost-savings calculation is one way to compare the operated liquid nitrogen costs of cryogenic piping systems.
It is important to know the benefits and limitations of each type of cryogenic piping. Work with an experienced cryogenic equipment supplier that will help you analyze your requirements, size your piping and provide a cost-effective design.