Selection and Installation Techniques of Instruments for Cryogenic Storage Tanks

Cryogenic storage tanks, used for substances such as LNG, liquid nitrogen, or liquid oxygen, require accurate and reliable instrumentation to monitor pressure, temperature, liquid level, and safety parameters. Proper selection and installation of instruments are essential for operational safety, efficiency, and maintenance.

1. Instrument Selection Considerations

Pressure Measurement:
Pressure gauges and transmitters must withstand both the low temperatures and the high pressures in the tank. Materials such as stainless steel or nickel alloys are preferred to resist embrittlement at cryogenic temperatures. Diaphragm seals are often used to isolate the sensing element from the liquid and prevent freezing.

Temperature Measurement:
Cryogenic thermocouples or resistance temperature detectors (RTDs) are selected for their accuracy and durability at extremely low temperatures. Temperature sensors are typically installed in well thermowells to avoid direct exposure to liquid flow and reduce mechanical damage risk.

Liquid Level Measurement:
Techniques include float systems, capacitance probes, differential pressure level transmitters, and ultrasonic sensors. Selection depends on tank size, liquid type, and required measurement precision. Non-contact ultrasonic or radar level sensors are preferred for high-purity or aggressive cryogenic liquids.

Flow Measurement:
Mass flow meters, Coriolis meters, or differential pressure flow meters are selected based on compatibility with cryogenic temperatures, low viscosity, and low density variations.

Safety and Alarm Devices:
Overpressure, high-level, and low-temperature alarm devices are critical for emergency protection. Redundant sensors may be installed to improve reliability.

2. Installation Techniques

Proper Mounting:
Instruments must be installed to minimize mechanical stress, vibration, and thermal contraction effects. Flexible connections and properly supported wiring reduce strain on sensors.

Insulation and Heat Tracing:
Instrument connections and wiring are insulated to prevent heat ingress, which could lead to freezing or measurement errors. In some cases, low-power heat tracing is applied to maintain sensor operability.

Isolation and Calibration:
Isolation valves and bypass lines enable maintenance and calibration without interrupting tank operation. Sensors should be calibrated at cryogenic conditions to ensure measurement accuracy.

Signal Transmission:
Use of appropriate signal cables, shielded wiring, and remote transmitters ensures reliable data acquisition despite low-temperature environments and electromagnetic interference.

Safety Compliance:
All instruments and installation methods must comply with applicable codes such as EN 14620 (Cryogenic Vessels), NFPA 55, and local regulatory standards.

Conclusion
Selecting and installing instruments for cryogenic storage tanks requires careful consideration of material compatibility, measurement accuracy, and installation techniques. Proper attention to these factors ensures reliable monitoring, operational safety, and long-term service life of both the instruments and the storage tank.

References

EN 14620 – Design and Manufacture of Cryogenic Vessels.

NFPA 55 – Compressed Gases and Cryogenic Fluids Code.

Barron, R.F. (1999). Cryogenic Systems, 2nd Edition. CRC Press.

Bratt, R., & Mort, P. (2015). Cryogenic Engineering: Fifty Years of Progress. Springer.

ISO 21014 – Cryogenic Vessels – Temperature and Pressure Measurement Guidelines.