LNG tanks are critical structures that require special attention with special equipment able to resist cryogenic temperature (-200C) during the whole life span of the tanks.
The Movement Monitoring system of LNG tanks is designed to monitor movements within the annular space, between the out concrete wall and the inner steel (with 9% Nickel) wall. The distance between these two walls is normally around 1m (3ft) and will be partially filled with a resilient blanket and then with a granular material called Perlite. Therefore, once these two isolation systems are in place, there is no access possible between the two walls and the only way to monitor what is going on between the two walls needs to be installed during construction.
Several movements will occur between the two walls during the operation of the tank:
- Settlement: the inside walls will “sink” compared to the outer wall due to settlement caused by the weight of the liquid natural gas contained.
- Horizontal movements: during normal operation, the tank will be filled at different levels, causing various pressures within the inside wall that will cause expansion, shortening the annular space by a significant portion
- Rotational movements: during various stages of filling, the inside wall will shrink unevenly, causing a rotational movement (compared to the outer wall) that is hard to predict and that could only be measured using this equipment.
All the sensors are equipped with Fiber Optic sensors (Fabry-Perot technology) that are Intrinsically Safe (IS) and can sustain very low temperatures. Since there is a minimal amount of mechanical parts, these sensors will last the life of the structure. Each sensor is connected to the control room for live monitoring.
List of similar projects: https://roctest.com/wp-content/uploads/2017/01/LNG-Ref_1911-ROCTEST.pdf