Traditional LNG tank monitoring uses multiple Resistance Temperature Detectors (RTDs) placed at fixed points inside a tank. The problem is straightforward: RTDs only measure where they’re installed. A leak developing between sensors can go undetected for a dangerously long time. Roctest’s DTS system eliminates this blind spot by turning an entire fiber optic cable into a continuous temperature sensor.
The Core Product: DiTemp Harsh+
Roctest’s DiTemp Harsh+ is a high-accuracy, long-range, distributed temperature sensing system designed for use as a stand-alone unit in harsh environments. Featuring low energy consumption and an extended operational temperature range, the DiTemp Harsh+ can measure temperature continuously over distances up to 30 km. The unit is sensitive enough to detect the subtle thermal shifts of early-stage cryogenic leakage, and carries ATEX certification for use in potentially explosive atmospheres which is a mandatory qualification for LNG environments.
How It’s Deployed in an LNG Tank
Rather than running dozens of individual sensors, a single fiber optic cable is installed at multiple levels around the tank perimeter, covering both critical zones:
Tank Annular Space (Spill Detection) The fiber runs within the sealed gap between the outer concrete wall and the inner steel liner. This space is permanently filled with perlite and inaccessible after construction. Any breach in the inner liner causes cryogenic LNG to migrate into this space, producing a sharp localized temperature drop. The DTS detects this cold anomaly and can pinpoint its location to within 1 meter.
Concrete Slab Base (Thermal Mapping) Fiber is also run through conduits in the foundation slab to feed temperature data to the tank’s ground-heating control system. LNG tanks require active underfloor heating to prevent frost heave, which can destabilize the structure. The DTS provides the thermal map needed to manage that heating while simultaneously flagging cold spots that could indicate seepage through the slab.
Why This Is Better Than RTD-Based Systems
With conventional RTDs, a leak developing between two sensors may not be detected until it grows large enough to affect a neighboring point. The DTS has no gaps as the entire cable is the sensor. Beyond safety, this also reduces installed cost: a single cable and readout unit replaces what might otherwise require hundreds of individual sensors and wiring runs.
Continuous Self-Testing With The ATTS
The Automatic Testing and Triggering System (ATTS) verifies the monitoring system is working at all times. It contains two short fiber sections, one at each end of the sensing cable, that are periodically heated or cooled to simulate the exact temperature signature of a real leak event. If the system fails to respond to this simulated alarm within a preset timeout, the ATTS raises an alert, catching system availability problems before they result in a missed real-world detection. Simulated tests run approximately every hour.
Integration and Visualization
All data feeds into Roctest’s DiView software, displaying temperature as a continuous color-mapped profile along the cable. Hot and cold spots are immediately visible without specialist interpretation. The system communicates over standard protocols — Modbus, Ethernet, RS-485 — feeding directly into the control room PLC alongside normal operational data.
Summary
Roctest’s DTS system transforms LNG tank leak detection from periodic point measurements into continuous spatial monitoring of the entire tank perimeter and foundation. For operators of LNG terminals, it is effectively the difference between spot-checking and a continuous, live thermal X-ray of the tank’s most inaccessible and critical zones.
Temperature Monitoring and Leak Detection FAQs
