26
LNG
INDUSTRY
SEPTEMBER
2014
maintenance-free and designed for
simplified outdoor installation.
With a long operating life, the fibre
is also able to stand the extra low
temperature, corrosion, lightening, static
electricity and electromagnetic effect.
All of this makes it a reliable sensor,
especially suitable for the environment of
LNG tanks.
In addition to DTS technology itself,
LIOS DTS includes patented optical
frequency domain reflectometry (OFDR)
technology, which provides an invariant
spatial resolution of the measurement
along the entire sensor length. This
identifies and clearly measures atypical
hotspots or temperature anomalies at
early stages, even at remote distances.
LIOS Technology GmbH develops and
supplies state-of-the-art frequency
domain-based DTS systems, which are
proven in critical applications such as power cable
monitoring, fire detection and temperature sensing in the
oil and gas industry. The company’s DTS system comprises
the following items:
WELL.DONE evaluation unit (one set) – mounted in the
control room.
Splice box (two sets) – installed on the roof of the
tanks.
Low-temperature sensing fibre (1000 m) – installed
along the inner tank.
Transmission fibre (750 m) – connect with the low
temperature fibre to the control room.
Fibre installation
The first channel of the controller starts with the
transmission fibre optic cable, which is connected
through the splice box to the low temperature sensing
fibre optic cable. The sensing cable is installed from an
injection point in the roof and runs downwards along
the wall of the inner tank. After reaching the bottom,
the cable circles around the foundation and goes back
up to the roof where it exits at the same point and is
spliced again with the transmission cable. This will bridge
the distance from the first tank to the second tank. The
sensing cable for the second tank is installed in the same
fashion as the first one.
Both the transmission and
sensing cable will run back
to the second channel
using the same route.
Figure 2 shows the exact
layout and Figure 3 shows
the installation method of
the cable from the drum.
As shown in Figure 4 (left hand image),
the clamps are fixed by screws and used
on the wall of the inner tank to fix the fibre
optic cable. The distance between two
neighbouring screws is 1 m. For the
installation at the foundation of the LNG
tank, the method shown in Figure 4
(right hand image) is applied. The distance
between two clamps is also 1 m. Figure 5
shows a live photo of the actual
installation.
Case study: Tianjin
LNG project
The Tianjin LNG terminal uses DTS
systems from LIOS Technology to detect
the possible leakage on LNG tanks at an
early stage. Based on the requirements,
one set of 4KM/4CH DTS systems have
been supplied for this project. With
the ability to use up to four optical
channels and a measurement range of
4 km per channel, the LIOS WELL.DONE DTS system is a
cost-effective solution.
The system uses a double-ended measurement mode
to ensure an accurate measurement, as both channels are
measuring from both directions and calibrate
automatically. The backscattering data is transmitted
through fibre optic cables to the evaluation unit (controller)
where the precise temperature data is calculated. Through
the distributed temperature profile, the real-time condition
of LNG tanks is monitored for any possible leakage.
Whenever there is a leakage on the tank, the local
temperature will drop significantly due to the
Joule-Thomson effect and eventually trigger the alarm at
the DTS system. The location and temperature of the alarm
will be recorded and sent via communication protocol to
the management system of the terminal.
Conclusion
DTS systems can monitor the real-time temperature
along the entire fibre optic cable. Through the accurate
measurement result, the real-time condition of the tank is
monitored and any possible leakage, even at early stages
with a small amount of leakage, can be detected through
the changes of temperature. The reliable system design as
well as state-of-the-art performance of the DTS system has
redefined modern leakage detection and ensured the safe
operation of the LNG tanks.
Figure 5.
Fibre optic cable on
the wall of an LNG tank.
Figure 4.
How to fix the fibre optic cable to the tank.
