Journal of Materials Science and Engineering B 8 (9-10) (2018) 188-194 doi: 10.17265/2161-6221/2018.9-10.002 Performing Reliable Early Leak Detection on Storage Tank Terminals: Retrofitting of Existing Facilities and New Buildings Raul Risi Oil & Gas Division Manager, TTK S.A.S., 75008 Paris, France Abstract: Liquid leak detection may represent a challenge for Oil & Gas operators, as indicated by operational feed-back and independent studies. Despite the availability of many different leak detection technologies, some systems may either fail to detect spills or generate frequent false alarms. In particular, possible soil contamination from pre-existing leaks and pollution carry-over by rain water is difficult to filter out by a leak sensing system. Typical case of false alarms relates to punctual sensors installed upstream the drain valve within the storage tank bunds, monitoring possible presence of leaks in rain water. Besides old soil contamination, other criteria should also be considered when selecting a spill detection technology, such as asset type to be monitored (storage tank, pipeline, …), system accuracy (minimum detectable quantity, ability to localize the leak), detection time, reliability over time, capital, installation and operating costs. The paper will include an evaluation of different external leak detection technologies with respect to the above-mentioned criteria, pointing out the capabilities and limitations of each system. Focus will be placed on reliability of leak monitoring systems in challenging environments. A new generation of digital, reusable sensing cables and probes, as well as the impact of sensitivity for different applications, will be discussed. Since leak sensor installation environment (positioning, adoption of special precautions, …) may significantly affect the system performance, different above ground and underground configurations will be presented, both for new builds and existing facilities. Key words: Liquid leak detection, addressable system, storage tank, pipeline. 1. Introduction Operational experience has shown how difficult it is to get reliable leak detection from a sensing system, although several different leak detection technologies are available today. On pipelines, studies, performed by others [1, 2] on real life pipeline incidents, have highlighted that conventional leak detection systems in place today on existing pipelines may fail to provide satisfactory pipeline monitoring. In particular, examination of 10 years of US federal data from the “Pipeline and Hazardous Materials Safety Administration” (PHMSA), provided in Ref. [2], has highlighted that, when analyzing 960 events of Corresponding author: Raul Risi, master in chemical engineering, Oil & Gas Division Manager at TTK S.A.S., research fields: environmental protection and safety—oil leak detection. pipeline spills on the USA network that took place over 10-year period, only 5% of them were spotted by leak detection systems in place. Moreover, only 20% of the “very significant” leaks (i.e. larger than 1,000 bbl) were detected by monitoring systems. Similarly, major leak incidents on storage tanks have been reported even recently [3]. This paper discusses the challenges relating to leak detection on storage tank terminals, presenting newly deployed solutions using addressable, reusable liquid sensing cables. 2. Challenges of Leak Monitoring on Storage Tank Terminals Based on operators’ feed-back, false alarms from leak sensors appear to be one of the main issues, if not THE primary concern on many sites. In particular, possible soil contamination from D DAVID PUBLISHING
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Journal of Materials Science and Engineering B 8 (9-10) (2018) 188-194 doi: 10.17265/2161-6221/2018.9-10.002
Performing Reliable Early Leak Detection on Storage
Tank Terminals: Retrofitting of Existing Facilities and
New Buildings
Raul Risi
Oil & Gas Division Manager, TTK S.A.S., 75008 Paris, France
Abstract: Liquid leak detection may represent a challenge for Oil & Gas operators, as indicated by operational feed-back and independent studies. Despite the availability of many different leak detection technologies, some systems may either fail to detect spills or generate frequent false alarms. In particular, possible soil contamination from pre-existing leaks and pollution carry-over by rain water is difficult to filter out by a leak sensing system. Typical case of false alarms relates to punctual sensors installed upstream the drain valve within the storage tank bunds, monitoring possible presence of leaks in rain water. Besides old soil contamination, other criteria should also be considered when selecting a spill detection technology, such as asset type to be monitored (storage tank, pipeline, …), system accuracy (minimum detectable quantity, ability to localize the leak), detection time, reliability over time, capital, installation and operating costs. The paper will include an evaluation of different external leak detection technologies with respect to the above-mentioned criteria, pointing out the capabilities and limitations of each system. Focus will be placed on reliability of leak monitoring systems in challenging environments. A new generation of digital, reusable sensing cables and probes, as well as the impact of sensitivity for different applications, will be discussed. Since leak sensor installation environment (positioning, adoption of special precautions, …) may significantly affect the system performance, different above ground and underground configurations will be presented, both for new builds and existing facilities.
Operational experience has shown how difficult it is
to get reliable leak detection from a sensing system,
although several different leak detection technologies
are available today.
On pipelines, studies, performed by others [1, 2] on
real life pipeline incidents, have highlighted that
conventional leak detection systems in place today on
existing pipelines may fail to provide satisfactory
pipeline monitoring.
In particular, examination of 10 years of US federal
data from the “Pipeline and Hazardous Materials
Safety Administration” (PHMSA), provided in Ref. [2],
has highlighted that, when analyzing 960 events of
Corresponding author: Raul Risi, master in chemical engineering, Oil & Gas Division Manager at TTK S.A.S., research fields: environmental protection and safety—oil leak detection.
pipeline spills on the USA network that took place over
10-year period, only 5% of them were spotted by leak
detection systems in place. Moreover, only 20% of the
“very significant” leaks (i.e. larger than 1,000 bbl)
were detected by monitoring systems.
Similarly, major leak incidents on storage tanks
have been reported even recently [3].
This paper discusses the challenges relating to leak
detection on storage tank terminals, presenting newly
deployed solutions using addressable, reusable liquid
sensing cables.
2. Challenges of Leak Monitoring on Storage Tank Terminals
Based on operators’ feed-back, false alarms from
leak sensors appear to be one of the main issues, if not
THE primary concern on many sites.
In particular, possible soil contamination from
D DAVID PUBLISHING
Performing Reliable Early Leak Detection on Storage Tank Terminals: Retrofitting of Existing Facilities and New Buildings
189
pre-existing leaks might result in false
alarms—following pollution carry-over by rain water.
Typical case of this type of false alarm relates to
punctual sensors monitoring rain water quality
installed upstream the drain valve, within the storage
tank bunds, monitoring possible presence of leaks in
rain water.
Besides pre-existing soil contamination, the
following criteria should be considered when selecting
a spill detection technology :
System accuracy in terms of :
o Minimum detectable quantity
o Ability to localize the leak
Responsiveness—detection time
Reliability over time
Operating costs :
o Non-reusable systems
o Need for recalibration
o Maintenance
o Discontinuous monitoring : recurrent expenses in
certain cases, e.g. use of tracers
For discontinuous monitoring: risk of
non-detected leaks
Retrofitting : possibility of system implementation
3. Leak Detection Technologies Available Today
Leak detection technologies for pipelines and
storage tanks can be either internally or externally
based:
(1) Internally based technologies
a. Volume or Mass balance
b. Statistical analysis
c. Rate of change in pressure (and flow for pipelines)
based leak detection technologies may not be able to
fulfill increasingly stringent requirements, in terms of
accuracy and/or reliability, imposed by some
regulatory standards or agencies.
Advantages and limitations of main external leak
detection technologies [4] are highlighted in Table 1.
4. Addressable Sensing Cable Technology
The French company TTK has developed a patented
addressable system [5, 6] based on sensing cables and
probes, allowing early stage, accurate and reliable leak
detection.
The structure of the sensing cable section is
presented in Fig. 1.
The functioning principle of TTK sensing cable is
the following:
sensing string divided in multiple cables (or
“sections”) of nominal length
each section provided with an embedded
microprocessor-based electronic module, housed in
liquid-proof shell (IP68 rated), so that each section
becomes autonomous from the rest the string
electronic modules communicating with a remote
electronic panel through a low-power digital
communication bus fit for hazardous areas (Ex zone 0)
sensor element composed of coextruded,
conductive silicone absorbing hydrocarbon liquids or
their vapors in case of physical contact with them
electrical resistance increasing as a consequence
of the induced swelling
When the electrical resistance reaches a factory
pre-set value, the alarm panel receives a leak alarm by
the electronic module with the localization of the leak
on the concerned element—thanks to its unique
address.
Performing Reliable Early Leak Detection on Storage Tank Terminals: Retrofitting of Existing Facilities and New Buildings
190
Since the hydrocarbon absorption process is
reversible, the sense cable can be reused. This allows
easy site leak testing after installation, under real
conditions.
The outer surface of the sensor element is
electrically insulated and highly hydrophobic and is not
affected by the environmental conditions such as water,
dust/dirt, etc.
TTK sensing cables are available in standard lengths
(3 m, 7 m, 12 m and 20 m) that can be interconnected
to form a continuous sensing string up to 800 m per
circuit.
Three references by TTK are available, with
different sensitivity:
Table 1 Advantages and limitations of main external leak detection technologies. Capabilities Limitations
Liquid Sensing Cable
Method can determine leak location Cannot estimate the size of the leak
A reasonably fast response time May not be able to trig emergency shutdown actions in a very quick time
Minimally affected by multi-component flow conditionsMultiphase flow leak may not be detected if only gas escaped
More sensitive than computational methods Installed cost is generally high. Retrofitting to existing pipelines could also be costly
Limited risk of false alarms thanks to direct product sensing
Some of the available liquid sensing cables are not reusable
More sensitive than computational methods and responds in seconds to minutes
Acoustic/vibration, strain and temperatures sensing are prone to false alarms due to other sources than the leaks
Fiber Optic Cable
Method can determine leak location Usually cannot estimate the size of the leak Method can estimate the concentration of the hydrocarbon and maybe the size of the leak (only for chemical sensing fibers)
Stability of the chemical coating is an issue which could lead to missed leaks (only for chemical sensing fibers)
A reasonably fast response time Re-calibration may be required
Minimally affected by multi-component flow conditions Multiphase flow is problematic for this technique Fiber optic is immune to electromagnetic interference (noise)
Installed cost is generally high. Retrofitting to existing pipelines could also be costly
Significant constraints for unit installation along the pipeline
Vapor tube
Location of the leak can be estimated Response time is slower than most other continuous external measurement types
The size of the leak can be estimated by concentration measurements
Retrofitting to existing pipelines could be costly
Minimally affected by multi-component or multiphase flow conditions
This method is not effective for above ground pipelines
More sensitive than computational methods and responds in seconds to minutes
Installed cost is generally high
Acoustic emissions
Method can determine the location of the leak High flow noise conditions may mask the leak signal (valve or pump noise, multiphase flow)
Size of leak can be estimated Numerous sensors may be needed to monitor long pipelines
Minimally affected by multi-component flow Installed cost is generally high More sensitive than computational methods and responds in essentially real-time
Potential false alarms due to other sources than the leaks, depending on the performance of the computational method
The acoustic emission method can be used on new or retrofitted to existing pipelines
Leak resolution is generally well above 20 m
Thermal Imaging
Method can determine the location of the leak Affected by environmental conditions
Size of leak can be estimated Numerous cameras are needed to monitor long pipelines
Minimally affected by multi-component flow Installed cost is generally high The method can be used on new or retrofitted to existing pipelines
Need frequent maintenance to ensure clear vision field
Easily accessible to vandalism or thefts
Low rate leaks cannot be detected reliably
Fig. 1 Addr
FG-OD
FG-OD
be present in
FG-OD
oil, HFO, v
FG-OD
In particu
some contam
fresh leaks.
TTK
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5. ImpleDetection
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recommende
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D: standard re
DR: less sensi
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DC: enhanced
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cleaning req
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iable Early Leitting of Exist
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voiding contac
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underground
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191
hus avoiding
pollution, as
sensing leaks
groundwater
side a slotted
well as shown
micro-drilling
False alarms
are avoided
hydrocarbon
cable.
including a
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available for
pits.
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192
Fig. 2 Recom
Fig. 3 Exam
Per
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tion with mon
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rage tank retr
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eak Detectionting Facilities
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main Oil & Ga
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as Operator in
Tank Terminuildings
Asia).
nals:
Fig. 4 Recom
Fig. 5 Exam
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iable Early Leitting of Exist
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eak Detectionting Facilities
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Tank Terminuildings
nals:
193
3
Performing Reliable Early Leak Detection on Storage Tank Terminals: Retrofitting of Existing Facilities and New Buildings
194
On above ground lines, it is recommended to strap
the sense cable at pipe bottom after placing it inside a
UV-protective braid, as shown in Fig. 5.
The arrangements described above, based on
reusable, addressable sense cable, constitute a new
approach to achieve accurate and reliable leak
monitoring of storage tank terminals.
References
[1] Shaw, D., Phillips, M., Baker, R., Munoz, E., Rehman, H., Gibson, C., and Mayernik, C. 2012. “Leak Detection Study-DTPH56-11-D-00001.” Final Report No. 12-173,
U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration.
[2] Song, L. 2012. “Few Oil Pipeline Spills
Detected by Much-Touted Technology.” Inside Climate
News.
[3] Wikipedia website:
https://en.wikipedia.org/wiki/List_of_oil_spills.
[4] Summa, J. 2011. “Pipeline Leak Detection Operational
Improvements.” Present at PTC 6th Pipeline Technical