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

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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)

d. Real Time Transient Model (RTTM)-pipelines

e. Negative pressure wave-pipelines

(2) Externally based technologies

a. Liquid sensing cable

b. Fiber optic cable

c. Vapor sensing tube

d. Acoustic sensor

e. Vapour sensor

f. Infrared camera

g. Tracer systems

h. Other technologies of punctual sensors—storage

tanks

Despite recent technology improvements, internally

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

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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

Conference 2011, Hannover, Germany.

[5] TTK. 2014. “Patent Application PCT/EP2014/073733.”

Gautier Olivier, Gillot Olivier, Balatchev Stefan.

[6] TTK. 2014. “Patent Application PCT/EP2014/074966.”

Balatchev Stefan, Gillot Olivier.