5 - Containment 8.28.09 Final HQ

8/8/2019 5 - Containment 8.28.09 Final HQ

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Information Paper No. 5 Containment

Managing LNG Risks ContainmentGIIGNLs Technical Study Group has overseen the development of this Information Se-ries of 7 papers to provide factual information about Liquefied Natural Gas (LNG), or GNLin French, Spanish, Portuguese or Italian speaking countries. This paper describes thetanks used to store LNG, which should be viewed as the primary means for safely con-

taining LNG and preventing the exposure of LNGs extremely cold temperatures andflammable vapours to facility workers or the public. Secondary containment, i.e., ways inwhich the tank contents will be captured on site in the unlikely event of a leak or spill, isalso discussed. For more information on these topics, additional references and web-links are provided at the end of this paper.

LNG Information Paper No. 5

Introduction

A primary safety requirement for the industry is tocontain LNG. LNG is stored in large tanks at liquefactionfacilities and import terminals. At an import terminal,LNG is stored until it is turned back into natural gasthrough regasification and then sent out to consumers inpipelines. A typical LNG import terminal has 2 to 4 LNGstorage tanks (although a small number have over 10tanks). LNG can also be imported and stored in anoffshore receiving terminal.

LNG tanks have more than one means of containment.The first layer of containment is provided by the tankwhich holds the LNG. All LNG storage tanks areconstructed with thermal insulation to prevent heattransfer, reduce evaporation, and protect the structurefrom cryogenic temperatures which could damage the

structural integrity of the tank. Secondary containment isprovided either by the use of dykes, berms andimpoundment dams around storage tanks, or by buildinga second tank around the primary storage tank tocontain the LNG in the unlikely event of a failure in theprimary tank.

The decision to use a particular design is influenced byavailable space and local requirements. The vastmajority of LNG storage tanks are above-ground. Japan

has constructed some tanks below ground to conserveexpensive land, and there are some floating storagetanks at offshore receiving terminals. This paper focuseson onshore storage tanks.

Storage Tanks

The tanks in which LNG is stored are the means forprimary containment. Safe and secure containment is inpart a function of the codes and standards whichcontribute to the operational integrity layer of protection(described in Information Paper No. 4); these codesand standards define suitable engineering designs andspecify appropriate materials for constructing storagetanks and other equipment at LNG facilities. Several

types of tanks are used to store LNG in the world today.In some places a reinforced concrete tank surrounds theinner tank. Types of onshore LNG storage tanks include:

Single containment tank,

Double containment tank,

Full containment tank,


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Membrane tank, and

In-ground tank.

Single Containment Tank

A single containment tank is composed of an inner

cylindrical container made of 9% nickel steel which isself-supporting (Figure 1). This inner tank is surroundedby an outer tank made of carbon steel which holds aninsulation material (usually an expanded material calledperlite) in the annular space. The carbon steel outer tankis not capable of containing cryogenic materials; thus theinner tank provides the only containment for thecryogenic liquid. However, single containment tanks arealways surrounded by a dyke or containment basinexternal to the tank, either of which provides at least100% secondary containment in the event of a completefailure of the inner tank. This type has an excellenthistory of reliability and represents the majority of tanks

in the world. Single containment tanks require arelatively large are of land.

Double Containment Tank

The double containment tank is similar to a singlecontainment tank, but instead of a containment dyke(there is an outer wall usually made of post-stressedconcrete (Figure 2). Therefore, if the inner tank fails, thesecondary container is capable of containing all of thecryogenic liquid.

Figure 1. Single containment tank (Source: Kawasaki Heavy Industries, Ltd.)

Key

1 suspended deck (insulated)2 post-stressed concrete secondary container3 elevated slab

4 base insulation5 outer shell (not able to contain liquid)6 loose fill insulation7 roof if required8 primary container

Figure 2. Double containment tank (Source: EN 1473)


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The outer concrete wall increases the cost of the tank,but less space is required because the containment dykeis eliminated. Should the inner tank fail, the liquid will becontained and vapours will escape through the annulargap, which is the space between the two tanks or thetanks and the concrete wall.

Full Containment Tank

A full containment tank is a double containment tank inwhich the annular gap between the outer and inner tanksis sealed (Figure 3). The majority of LNG storage tanksbuilt in the last 10 years worldwide have been designedas full containment tanks.

In this tank, the secondary container is liquid- andvapour-tight in normal operations. In case of leakage ofthe primary barrier, the secondary container remainsLNG- tight. The secondary container wall is generallymade of post-stressed concrete and the roof is usuallyreinforced concrete, although under EN 1473 metal roofsmay be allowed.

Membrane Tank

The membrane type of storage tank is a post-stressedconcrete tank with a layer of internal load-bearinginsulation covered by a thin stainless-steel corrugatedmembrane (Figure 4). In this design, the concrete tanksupports the hydrostatic load (weight of the liquid) which

Figure 3. Full containment tank (Source: Kawasaki Heavy Industries, Ltd.)

Key

1 suspended deck (insulated)

2 post-stressed concrete secondary

3 elevated concrete raft

4 base insulation5 loose fill insulation container

6 reinforced concrete roof

7 primary container membrane

Figure 4. Membrane tank (Source: EN 1473)


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is transferred through the membrane and insulation (inother words, the membrane is not self-supporting). Themembrane is able to shrink and expand with changingtemperatures.

These tanks were constructed primarily in France andKorea in the 1970s and 1980s.

In-ground Tanks

In-ground LNG tanks are obviously less visible in theirsurroundings (Figure 5). They are mainly used in Japanand some other Asian countries. They were developedby Tokyo Gas Engineering (TGE) in the early 1970s,based on earlier designs in the UK, US and Algeria, andsubsequently used by other Japanese companies. As of2005, there were 61 in-ground storage tanks in Japan.The record for the largest LNG tank in the world was firstset by an in-ground tank (200,000 m3), although severalabove-ground tanks have recently been built with asimilar capacity.

These tanks are more expensive and take longer to buildthan an above-ground tank about 4 to 5 yearscompared to 3 years for a tank built above ground. Theterminals with in-ground tanks are designed to

harmonise with the surroundings and ensure safety atevery stage of the lifecycle. These tanks do not need tobe surrounded by a dyke or bund wall, so the separationdistance from adjacent land is less than that of othertypes of tanks. This is especially important for countriessuch as Japan, Korea, and Taiwan. The likelihood ofspills is also reduced since the LNG level is belowground. In 45 years, there have not been any incidentsconcerning LNG tanks which have had any impact

beyond the terminal boundary.

Leak and Spill Capture

LNG terminals are designed to detect any vapour leaks,as well as to detect and capture liquid leaks. LNGcontainment is a system which consists of the primarycontainment in the tank plus secondary containment,e.g., the impoundment around the tank to capture andkeep in place any leakage of LNG. Storage tanks alsoincorporate the following measures to prevent leaks ordetect leaks immediately at the source:

Tank construction of special materials andequipment with systems designed to safelyinsulate and store LNG at temperatures of-162C (-259F);

Figure 5. In-ground storage tank (Source: Kawasaki Heavy Industries, Ltd.)


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Cool down temperature sensors on the tank walland base;

Leak detection temperature sensors located inthe annular space to signal a low temperaturealarm;

LNG tank gauging systems to provide remotereadings and high/low level alarms;

Level temperature density gauge to detectrollover potential;

Pressure controllers and relief valves;

Passive fire protection, e.g., fireproofing, fireresistant barriers and coatings; and

Various codes and standards for maintenanceand inspection of equipment in LNG service.

Many of these safety measures in tank design and

construction were implemented to prevent areoccurrence of the incident at a peak-shaving facility inCleveland, Ohio, US in 1944, 20 years before LNGbecame a significant industry. Post-incident analysisclearly demonstrated that the size of the design of thecapture basin was inadequate. Since then, codes andstandards have been developed to require a secondlayer of protection around the primary containment (ofsingle-containment tanks). Single-containment tanksnow must be designed to prevent the spread of an LNGspill. Dykes, berms, and dam impoundments surroundeach single-containment storage tank to capture theLNG in case of a spill. The size of impoundment areas

must be able to capture a volume which exceeds that ofthe storage tank. Dykes are designed to contain 100-110% of the tank volume and to be high enough so thetrajectory of a leak at the upper liquid level in the tankcan not overshoot the edge of the dyke. Impoundmentareas often have concrete or earthen liners and employsome method for extracting rain and deluge water.

In the unlikely event of a leak of any kind, all LNGfacilities have many types of equipment to detect arelease, and initiate immediate notification and control ofthe leak or spill. Standard detection and initial responseequipment in various areas of an import terminal include:

Cryogenic liquid detection;

Gas or vapour detection;

Smoke detectors;

Flame detectors;

Safety alarms;

Emergency shutdown valves on piping to stopthe flow of LNG and limit the quantity of LNGreleased; and

Secondary containment designed to mitigate theconsequence(s) of release.

Vapour and liquid detection equipment is used to detect,

set off alarms and monitor flammable vapours. Mostdevices have remote monitoring screens, e.g., in acontrol room, and provide a safe and secure way tomonitor the situation and manage the overall facility.Continuous improvements are made in detectionsystems and there are vendors who specialise insystems just for LNG.

LNG facilities develop and maintain emergencyresponse plans for the unlikely event of any leak. Theseplans identify potential credible incident scenarios andthen develop specific actions to control and mitigate theconsequences of these incidents.

Key Points and Conclusions

In closing, the reader should remember the key points ofthis information paper:

1. In an industry in which safety considerations areparamount, as underscored by the degree to whichrelated codes, equipment, regulations, proceduresand systems permeate all of our efforts, containmentis the primary requirement for LNG safety.

2. LNG facilities and terminals have more than onemeans of containment. Beyond the first layer (thespecifically-designed and constructed tanks), variousmethodologies (including berms, dykes,impoundment dams and secondary tanks) are usedto provide another layer of protection.

3. Various kinds of tanks are used around the world,including Single Containment Tanks, DoubleContainment Tanks, Full Containment Tanks,Membrane Tanks and In-ground Tanks.

4. Liquid and gas/vapour leak detection and responsesystems incorporate a wide array of relevant devices

and technologies, including alarms, emergencyplans and shutdown valves, fireproofing/fire-resistantbarriers and coatings, flame detectors, gaugingdevices, pressure controllers, relief valves, smokedetectors and temperature sensors.

5. Most devices have remote monitoring screens, e.g.,in a control room, to provide a safe and secure wayto monitor the situation and manage the overallfacility.


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Next, in Information Paper No. 6: Industry SafeguardSystems, we will review leak prevention and detectionsystems, emergency plans and emergencypreparedness in greater detail. This paper will againtouch upon the profound importance of safetyconsiderations in every facet of the LNG industry. Asgraphically reflected in the Multiple Safety Layers figureon the last page, these layers assure LNG safety, andare firmly based on a foundation of solid Industry

Standards, Regulatory Compliance and Codes. Thesesafety layers incorporate several key components ofthe industrys risk management framework: includingPrimary and Secondary Containment, Control Systemswhich promote Operational Integrity, Protocols, OperatorKnowledge and Experience (which are reinforced bycomprehensive and ongoing training). A protectiveumbrella of Safeguard Systems, Separation Distances,Contingency Planning and Exercises further enhancesthe safe management of LNG.

References and Additional Resources

British Standards Institution (BSI) BS 7777: 1993 Parts1: http://www.hse.gov.uk/hid/land/comah/level3/5C39A0F.htm

Bureau Veritas , 2009

Center for LNG - www.lngfacts.org

Foss, Michelle Michot. October 2003. LNG Safety andSecurity. Available from: http://www.beg.utexas.edu/energyecon/lng/documents/CEE_LNG_Safety_and_Security.pdf

Foss, Michelle Michot. Introduction to LNG. UpdatedJanuary 2007. Center for Energy Economics.Available from: http://www.beg.utexas.edu/energyecon/lng/documents/CEE_INTRODUCTION_TO_LNG_FINAL.pdf

GIIGNL - The International Group of Liquefied NaturalGas Importers website - www.GIIGNL.org

Society of International Gas Tanker and Terminal

Operators (SIGTTO) website - www.sigtto.orgTokyo Gas inground tanks. http://www.tokyo-gas.co.jp/

lngtech/ug-tank/index.html

World Bank Group International Finance Corporation.Guidelines for Liquefied Natural Gas (LNG) Facilities.h t t p : / / w w w . i f c . o r g / i f c e x t / s u s t a i n a b i l i t y . n s f /AttachmentsByTitle/gui_EHSGuidelines2007_LNG/$FILE/Final+-+LNG.pdf


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Multiple Safety LayersManage LNG Risk

The GIIGNL Technical Study Group ha

developed this 7-paper series to providpublic readers with factual informatioabout the LNG industrys multiple layers safety beyond the foundation of induststandards, regulatory compliance ancodes as illustrated in the figure to the left

The GIIGNL Information Papers include:

No. 1 Basic Properties of LNG

No. 2 The LNG Process Chain

No. 3 LNG Ships

No. 4 Managing LNG Risks Op-erational Integrity, Regulations,Codes, and Industry Organisations

No. 5 Managing LNG Risks Containment

No. 6 Managing LNG Risks In-dustry Safeguard Systems

No. 7 Questions and Answers(Q&As)

For more information about these and other topics, or to obtain copies of this report series contact:

GIIGNL22 rue Marius Aufan92300 Levallois (France)

Telephone: +33 01 41 05 07 13

Fax: + 33 01 47 54 81 80

Email: [email protected]

Web address: http://www.giignl.org

Liquefied Natural Gas(LNG)

Primary Containment

Safeguard Systems, Separation Distances,Contingency Planning and Exercises

Secondary Containment

Industry Standards, Regulatory Compliance & Codes

Control Systems, Operational Integrity & Protocols,Operator Knowledge, Training & Experience

(Source: SEA Consulting, Inc.)

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