Storage of Liquid Chlorine

Storage of Liquid Chlorine

GEST 73/17

7th Edition

January 2014

EURO CHLOR PUBLICATION

This document can be obtained from:

EURO CHLOR - Avenue E. Van Nieuwenhuyse 4, Box 2 - B-1160 BRUSSELS

Telephone: 32-(0)2-676 72 65 - Telefax: 32-(0)2-676 72 41

GEST 73/17 7

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January 2014 Page 2 of 26

Euro Chlor

Euro Chlor is the European federation which represents the producers of

chlorine and its primary derivatives.

Euro Chlor is working to:

improve awareness and understanding of the contribution that chlorine

chemistry has made to the thousands of products, which have improved

our health, nutrition, standard of living and quality of life;

maintain open and timely dialogue with regulators, politicians, scientists,

the media and other interested stakeholders in the debate on chlorine;

ensure our industry contributes actively to any public, regulatory or

scientific debate and provides balanced and objective science-based

information to help answer questions about chlorine and its derivatives;

promote the best safety, health and environmental practices in the

manufacture, handling and use of chlor-alkali products in order to assist

our members in achieving continuous improvements (Responsible Care).

***********

This document has been produced by the members of Euro Chlor and should not be reproduced in

whole or in part without the prior written consent of Euro Chlor.

It is intended to give only guidelines and recommendations. The information is provided in good

faith and was based on the best information available at the time of publication. The information

is to be relied upon at the user’s own risk. Euro Chlor and its members make no guarantee and

assume no liability whatsoever for the use and the interpretation of or the reliance on any of the

information provided.

This document was originally prepared in English by our technical experts. For our members’

convenience, it may have been translated into other EU languages by translators / Euro Chlor

members. Although every effort was made to ensure that the translations were accurate, Euro

Chlor shall not be liable for any losses of accuracy or information due to the translation process.

Prior to 1990, Euro Chlor’s technical activities took place under the name BITC (Bureau

International Technique du Chlore). References to BITC documents may be assumed to be to Euro

Chlor documents.

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RESPONSIBLE CARE IN ACTION

Chlorine is essential in the chemical industry and consequently there is a need

for chlorine to be produced, stored, transported and used. The chlorine

industry has co-operated over many years to ensure the well-being of its

employees, local communities and the wider environment. This document is one

in a series which the European producers, acting through Euro Chlor, have drawn

up to promote continuous improvement in the general standards of health,

safety and the environment associated with chlorine manufacture in the spirit of

Responsible Care.

The voluntary recommendations, techniques and standards presented in these

documents are based on the experiences and best practices adopted by member

companies of Euro Chlor at their date of issue. They can be taken into account

in full or partly, whenever companies decide it individually, in the operation of

existing processes and in the design of new installations. They are in no way

intended as a substitute for the relevant national or international regulations

which should be fully complied with.

It has been assumed in the preparation of these publications that the users will

ensure that the contents are relevant to the application selected and are

correctly applied by appropriately qualified and experienced people for whose

guidance they have been prepared. The contents are based on the most

authoritative information available at the time of writing and on good

engineering, medical or technical practice but it is essential to take account of

appropriate subsequent developments or legislation. As a result, the text may

be modified in the future to incorporate evolution of these and other factors.

This edition of the document has been drawn up by the Equipment working

group to whom all suggestions concerning possible revision should be addressed

through the offices of Euro Chlor.

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Summary of the Main Modifications in this version

Section Nature

All Merge with GEST 72/10 on pressure storage of liquid chlorine

and adapt the terminology (refrigerated and non-refrigerated)

All Clarification on double-jacketed storage tanks

3.2.5. Updated thermal insulation paragraph

3.4. Precision that stress relief is done after welding

4.2. Precision added for cases where chlorine withdraw is from the

bottom of the tank

4.5.1. Removal of chlorinated fluorocarbons as example, as there is no

practical experience mentioned

5.8. Added paragraph on inspection (after washing)

5.10. Addition of paragraph on fighting a big leak

Table of Contents

1. GENERAL POINTS 6

1.1. The Choice between Storage with or without Refrigeration 6 1.2. Unit Capacities 6 1.3. Number of Storage Tanks 7

2. BASIC DESIGN AND LOCATION OF THE STORAGE SYSTEM 7

2.1. Design and Permits 7 2.2. Principle 8 2.3. Location 8

2.3.1. Outside or Inside Location 8 2.3.2. Protection from External Damage 8 2.3.3. Distance from Rails and Roads 8 2.3.4. Distance from Another Operating Process 8 2.3.5. Distance from the Boundary of the Factory 9 2.3.6. Distance between two Adjacent Storage Tanks 9

2.4. Bunding 9 2.5. Emergency Capacity 9

3. CONSTRUCTION OF STORAGE TANKS 10

3.1. Basis of Design 10 3.1.1. Design Pressure 10 3.1.2. Design Temperature 11 3.1.3. Corrosion Allowance 11 3.1.4. Thermal Insulation 12

3.2. Materials of Construction 12 3.2.1. Steel 12 3.2.2. Branches, Flanges, Nuts and Bolts 13

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3.2.3. Pipework 13 3.2.4. Quality of Jointing Materials 13 3.2.5. Thermal Insulation 13

3.3. Foundations and Supports 14 3.3.1. Foundations 14 3.3.2. Supports 14

3.4. Stress Relief 14 3.5. Inspection and Testing 14

3.5.1. Inspection of Construction Materials 14 3.5.2. Inspection during Fabrication 15

4. ACCESSORIES 15

4.1. Branches 15 4.2. Valves and Isolation 16 4.3. Pipework 16 4.4. Measuring Equipment 17 4.5. Safety Equipment 17

4.5.1. Over and Under-Pressure 17 4.5.2. Protection of the External Shell 18

4.6. Filling Ratio 18 4.7. Thermal Expansion Bellows for Double-Jacketed Tanks 18 4.8. Filling, Emptying and Venting Equipment 19

4.8.1. Filling 19 4.8.2. Emptying 19 4.8.3. Venting 19

5. OPERATION 19

5.1. Cleaning and Drying before Chlorine can be Admitted 19 5.2. Leak Testing 19 5.3. Commissioning 20 5.4. Total Emptying 20 5.5. Reactive Materials 21 5.6. Filling and Emptying in Normal Operation 21

5.6.1. Quality of Chlorine Introduced 21 5.6.2. Temperature and Pressure of the Liquid Chlorine Introduced 21 5.6.3. Emptying the Tank 21

5.7. Venting and Isolated Systems (Cold Chlorine Storage) 22 5.8. Periodic Inspection and Testing 22

5.8.1. External inspection 22 5.8.2. Internal inspection 23

5.9. Methods of Protection and Alarm 23 5.10. Response to a significant loss of primary containment - Methods and Equipment 24

6. REFERENCES 25

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DEFINITIONS

This recommendation concerns storage systems provided by fixed liquid chlorine

storage tanks constructed to operate with or without refrigeration.

1. GENERAL POINTS

1.1. The Choice between Storage with or without

Refrigeration

Ambient temperature chlorine storage means storage at high pressure. The

advantages of ambient temperature storage are:

Simplicity of operation

Easy visual external inspection (no thermal insulation)

Lower investment cost

Refrigerated chlorine storage means storage at lower pressure, in some cases at

atmospheric pressure. The advantages of refrigerated storage are:

Lower initial emission in case of loss of containment if at atmospheric

pressure (lower initial flash of chlorine gas due to the fact that liquid

chlorine is at lower temperatures compared to pressurized storage)

The complexities of refrigerated storage and its associated systems mean it is

unsuitable for small chlorine users.

1.2. Unit Capacities

In order to minimise hazard, the inventory should be limited to the minimum

strictly necessary. The unit capacity is chosen taking into account:

The process requirements (operation continuity, maintenance/inspections

works),

The loading/off-loading requirements; the tank must normally be larger

than the contents of one mobile tanker.

Based on practical long term field experience, the probability of a total tank

failure can be assumed as negligible.

The most important safety feature depends primarily on the design, operation

and inspection of the storage system.

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1.3. Number of Storage Tanks

In order to provide the desired storage capacity and the continuity of the

supply, a compromise may be required between the individual unit capacities

and the number of storage tanks.

It should be noted that increasing the number of tanks leads to a proportional

increase in the number of accessories, with the related various risks of mal-

operation and mal-functioning. It is therefore desirable to limit the number of

tanks, without forgetting the necessity of an available safety capacity (see point

2.5.).

2. BASIC DESIGN AND LOCATION OF THE STORAGE

SYSTEM

2.1. Design and Permits

A careful risk assessment study, periodically updated, is necessary to ensure

that the required level of safety is attained.

The methods used should be agreed with the relevant national/local authorities.

In some countries scenarios and models are required.

Some consideration is given below to the choice of the worst case scenario (see

paragraph 2.2. Principles).

Simple models are usually sufficient to evaluate the physical effects. However,

relevant expertise is always needed to define the scenarios, to use and to

interpret the results of such models correctly. To assess the effect on people

(workers and neighbouring population) recognised toxicity “probit function”1

will be used. The study must show that the risk is acceptable and that adequate

measures have been taken to protect people and the environment.

In some cases, storage tanks may be designed with double jacket; Usually,

double jacket means that the outer wall is designed to resist a lower pressure

than the inner wall as it is primarily used to monitor possible small leaks of the

chlorine inner storage tank (for example PN 10). The space inside the double

jacket should be monitored, e.g. by a permanent flow of dry air or nitrogen with

a chlorine detector at the outlet of the flushing gas with alarm; alternatively

the space can be kept under nitrogen pressure with alarm.

1 The probit function is a statistical function describing the range of susceptibility in a population to a harmful consequence; it uses a criterion in the form of an equation which expresses the percentage of a defined population which will suffer a defined level of harm (normally death) when exposed to a specified dangerous load (time and intensity/concentration)..

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In some cases, the outer wall is also used as bunding and its design conditions

will then be identical to those of the inner wall.

2.2. Principle

Liquid chlorine bulk storage could be the potential source of the worst case of

loss of primary containment. However, a chlorine storage system can be

designed and operated safely so that the risk of complete tank failure and

release of much of its contents can be assumed negligible.

The principles which must be followed to achieve this are discussed in the

following chapters.

It is also recommended to use GEST 87/130 - Hazard Analysis for Chlorine

Plant' for the design of the storage system.

2.3. Location

2.3.1. Outside or Inside Location

Storage system can be located in the open air or in a closed building.

The decision on this matter must be based on a careful risk assessment taking

into account the advantages and disadvantages of each alternative listed in the

Position paper XII - Memorandum on Confinement of Liquid Chlorine Plants.

2.3.2. Protection from External Damage

Chlorine storage must be located in an area with protective barriers so that it is

fully protected from external damage from vehicle impact.

The location and design of a storage tank has to be chosen to minimise the

possible effects resulting from traffic (see 2.3.3), flooding, subsidence,

earthquake, fire or explosion in a neighbouring plant.

2.3.3. Distance from Rails and Roads

Installations should be located at least 25 m from public roads and railway lines

to minimise the risk of damage to the storage in the event of an accident. This

distance has to be defined taking into account the local conditions, rules and

regulations.

2.3.4. Distance from Another Operating Process

If a neighbouring unit does not present risk of fire or explosion, the minimum

recommended separation is 10 m taking into account the local situation.

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If a fire or explosion risk exists, greater distances or means of protection will be

required. These must be established for each individual case, based on a risk

assessment and taking any national and local rules and regulations into account.

2.3.5. Distance from the Boundary of the Factory

The minimum recommended separation is 10 m taking into account the local

situation and the size of the storage.

In all cases, suitable fences, together with adequate security supervision, should

be provided to prevent unauthorised access (see also GEST 05/316 – Guideline

for site security of chlorine production facilities).

2.3.6. Distance between two Adjacent Storage Tanks

It is recommended that sufficient distance should be provided between adjacent

storage tanks, to give good access to the tanks for operation, maintenance and

inspection, and to permit the passage of personnel equipped with self-contained

breathing apparatus in case of incident.

2.4. Bunding

All above ground storage tanks should be placed in a liquid tight bund.

The volume of the bund should be calculated to receive at least the full

contents of the worst realistic case scenario. A retention capacity of one storage

tank is generally considered adequate. As a single bund may contain more than

one storage tank, its capacity shall be based on the largest tank contained.

The bund should be designed to limit the surface area in order to reduce the

rate of evaporation of liquid chlorine in the event of a leakage, but without

restricting access (see sections 5.9 and 5.10.

The bund shall never be directly connected to a drain. Collected water (rain …)

shall be removed by a pump or an ejector which shall be manually operated only

after checks on the bund contents.

In case of double-jacketed tank, the outer wall can be designed to provide such

a bunding facility.

2.5. Emergency Capacity

It is essential that a damaged storage tank can be emptied rapidly into a spare

capacity, preferably a spare tank.

If the emergency capacity is in the form of an empty tank, there should be a

means to maintain it at low pressure, e.g. a system of degassing to an

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absorption system or a chlorine consuming unit, or a large liquefaction set, the

reliable operation of which should be assured.

The use of a double-jacketed storage tank with the external wall designed as

bunding facility means that any chlorine leakage will be contained and will not

affect the external environment. In this case it is therefore not necessary to

provide spare capacity to which the contents of a leaking tank can be

immediately transferred.

3. CONSTRUCTION OF STORAGE TANKS

3.1. Basis of Design

3.1.1. Design Pressure

The design pressure should be chosen on the basis of detailed consideration of

all circumstances which will arise during operation of the storage system. The

principal factor to be taken into account is the vapour pressure of chlorine at

the maximum temperature to which the storage system can be subjected.

Allowance must also be made for the maximum pressure resulting from the

presence of any padding gas.

Once the design pressure has been chosen, all reasonable measures must be

taken to ensure that it is not exceeded in the course of subsequent operations.

It is also necessary to consider a minimum design pressure.

In case of double-jacketed tank, these minimum and maximum design pressures

have to be determined both for the internal and the external shells.

Storage tank (inner shell in case of double-jacketed tank)

The minimum design pressure should be calculated taking into account:

the minimum temperature of the chlorine introduced

the means of emptying and venting chlorine (connection to absorption

unit or suction of a compressor)

the maximum venting rate, even under accidental circumstances

the pressure from any purge gas between the two walls of double-

jacketed tanks

the possible accidental presence of some chlorine between the two walls

of double-jacketed tanks.

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The maximum pressure should be calculated as a function of:

the vapour pressure of chlorine at the maximum temperature to which

the storage tank can be subjected, including a margin for the presence of

inert gasses

the internal conditions within the storage tank when it is isolated (for

example roll over of the liquid chlorine)

the hydrostatic pressure due to the height of liquid chlorine

any transient conditions during filling and emptying.

External Shell (if double-jacketed tank)

The weight of the external thermal insulation, if present, shall be taken into

account.

If the external wall is designed as bunding facility, the minimum and maximum

pressures should be identical to the inner wall to account for the extreme

conditions in case of failure.

3.1.2. Design Temperature

The minimum design temperature is minus 40°C (considering that an excess of

inert gasses can lower the vaporisation temperature of the chlorine).

The maximum design temperature can be calculated from possible solar heating,

taking into account of any insulation.

In case of a double-jacketed tank, the choice of minimum design temperature

for the external shell depends on its extended purpose. As it is intended to

provide secure containment in the event of a leak from the internal tank, it

should be designed for minus 40°C. If it is only intended to monitor possible

small leak of the internal wall, it may be designed for ambient temperatures.

The overall construction must take account of differential thermal expansion

between the internal tank and the external shell, particularly in relation to

supports, branches and other equipment; the maximum allowed differential

temperature should be defined during the design.

3.1.3. Corrosion Allowance

A corrosion allowance of 1 mm is considered a minimum for the tank (also for

the external shell if it is designed to act as a bund in the event of a leak). This

value will be added to the calculated thickness before choosing the schedule

just above the resulting total thickness.

Thermally insulated or not, the external surface of the equipment will be

painted with a corrosion protective coating.

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3.1.4. Thermal Insulation

For chlorine storage tanks, insulation may be required for different reasons:

avoid water condensation or ice formation on equipment

protection of personnel for cold temperature

protection from possible external heating

If installed, the thermal insulation should be based on the minimum chlorine

temperature and the maximum external temperature appropriate for the

geographical location. The thickness is determined by, amongst others, the

capabilities of the facilities to handle the evaporated chlorine gas due to the

heat input (liquefaction unit, absorption unit or refrigeration unit) see section

5.7.

Care will be taken to avoid any accumulation of moisture between the insulation

layer and the equipment surface in order to prevent corrosion under insulation

(CUI).

Proper painting or coating of the equipment or piping is strongly recommended

to prevent external surface corrosion, as well as good insulation surveillance,

inspection and repair programs.

Operating discipline must be applied to ensure that insulation stripped or

removed for maintenance or inspection purposes is replaced and sealed in a

timely manner.

The quality of installation is important for the corrosion protection of the

pipe/equipment and the tightness of the jacketing can be improved by tapes or

mastic sealing; particular attention shall be paid at branching points.

3.2. Materials of Construction

3.2.1. Steel

The plate chosen for the construction of storage tanks should be made of fine

grain steel with good welding properties and which has satisfactory impact

strength at minus 40°C after welding (see also GEST 79/82 - Choice of

Materials of Construction for Use in Contact with Chlorine).

These tests are particularly important concerning the impact strength of the

metal before and after welding.

If double-jacketed tank, the quality of the steel can be different for the internal

tank and the external shell, to take into account of the minimum design

temperature chosen for each.

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3.2.2. Branches, Flanges, Nuts and Bolts

The metal used for flanges and branches should have the same quality as the

material used in the construction of the storage tank itself. Bolting equipment

should conform to GEST 88/134 - Stud Bolts, Hexagon Head Bolts and Nuts for

Liquid Chlorine.

The overall arrangement of flanges and jointing material should prevent the

gasket being expelled by excess pressure.

3.2.3. Pipework

Pipework used for handling chlorine should be designed to have an adequate

wall thickness and should use a quality of steel suitable for the temperature and

pressure of the operation.

As far as possible, l00% radiography of the welds should be carried out. In

circumstances where radiography is not possible welds should be inspected by a

dye penetrant test, ultrasonic or magnetic inspection. For further information,

refer to GEST 73/25 - Transport of Dry Chlorine by Pipeline.

3.2.4. Quality of Jointing Materials

The jointing material used must be an asbestos free material. See GEST 94/216

- Experience of Non-Asbestos Gaskets on Liquid and Dry Chlorine Gas

Service.

3.2.5. Thermal Insulation

The material used for thermal insulation needs to be:

inert in presence of chlorine

not flammable or combustible, or at least self-extinguishing

For cold liquid chlorine, there is no predominant insulation material but the

following are satisfactorily used:

polyurethane foams

foam glass

mineral wool

Other materials are sometimes used (phenolic resins …).

Vapour barriers must be utilised to prevent the ingress of moisture on any

insulated pipe/equipment that operates at temperatures below ambient

temperature).

For the cladding used to protect externally the insulation layer and to prevent

as far as possible ingress of water, several materials can be used, according to

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the local environment (aluminium, stainless steel, coated carbon steel, plastic,

resin, fibre reinforced resin …).

For double-jacketed tanks, no insulation will be installed in the inner space.

3.3. Foundations and Supports

3.3.1. Foundations

The design of the foundation will take into account the wind and seismic loads.

3.3.2. Supports

Supports should be designed in accordance with a recognised standard and in

such a manner that they provide overall mechanical stability for the storage

tank and do not lead to any abnormal stresses on its walls. They must permit

thermal expansion and contraction due to variations in temperature which can

occur. They must limit local thermal losses by conduction.

The design of the supports will take into account the wind and seismic loads.

Special consideration may be necessary where load cells or balances are used in

determining the contents of the tank.

3.4. Stress Relief

Stress relieving is recommended and should be carried out, after welding, in

accordance with the quality of steel used and with the method of welding. It is

specifically recommended for the support legs and branches and especially for

areas of greater wall thickness.

3.5. Inspection and Testing

3.5.1. Inspection of Construction Materials

The steel plate supplied for the tank should be tested mechanically and

chemically in order to confirm the material is in compliance with the

specifications (in addition to checking the certificates).

These tests are particularly important to establish the impact strength of the

metal at the proposed design temperature.

The metal used for flanges, blanks, nuts, bolts, welding rods etc. should also be

subject to acceptance tests to meet a specification compatible with the above

requirements.

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3.5.2. Inspection during Fabrication

The inspection procedures during the construction of the liquid chlorine storage

system should conform to the codes being applied, particularly regarding (not

exhaustive and not in chronological order):

qualification of the welders and the welding procedures

100% radiography of welds

tensile strength, bending, hardness and impact strength tests on test

pieces of the welds

thickness measurement and detection of cracks or laminations by

ultrasonic means

pressure test

Additionally, inspection to determine gas tightness by halogen or helium testing

could be realised.

Conformance to the relevant codes should be confirmed by an independent third

party.

The objective is to guarantee a fault free construction. The quality of the

construction is considered to be an essential requirement for the safety of

future operation.

4. ACCESSORIES

4.1. Branches

The wall thickness should be according to GEST 73/25 – Transport of Dry

Chlorine by Pipeline. The number and sizes of branches should be limited to

the minimum necessary for the installation of equipment required in the gas or

liquid phase.

For mechanical robustness, the recommended minimum diameter of the

branches should be 40 mm.

Except for the liquid chlorine extraction connection, if realised on the bottom

of the tank, all branches should be installed on manhole covers.

Top connection is preferred. In the case of a bottom connection it should be

limited to one connection and the construction must be strong enough to

withstand accidental mechanical loads.

A dimension of 150 mm is considered as a maximum for the liquid phase.

Larger branches such as those required for manholes, introduction of pumps etc.

should be located in the gaseous phase of the storage tank.

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There should not be bi-directional connections between the gas phase of the

tank and the gaseous chlorine network that could contain some hydrogen (see

also GEST 08/360).

4.2. Valves and Isolation

It is necessary to provide valves on each branch of the storage tank which

enable it to be isolated. It is recommended that remotely operable valves be

fitted at least on liquid chlorine inlet and outlet connections. All manually

operated valves should be installed in a way allowing easy access.

All valves installed on the storage tank should be of a design specifically

developed for liquid chlorine duty. The materials of construction of these valves

should correspond to the intended operating temperature and pressures. GEST

06/318 – Valves Requirements and Design for Use on Liquid Chlorine and

GEST 94/204 – Pneumatically Operated Valves for Use on fixed Storage

Tanks, Rail and Road Tankers and ISO-Containers for Liquid Chlorine provide

specifications for valve types suitable for use on storage tanks. Other valves may

be suitable but should be assessed carefully to ensure they deliver equivalent

safety.

When the storage tank is fitted with a bottom connection, it is normally

recommended that a secondary internal globe valve is provided, capable of

isolating the branch in the event of failure of the external isolation valve or of

the associated joint. This internal globe valve should also be remotely operable,

independently of the external valve.

As an alternative to the secondary internal valve for both bottom liquid

connections, the storage tank may be located in a closed and sealed building

(secondary containment) connected to an absorption unit with sufficient

absorption capacity to process possible chlorine leak (see 2.3.2 regarding indoor

tanks). In any case, the number of connections/valves should be strictly limited.

On connections to storage tanks used to withdraw liquid chlorine from the top,

dip tubes will be installed.

4.3. Pipework

All pipework connections to the storage tank should be designed to suit the

temperature and pressure of the chlorine and should be of an adequate wall

thickness (See GEST 73/25 – Transport of Dry Chlorine by Pipeline).

100% radiography of welds on this pipework is recommended. In circumstances

where radiography is not possible welds should be tested by dye penetrant test

ultrasonic or magnetic inspection.

The specific connections between the storage system and loading or off-loading

installations should conform to the recommended guideline GEST 78/73 -

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Design Principles and Operational Procedures for Loading/Off-Loading Liquid

Chlorine Road and Rail Tankers and ISO-Containers.

4.4. Measuring Equipment

The following instrumentation is recommended to check the status of the tanks

from the control room:

an indication of level (weighbridge, load cells, radioactive measuring

system or other adapted for chlorine duty)

high level alarm

pressure indicator with alarm

The high level alarm should be provided by a separate device to that used for

normal measurement of level and should ensure that the filling ratio indicated

in section 4.6 below is not exceeded.

Any hydraulic fluids or oils used in the instrumentation should be compatible

with chlorine (chloro-fluorinated oil).

Additionally, double-jacketed tanks should be provided with:

maximum, minimum and differential pressure alarm for the annular space

flow rate of annular purge air

humidity of the purge gas

chlorine content of the purge gas leaving the space between the inner

and outer tanks

temperature measurement on the walls of the internal tank.

Temperature measurement is important to avoid thermal shock or stresses. At

least four measurement points should be provided on the wall of the internal

tank. The indication given by these measurements is particularly important

during the commissioning of the tank to avoid the maximum temperature

differential used in the differential expansion calculation for the tank, being

exceeded.

4.5. Safety Equipment

4.5.1. Over and Under-Pressure

The internal tank (and the external shell) should be fitted with means to protect

them against over-pressure (relief valves, hydraulic guards, etc.). Bursting discs

may be used to prevent small leaks at safety valves. In those cases the space

between the valve and the disc has to be monitored closely and leaks (pressure

rise) is to be alarmed. The application of bursting discs without safety valves is

not recommended because chlorine flow would not stop when the pressure

returns to normal value.

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If the tank is not designed for the maximum under-pressure that can occur,

additional protective measures may be required (e.g. hydraulic guards,

blanketing …).

These systems should be capable of isolation for maintenance or after

operation, by means which provide an adequate level of safety such as, for

example, the use of valves which are locked open or the use of a double

inter-connected valve system.

Relief valves should conform to the recommended guideline GEST 87/133 –

Overpressure Relief of Chlorine Installations.

Where a hydraulic guard can be used, the liquid chosen should be suitable for

operating in an atmosphere of chlorine, for example sulphuric acid of 92-95%

strength.

The operating pressure of the relief systems should be consistent with the design

pressure and operating pressure chosen. The design of the relief systems should

take all possible scenarios into account.

The vent from a relief stream should be retained in a suitable installation - a

compression and liquefaction system or an absorption system. To cope with

potential pressure surges, and to avoid liquid entrainment in a system designed

for gas, a large enough buffer tank must be installed downstream of the relief

system.

4.5.2. Protection of the External Shell

The annular space between the two shells should be permanently purged by dry

air or nitrogen. This compensates for the effect of breathing between the two

shells, and allows also confirming the absence of humidity or chlorine.

4.6. Filling Ratio

The total load should not exceed the filling ratio multiplied by the volume of the

chlorine tank. The filling ratio used shall comply with the applicable national or

international legislation.

The filling ratio usually considered within Europe is 1.25 t/m³.

4.7. Thermal Expansion Bellows for Double-Jacketed Tanks

As the internal and external shells can be at very different temperature, it is

essential to allow for the differential thermal expansion which may occur

between the walls of the internal tank and the external shell. This should be

calculated for the extreme conditions of service, including those arising during

commissioning or total emptying of the storage system (with possible liquid

chlorine cooled down by partial vaporisation). To do this, all branches should be

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designed to take the full variation in temperature into account. This may be

achieved by use of expansion bellows.

The expansion bellows should generally be constructed of high nickel alloy,

without any corrosion allowance. Expansion bellows are an important feature of

the construction which should be given careful study. Radiographic examination

should be carried out on all welds. In addition, particular care should be taken

during installation.

4.8. Filling, Emptying and Venting Equipment

4.8.1. Filling

The transfer of chlorine into the tank is generally done through a dip pipe.

4.8.2. Emptying

Empting by means of nitrogen or dry air pressure is often applied.

Alternatively, vertical submerged pumps can be installed inside the tank or in an

individual duct connected to the tank or canned pumps can be located below

the storage tank.

4.8.3. Venting

The chlorine vent gas should be retained in a suitable installation - a

compression and liquefaction system or an absorption system. In either case, the

chosen system must be designed to be permanently available.

5. OPERATION

5.1. Cleaning and Drying before Chlorine can be Admitted

Before chlorine is admitted, the tank and all its accessories should be rigorously

degreased, cleaned and dried (see also GEST 80/84 – Commissioning and

Decommissioning of Installations for Dry Chlorine Gas and Liquid). The drying

should be carried out to achieve and confirm a dew point of minus 40°C on the

purge gas at the exit of the system. For all internal equipment which requires to

be greased, and where there is a risk of it coming in contact with chlorine, only

grease which is compatible with chlorine may be used (chloro-fluorinated

greases).

5.2. Leak Testing

Before commissioning, all valves and accessories should be tested to guarantee

their gas tightness under the conditions of operation.

GEST 73/17 7

th Edition


The following methods may be used:

1. a helium test in a calm and non-ventilated atmosphere

2. testing with a chlorine/dry gas mixture with the various joints etc.

checked by the use of ammonia

3. a pneumatic test using soap and water to detect leaks.

5.3. Commissioning

The procedure given in GEST 80/84 - Code of Good Practice for the

Commissioning of Installations for Dry Chlorine Gas and Liquid should be

strictly observed.

A number of precautions need to be taken before commissioning:

confirmation of the quality of the chlorine introduced

o moisture content below 20 mg/kg (see GEST 10/362)

o nitrogen trichloride (see GEST 76/55 - Maximum Levels of

Nitrogen Trichloride in Liquid Chlorine)

check on the temperature differential from top to bottom of the tank (for

double-jacketed tanks, see paragraph 3.1.2).

One method of commissioning consists of filling the tank in batches, and waiting

between each introduction of liquid until thermal equilibrium has been

established. It is desirable to take the system up to the maximum operating

pressure for each of these introductions of liquid. It is desirable to limit the rate

at which chlorine is introduced to limit the vent rate and the temperature

differential between the different points of the tank (for double-jacketed

tanks).

5.4. Total Emptying

A number of precautions need to be taken before total emptying:

removal of the maximum amount of chlorine in the liquid phase

final dilution of the residual chlorine contained in the tank by chlorine

known to have a low nitrogen trichloride level

check on the quality of chlorine remaining in the tank in order to ensure

that it contains an acceptable level of nitrogen trichloride for total

vaporisation

purging with dry air or an inert gas (dew point minus 40°C at atmospheric

pressure), using a connection to the tank which is only made immediately

before its time of use; alternatively, a permanent connection can be

installed with backflow protection and double block and bleed.

GEST 73/17 7

th Edition


5.5. Reactive Materials

All precautions must be taken to avoid the entry of humidity, reactive materials,

or hydrogen into the storage tank.

In addition, if inert gas is being used for the transfer or purging of chlorine, this

should not be source of contamination by reactive materials (see 5.6.3).

5.6. Filling and Emptying in Normal Operation

5.6.1. Quality of Chlorine Introduced

The chlorine introduced into a storage system should be periodically tested in

particular to meet the following points:

moisture content (lower than 20 mg/kg)

nitrogen trichloride (for values see GEST 76/55 - Maximum Levels of

Nitrogen Trichloride in Liquid Chlorine)

All precautions must be taken to avoid accumulating hydrogen in the gas phase

of the tank.

5.6.2. Temperature and Pressure of the Liquid Chlorine Introduced

For refrigerated liquid storage, the temperature of the liquid chlorine

introduced should be sufficiently close to that of the chlorine already contained

in the tank to ensure the evaporation rate in the tank does not exceed the

design conditions of the system. This point is particularly important when

chlorine is being imported directly from mobile containers.

During the operation of filling and emptying, the connections between the cold

liquid storage tank, and all other external equipment, should be carefully

checked and supervised to avoid any scenario which could unintentionally

connect high pressure gas (chlorine or inert gas) to the tank gas phase.

To avoid thermal shock on the steel shell, it is preferable to cool down the tank

prior to the first liquid introduction (using for example a cool gas).

5.6.3. Emptying the Tank

The liquid chlorine can be extracted from the tank with the help of a pump or

with padding with uncontaminated dry inert gas having a dew point below minus

40°C at atmospheric pressure.

The volume of liquid removed can be compensated with dry gaseous chlorine

exempt of hydrogen or with dry air or inert gas (a dew point lower than minus

40°C at atmospheric pressure).

GEST 73/17 7

th Edition


To prevent possible backflow, the pressure of the inert gas should be at least 1

bar greater than the operating pressure of the tank and this differential pressure

must be permanently maintained. The total pressure should not exceed the

design pressure.

5.7. Venting and Isolated Systems (Cold Chlorine Storage)

The vent rates depend on the level of liquid chlorine (variation in surface area),

the pressure of the vent system and possibly external atmospheric conditions

(temperature, rain, etc).

The autonomy of the storage system (the time for which it can remain totally

isolated) depends on:

the ratio of surface to volume of the tank

the filling ratio

the thermal insulation chosen

the difference between the pressure at the time of the tank isolation and

the maximum operating pressure.

Two days should be considered a minimum for an isolated system to be

sustained.

5.8. Periodic Inspection and Testing

Periodic inspection of the whole storage system is necessary. This includes the

inner tank, the shell, pipework, valves, pressure relief devices, instruments,

safety loops, etc.

The internal inspections are done after having completely emptied, vented and

washed the tanks to avoid the potential risk coming from residual chlorine.

5.8.1. External inspection

The first inspection is recommended two years after the first commissioning.

The periodicity of inspection will be determined by local regulations but should

not exceed 6 years.

Inspection should include the following aspects:

visual examination, particularly of the welds

(ultrasonic) thickness testing of walls, flanges and branches

verification of all accessories

inspection of lagging and painted surfaces (including under the lagging).

As a general rule, all equipment should be replaced systematically before there

is any risk of it becoming defective.

GEST 73/17 7

th Edition


5.8.2. Internal inspection

Here also the inspection frequencies will depend on the requirements of the

authorities. Based on the inspections history with consecutive good results and

other control measures in place to avoid corrosion, it is advised to discuss with

the authorities an extension of the inspection interval as long as appropriate

because the procedure itself introduces the risk of corrosion.

Inspection should include the following aspects:

visual examination, particularly of the welds, the bottom line and around

gas-liquid interface level

(ultrasonic) thickness testing of walls

verification of all internal accessories

Where a storage tank has been washed out or where a hydraulic test is imposed

by local regulations, specific procedures need to be laid down in order to reduce

to a minimum the effects of corrosion (see GEST 80/84 - Code of Good Practice

for the Commissioning of Installations for Dry Chlorine Gas and Liquid). Too

frequent hydraulic retesting is not recommended because of the risk of

corrosion which is associated with it.

5.9. Methods of Protection and Alarm

The following precautions should be taken:

an emergency plan, giving the detailed instructions to be followed in the

event of emergency, should be permanently available and understood by

plant personnel; this emergency plan should contain detailed instructions

for transferring the content of a leaking storage tank into another tank

chlorine leak detectors should be provided to warn the operators of the

existence of a leak; see also GEST 94/213 - Guidelines for the Selection

and use of Fixed Chlorine Detection Systems in Chlorine Plants

the operator should be able to use a fixed water spray curtain or the site

fire brigade should be able to rapidly use a mobile water spray curtain to

control the spread of any chlorine gas cloud; this operation should avoid,

as far as possible, any direct contact between the water and the liquid

chlorine

for small leaks, a funnel connected with flexible hoses to an absorption

system can be applied to the leak

if the storage system is installed within a bund, measures should be taken

to reduce the rate of evaporation of any chlorine contained within the

bund e.g. walls of the bund with a low thermal conductivity, slope in the

bund which allows the liquid chlorine to accumulate in a small area, or

use of a protein foam or a plastic sheet to form an insulating layer on the

liquid chlorine pool

GEST 73/17 7

th Edition


if the chlorine cloud comes from a leakage in liquid phase, an alternative

method with an emergency funnel can be used; the funnel is connected

at the leakage and reduces the access of air to droplets of chlorine (less

energy available and fewer droplets evaporated). The droplets coalesce

to liquid chlorine in the funnel and can be collected in a (temporary)

emergency tank at the outlet of the funnel, reducing the chlorine cloud

self-contained breathing sets and protective clothing suitable for dealing

with a chlorine leak should be always available in various locations in the

vicinity of the storage system and always accessible in case of emergency

(cartridge respirators should not be used for intervention and particularly

when there is any risk of a high concentration of chlorine)

a means of indicating the wind direction should be installed to tell the

operator of the possible direction of dispersion of gas that will occur in

the event of an accident; it is important to remember that heavy chlorine

gas clouds behave like liquid and will tend to flow to the deepest area

all operators and maintenance personnel should be trained to deal with

leaks of chlorine, and periodic exercises should be organised to ensure

that this standard of training is maintained.

5.10. Response to a significant loss of primary containment -

Methods and Equipment

Depending on local circumstances, several solutions are possible to respond to a

significant liquid chlorine leak. Some practical examples are given below:

spread foam (medium expansion protein foam, e.g. FP 70) on the

containment bund

spray water curtains around the area (do not spray into the bundle)

start air aspiration above the containment bund, and send it to the

absorption unit

connect the containment bund to an underground tank to minimise the

evaporation area and allow localised connection to the absorption unit

(avoid sending liquid chlorine to the absorption unit)

transfer the liquid chlorine from the leaking tank into an empty spare

tank; this one is vented to the absorption unit to neutralise progressively

all the chlorine. This transfer can be achieved by the pressure difference

between the leaking tank and the relatively depressurised spare tank or

by means of a pump. Those transfer capabilities are preferably remotely

controlled.

Remarks:

the foam is effective to drastically reduce the chlorine evaporation,

giving time to organise the collection of the liquid chlorine, but a

GEST 73/17 7

th Edition


temporary increase of chlorine vaporisation occurs when the foam is

sprayed

the water curtains have only a local impact; by creating a significant air

mixing, they reduce the chlorine concentration behind the curtain, but

have no long distance impact; precautions must be taken to avoid

increased corrosion by spraying water on the leak, and to increase the

vaporisation by adding water into the containment bund.

6. REFERENCES

GEST 73/25 - Transport of Dry Chlorine by Pipeline

GEST 76/55 - Maximum Levels of Nitrogen Trichloride in Liquid

Chlorine

GEST 78/73 - Design Principles and Operational Procedures for

Loading/Off-Loading Liquid Chlorine Road and Rail Tankers and ISO-

Containers

GEST 80/84 - Code of Good Practice for the Commissioning of

Installations for Dry Chlorine Gas and Liquid

GEST 87/133 – Overpressure Relief of Chlorine Installations

GEST 88/134 - Stud Bolts, Hexagon Head Bolts and Nuts for Liquid

Chlorine

GEST 94/204 – Pneumatically Operated Valves for Use on fixed

Storage Tanks, Rail and Road Tankers and ISO-Containers for Liquid

Chlorine

GEST 94/213 - Guidelines for the Selection and use of Fixed Chlorine

Detection Systems in Chlorine Plants

GEST 94/216 - Experience of Non-Asbestos Gaskets on Liquid and Dry

Chlorine Gas Service

GEST 05/316 – Guideline for site security of chlorine production

facilities

GEST 06/318 – Valves Requirements and Design for Use on Liquid

Chlorine

Position Paper XII - Memorandum on Confinement of Liquid Chlorine

Plants

TSEM 90/161 - Quantitative Risk Assessment

GEST 73/17 7

th Edition


Industrial consumers of chlorine, engineering and equipment supply companies

worldwide and chlorine producers outside Europe may establish a permanent

relationship with Euro Chlor by becoming Associate Members or Technical

Correspondents.

Details of membership categories and fees are available from:

Euro Chlor

Avenue E Van Nieuwenhuyse 4

Box 2

B-1160 Brussels

Belgium

Tel: +32 2 676 7211

Fax: +32 2 676 7241

e-mail: [email protected]

Internet: http://www.eurochlor.org

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