THE ENGINEERING EQUIPMENT AND MATERIALS USERS ASSOCIATION
RECOMMENDATIONS FOR THE
DESIGN AND CONSTRUCTION OF
REFRIGERATED LIQUEFIED GAS
STORAGE TANKS
PUBLICATION No. 147 : 1986
Copyright 0 1986 The Engineering Equipment and Materials Users Association
ISBN 085931 113 9
3rdFloor, 20 Long Lane
LONDON EClA 9HL
Telephone
: 020 7796 1293
Fax
: 020 7796 1294
&mail
: sales@eemua.co.uk
: www.eemua.co.uk
website
THE ENGINEERING EQUIPMENT AND MATERIALS USERS
ASSOCIATION
The Engineering Equipment and Materials Users Association-EEMUA-was
formed in 1983
by the Amalgamation of the Oil Companies Materials Association (OCMA) and the Engineering
Equipment Users Association (EEUA). It is an organisation of substantial purchasers and
users of engineering products, whose members include leading national and multinational
companies in the petroleum, gas, chemical and energy industries, and engineering contractors
that provide services to those companies. A list of Full and Associate Members (the latter
being limited to membership of three technical committees) is given below. EEMUA is
concerned with the design, installation, operation and maintenance of the engineering plant
used by members in pursuing their business activities.
The Association aims to reduce members' costs by providing the opportunity for them to share
resources and expertise in order to keep abreast of technological developments and improve
the effectiveness and efficiency of their engineering activities. EEMUA supports the British
Standards Institution, works with other institutions, associations, government departments,
regulatory authorities and the Confederation of British Industry, and is also actively involved
with other standards-making bodies, both national and international, such as the American
Petroleum Institute.
Work, which is carried out in-house by members alone or with the help of other organisations,
may lead to the production of Association publications. These are prepared primarily for
members' use, but are usually offered for sale and thus for more general use. Such
publications may also be submitted, normally through the British Standards Institution, as
bases for appropriate national, European or international standards.
A list of current EEMUA publications which may be purchased from the Association is given at
the end of this publication.
Full Members
Associate Members
ABB (Process Industries UK)
Associated Octel
BP
ConocoPhillips
Dow Corning
ExxonMobil
Foster Wheeler Energy
lnnogy
PowerGen
Shell
Total (was TotalFinaElf)
TXU Energi
AstraZeneca
BASF
CAN (Offshore)
ChevronTexaco
D&C Engineering/MERCON[Netherlands]
Flexsys
ICI
MB Inspection
Norsk Hydro
01s
Royal Vopak [Netherlands]
Syngenta
Veritec
Affiliate Members
British Compressed Gases Association
ii
Previous page
is blank
ABOUT THIS PUBLICATION: LEGAL ASPECTS
In order to ensure that nothing in this publication can in any manner offend against or
be affected by the provisions of the Restrictive Trade Practices Act 1976, the
recommendations which it contains will not take effect until the day following that on
which its particulars are furnished to the Office of Fair Trading.
As the subject dealt with seems likely to be of wide interest, this publication is also
being made available for sale to non-members of the Association. Any person who
encounters an inaccuracy or ambiguity when making use of this publication is asked to
notify EEMUA without delay so that the matter may be investigated and appropriate
action taken.
It has been assumed in the preparation of this publication that the user will ensure
selection of those parts of its contents appropriate to the intended application, and that
such selection and application are correctly carried out by appropriately qualified and
competent persons for whose guidance the publication has been prepared. EEMUA
does not, and indeed cannot, make any representation or give any warranty or
guarantee in connection with material contained in its publications, and expressly
disclaims any liability or responsibility for damage or loss resulting from their use. Any
recommendations contained herein are based on the most authoritative information
available at the time of writing and on good engineering practice, but it is essential for
the user to take account of pertinent subsequent developments andlor legislation.
All rights are reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means: electronic, mechanical,
photocopying, recording or other.
Infringement of copyright is not only illegal, but also reduces the Association's income
thereby jeopardising its ability to fund the production of future publications.
iii
CONTENTS
1.
2.
3.
4.
FOREWORD
Page Nos.
1
1.1
Background
1
1.2
Scope
1
1.3
Related Standards
1
1.4
Definitions of Terms
CLASSIFICATION OF STORAGE S U E M S
2.1
2.1.1
General
Summary of Loadings, Conditions and Considerations
2.2
2.2.1
2.2.2
2.2.3
Definitions o f Containments
Single Containment
Double Containment
FulIContainment
S A F R Y REQUIREMENTS AND SPECIAL PROVISIONS
1-2
3
5
3.1
3.1.1
Environment and General Considerations
Basic Requirements for Pressure and Vacuum Relief
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5.
3.2.6.
Leakage and Spillage
General
Risk of External Leakage to Atmosphere
Local Internal Leaks
Internal Condensation
Overfilling
Spillage
11
11
12
12
3.3
3.3.1
3.3.2
Tank Layout and Spacing
Location and Spacing
Radiation Flux Levels
12
12
12
3.4
Requirements for Fire Protection/Loss Control Systems
13
3.5
Protection Against Explosion and Impact
13
3.6
Lightning Protection
13
3.7
Effect of Radio Transmission, Static Electricity and Cathodic
Protection Systems
3.8
Earthquakes
LOADING CASES AND DESIGN CONSIDERATIONS
5
5-10
11
11
11
13-14
14
15
4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7
4.1.8
4.1.9
4.1.10
4.1.11
Normal Loading Cases
Dead Load
Imposed Load
Snow Load
Internal Vacuum
Internal Pressure
Wind Load
Product Liquid Loading
Hydrostatic Testing
Pressure from Insulation on Inner Tank Shells
Applied Loads
Settlement
15
15
15
15
15
15
15
15
15
16
16
16
4.2
4.2.1
Abnormal Loading Cases
Earthquakes
16
16
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
5.
MATERIALS
16-17
17
17
17
17
17
17
19
Inner Tank Materials (Primary Containers)
Plate and Fitting Materials
Shell Plate Thickness
Welding Process
Bolting Materials
Aluminium Alloy Bolting
Mountings
19
19
19
20
21
21
21
5.2.2
5.2.3
5.2.4
Steel for Outer Tanks
Secondary Liquid Containers (with Internal or External Insulation)
for Double and Full Containment Tanks
Outer Gas Containers for Single Containment Tanks
Steel Liners and Membranes
Corrosion Protection
21
22
22
22
22
23
5.3
5.3.1
5.3.2
5.3.3
Reinforcing Steels for Concrete
General
Quality Assurance
Impact Requirements
23
23
23
23-24
5.4
5.4.1
5.4.2
Prestressing Steel and Anchors
General
Materials
24
24-25
25
5.5
Concrete
25-26
5.6
5.6.1
5.6.2
5.6.3
5.6.4
5.6.5
Insulation
Insulation Categories
Tank Base Insulation
Tank Shell Internal Insulation
Tank Shell External and Roof Insulation
Suspended Deck Insulation
26
26
26
26
26
27
5.7
Earth Embankment
27
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.2
5.2.1
6.
External Explosions and Their Effects
Fire Hazards
Leakage o f the Inner Tank o f Double and Full Containment
Sudden Failure of the Inner Tank
Overfill of the Inner Tank
Roll-Over
De-Commissioning (See Chapter 9)
DESIGN
29
6.1
6.1.1
6.1.2
6.1.3
6.1.4
Foundations
General
Soil Investigation
Foundation Design
Types of Foundation and Tank Floors
6.2
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
Design of Steel Tanks of Single Containment or Steel Inner or
Outer Tanks of Double or full Containment
Tank Bottom Design
Shell Design
Interna I Loadings
Shell Openings
Access to Inner Tank
34
34
34
36
37
37
6.3
Vapour Containing Outer Tanks
37
6.4
Reinforced Concrete Outer Tanks with Earth Embankment
37
29
29
29-30
30-33
33
6.1 1
6.4.2
6.4.3
6.4.4
37
39
40
40
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
Prestressed Concrete Outer Tanks
General
Base Design
Wall to Base Junction
Wall Design
Wall to Roof Junction and Roof Design
6.6
6.6.1
6.6.2
6.6.3
6.6.4
6.6.5
6.6.6
Insulation Design
General
Influence of Service on Thermal Characteristics of Foams
Water Vapour Barrier
Chemical Properties
Mechanical Properties
Fire
45
45
45
45-46
6.7
6.7.1
6.7.2
6.7.3
Membranes and Linings
General
Design Philosophy
Liner Design
46
46
46-47
47
6.8
6.8.1
6.8.2
6.8.3
6.8.4
6.8.5
6.8.6
Base and Wall Heating Design
Tank Base and Wall
Heater Layout and Output
Heating Control
Spare Temperature Sensors
Electrical Failure
Electrical Failure of Main Power Supply
6.9
Pressure and Vacuum Relief
6.10
6.10.1
6.10.2
7.
Generz
Wall to Bottom Junction
Shell to Roof Connection
Earth Embankment
Venting and Drainage of the annulus of double containment tanks
Venting
Drainage from the Annulus
6.1 1
Earthquake Design (See Appendix F)
6.12
Special Nozzles and Access Openings
40
40-42
42
42
43
44
44
44
44
47
47
48
48
48
48
48
48-49
50
50
50
50
50-51
MANUFACTURE AND CONSTRUCTION
53
7.1
7.1.1
7.1.2
7.1.3
7.1.4
7.1.5
Steel Tanks
Shop Fabrication
Site Erection
Welding
Radiographic Inspection
Inspection Guidelines for RLG Steel Tanks
53
53
53
53
53
54
7.2
7.2.1
7.2.2
7.2.3
7.2.4
Reinforced and Prestressed Concrete Construction
General
Foundations
Reinforced Concrete
Prestressed Concrete
54
54
54
54
54
7.3
7.3.1
7.3.2
Installation of the Insulation
GeneraI
Quality Control and Inspection
55
55
56
7.4
Earth Embankment
56
8.
9.
10.
HYDROSTATIC AND LEAK TESTING
57
8.1
General
57
8.2
Inner Steel Tank Testing
57
8.3
Testing of Outer Steel Tanks o f Double and Full Containment
57
8.4
Filling Rates and Level Checks
57
8.5
Outer Concrete Tank Testing
57
8.6
Pneumatic Testing
57
COMMISSIONING AND DE-COMMISSIONING
59
9.1
9.2
Com missioning
De-com missioni ng
59
59
RECOMMENDATIONS H)R OPERATION
61
10.1
Cool-Down of the Tank
61
10.2
Prevention of an Overfill
61
10.3
Prevention of Overpressure
61
10.4
Prevention of Vacuum
61
10.5
Prevention of Condensation
61
10.6
Tank Heating System
63
10.7
Liquid in the Annulus
63
APPENDICES
A
B
C
D
E
F
G
67
Examples of Single, Double and Full Containment Tanks
Typical Characteristics and Property Limits of lnsulants
Determination of AT for Impact Testing Steels
Steels for Reinforcement o f Concrete for cryogenic service
Design Criteria for Concrete Structures
Design Consideration for Earthquake Loadings
References
TABLES
67-69
71-75
77-79
81
83-85
87-88
89-91
19
Note: Figures and Tables are numbered i n accordance with the number of the clause
they refer t o and so are not numbered consecutively.
5.1.1
5.1.2
Materials for Tank Shells and Bottoms
Longitudinal Charpy V-Notch Impact Requirements
19
20
5.2.1
Steels for Outer Tank Shells and Roofs where the M i n i m u m
Design Temperature is based on ambient
22
5.2.2
Steels for Outer Gas Containers for Single Containment Tanks
22
5.3.3
Use of Sub size Charpy Impact Test Specimens
24
6.2
Design of Steel Containment: Steel Inner and Outer Tank
35
6.2.2.1
The Maximum Allowable Design Stress
36
6.5.3
Wall to Base Joints
42
6.6.2
Environmental Effect on Thermal Conductivity
44
B.1
Typical Characteristics and Property Limits of Insulation Material:
Cellular Glass
Typical Characteristics and Property Limits of Insulation Material:
Polyurethane Foam
8.2
71
72
8.3
6.4
Typical characteristics and Property Limits of Insulation Material:
Polyisocyanurate Foam
Typical Characteristics and Property Limits of Insulation Material:
Phenolic Foam
73
74
c.1
Test Plate and Welding requirements
79
E.2
Typical Example of Design Loading'Summary (for R.C. tank
with earth embankment)
Partial Safety Factors for Abnormal Load Cases
84
85
Pilot-operated pressure relief valve
Weight loaded (pallet-type) tank vent valve
Pilot-operated low-pressure relief valve
Weight-loaded, pallet-type vacuum breaker valve
Arrangement of pressure control valves t o flare, and pressure
relief valve t o atmosphere, vacuum breaker valves, locked block
valves and spare positions
10
Typical Section of a Tank with a Reinforced Concrete Outer Tank
with Earth Embankment
38
10.2
10.5
10.6a
10.6b
10.7
Typical Example for level alarms
Typical Example of Condensation i n Dome Roof for Butane Gas
Sensors under Tank Bottom
Typical Heating Time Recording Curve
Floating of the Inner Tank
62
62
64
64
65
A. 1
A.2
A.3
Examples o f Single Containment Tanks
Examples of Double Containment Tanks
Examples of Full Containment Tanks
67
68
69
c.1
c.2
c.3
Details of Test Plate
Location of Charpy Impact Specimens
Shift i n Temperature of 27J transition temperature
79
79
79
E.3
FIGURES
3.1.1.1 a
3.1.1.1 b
3.1.1.1~
3.1.1.2
3.1.1.4
6.4.1
1.
FOREWORD
1.1
Background
T h e design of tanks for refrigerated liquefied gases have traditionally been of the single
containment type, which means that the liquid containing tank was surrounded by a
low bund wall at a considerable distance. Where double wall tanks were used the outer
wall was mainly intended t o cpntain. the insulation.
Since the mid 1970s it has become increasingly the practice in a number of countries,
including the United Kingdom, to surround the primary liquid container by a secondary
container at a close distance. This secondary container should prevent release of the
liquefied products into the surrounding area in case of leakage or damage to the
p r i m a r y container. This philosophy results in increased safety for the surrounding area.
These double and full containment tanks generally have secondary containers made
from low temperature steel, prestressed concrete or reinforced concrete with an earth
embankment.
T h e existing codes, BS 4741, BS 5387, API 620 Q and R, specify the requirements for
single containment tanks only. Consequently these codes d o not include all essential
requirements for material selection, design, construction, loading cases etc, necessary
for all tank designs now being built.
1.2
Scope
It i s the purpose of this EEMUA document t o supply the outline information necessary
for t h e design and construction of single, double and full containment tanks for the bulk
storage of refrigerated liquefied gases down to -165"C, and essentially at atmospheric
pressure.
Liquids covered by the scope of this document include LPG, ethylene, ethane, LNG and
similar hydrocarbons, together with ammonia.
T h e tank design for a specific project should be selected from within the three tank
types covered in this document, based o n all local circumstances and local
requirements.
1.3
Related Standards
These guidelines make reference to the following related standards for the selection
a n d design of tanks covered by this document.
BS 4741, BS 5387 and API 620 Q and R cover the design requirements for steel primary
(inner) tanks and the steel parts of the secondary (outer) tank.
BS 8110 and the 'Guide t o Good Practice' FIP/3/6 of the FIP organisation have been used
as a basis for the design requirement of prestressed concrete tanks.
BS 81 10 has been used as the basis for reinforced concrete structures.
Safety requirements are based on the Institute of Petroleum code for LPG, NFPA 59A
for LNG and CIA Code of Practice for Large Scale Storage of Fully Refrigerated
Anhydrous Ammonia.
1.4
Definitions of Terms
Bund Wall
A low wall of earth or concrete surrounding the storage tank at a considerable distance
appropriate to contain spilled liquid.
Purchaser
Purchaser, for the purpose of this document, is the company or its agents which
prepare and agree a proposal with a Contractor or Contractors for the design,
construction, testing and commissioning of a tank for storing a refrigerated liquefied
gas. It is n o t the purpose of this document to define terms of reference or to allocate
1
responsibilities between contracting parties when the Purchaser is not to be the owner
or operator of the storage plant.
Boil-Off
Boil-off is the process of vapourisation of very small quantities of refrigerated liquid by
heat conducted through the insulation surrounding the storage tank.
Embankment
A bank of selected earth and other materials placed against the outer face of a
reinforced concrete tank,or high wall.
Contractor
The Contractor, for the purpose of this document, is the company with which the
Purchaser agrees a proposal for the design, construction, testing and commissioning of
a tank for storing a refrigerated liquefied gas. The document, in the interest of
simplicity, considers the Contractor as being responsible for all works, materials,
equipment and service.
Roll-Over
Roll-Over is the uncontrolled mass movement of a stored liquid, correcting an unstable
state of stratified liquids of different density, which results from differences in
temperature or composition throughout the depth of the liquid. It is generally
accompanied by a large release of vapour inside the tank.
2
2.
CLASSIFICATION OF STORAGE SYSTEMS
2.1
General
In the past the most common type of refrigerated storage System consisted of a tank
with a single liquid retaining compartment - now referred to as a "single containment
tank" - surrounded by a traditional low bund wall.
It is evident that a failure of a single containment tank would result in an immediate
release of liquid and/or vapour to the environment, representing a possible major
hazard.
Although experience has demonstrated that the probability of failure of a single
containment tank is very low, the probability can be further reduced by more stringent
requirements for material selection, design, construction, inspection and testing.
Whilst these requirements will reduce the probability of failure to a very low level, the
consequences of a failure may be considered so serious that a secondary passive
system, of either "double containment" or "full containment" is necessary to eliminate
the risk of a large flooded area around the tank in case of leakage or failure of the
primary container.
The above design measures will result in the tanks having an increased tolerance to
maloperation and unforeseen loadings.
Summarizing; there are three types of refrigerated. storage systems: (For full
descriptions refer to 2.2)
1) Single containment
2)
Double containment
3) Full containment.
The selection of the type of storage system will be considerably influenced by the
location, the operational conditions, the adjacent installations, loadings and
environmental considerations.
2.1.1
Summary of Loadings, Conditions and Considerations
The following list summarizes a number of loadings, conditions and considerations
that may have an influence on the selection of the type of storage system.
NOT SUBJECT TO CONTROL
Earthquake
Wind, snow, climate
Objects flying from outside the plant.
SUBJECT TO LIMITED CONTROL
In plant flying objects
Maintenance hazards
Fire in bund or at adjacent tank, plant, etc.
Overfill
Overpressure (process)
Roll-over
Major metal failure e.g. brittle fracture
Minor metal failure e.g. leakage
Metal fatigue
Corrosion
Failure of pipework attached to bottom, shell or roof
Foundation behaviour
SUBJECT TO FULL CONTROL
Proximity of other plant
Proximity of control rooms, offices and other buildings within plant
Proximity of habitation outside plant
National or local authority requirements
Requirements of the applied design codes
3
Consideration of the sudden tailure of the inner tank is not a design requirement of this
document. In cases where this consideration is specified, the outer tank shall be
designed to withstand the consequent impact loading which shall be defined by the
Purchaser. (See also 4.2.5.)
It is the responsibility of the Purchaser to specify the selected storage system, taking
into account the national or local authority requirements and the influence of loadings,
conditions and considerations listed under 2.1.1 applicable for the location concerned.
2.2
Definitions of Containments
2.2. a
Single Containment Either a single or double wall tank designed and constructed so that only the containing
element in contact with the refrigerated product is required to meet the low
temperature ductility requirements for storage of the product. The outer wall (if any) of
a single containment storage system is primarily for the retention and protection of
insulation and is not designed to contain liquid in the event of product leakage from the
inner container.
A single containment tank will be surrounded by a traditional low bund wall to contain
any leakage. (See Appendix A, Figure Al.)
2.2.2
Double Containment A double wall tank designed and constructed so that both inner and outer walls shall be
capable of containing the refrigerated liquid stored. To minimise the pool of escaping
liquid the outer wall should generally be located at a distance not exceeding 6 metres
from the inner wall. The inner tank shall store the refrigerated liquid under normal
operating conditions. The outer tank shall be able to contain the refrigerated liquid
product leakage from the inner tank.
The outer tank will not be designed to contain vapour released due to product leakage
from the inner tank. (See Appendix A, Figure A2.1
2.2.3
Full Containment A double wall tank designed and constructed so that both inner and outer tanks shall be
capable of containing the refrigerated liquid stored. The outer wall to be approximately
1 to 2 metres distance from the inner wall.
The inner tank shall store the refrigerated liquid under normal operating conditions.
The outer roof is supported by the outer wall.
The outer tank shall be capable of containing the refrigerated liquid and vapour
resulting from product leakage from the inner tank. (See Appendix A, Figure A3.)
4
3.
SAFETY REQUIREMENTS AND SPECIAL PROVISIONS
3.1
Environmental and General Considerations
Two o f the special aspects relating t o the storage of refrigerated liquid gases warrant
particular attention. One is that the liquid concerned is maintained i n that state only by
virtue of artificially created thermal conditions; if it should escape from its container it
would revert to a much greater volume o f gas. The other aspect is economic. The value
of the contents of a large storage system is several million pounds sterling. Therefore
there are unusually strong incentives, both financial and environmental, t o ensure that
the contained liquid cannot escape.
Long experience has shown that single containment systems, be they of concrete or
metal, can be operated for many years without trouble and the safety record of RLG
storage i s very good. However, modern requirements o f environmental safety and the
limitation of social risk may involve enhanced safety measures, often t o guard against
events (see 2.1.1) which are beyond the control of the owner or operator o f the system.
Safeguards of this type are embodied in national and local authority requirements and
regulations. These vary from country t o country and sometimes in areas within the
same country. The requirements for a particular site are determined by consultation
between the owner/operator and the relevant authorities and it is logically the
responsibility of the owner t o ensure that they are included in the statement of design
philosophy. The wide variations in specific site requirements make i t difficult to lay
d o w n hard and fast rules, but guidance can be obtained from the codes listed in the
bibliography. (See Appendix G).
It is becoming common practice for the owner/operator, in conjunction with the
approving authority, t o perform a hazard and systems analysis for proposed RLG
storage sites and designs. The analysis includes a probability assessment of various
accident scenarios and the effects of safety measures. The consequences of credible
accidents are considered, and the physical implications of possible leaks and spills are
derived; computational models incorporating dynamic effects, and the response
behaviour of the storage system and its components are employed. The components
considered should include the support system and the foundation/soil interaction.
3.1.1
Basic Requirementsfor Pressure and Vacuum Relief
3.1.1.1
Pressure relief safety valves
Pressure relief safety valves should be entirely separate f r o m the vacuum relief valves
and should relieve from the inner tank. This requires the inlet piping t o penetrate the
suspended roof where applicable, preventing cold vapour entering the warm space
between outer roof and suspended roof under relieving conditions. The influence of
this piping must be considered in relief valve capacity calculations.
Pilot-operated pressure relief valves are preferred over pallet operated valves for
refrigerated storage tanks. These valves stay very tight u p t o the set pressure and open
wide when this pressure is reached; see Figs. 3.1.1.la and 3.1.1.lb. This no-flow/fuIIflow characteristic prevents icing at the valve seats which could cause leakage in the
shut position.
Other advantages of pilot-operated pressure relief valves are that the valve (pilot)
setting can be verified i n situ, and that, because the pilot operates against atmosphere,
their set pressure does not v a r y with back-pressure, which is important in the case of
discharge into a vent or flare system. (See Fig. 3.1.1.1~)
A disadvantage of this type of valve is that if blockage occurs i n the pilot sense line with
the tank pressure near set pressure, the relieving pressure of the valve can be as high as
twice set pressure. For those tanks requiring only one or t w o relief valves, an extra
valve should be installed i n order t o allow for the possible maloperation of one. If three
or more relief valves are required (to meet infrequent worst case conditions), an
additional valve need not be installed.
5
U)
W
h'
E
em
E
c
rn
a
Blowdown
1
/
Flowrate
Seating force
Fig. 3.1.1.la: Pilot-operated pressure relief valve
W
>
m
>
L
. w
6
a
a
/
/
/
/
/
/
/
e
/
I
Seating force
Flowrate
Fig. 3.1.1.lb: Weight loaded (pallet-type) tank vent valve
6
. .. ..
Pilot valve assembly
Blowdown adj.
Guide tower
-
Tower seal
Bellows ass'y
Cap
-
-Guide
assembly
-Seat
plate
-Seat
retainer
Retainer disc
Body
Supply tube
Dipper tube
I
I-----
-
P<P
P > Pset
P
Fig. 3.1.1 .lc: Pilot-operated low-pressure relief valve
P
.. . ..
..
3.1-1.2
Vacuum safety valves
Separate vacuum safety valves should allow air into the vapour space between the
outer roof and the suspended roof for the following reasons:
- a long inlet pipe would restrict flow in view of the low differential pressure
available across the valve;
-
condensation'problems if wet air enters the cold inner tank.
Pilot-operated vacuum relief valves are not acceptable for vacuum protection because
the valve action is not fail-safe against main valve diaphragm or bellows rupture.
Conventional pallet type vacuum valves should be used. Since the tanks normally
operate at a slight overpressure, there will be enough margin between operating
pressure and vacuum valve setting to keep the valve tightly shut. (See Fig. 3.1.1.2)
3.1.1.3
Valve settings, maximum relief pressures
The set pressure of relief safety valves shall not exceed the design pressure of the tank.
The valve capacity shall be such that the maximum relief pressure does not exceed 1.1
times the design pressure for all emergencies except an external fire. For fire conditions
the maximum relief pressure shall not exceed 1.2 times the design pressure.
3.1.1.4
Spare venting capacity
Pressure and vacuum relief valves o n refrigerated storage tanks must be provided with
interlocked block valves and spare positions, so that a faulty relief valve can be
exchanged without opening the tank t o atmosphere. (See Fig. 3.1.1.4)
3.1.1.5
Relief to flare system/atmosphere
1.
Relief to a controlled system
Vapour relieved f r o m the tank's pressure relief valves must be conducted to a
location where it can be safely discharged e.g. a flare system.
2.
Relief t o atmosphere
Vapours may safely be disposed of directly to atmosphere, provided that this can
be accomplished without creating problems such as:
-
Formation of flammable toxic mixtures at ground level or on elevated
structures where personnel are likely to perform their duties.
-
Ignition o f the relieved vapours at point of emission.
Notes:
-
The outflow of hydrocarbon vapours from relief valves may be ignited
by :
Lightning
Except for emergency reliefs associated with power failures which may
occur during thunderstorms, the probability of lightning occurring
simultaneously with the opening of a relief valve is negligible. Leaking
relief valves increase the probability of lightning ignition.
The inert gas snuffing system connected to the discharge pipework may
be used t o extinguish the ignited vapours.
- Adjacent tank fire
The expansion of vapours i n the dome of a tank, subject to radiation
from an adjacent tank fire could cause the atmospheric relief valves to
open. If the venting vapours ignited, the additional radiation from the
vent fires would cause further expansion, requiring additional venting
capacity and causing high roof-plate temperatures.
The inert gas snuffing system would not normally be designed t o
extinguish the flames and use must be made of adequate water
spray/exposure protection facilities.
8
18-8 S.S. Guide rod bolt
\\
Pipe cap for
vacuum service only
\
I
18-8 S.S.
Cap bolt
304 S.S. Guide
TEFLON coated
/
7
Aluminium
guide
Buna-N,
EPR or
VITON
gasket
/
18-8 S.S. Seat
\
I
KEL-F
Bolt seal
L Vacuum inlet screen
3031304 S.S. steel
I
1 in. Mesh, .080 dia. wire
I
inlet
(from vessel)
Buna-N, EPR or
VITON 0-ring
Neoprene, EPR or VlTON
closed cellular sponge
Fig. 3.1.1.2: Weight-loaded, pallet-type vacuum breaker valve
9
1
.
......... ...
To atmosphere
L
LO
1
I '
= Locked closed
= Locked open
PCV let-down to
common system
Motor-operated
valve
BoiI -off header
Low pressure flarelvent header
-0
Fig. 3.1.1.4: Arrangement of pressure control valves to flare, and pressure relief valve to atmosphere, vacuum
breaker valves, locked block valves and spare positions
3.2
Leakage and Spillage
3.2.1
General
In considering the consequence of leakage or spillage, account should be taken both of
the volume of the leak or spill and of the nature of the product itself. All refrigerated
liquids when spilled will evaporate at a rate which is directly related to the surface area
of the spilled liquid. Small leaks and spills may require forced ventilation of potential
pockets of gas, for instance under the bases of above-ground tanks. This is particularly
the case with heavy gases such as butane or propane. In this connection gases (such as
methane) which are lighter than air at ambient temperatures are usually denser than air
when they are first evolved, and are thus capable of forming a low lying vapour. When
larger spills are to be taken into account, measures are normally taken to limit the
surface area (pool diameter) of the spill and hence the rate of vapour formation. These
may take the form of concrete guard walls, earth bunds, or a system of channels
leading to a remote collection area. Some tanks are located below ground level for
similar reasons.
Vapour cloud generation may be unwelcome for reasons other than those associated
with fire and explosion. Ammonia, for instance, can be highly poisonous in
comparatively small concentrations, and thus requires special consideration. Dense
vapour clouds can cause suffocation-andthe low temperature of the liquid and vapour
is a hazard.
3.2.2
Risk of External Leakage to Atmosphere
The risk of leakage can be minimised by:
3.2.3
-
Limiting both the number and size of, or preferably avoiding, all connections on
the tank below the maximum liquid level.
-
The use of emergency remote control andor automatic fail safe shut-off valves on
liquid connections on the tank and other important locations.
-
The double valving of all liquid connections on the tank below the maximum
liquid level, the first being as near to the tank shell as practicable.
-
The use of welded connections upstream of the first shut-off valve on each
connection below the maximum liquid level.
Local Internal Leaks
The recommendations in this and related codes and standards for storage tanks are
naturally designed to ensure that the tanks are liquid-tight.
It istherefore in that respect important to highlight the need for attention to detail in the
design, construction and testing of each tank bottom and its attachment to the lowest
course of the shell. The recommendations made should be applied to both inner and
outer tanks, leak-tightness being further confirmed by vacuum box testing of the welds
in the inner tank after the hydrostatic test (8.1 - Hydrostatic and leak testing).
Any local cooling in the tank interbottom space could lead to setting up of unacceptably
high local thermal stresses in the outer tank bottom. To prevent the possibility of outer
bottom failure due to thermal stress, consideration should be given to provision of
suitable protective layers of liquid proof thermal insulation over the outer tank bottom
or provision of low temperature quality steel for the outer tank bottom and the lower
shell course. In the double and full containment tanks, by definition, (see paragraph
5.2.1.1) a suitable low temperature quality steel must be provided for the outer tank
bottom, shell or the liners, unless, in the case of outer concrete tanks, the concrete is
designed for direct contact with the liquid.
3.2.4
Internal Condensation
In tanks containing product gas in the annular space, the possibility of condensation of
the product gas in the interbottom space and the intershell annulus exists. The
11
.
presence of product liquid on the outer tank floor may result in flotation of the inner
tank and significant damage to inner and outer tanks.
Instrumentation enabling the operator to be warned of the existence of such
condensation and means of its removal shall be considered at the tank design stage
and specified if the probability of condensation is realistic.
At certain locations, where the outside temperature in winter can drop below the
atmospheric boiling point of the product, say -5°C for butane, condensation in the tank
against the underside of the roof will occur. Large quantities of condensate,
comparable with a very heavy rain, may drop down on the suspended deck. Therefore
drainage holes are to be provided in the deck so that the liquid can enter the inner tank.
A drain protection system shall be provided above the shell annulus, so that the
condensate is directed to the inner tank, because no liquid should enter the shell
annulus. (See figure 10.5.)
3.2.5
Overfilling
To prevent overfilling three separate independent level gauges should be provided.
The level gauges should be equipped to provide remote readings and high level alarm
signals in the control room. As back up to these level gauges separate independent
level high alarm (LHA) and level high, high alarms with cut out (LHHA (CO)) are
recommended. The LHHA (CO) should be hard wired directly to close the motor
operated liquid inlet valves to the tank.
3.2.6
Spillage
The outer tank shall be protected from adverse effects of any accidental spillage of
product onto the tank roof and shell.
Areas on the tank roof where the spillage is most likely to occur are the atmospheric
discharge outlets from the safety valves and the area close to liquid product valves.
The tank areas where such spillage is possible, shall be protected by provision of
product catchment trays, liquid proof insulation and suitable drainage directing the
spillage to a safe disposal area. The size of these trays shall take account of wind
dispersion.
3 -3
Tank Layout and Spacing
For tank layout and spacing reference should be made to IP Code "Refrigerated Storage
Chapter 3".
Various other national codes include requirements for minimum distances between
steel tanks, distances to property lines and secondary bunds e.g. The American Federal
Safety Standard 49 CFR 193, NFPA 59 Standard for the Storage and Handling of LPG at
Utility Gas Plants, NFPA 59A Standard for the Production, Storage and Handling of LNG
and the CIA Code of Practice for Large Scale Storage of Fully Refrigerated Anhydrous
Ammonia in the United Kingdom.
3.3.1
Location and Spacing
Containment systems i.e. tanks and their associated bunds and impounding basins,
shall be located and spaced so that in the event of a tank fire, or a fire in a
bundimpounding basin resulting from the ignition of spillage, radiation flux levels will
be in accordance with the requirements of the I.P. Code.
3.3.2
Radiation Flux Levels
The radiation flux levels laid down in the I.P. Code shall be based on the ignition of
product either in the tank or spilling from it and forming a pool of a size as dictated by
the spillage rate, evaporation rate and duration covered by the I.P. Code and the
topographyllocation of the bundlimpounding basin. The I.P. Code includes example
calculations of radiation levels.
12
3.4
Requirements for Fire Protection/Loss Control Systems
Requirements for these items are to be found i n the I.P. Code on Refrigerated Storage
Systems and the following additional requirements.
- For a concrete outer containment tank, the fire rating will affect such aspects as
t h e selection o f aggregates, the cover over the reinforcement and prestressing
tendons or wires.
3.5
The installation of at least four combustible gas detectors equally spaced around a
tank is recommended. Alarms should be located in the control room. In some
cases these detectors should automatically close the tank liquid valves.
Pumps and compressors should not b e located within the storage tank bund for a
single containment tank as they have a higher potential for leaks or fires than most
other equipment.
Protection Against Explosion and Impact
In any industrial plant handling hazardous liquids the possibility of an explosion cannot
be entirely. ruled out. The credibility of such events forms part of the hazard analysis;
the' physical implications are assessed to provide the basis for the design philosophy
and requirements and commonly include an external blast overpressure and external
missile impact. Since the blast loading is time dependant, a full dynamic analysis is
needed t o determine its effects on the complete storage system and its elements,
including the foundations.
3.6
Lightning Protection
The structure shall be provided with adequate protection t o prevent damage and fire b y
lightning. The requirements of local codes shall be observed in full.
Where tankage is required to be protected against lightning the following
recommendations are made:
1.
Provided there is a minimum steel thickness of 5 mm, a lightning discharge will
not penetrate the tank and the absolute value of the earthing of a vertical storage
tank is not important as far as the tank is concerned.
Where it is necessary t o earth a storage tank for other reasons, e.g. because of
electrical equipment, static discharge, or protection of the supporting structures,
the absolute value of the earthing resistance should be determined by those
factors.
2.
Electrical appliances and cabling either on or i n tankage must be electrically
earthed.
Any metal part which may be electrically isolated f r o m the tank, e.g. b y a gasket or
even by a rust layer, must be bonded t o the tank by the shortest possible route.
3.
3.7
.
Where tank or pipeline are cathodically protected, either spark arresters, enclosed
spark gap devices or similar devices should be fitted across any insulated flanges.
Effect of Radio Transmissions, Static Electricity and Cathodic Protection
Systems
In'some circumstances a hazard may exist when a flammable substance is stored in the
vicinity of certain types of radio transmitters. Radio waves can induce sufficient energy
i n steel members to cause incendive'sparks at distances up to 20 K m (based on MF
Broadcast Radio Transmitter of 150 Kw and a Group IIC Gas) from certain high power
transmitters. Normal provision of on-site radio systems, amateur and CB radios should
not create a hazard at distances above 200m. If there is any doubt on the possibility of a
hazard existing then expert advice should be sought. See BS 6656.
Static voltages can also b e built up in unearthed metalwork with a danger of spark
creation.
_.
Cathodic protection systems for buried steelwork can also give rise to break sparks. If
any of these hazards are relevant to a particular location a more detailed study should
be undertaken. Enhanced earthing provisions may be necessary to overcome the
danger thus arising.
3.8
Earthquakes
Few, if any, areas of the globe are entirely free from earthquakes and both the probable
magnitudes of earthquake forces and the response of the structure should always be
considered in the design of RLG storage systems.
Useful guidance is given in the documents FIP/3/2 and FIP/3/6. However, the response
of a container supported on relatively fragile insulation may differ significantly from
that of a container supported on a more rigid foundation. This should be borne in mind
when evaluating the response of RLG storage systems to earthquake effects.
Consideration should also be given to the possibility of sloshing of the stored liquid.
I _
API 650 Appendix E establishes recommended minimum basic requirements for the
design of storage tanks subject to seismic loads. These requirements represent
accepted practice for application t o flat bottom oil storage tanks. These requirements
will be generally applicable to single containment tanks although the response of the
shell may differ due t o the effect of the bottom insulation.
Due to the complexity of the evaluation of the response of RLG storage systems to
earthquake effects it is recommended that specialist assistance is obtained in
conducting such an evaluation.
Further information on design considerations for earthquake loadings is given in
Appendix F of this document.
14
4.
LOADING CASES AND DESIGN CONSIDERATIONS
This section describes the loading cases and design considerations for singlecontainment, double-containment and full-containment tanks.
4.1
Normal Loading Cases
4.1.1
Dead Load
Dead load of the tank, accessories, insulation, piping, valves, platforms, railings,
foundation etc.
4.1 -2
Imposed Load
(a)
Roof
A uniformly distributed load of 1.2 kN/m2 of projected area shall be used. In
addition the roof shall be able to carry a load of 5 kN over an area of 0.1 m2 placed
at any location on the roof.
(b)
Platforms and Accessways
A uniformly distributed load of 5 kN/mZshall be used.
4.1.3
Snow Load
The snow load is included in the imposed load specified under 4.1.2.
4.1.4
Internal Vacuum
For the roof design the normal internal vacuum is 6 mbarg. This is included in the
imposed load specified under 4.1.2.
4.1.5
Internal Pressure
The value for the internal pressure shall be specified by the purchaser.
Note: the design maximum internal pressure for tanks with a steel roof does not
normally exceed 140 mbarg. For concrete roofs the pressure may be
slightly higher.
4.1.6
Wind Load
The wind load shall be calculated in accordance with British Standard CP3, Chapter V,
Part 2.
4.1.7
Product Liquid Loading
(11
Inner Tanks
The inner tank shall be designed for a liquid load at the minimum design
temperature specified.
The design product level shall be the maximum product level specified or the level
0.5 m below the top of the shell, whichever is the higher. The ullage for earthquake
sloshing need not be included in the design product level.
(2)
Outer Tanks (double and full-containment tanks only)
The outer tank shall be designed to contain the maximum liquid content of the
inner tank at the minimum design temperature specified.
4.1.8
Hydrostatic Testing
(1)
Inner Tanks
The inner tank shall be water-tested to a level equal to the maximum product level
specified or the level 0.5 m below the top of the shell, whichever is the higher. The
15
ullage for earthquake sloshing need not be included in the design water test
height.
(21
Outer Tanks
(i) Steel outer tanks for Double and Full Containment
Outer tanks constructed from steel shall be water-tested to the level reached
when all test water of the inner tank is contained by the outer tank.
(ii) Prestressed concrete outer tanks and reinforced concrete tanks with an earth
embankment.
Outer tanks of these types do not require water testing unless specified by
the user or the approving authorities. (See 8.5).
Note: During hydrostatic testing of the outer tank, the water level in the inner tank
shall always be kept above the water level in the outer tank to prevent
damage to the inner tank.
4.1.9
Pressure From Insulation on Inner Tank Shells
The loose perlite powder in the annular space between the inner and outer shells will
exert a pressure on the inner tank shell, although reduced b y the presence of resilient
blankets on the outside of the inner tank.
The compressive load acting on the inner tank shell shall be stated by the tank
contractor based on investigations and test work carried out.
4.1.10
Applied Loads
Loads resulting from thermal and settlement effects on roof and shell from piping and
other accessories.
4.1.11
Settle ment
The storage tank and its foundation shall be designed taking account of the predicted
maximum total and differential settlements that can occur during the life of the tank.
(See 6.1.3.3 and 6.1.3.4).
4.2
Abnormal Loading Cases
4.2.1
Earthquakes
For guidance on earthquake loadings, refer to Appendix F and 3.8.
4.2.2
External Explosions and Their Effects
Depending on the location of the storage tanks from an environmental aspect, and in
relation to associated or other plant items either within the owner's boundary or in
adjacent third-party owned properties, consideration should be given to the possibility
of an explosion occurring within the vicinity of the tank, with the following
consequences:
(i) A resultant blast or pressure.
A blast or a pressure wave produced by a nearby explosion will be "reflected" by
the outer wall and roof of the tank. Such pressure waves are of short duration and
are time-dependent. Thus the dynamic response of the complex structure,
including foundations must be taken into account in the design calculations. The
values for the intensity and time duration of reflected blast pressures shall be as
specified by the user.' Where authorities are involved the user is responsible for
ensuring that their requirements are taken into account in the design specification.
16
(ii) Possible flying objects acting on the tank.
The storage tanks shall be able to withstand flying objects resulting from external
explosions that could hit the tank.
As a guideline it may be considered reasonable to use the impact from a 4 inch
diameter valve travelling at 160 km/h (approximately 45 m/s).
4.2.3
Fire Hazards
A fire occurring near a tank will result in heat radiation and a subsequent temperature
increase of the tank structure. The temperature rise shall be limited to prevent strength
reduction of the tank-components.
The fires to be considered may consist of; a pool of burning liquid in catchment or
bunded area, fires from a leaking pipe, a burning atmospheric vent pipe and
neighbouring tank fire.
The radiation heat flux from the assumed fire shall be calculated and from the heat flux
figures the structure temperature rise shall be determined taking into account the
presence of an active fire protection system and considering the reliability of the
system. The temperature of the steel tank, roof and shell, shall not exceed 300°C.
Reinforced and prestressed concrete tanks shall be designed to comply with the fire
resistance requirements given in BS 81 10, Part 2, Section Four.
The above requirements may determine the minimum spacing of tanks.
4.2.4
Leakage of the Inner Tank of Double and Full Containment
The outer tank shall be designed and constructed in such a manner that it can contain
the maximum liquid content of the inner tank, assuming that the annular space
between the shells is filled gradually.
For a full containment tank, liquids or vapours shall not penetrate the outer tank.
4.2.5
Sudden Failure of the Inner Tank
The sudden failure of the inner tank resulting either from material failure or earthquake
action is not a design requirement of this document. In cases where a sudden failure is
specified, the outer tank shall be designed to withstand the consequent impact loading
which shall be defined by the Purchaser. (See 2.1.1).
4.2.6
Overfill of the Inner Tank
Multiple independent facilities shall be provided to prevent overfill of the inner tank (i.e.
level measuring, alarms, automatic switch-off). These precautions shall be such that
overfilling cannot be considered a design requirement of this document. (See 3.2.5).
4.2.7
Roll-Over
Precautions (e.g. mixing) shall be taken to prevent roll-over.
4.2.8
De-Commissioning
(See Chapter 9.)
17
5.
MATERIALS
5.1
Inner Tank Materials (Primary Containers)
The material selection given in this Chapter does not constitute a new interpretation of
l o w temperature toughness capabilities of carbon manganese and low nickel steels
already in use for sub zero equipment design applications. It differs from these b y the
incorporation of some o f the environmental factors associated with large IOW
temperature and cryogenic storage systems.
The material selection given is intended t o define stringent quality control Charpy
V-notch impact test requirements for base material, subject t o welding (see also
Appendix C), which, in conjunction with other design, inspection and testing
requirements of this document, will satisfy the objectives set out in Clause 2.1.
5.1.1
Plate and Fitting Materials
All plate materials to be used in the manufacture of the tanks to the requirements o f this
document shall be in accordance with Table 5.1.1 and Table 5.1.2 and where applicable,
Appendix C, and in addition shall meet the "General Requirements" and "Specific
Requirements for Testing" of BS 1501 for steels and BS 1470 for aluminium alloys.
Other product forms, shall comply with the specific requirements of this document and
the general and testing requirements of the following standards.
Forgings
Piping
BS 1503 and BS 1472
BS 3603, BS 3605 and BS 1471
Table 5.1.1
Materials for Tank Shells and Bottoms
_
_
~
~
Product
Single
Containment
Double or full
Containment
Typical Product
Storage Temperature
Butane
Ammonia
Propane
EthaneIEthylene
Methane
Type II
Type I I
Type I l l
Type IV
Type v
Type I
Type I
Type II
Type IV
Type IV
- 10°C
-35°C
- 50°C
- 105°C
- 165°C
For explanation of material type see table 5.1.2.
5.1.2
Shell Plate Thickness
This standard is applicable t o the following maximum shell plate thickness:
Carbon manganese steel
Improved toughness carbon manganese and low nickel steel
9% nickel steel
Austenitic stainless steel
Aluminium magnesium alloy
30 m m
25 mm
25 mm
25 mm
55 mm
When material thicknesses are required in excess of these values, additional
requirements t o maintain the same level of safety shall be agreed between purchaser
and manufacturer.
Local thinning due t o rolled-in scattered scale remote from the plate edge on the
surface of 9% Ni steel is not regarded as deleterious provided that the measured
thickness is not less than approximately 90% of the calculated thickness of the plate.
This is permissible when design thicknesses are based o n weld metal strengths and not
the stronger plate material properties.
previous Page
is blank
19
.
Table 5.1.2
Longitudinal Charpy V-Notch Impact Requirements
Energy Valves are minimum average o f 3 specimens with no value less than 75% o f the
value specified.
Steel
Tested
120J tested per
per plate
40t Batch
Type
Type I
Normalised C-Mn
27J at -50"
N.R."
Type II
Improved Toughness C-Mn
27J at -50°C -AT*
-20°C
Type 111 Low Ni Steels
27J at -80°C -AT*
-50°C
35J at -196°C
N.R.**
Type IV 9% Ni Steel
Improved 9% Ni or
lOOJ at -196°C
N.R."
Type V
Austenitic
)
Stainless
)
Steel or
1
No impact testing required
Aluminium )
Magnesium )
Alloy
1
~
Note: Impact testing shall be carried out on each plate to demonstrate the required impact value
and in addition, testing at a frequency of one per 40 tonne batch shall be carried out to
demonstrate the 120J requirement. The definitions of plate and batch as per BS4360. For
material thickness less than 11 mm, 10 x 5 mm sub size specimens shall be used and shall
demonstrate 70% of the value specified above.
See Appendix C
** N.R. Not required
5.1.3
Welding Process
The welding process to b e used for t h e construction of the steel tanks shall be that used
in t h e weld procedure approval tests. All welding procedures shall be approved i n
accordance with 7.1 -3.
The w e l d metal of shell, bottom annular and roof compression area butt welds,
including the connections between bottom annular to shell, a n d nozzles and mountings
shall meet the following Charpy V-Notch requirements in the weld procedure tests:
W e l d metals for materials used at ambient temperatures
Weld metals f o r Type I materials
Weld metals for Type I I materials
Weld metals for Type Ill materials
Weld metals for Type IV materials
Weld metals for Type V materials
27 J at -10°C
50 J at -30°C
50 J at -50°C
50 J at -80°C
35 J at - 196°C
35 J at -196°C
The minimum impact requirements for the weld metal for Types IV and V should b e
based on the high nickel, austenitic w e l d metal. In the event o f w e l d metal being offered
in composition matching that of 9% Ni plate, additional specialist advice should b e
obtained.
(Energy values are minimum average of 3 specimens with n o value less than 75% of
the value specified.)
(Note: The intent o f this document is t o assure that t h e production welds in the tank
would meet 20 J minimum at the test temperature given above. In order t o
achieve this, t h e procedure test for weld metals f o r Types I, II a n d Ill steels must
therefore, demonstrate a higher Charpy V-Notch energy value t o compensate
for the scatter of results inherent in Charpy V testing of w e l d materials, which is
influenced by m a n y factors.
With t h e above welding procedure requirements, Production test plates are
unnecessary a n d are NOT a requirement of this document. If, for any reason,
production test plates are called for b y the purchaser, energy values of 27 J
minimum average of 3 specimens with n o value less than 20 J would be
required at t h e test temperature given above).
20
5.1 -4
Bolting Materials
Bolting materials shall be in accordance with BS 1506 and shall demonstrate 27J a t the
design temperature. Where austenitic steel is used e.g. grades 801,821 Ti or 821 Nb as
specified in BS 1506, attention is drawn t o the fact that bolts may relax on cooling down
to sub-zero temperatures. This is caused by a permanent transformation of the
structure from austenite t o martensite, which results i n an increase of length. The
extent of transformation increases with the applied stress. Bolts that cannot be
retightened after cooling should be made from steels having a stable structure, e.g.
from bar having the analysis and properties of 25 Cr 20 Ni steel t o BS 1501-31OS24 or
nitrogen bearing austenitic steel to BS 501-347S67 or BS 1501-304S65.
5.1.5
Aluminium Alloy Bolting
The following bolting material is recommended for bolting of aluminium alloy
components:
Alloy
Specification
BS 1474
AI Mg 5
AlCu4SiMg
AI Si Mg Mn
-NB6
-HB15
-HB30
-H4
-TF
-TF
5.1.6
Mountings
5.1.6.1
Nozzle bodies and insert plates shall be of the same nominal strength as the plates t o
which they are attached.
5.1.6.2
Permanent attachments, insert plates, nozzle bodies and flanges shall meet the notch
ductility requirements of 5.1.1.
5.1.6.3
Pipe flanges or pipes of austenitic steels may be welded to 9% Ni steel nozzles provided
that the thermal stresses are analysed and proved acceptable.
5.2
Steel for Outer Tanks
5.2.1
Secondary Liquid Containers (with Internal or External Insulation) for Double
and Full Containment Tanks
5.2.1.1
The requirements for outer tank shells, bottoms, reinforcing plates, mountings and
permanent attachments shall be i n accordance with Table 5.1.1 Double or Full
Containment.
The requirements for compression areas, roof, roof structure and roof fittings, where
the minimum design temperature is based on the product temperature, shall be i n
accordance with Table 5.1.1 Double or Full Containment requirements, except that the
maximum thickness may be increased t o 1.5 times the permitted limits of 5.1.2.
5.2.1.2
Where the minimum design temperature is based on ambient, the requirements for
outer tank roof plates, roof structure and roof fittings and where applicable also for
outer shell and compression area, shall be in accordance with Table 5.2.1.
21
Table 5.2.1
Steels for Outer Tank Shells and Roofs where the Minimum Design Temperature is
based o n ambient.
Minimum
Ambient Temp
Thickness
Material*
3 0°C
d 15 rnm
15C35mm
BS 4360-43A or 508
BS 436043C or 5oC
d 15 rnrn
15 d 35 mrn
BS 4360438 or 50C
BS 4360-430 or 500
3 -20°C
Other materials may be used provided such materials are equivalent to those specified and
provided the purchaser and manufacturer agree to such substitution.
5.2.2
O u t e r Gas Containers for S i n g l e C o n t a i n m e n t Tanks
The requirements for material selection for outer gas containing tanks are based on the
design metal temperature of the tank shell, bottom, roof etc. being not less than
ambient temperature. The materials shall be in accordance with Table 5.2.2.
Table 5.2.2
Steels for Outer Gas Containers for Single Containment Tanks
Minimum
Thickness
Material*
d 30
BS 436043A or 508
4 15 mm
BS 436043A or 508
BS 436043B or 508
BS 436043C or 50C
Ambient Temp
3
+ 10°C
+ 10°C 3 0°C
15 d 25 rnrn
25 d 35 rnrn
0°C 2 -20°C
BS 4360-43A or 506
d 12.5 rnrn
12.5 d 20 rnrn
20 d 35 mrn
BS 436043C or 50C
BS 4360430 or 50D
See Note to Table 5.2.1
5.2.3
Steel Liners a n d M e m b r a n e s
5.2.3.1
Steel liners and membranes not exposed t o refrigerated temperatures
The material requirements for liners and membranes for concrete outer tanks, where
the liner will not be exposed to the refrigerated temperature, shall be in accordance
with BS 436043C (other materials may be used provided such materials are equivalent
to that specified and provided the purchaser and manufacturer agree t o such a
substitution).
5.2.3.2
Steel liners and membranes exposed t o refrigerated temperatures
Where contact with a product can occur as a result of spillage and/or leakage, the
material of liners and membranes shall be selected t o withstand the product
temperature. (Refer also to 5.1.1 and 5.1.2).
22
5.2.4
Corrosion Protection
Corrosion protection should be applied where considered necessary. Corrosion
protection shall be specified by the Purchaser.
5.3
Reinforcing Steels for Concrete
5.3.1
General
(a)
Steel bars or wire for reinforcing concrete designed for use at ambient
temperatures should comply with requirements in BS 8110 and in the
specifications BS 4449 and BS 4461 for bar, BS 4482 for wire and BS 4483 for steel
fabric, as appropriate. The above specifications include requirements for ductility
(elongation) in the tensile test and purchasers should exercise options t o ensure
that these requirements are met.
(b)
The specifications noted in (a) do not include specific requirements for insuring
against risk of brittle fracture at low temperatures, and in that respect the
following are of note:
(i)
Reinforced concrete is a heterogeneous material and the reinforcing
elements are separate items, fracture of one element entails re-distribution of
its load over adjacent elements without propagating its failure to those
elements.
(ii) The American Standard NFPA 59A (1985) recommends maximum allowable
tensile stresses for reinforcement serving at -1 65°C (LNG temperature),
which are significantly lower than those used for designs for ambient
temperature service, and this can result in uneconomic design.
(iii) Steels have been developed for service at low/cryogenic temperatures. The
compositions range from carbon manganese, through 9% nickel to the
austenitic stainless steel grades, with mechanical properties and condition
(as rolled/heat treated) according to the grade and manufacturer's process.
Reference should also be made to Appendix D
The recommendations in 5.3.2, 5.3.3 and Table 5.3.3 should be followed when
considering the steels for reinforcing concrete for service at low/cryogenic
temperatures.
5.3.2
Quality Assurance
It is recommended that the Purchaser should consider the following as requiring
agreement with the Contractor for purchase of steels for reinforcing elements.
(a)
composition of the steel
(b)
method of production and related quality control
(c)
test methods and frequency of sampling for test
(d)
recording of results
The requirements should be supplementary to the appropriate standard used for the
purchase of ordinary steels for reinforcement of concrete.
The determination of mechanical properties should cover the full range of size of
materials used, with fracture toughness (impact requirements) in accordance with
5.3.3.
5.3.3
Impact Requirements
(a)
Testing of reinforcing bars for low temperaturekryogenic service should include
the Charpy V-Notch impact test.
Whenever possible the full size 10 mm x 10 mm test piece should be used but
where the bar is less than 16 mm diameter a reduced size, as specified in Table
23
5.3.3 should be used consistent with obtaining the maximum possible size from
the specific bar.
Preparation and testing should be i n accordance with BS 131. Tests should be at
the minimum design temperature (including emergency conditions).
The-average energy value for acceptance should be 27 J minimum, with no
individual value (of a set of three test pieces) below 20 J.
Table 5.3.3
Use of Subsize Charpy Impact Test Specimens.
10 x 10 mm
10 x 7.5 mm
10 x 6.7 mm
1Ox5mm
27 J
22 J
20 J
19 J
The testing of subsize specimens from reinforcing bars may be carried out at the
test temperature with a reduction in energy values based o n the above table.
(b)
Small Diameter Bars
In the case where it is not possible t o obtain a Charpy impact test piece, the
Purchaser should consider with the Contractor the feasibility of characterising
each cast of steel by testing bar of 16 mm diameter cut from "bar" at an earlier
stage in rolling.
(c)
Design T e m p e r a t u r f l e s t Temperature
The design temperature of the embedded bar m a y be calculated from the
temperature gradient that will be present in the concrete section in service.
5.4
Prestressing Steel and Anchors
5.4.1
General
As stated in 5.3.1, it should be recognised that reinforced concrete is a heterogeneous
material. Prestressed concrete is a form of reinforced concrete that'is maintained i n a
state of compression, as a result of the tensile forces applied t o the prestressing steel
tendons within the concrete structure. A residual compression is required under service
load conditions. The greatest forces or loads to the structure are applied during
construction, when stressing or applying the tensile load to the prestressing steel
tendons or bars, and this initial stress in the steel corresponds t o 65% to 70% of the
actual ultimate tensile strength of the steel. Thereafter the applied stress to the steel
tendons reduces due t o lock-off or transfer, relaxation and creep, thereby increasing the
factor of safety.
To date, prestressed concrete RLG containments have utilised a fully bonded system
between the tendons and the concrete, either by cementitious grouting of ducts after
stressing the tendons, or b y applying a gunite or pneumatic concrete coating to
externally wire wound prestressing systems. It is essential that a meticulously reliable
system of bonding is utilised and there is n o likelihood of slipping of the tendon, or any
part of it at the design temperature envisaged.
From test results it has been noted that considerable ductility is retained in prestressing
tendons at l o w temperature. Notch sensitivity can be increased but there is no risk of a
failure propagating t o adjacent bars or strands of a tendon. Furthermore, within a short
distance of a failed bar or strand, full strength is regained due to the bond between the
steel and the concrete.
Reference can be made t o the following publications of which the first three are from
the "Federation lnternationale de la Precontrainte" f o r further information and
guidelines on prestressed concrete:-
24
(i)
Preliminary recommendations for the design of prestressed concrete containment
structures for the storage of refrigerated liquified gases (RLG) - Sept 1982.
(ii) Cryogenic behaviour of materials for prestressed concrete - May 1982.
(iii) Assessment of mechanical properties of reinforcing steel and prestressin9
systems for cryogenic applications (Report to be published).
(iv) Prestressed concrete for the storage of liquefied gases b y Professor Dr. Ing. A.S.G.
Bruggeling.
In general, it is concluded that impact tests o n prestressing steel strands or tendons are
not necessary.
5.4.2
Materials
5.4.2.1
Tendons
Prestressing steel may be in the form of wires, strands or bars. They shall comply with
the requirements of: BS 4486: "Hot rolled and processed high tensile alloy steel bars
for the prestressing of concrete". (Bars). BS 5896: "High tensile steel wire strand for the
prestressing o f concrete". (Wires and seven-wire strands).
With seven wire strand systems it is recommended that suitable tests are carried out to
the satisfaction of the purchaser to demonstrate that king wire slippage cannot occur at
m i n i m u m service temperature.
5.4.2.2
Anchorages
Anchors for prestressing steel shall coinply with the requirements of: BS 4447: "The
performance of prestressing anchorages for post-tensioned construction".
It should be recognised that these recommendations only apply t o fully bonded tendon
systems of prestressing. Thus in the unlikely event of a fracture of a prestressing strand
or tendon a full strength anchorage is re-established within a bond length of a strand or
tendon.
Nevertheless wedge or "pull-in" type anchorages can result in indentations in the
strand or tendon and stress concentrations occur at anchorages.
Thus in addition t o the aforementioned requirements the following requirements must
be satisfied:-
5.5
1)
The material of which the anchors are made shall be suitable for thc temperatures
t o which they may be subject. For example, cast iron would not be regarded as
suitable for use at l o w temperatures.
2)
The suitability of the anchors for use at the intended temperatures shall be or have
been demonstrated t o the satisfaction of the purchaser by means of appropriate
tests.
3)
Anchor systems (such as wedge anchors for strand) which involve "pull-in" shall
be employed only when the purchaser is satisfied, b y means of additional tests,
that the full load-elongation charactertistic can be developed.
Concrete
Concrete and its constituent materials shall comply with rhe requirements of:
BS 8110: "Structural use of concrete".
Prestressed concrete shall be Grade 40 or stronger.
In addition, the purchaser may require that the m i x design shall be such as to enhance
the following characteristics:
1)
Impermeability.
2)
Freedom from cracks.
3)
Fire resistance.
25
4)
Behaviour a t l o w temperatures.
5)
Durability
61
Resistance t o sulphate and chloride attack.
It is recommended that the concrete should contain about 5% entrained air
5.6
Insulation
5.6.1
Insulation Categories
The materials f o r the insulation for RLG storage may be divided into the following
categories:
(a)
tank base insulation
(b)
tank shell internal insulation
(c)
tank shell external insulation
(d) tank roof insulation
(e)
5.6.2
Suspended deck insulation
Tank Base Insulation
The material selected for this duty should provide the necessary load carrying capacity
as well as the required thermal characteristics.
Typical materials used for this purpose, either alone o r in combinations, are blocks of:-
(i) cellular glass
(ii)
perlite concrete
(iii) foamed or aerated concrete
(iv)
plastics foam (e.g. polystyrene) concrete.
(v)
polyvinyl chloride foam
(vi) glass reinforced polyurethane foam
(vii) timber
5.6.3
Tank Shell Internal Insulation
Typical materials which m a y be used for this purpose either alone o r in combination
are:(i)
cellular glass
(ii) polyurethane foam
(iii) polyisocyanurate foam
(iv) phenolic foam
(v)
polystyrene foam
(vi) expanded perlite (loose fill) o r vermiculite
(vii) mineral w o o l o r glass fibre blankets
5.6.4
Tank Shell External and Roof Insulation
Typical materials which m a y be used for this purpose are:-
(i)
cellular glass
(ii)
polyurethane foam
(iii) polyisocyanurate foam
(iv)
phenolic foam
26
5.6.5
Suspended Deck i n s u l a t i o n
Typical materials which may be used for this purpose are:(i)
mineral wool or glass fibre blankets
(ii) loose fill insulants - perlite. vermiculite or similar
(iii) bagged loose fill material as (ii) above
5.7
Earth Embankment
The fill for the embankment shall consist of selected material which is not sensitive to
settlements. The settlements of the embankment may damage the slope protection and
the roads located o n the embankment. In addition it will produce a downward loading
o n t h e wall due t o friction between soil and the concrete wall. Fill consisting of rock or
granular soil can be used. The rock fill shall be durable hard type rock. Weak rock, such
as mudstone, shales, mar1 and chalk are not suitable for the heavy loaded embankment
fill. Granular soils placed and compacted in layers also f o r m a high quality fill material.
For compaction it is preferred that the material is not single-sized but contains variation
in grain size. The permeability of the fill should be guaranteed so that pore water
pressure cannot develop during construction of the embankment.
Cohesive soils have a l o w permeability and this may result in very little consolidation
during the construction of the embankment. Therefore, soils with 35% or more material
finer than 0.06 mm, organic soils and peat, shall not be used for fill of the embankment.
In practice material with a density higher than 1750 kg/m3 and an angle of internal
friction of at least 30" is used.
At some locations the subsoil consists of impermeable material and a bottom drainage
layer under the tank and the embankment may be required. The material for the
drainage layer shall be selected carefully. It may consist of rock or coarse fill and very
fine material with the silt and clay content limited t o max. 4%. This is t o prevent
possible clogging of the drainage system. The drainage layer shall be protected by a
filter layer so that fine material of the embankment fill cannot penetrate into the coarse
material.
As an alternative to natural filter layers, there are various types of geotextile materials
o n the market. For detailed information and application reference should be made to
the manufacturer.
The access roads located on the embankment are i n general designed for maintenance
purposes only. The construction of the road is of a light duty type and the materials
required shou Id be se Iected accordingIy.
27
6.
DESIGN
6.1
Foundations
6.1.1
General
The following recommendations are intended t o establish general principles for the
design and construction of foundations under refrigerated liquefied gas (RLG) storage
tanks to ensure they will support the loadings adequately and do not impair the
structural integrity of the tank. The recommendations are offered as an outline of good
practice and requirements and point out some precautions which should be observed
in design and construction of such foundations.
Because of the wide variety of soil surface and sub-surface, climatic conditions, and
design of storage tanks, it is not practicable to establish in this document design data to
cover all situations. The allowable soil loading and foundation system must be decided
for each individual case.
The design of foundations for refrigerated liquefied gas storage tanks represents a
unique problem for the following reasons:
(a)
’
Unlike foundations for buildings and other conventional or traditional structures,
tank foundations are subject to live loads representing the overwhelming
proportion of total gravity load. These live loads are frequently fully attained, but
can also vary frequently as the contained liquid level is changed; thus the live load
will be of a cyclic nature during the design life of the tank.
(b) The contents of a n RLG storage system represent a high concentration of energy
and their accidental release could have severe consequences.
(c)
The low temperature of the tank contents could, unless protective measures are
adopted in the foundation system, cause problems of ground freezing for certain
types of soil and rock.
6.1.2
Soil Investigation
6.1.2.1
General
Wherever possible, RLG storage tanks should be sited in an area where subsoil
conditions are homogeneous, and have good characteristics in respect of load bearing,
settlement and frost heave.
Prior to the start of design and construction of the foundation a thorough geotechnical
investigation should be conducted by a qualified geotechnical engineer, to determine
the stratigraphy and physical properties of the soils underlying the site. The soils
investigation should be at least carried out in accordance with BS 5930.
In addition to the requirements given in
thermal properties shall be determined.
BS 5930, the soil resistivity,
conductivity and
Additional useful information may be obtained from a review of the regional geology
and sub-surface conditions and the history of similar structures in the vicinity.
6.1-2.2
Water tables
Full details including seasonal variation with depth of the ground water table, perched
water tables and possible sub-surface.water flows, should be identified over the area of
the planned storage, together with data on the permeability of the soils and possible
susceptibility to frost heave. Consideration must be given t o possible changes that can
result in the above data from construction works.
6.1.2.3
Seismic investigation
No country is entirely free from earth tremors, though their effects may not be
significant in the design of conventional structures. A thorounh investigation is
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29
appropriate for RLG storage systems i n view of the hazards arising from the leakage of
the stored contents. The extent of the investigation required will depend on the
assessment of seismic intensity for the site and-the recurrence interval consistent with
the risk levels assumed in the design. Reference should be made t o 3.8 of this
document.
6.1.2.4
Sites to be avoided
The following are some of the many variations in conditions that will require special
consideration as regard foundation design and they should be avoided if economic
considerations permit selection of alternative areas.
(1) Sites where part o f a tank may be on rock or other firm undisturbed ground and
part o n fill; or where the depth of required fill is variable; or where ground under
part of the tank area has been preconsolidated.
(2)
Sites o n swamps or where layers of highly compressible material are below the
surface.
(3) Sites where stability of the ground is questionable, such as adjacent t o deep water
courses, mining operations, excavations or steeply sloping hillsides. Karst
topography or gypsiferous materials which could include solution features,
should also be avoided.
(4)
Sites where tanks may be exposed t o flood waters, resulting i n possible uplift,
displacement or scour, or conversely where any subsequent lowering of the
groundwater table could lead t o additional differential settlement.
(5) Near t o active faults or o n soils susceptible t o liquefaction in areas subject t o
earthquakes.
6.1.3
Foundation Design
6.1.3.1
General
The tank floor and foundation of the containment system shall be designed to transmit
all of the loads to a suitable load bearing strata, t o be liquid tight and gas tight, and to
be able t o accommodate the anticipated differential and total settlement without
distress.
The foundations of refrigerated liquefied gas storage tanks should be designed by
engineers with relevant experience and constructed in accordance with recognised
engineering practices. The design should generally be in accordance with the
recommendations of BS CP 2004 and take account of the special nature of the
soil/structure interactions, the definition of the liquid loads and the vulnerability of
these tanks t o foundation settlements, the possibility of frost heave of underlying soils
and the possibility of earthquake loadings. The enhanced properties that are known to
exist for the materials of construction at low temperatures shall not b e used i n
determining the material safety factors.
6.1.3.2
Loading conditions
The different stages of the life of the structure should be considered i n the design, i.e.
construction, testing, commissioning, service and maintenance. Abnormal events must
also be considered. The normal service loads and the abnormal loads that are required
t o be taken into account are shown in 4 and Appendix E.
6.1.3.3
Allowable soil loading
The allowable bearing capacity shall be decided as a result of the geotechnical
investigation giving due consideration t o the accuracy of predictions of ultimate
bearing capacity and settlements. Advantage may be taken o f modern computer
techniques t o investigate soillstructure interaction, in addition t o any traditional
analysis.
30
6.1.3.4
Settlement
The prime aim of the foundation designer shall be to determine the predicted
maximum total and differential settlements for the life of the facility so that comparison
can be made with permissible settlements, which for steel tanks are defined i n BS 5387
and BS 4741.
The permissible settlements are the maximum allowable design limits for deformation
of the tank after allowance has been made for construction tolerances. These limits are
t o be agreed between the foundation designer and tank designer for the total
settlement and differential settlement which may comprise combinations of:
(a)
tilt o f the tank
(b)
tank floor settlement along a radial line from the periphery t o the tank centre
(c) settlement around the periphery of the tank.
The considerations affecting the limits of permissible settlement include but are not
necessarily limited to:
(1)
The dimensions and aspect ratio of the tank and the stiffness of its foundation.
(2)
The stiffness of the tank and its components.
(3)
The reliability of the investigation (investigations in uniform ground conditions
are more reliable than those i n variable ground).
(4)
The possibility of any interactive effects with adjacent tanks and integral earth
embankments.
Settlement calculations are of limited accuracy even with detailed investigation and
sophisticated analysis. Tanks should not therefore be designed to depend for their
structural integrity on theoretical settlement predictions and appropriate safety
margins should be included.
Where significant settlement is predicted, it is recommended that actual settlements
are monitored during the various phases covering the complete life of the installation
including construction, hydrostatic testing, commissioning and operation. A variety of
instruments are available for the remote measurement of the insitu settlement of the
soil immediately below any part of the earth embankment and the foundations for the
tank and outer wall. However, all these instruments measure settlement by traversing
within special conduits buried in the foundation. Hence, these conduits have to be
installed at the time of the initial construction. The location and number of conduits
provided shall be commensurate with the accuracy required for the assessment of total
and differential settlement i n the critical areas described in the preceding paragraphs.
The monitoring frequency shall be commensurate with the predicted time and load
dependent rate of change o f settlement.
6.1.3.5
Soil improvement and piling
If the subsoil supporting the foundation is weak and inadequate t o carry the load of the
filled tank without excessive settlements, the following methods of improvement may
be considered.
(1)
Removal and replacement of unsatisfactory material by suitable compacted
granular fill that is not frost susceptible.
(2)
Improvement of the soft or loose materials by vibration or dynamic compaction.
(3)
Pre-loading with a temporary overburden.
(4)
Enhanced subsoil drainage with or without pre-loading.
(5)
Stabilisation b y chemical or grout injection methods.
(6)
Piling.
31
6.1.3.6
Frost heave
The ground beneath an RLG tank will lose heat to the tank, even though the tank floor
construction incorporates insulation. This loss of heat from the soil could lead to frost
heave, which must be avoided. Commonly used methods of avoiding frost heave are
either:
(a)
electrical heating elements within ducts or warm-water circulating systems,
located within the subgrade or more usually within the concrete base slab. Such
systems must be readily serviceable and replaceable.
or
(b) the base slab elevated above ground level so as to allow circulation of air below
the tank.
The foundation designer shall define the minimum control temperature assumed for
the foundation design. In general the temperature of the supporting soil or the
concrete, during normal operations, should not fall below 3" to 5°C.
Consideration should also be given to possible maximum temperatures of the
foundation, and the sensitivity of the soil to possible drying shrinkage.
If a heating system is used it shall be designed to minimise excessive temperatures that
could lead t o high boil off rates and permit functional and performance monitoring. The
arrangement shall take account of any variations in the heat transfer characteristics of
the materials of construction particularly around the tank perimeter or around a bottom
entry if applicable. The system shall be installed so that any heating element or
temperature sensor used for control can be readily replaced. The design of the system
should be such as to permit the regular monitoring of its performance.
6.1.3.7
Drainage
Areas around storage tanks should be properly drained away from the tank to prevent
water accumulation, including firewater run off where applicable, around the
foundations.
Control systems should be provided to prevent RLG contaminating the drainage
system in the event of spillage.
For single and double containment systems the sealing arrangements around the base
of the tank and the insulation cladding should be carefully detailed to eliminate the
possibility of water migration to the cold tank surfaces and foundations.
6.1.3.8
Resistance t o uplift
In the case of steel tanks, anchorages are required to resist uplift of the shell due to the
effects of internal tank vapour pressure (and wind load or earthquake when applicable).
The anchorage shall generally be in accordance with BS 5387.
6.1.3.9
Bottom insulation
For details of bottom insulation, see 6.6.
6.1.3.10
MembraneNapour barrier
Reference should be made to the appropriate clauses of the FIP Guide regarding
requirements for a bottom or floor membrane. The membrane shall be provided below
and around the insulation material supporting the tank. In the selection of the
membrane, consideration shall be given to the temperature and stresses to which it
may be subject in service and under abnormal upset conditions. Only materials that
have been proved capable of retaining their impermeability in these conditions shall be
used. If the membrane takes the form of a coating applied t o the slab, its coefficient of
thermal expansiodcontraction shall be compatible with that of concrete throughout the
relevant temperature range.
32
In the case of a full or double containment systems, this barrier may be metallic and
form the outer containment member.
6.1.4
Types of Foundations and Tank Floors
6.1.4.1
General
There are four main types of foundations used in RLG storage schemes:
6.1.4.2
-
Ring Beam
-
Surface Raft
-
Elevated Slab
Pile Supported Raft
Ring beam foundations
Where the surface and sub-surface soils have the capability to support adequately all
applied loads from the tank and contents, an earth mound foundation may be
considered. A concrete ring beam may be required to resist uplift of single containment
tanks or inner tanks of double containment systems and provide a foundation for high
tank shell loads. The ring beam shall be designed to withstand horizontal pressures
from the contained earth mound including all surcharge effects from the tank and
contents. Some form of transition support is advisable between the inside of the ring
beam and the compacted earth mound, to smooth out sharp changes in settlement.
6.1.4.3
Surface raft foundations
Where sub-surface soils exhibit suitable characteristic properties to support all possible
loadings, a soil supported reinforced concrete surface raft may be suitable. Such a raft
or slab normally incorporates an increased thickness as necessary under the shell of
single containment tanks or the inner and outer walls of double or full containment
tanks, depending on the dead loads (concrete, steel etc.) and imposed loads (including
abnormal loads) that apply.
In the design of the slab, provision shall be made to accommodate the effects of local
differential settlements, drying shrinkage, creep and thermal strains during service or
under upset conditions. Such requirements may involve:
-
Additional reinforcement
-
Prestress
-
Constructing the slab in bays. In this case the construction joints should
incorporate suitable barriers to prevent the passage of liquid, gas or water vapour.
The use of special curing techniques andor concrete admixtures.
Where an outer concrete tank with an earth embankment is used, the high
concentration of load from the outer wall combined with vertical load from the
embankment will normally require the wall and base slab t o be independent.
The wall base is generally designed as a separate foundation to a level below the
underside of the base slab. The use of a bitumen slip layer on the external face of the
wall will minimise the friction downdrag from the embankment but special measures
may still be necessary to minimise differential settlement between the wall and base
slab so that the integrity of the membrane and heating conduits is not impaired.
6.1.4.4
Pile supported raft
6.1.4.4.1
When subsoil conditions do not permit a soil supported foundation the slab may be
supported on piles.
The slab design shall take account of potential variations in pile stiffness. The integrity
of the piles should be checked on completion of installation. Unless the design of the
33
piling system is such that it is possible to prove the integrity of each pile by field tests,
consideration shall be given to designing the slab and pile system to accommodate
redistribution of load to adjacent piles in the event of failure of an individual pile.
6.1.4.4.2
Drying shrinkage, creep, thermal changes and cold spots due to small leaks will cause
horizontal deformations in the slab, the amount of deformation decaying towards the
centre of the slab. Vertical thermal gradients in the slab will also tend to induce
moments in the slab and piles. In double or full containment systems horizontal forces
and moments from upset conditions or abnormal loads on the storge tank may also be
transferred to the base slab. Careful consideration shall be given to the joint between
pile supports and the base slab. If the subsoil characteristics are suitable, closely
spaced short slender piles could be rigidly connected to the base slab. Where large
diameter in-situ formed piles are used it may be possible to use rigid connections for
the piles near the centre of the tank and provide a sliding joint for the remainder.
6.1-4.4.3
Adequate attention must be given to possible problems of ground heave and/or pile
heave, if a displacement pile system is adopted.
6.1-4.5
Elevated slab foundation
6.1.4.5.1
The concrete slab to the tank floor can be located above ground level so as to provide
free circulation of air beneath. Heat loss from the ground to the tank via the support
columns, will be minimal.
The elevated concrete slab is supported by closely spaced columns. These may be
extensions of piles or based on shallow foundations, depending upon the type of
subsoil. The clear space beneath the concrete slab should be at least 1.O m above grade
to permit access for inspection and maintenance.
The area beneath the tank should be such as to prevent liquid pooling beneath the tank.
The space beneath an elevated slab foundation shall be provided with gas detection
equipment, in case ventilation is insufficient to prevent formation of gas pockets
emanating from leaks in the storage system or associated piping.
6.1.4.5.2
The considerations listed in 6.1.4.4 (regarding pile supported rafts) also apply to
elevated slabs, whether the columns are supported by piled foundations or shallow
foundations. In addition, consideration shall be given to the thermal effects of a spill
sufficient to flood the underlying airspace with R.L.G.
6.2
Design of Steel Tanks of Single Containment or Steel Inner or Outer
Tanks of Double or Full Containment
The detailed design of storage tank components shall follow the precepts given in BS
5387 as specified in Table 6.2 as well as any additional information given in the
following paragraphs of this section.
6.2.1
Tank Bottom Design
The leg length of each fillet weld in BS 5387 clause 14.2.3 shall not be greater than 15
mm.
6.2.2
Shell Design
6.2.2.1
Design stress
The maximum allowable stress in any plate under water test shall be limited to 85% of
the specified minimum yield strength or proof stress of the parent plate or weld metal,
whichever is the lower.
The maximum allowable design stress in service in any plate shall be the value
determined from Table 6.2.2.1 or 260 N/mm2 (or 93 N/mmZ for Aluminium alloys)
whichever is the least.
34
$m
oh;
-
- 0
oiz
-
U
z
-U
2
-
-
1
D
2
a
z
n
C
0
.-"
0
Y
C
m
E
:
c
m
-
C
C
x
-W
C
35
Table 6.2.2.1
The Maximum Allowable Design Stress
Carbon Manganese steels
UTS/2 .35
or
ys11.5
Improved Toughness Carbon Manganese steels UTS/2.35
Low Nickel Steels
UTS/2.35
9% Ni Steel
UTS/2-35
or
ys/l .5
or
0.2%PS/1.5
or
0.2%PS/1.5
Austenitic Stainless Steels
or
or
1%PSI1-5
O.2%PS/1.33
UTS/2. 5
UTS/2.67
Aluminium Magnesium Alloys
The tensile (UTS), proof stress (PS)and yield strength (YS) shall be the specified
minimum or guaranteed value given in the appropriate material specification for the
parent plate. In the case of weld metal, the tensile and proof strengths shall be
demonstrated t o have been achieved in the tensile test specified-in BS 5387 Clause
25.3.4.
6.2.2.2
Thickness
For construction purposes, the nominal thickness shall not be less than the following:For tank diameters
< 30 m, minimum thickness 8mm
2 30 m < 50 m, minimum thickness
For tank diameters
5 50 m, minimum thickness 12 mm
For tank diameters
10 m m
where this thickness may include any corrosion allowance provided that the shell is
shown b y calculation to be safe i n the corroded condition and i n accordance with the
requirements of 6.2.3.2.
The maximum thickness shall not exceed those specified in 5.1.2.
-
6.2.3
Internal Loadings
6.2.3.1
The forces in the tank shall be computed on the basis that the tank is filled to the design
product height (see 4.1.7 (1)) with product plus the superimposed design roof pressure
or filled t o the design product height with test water plus the superimposed test roof
pressure. The design shall ensure that the tank cannot be filled with'-product above the
maximum product filling height upon which the design is based under normal or
emergency operating conditions.
6.2.3.2
The thickness of the shell plate shall be determined as the greater of t, or t as
determined from the following:1.
The following formula shall be used i n calculating the thickness of shell plates
under test conditions:[98'W, (H - 0.3)
where t,
H
is the calculated minimum plate thickness ( m m )
is the height from the bottom of the course under consideration t o
the highest liquid level (m)
is the tank diameter ( m l
is the maximum density of the test water (g/ml)
is the allowable stress under test conditions - see 6.2.2.1 (N/mm2)
is the test pressure and equal to zero in the case of an inner tank with
no attached roof ( m bar gauge).
20s,
D
W,
S,
P,
-
2.
+ P,]
t, =-
The following formula shall be used i n calculating the thickness of shell plates
under product conditions:t=-
20s
I98 W (H - 0.3)
+ PI + C
36
where t
H
is the calculated m i n i m u m plate thickness ( m m )
is the height from the bottom of course under consideration to the
highest liquid level (m)
is the tank diameter (m)
is the maximum density of the liquid under storge conditions (g/mI)
is the allowable design stress - See 6.2.2.1 (N/mmz)
is the design pressure and equal to zero in the case of an inner tank
with n o attached roof ( m bar gauge)
is the corrosion allowance (mm)
D
W
S
P
C
6.2.3.3
No course shall be constructed of thickness less than that of the course above,
irrespective of materials of construction.
6.2.4
Shell Openings
Refer to BS 5387 with the addition that carbon manganese steels may have the same
thickness as stainless steel and 9 % nickel steel in Table 5 of BS 5387.
6.2.5
Access t o Inner Tank
Access t o the inner tank is preferred via the roof manway in which case a suitable
platform i s required a t t h e t o p of the inner tank immediately below the manway.
,
6.3
A ladder should lead from,this platform t o the bottom o f the tank. This vertical ladder
shall be fitted with a safety cage and rest platforms.
Vapour Containing Outer Tanks
The detailed design of storage tank components shall follow the precepts given i n BS
5387 as specified in Table 6.2 in this document as well as any additional information
given in the following paragraphs o f this section.
6.4
Reinforced Concrete Outer Tanks with Earth Embankment
6.4.1
General
A reinforced concrete outer tank with an earth embankment can be used as the
secondary liquid container for a double or full containment tank. This.code excludes the
possibility of a reinforced concrete outer tank without an earth embankment since there
is n o experience of this type of construction. Figure 6.4.1 shows a typical example of
such a tank (LPG) with an earth embankment. Insulation is present under the inner tank
bottom, on the inside of the outer wall and on the suspended deck. A concrete roof can
be used as an alternative.
6.4.1.1
The Design of the Concrete Structure
The design of the concrete structure shall be based o n the following:
BS 81 10:
Structural use of Concrete
BS 5337:
Structural use of Concrete for Retaining Aqueous Liquids
BS 81 10 shall be used as the base document, with appropriate clauses from BS 5337.
For LNG tanks reference can be made to:
NFPA 59A Standard for the production, storage and handling of liquefied natural gas
(LNG). National Fire Protection Association Boston, Massachusets, USA.
The designer shall determine all possible loading combinations which can occur during
the construction and operational lifetime of the tank. The code provides load and
material factors for construction and normal operation. For emergency load
combinations during fires, earthquakes and inner tank leakages, no factors are
provided. Reduced factors may be considered. This is in view of the low probability of
occurrence of such an event. For more detailed information reference should be made
t o Appendix E.
37
b
Fig. 6.4.1: Typical Section of a Tank with a Reinforced Concrete Outer Tank with Earth Embankment
38
6.4.1-2
Concrete properties under low temperatures
Under cryogenic conditions most o f the concrete properties are not affected adversely
b y the l o w temperature and i n fact are frequently enhanced. However for design
purposes the values f o r compressive strength, poisson's ratio and elastic modulus shall
be those specified i n BS 81 10 for normal temperature conditions.
The thermal expansion coefficient however, reduces at l o w temperatures. This
reduction effect may be taken into account i n the design.
6.4.1.3
Reinforcing steel
Concrete can withstand significant compressive stress, however the tensile strength of
concrete i s relatively low, and the failure mode under tensile loading is brittle.
Reinforcing steel bars are therefore incorporated within the concrete to form a
composite section, concrete taking the compressive stress and the steel rebar taking
tensile stress. The concrete i n the tensile stressed areas can crack under load and both
the spacing and width of cracks must be controlled b y means o f adequate design.
6.4.2
Wall t o Bottom Junction
Important considerations i n the design of this connection are:
A.
liquid and gas tightness.
B.
provision for the differential radial compressive movement or strain caused by the
embankment loadings.
C.
provision for the subsequent radial thermal contraction and expansion, as a
consequence either of the service conditions or of the abnormal conditions
specified i n the design philosophy. The latter may include thermal shock.
D.
resistance t o any abnormal loads (blast, fire, seismic) specified in the design
philosophy.
E.
the ability of the liner and insulation t o accommodate the displacements at the
junctions.
The types of junctions may also be influenced b y other considerations affecting the
connected components, which are described below:
(a)
the nature of the joint i.e. sliding, fixed or pinned.
(b)
the method of construction.
(c)
the position of the wall membrane - internal, external or embedded - and its
ability t o resist l o w temperatures.
Three designs are considered:
1.
Sliding Joint
In this design the wall is left free to move. It is supported by the soil or by the base
slab. Radial guides may be provided, to ensure that the movement is concentric
with the main tank. A seal, commonly i n the form o f a stainless steel strip is
provided to prevent leakage o f liquid or gas.
2.
Fixed Joint
This design prevents movement of the wall and accepts the relatively large
moments and shears which arise as a consequence.
3.
Pinned Joint
In this design, substantial shears are transferred f r o m shell t o base, but the joint is
not required t o have a capacity t o resist bending moments.
A summary of the advantages and disadvantages of each design is given in Table 6.5.3.
I
39
6.4.3
Shell t o Roof C o n n e c t i o n
The design considerations for this connection are the same as for the wall to bottom
design.
6.4.4
Earth E m b a n k m e n t
A tank with an earth embankment is rather sensitive to settlements. Large differential
settlements between the wall and the slab cannot be accommodated by wall and slab
connections and therefore they are not acceptable. If the bearing capacity of the subsoil
is poor and large settlements are predicted, a pile foundation shall be used.
The cross section of an embankment is determined by the width of the maintenance
road, by the height of the embankment and by the slope of the embankment. The slope
depends o n the geotechnical properties o f the fill material. The minimum required
slope shall be determined by stability calculations. A slope of 1:2 is generally adequate
f o r a granular fill material. Retaining walls may be used at the bottom of the
embankment t o reduce the area required. The routing of the access roads t o the top
should be determined. Two independent roads, one up and one down, are
recommended.
The settlement of the embankment shall be calculated in combination with the
settlements of the subsoil and the tank. This should be done b y finite element analysis
for complex situations.
The height of the embankment depends o n the design failure condition of the inner
tank and the degree of safety against external loading required. The purchaser shall
specify the minimum height of the embankment. Maximum protection will be obtained
when the height of the embankment is the same as the maximum fill height of the inner
tank.
The f i l l of the embankment shall be protected against erosion and, if necessary, against
water penetration. A mortar, concrete, asphalt or a sand bitumen layer may be used t o
a thickness of 50 mm t o 100 mm. Grass i n combination with a top soil layer may also be
used. Water tight expansion joints should be provided where rigid materials (concrete,
mortar, etc) are used t o prevent damage to the slope protection i n the event of
sett1e m ents.
The base of the outer tank should preferably be located above the,ground water table
so that uplift forces cannot act on the bottom slab. Where the tank is located in an area
that would intercept the natural ground water regime e.g. a tank built against a hillside
with a layer of impermeable material, it will be necessary t o provide a ground water
drainage system around the tank so that pore water pressure does not build up. A
typical ground water drainage system may consist of perforated pipes with adequate
granular material surround. Provisions shall be made t o monitor the water table level
e.g. stand pipes.
6.5
Prestressed Concrete Outer Tanks
6.5.1
General
6.5.1.1
Introductory note o n prestressing
Prestressing is a general technique whereby pre-determined forces (usually
compressive) are applied t o a member or structure, t o achieve a controlled change i n its
behaviour properties.
Prestressing modifies the behaviour of a concrete member or structure in several ways
-these include:
(1)
An improvement in its ability t o resist subsequently applied loads which give rise
t o tensile stresses.
40
The tensile strength of concrete is relatively small (between one-tenth and
one-fifth of its compressive strength) and is also unreliable. Prestressing is
therefore applied to create a pre-compression in a member or structure or those
parts of a member or structure which will subsequently be subjected to loads
which give rise to tensile stresses. The magnitude of this pre-compression is
designed to equal or exceed the subsequent tension. The behaviour of concrete in
shear is improved in the same way, since the critical principal tensile stresses
(which determine the shear strength) are counteracted by the pre-compression.
A change in the mode of tensile failure.
In plain concrete, failure in tension takes place in a brittle manner. In reinforced
concrete, the cracking is controlled by the reinforcement; cracks due to overload
remain open when the overload has been removed. In prestressed concrete with
bonded steel, overload causes cracks as in reinforced concrete; but the continuing
presence of the prestressing force ensures that the cracks close again when the
overload has been removed. In prestressed concrete with non-bonded steel the
behaviour is different in that a small number of wide cracks develop; nevertheless,
they still close again on removal of the overload.
Changes in the behaviour of the material.
The magnitude of the prestressing force and the load/deflection characteristics of
the concrete are both time-dependent. Thus prestressed concrete members and
structures tend to be "live''; they undergo movements (even in the absence of
other loadings) which vary with time.
The presence of the prestressing force also imparts a considerable degree of
resilience or springiness to a prestressed structure or member. These
characteristics exist; whether they are advantageous or not will depend to a
considerable degree on the application considered.
6.5.1.2
Methods of prestressing
The two main methods of prestressing are known as pre-tensioning and posttensioning. The terms relate to the time at which the tension is applied to the
prestressing steel, relative to the casting of the concrete.
Pre-tensioning is employed mainly for precast factory made units. The tendons are
tensioned against independent supports; the concrete is then cast around the tendons,
to which it becomes bonded. The tension is then removed from the ends of the
tendons, and is transferred to the precast units solely by the bond.
Post-tensioning is primarily a site technique. The concrete is formed around the
untensioned tendons in such a way that they remain free to move within the concrete.
Alternatively, ducts may be formed within the concrete, in circular structures such as
tanks, the tendons may be wrapped around the outer face by one of several techniques.
In each case, the tendons are tensioned after the concrete has hardened; the concrete is
used as the jacking abutment. The tensioned tendons are locked into anchors; the jacks
are depressurised and removed; the tendons are finally protected by pumping grout
into the tendon ducts. For some applications, involving tendons which are pre-greased
and sleeved, the grouting operation is not needed.
6.5.1.3
Loss of prestress
Whichever method (pre-tensioning or post-tensioning) is adopted, the prestress in the
steel (and thus in the concrete) is reduced over a period of time by various losses.
These are due to the compression shrinkage and creep of the concrete, relaxation of the
steel, pull-in at the anchors and friction between steel and concrete during the stressing
operation. The total loss of stress in the steel may be up to 300 N/mm2. It is necessary
therefore to ensure an adequate level of stress after the losses have occurred. Stresses
of this magnitude in the steel require in turn that the concrete should also be of good
quality, with a strength of 40 N/mm2 or more.
41
6.5.2
Base Design
In principle, the tank base may be of reinforced concrete or of prestressed concrete.
With prestressed concrete, the base is likely to be a continuous slab. If piles are also
employed, provision may be needed to allow the slab to slide relative to the piles.
With reinforced concrete, the base may be divided into a number of relatively small
bays, bridged by cryogenic expansiodcontraction joints; or it may be cast as a
continuous slab. The choice may depend on the metal lining over the base slab; if this
is not of low temperature steel the adoption of a number of bays might be prudent. If a
low temperature liner is provided, a continuous slab might be favoured.
6.5.3
Wall to Base Junction
The junction of the wall and base is important for the integrity of the whole outer tank,
and a satisfactory solution of this problem is therefore essential.
When the circumferential prestress is applied to the wall, it tends to contract.
Subsequently, if (under hazard conditions) the wall is loaded by the internal pressure
from a cryogenic liquid, it tends first to expand, by an amount slightly less than the
previous compression, due to the pressure of liquid; thereafter this expansion tends to
be reduced, over a period of hours, by shrinkage due to thermal effects.
For design consideration of the wall to base junction refer to 6.4.2
In the case of pinned joints the wall is allowed to slide while it is being prestressed;
thereafter it is pinned in position, by one of several devices, but not prevented from
vertical rotation.
Table 6.5.3 summarises the advantages and disadvantages of w a l l to base joints.
Table 6.5.3
t
Wall t o Base Joints
~~~
~
System
Advantages
Disadvantages
Sliding joint
Stresses can be predicted with
good reliability.
Secondan/ stresses are relatively
small.
Dependent on adequacy of joint seal.
Some uncertainty over degree of
sliding obtained.
Robust f o r m of construction
Prediction of stresses may be uncertain.
Fixed joint
.L
Large moments and shears
May necessitate continuous
prestressed base.
Maximum moment occurs at the joint.
Pinned joint
Prestress can be predicted with
good reliability.
Subsequent secondary stresses are less
reliable.
Maximum moment occurs in wall
away f r o m the joints, at level where
“end effects” from vertical tendons
are largely smoothed out.
Large shears; fairly large moments.
42
6.5.4
Wall Design
Prestressing
In general the applications of prestressed concrete described in this document relate to
components which are at ambient temperatures during construction and normal
service conditions. Hence the design and construction of prestressed RLG storage tanks
is governed to a considerable degree by the normal codes and standards. (See
Appendix G).
6.5.4.1
Prestressing systems
Circumferential prestress may be provided by means of wire winding or by linear
prestressing systems in conjunction with stressing piers. Of the wire winding systems
the most widely used has been the system, in which the tension is imposed on wire by
drawing it through a die. The stressing carriage is suspended from a top cradle, and
propels itself around the tank by the means of a continuous chain. In recent practice,
the wires are concentrated in a number of separate bands,. rather than being applied
uniformly over the whole exterior of the tank. The bands may include several hundred
wires, in multiple layers; each layer is embedded in mortar and each complete band is
protected by a layer of sprayed'concrete.
Other wire winding systems usually employ friction braking to impart the tension to the
wire. While details often vary, the general concept is similar.
With linear prestressing system.s, the tendons are embedded within the concrete of the
wall, about 100 mm or so from the outer face. They are anchored at stressing piers,
where they are crossed over to provide double prestress within the crossover zone; this
compensates for the approximate doubling of the wall thickness at the piers.
Cylindrical walls are prestressed both vertically and circumferentially. The vertical
prestress is applied before the horizontal prestress; this is to guard against the
possibility that transient vertical bending induced during the circumferential
prestressing might otherwise cause horizontal cracking.
Non-tensioned reinforcement is often used in addition to control cracking.
6.5.4.2
Bonded and non-bonded tendons
When linear tendons are employed, a choice may be made between bonded tendons
which are placed within metal ducts and subsequently grouted, and non-bonded
tendons which comprise separate strands or bars, greased and sleeved in rubber or
polypropylene, before delivery. The latter are cast directly into the concrete, without
ducts, and no subsequent grouting is needed.
Both types of tendons provide similar performances under normal service conditions;
but their behaviour differs under abnormal conditions. With bonded tendons, a large
number of narrow cracks are developed in the concrete, whereas with non-bonded
tendons a small number of wide cracks tend to appear. Hence it may be necessary, with
non-bonded tendons, to adopt additional non-tensioned reinforcement for crack
control purposes.
Non-bonded tendons rely solely for their performance on the integrity of the anchors;
bonded tendons, on the other hand, derive some additional security from the grout.
6.5.4.3
Design of tendons
The design of the prestressed tendons shall be in accordance with BS 81 10 with due
attention given t o transfer and residual stresses. The amount of prestress loss shall be
calculated with due regard given to the loss from frictional effects in curved tendons.
In addition the following points should be noted:
Although not considered for design purposes (except at transfer) concrete exhibits
some tensile strength. At low temperature the tensile strength increases.
43
. .. .
.,...
-.
The tendons shall be protected from corrosion during the life of the tank.
It should be a design parameter that the overall strength of the tendons, including any
non-stressed reinforcement shall be greater than the tensile strength of the concrete a t
the design temperature, this being assessed from experimental data. This is to ensure
that in the event of overloading, sudden failure or bursting o f the tank is a non credible
event.
6.5.4.4
Positions of tendons
In general, the circumferential prestressing steel should be placed as closely as
practical t o the outer face of the wall, and the vertical tendons should be at the centre of
the wall.
6.5.4.5
Protection of tendons
Provisions should be made t o protect the tendons in accordance with.the requirements
of BS 81 10.
Such precautions m a y need to be more stringent in the case of wire winding systems,
where the tendons are usually closer t o the surface of the concrete.
6.5.4.6
Stresses
The stresses in prestressed concrete shall be in accordance with BS 81 10 and BS 5337.
(See also 6.4.1.1).
Under normal loading conditions a minimum residual compressive stress of 1.O
N/mm2, after allowances made for all losses, should be provided i n the two principal
directions within the concrete. The purchaser may also specify other stress
requirements for abnormal loads and conditions.
6.5.5
Wall to Roof Junction & Roof Design
Refer t o 6.4.2 and 6.4.3
6.6
Insulation Design
6.6.1
General
Apart from the insulating properties two important parameters t o be considered in the
use of insulating materials are the need to exclude water vapour from the insulant and
the effect of the environment on the properties of the material selected. A full list of
insulation materials for shell, base, roof and suspended deck is given i n 5.6.
6.6.2
Influence of Service on Thermal Characteristics
of Foams
Thermal insulants for l o w temperature applications work best if they have a completely
closed cell structure with a low thermal conductivity gas retained within the individual
cells. I n practice this gas permeates from the cells in time t o be replaced by air or the
gas being stored in the case of insulation used inside a tank shell. Water vapour can
also permeate into the cells and this may not only produce icing but also an increase i n
the thermal conductivity of the insulant. The data given i n Table 6.6.2 show the likely
effect of the environment on the thermal conductivity of a typical foam.
Table 6.6.2
Environmental Effect on Thermal Conductivity
Environment
Thermal Conductivity at 20°C
W/m"C
Still dry air
Water
Ice
Methane
Propane
Hydrogen
0.024
0.591
2.180 (at OOC)
0.030
0.017
0.168
44
6.6.3
Water Vapour Barrier
Below ambient temperatures the reduced vapour pressure causes an imbalance which
attracts water vapour to the colder surface. Once the water is below 0°C icing will occur
which will produce cracks i n most materials due t o the expansion in volume from the
liquid t o solid state. As temperatures cycle, the freeze-thaw effect can result in
progressive degeneration of the insulant which can result in ice forming at the cold
metal surface and eventually at the warm side of the insulation. The recognised way of
combating this effect, and the damage it can cause t o insulants, is t o have a vapour
barrier o n the w a r m face t o exclude moisture penetration. These vapour barriers may
b e metallic sheet, such as galvanised steel or aluminium, or an elastomeric material
based on synthetic rubber. The former provides the most impermeable and successful
method, providing the sheet can be securely bonded t o the insulant and the joints can
b e sealed. Elastomeric materials are difficult t o apply to a n even thickness and they
suffer from ultra-violet degradation which induces brittleness and reduces their ability
to expand and contract due t o temperature cycling. They are not impermeable and
some passage of vapour is inevitable.
An impermeable vapour or gas barrier will eliminate or reduce this effect.
6.6.4
Chemical Properties
The chemical properties o f the insulant selected are important. The resistance to
liquefied gases, should these come into contact with the insulant, should be checked. If
water penetrates some plastic foams, particularly polyurethane, polyisocyanurate or
phenolic, an acidic condition can be formed. This may corrode unprotected steel and is
a further reason for ensuring that all water is eliminated from the insulant.
6.6.5
Mechanical Properties
lnsulants placed beneath a tank bottom shall be able to withstand the loads imposed
upon them. For service and test conditions, the safety factor for cellular glass should be
at least 3 based on the average compressive strength properties of the grade selected,
or 2.5 based o n the minimum compressive strength guaranteed. Other materials
should be viewed in the same manner, and it is preferable t o use minimum guaranteed
compressive strength figures rather than average values.
The insulating materials used should be suitable for use over the complete thermal
range envisaged. The mechanical properties of the insulants should withstand the
forces induced during cool-down, which should be as gradual as possible, and any
thermal cycling during service. It should be remembered that most plastic foams have a
coefficient o f linear expansion some 6 t o 20 times that of steel and this effect must be
catered for i n the design.
Some insulating materials, especially plastic foams, have properties which vary
according to the direction of foaming during manufacture, i.e. the properties are
anisotropic. Such variations shall be taken account o f in the design and during
installation. It is possible t o spray apply some grades of polyurethane foam, rather than
lay blocks. This has the advantages of ease of application, lower cost and speed of
operation. The spray application of polyurethane is a specialist job requiring
experienced contractors.
Blocks can be statistically sampled and checked for conformance with the standard.
The separate blocks must be bonded to the substrate and each other and overlapping
layers should always be used. Differential movement between blocks and the substrate
caused by the thermal gradient may cause breakdown of the joint sealant. Appendix B
gives typical properties for various insulants.
6.6.6
Fire
The possibility o f an adjacent tank on fire (see also 4.2.3) must be taken into
consideration when designing insulation for RLG storage. Tank spacing, water deluge
45
systems, quantity and hazard index of contents, locality, vulnerability and the
implications of potential loss of production are all factors which must be Considered
when specifying insulating materials especially when it is proposed to use a plastic
foam insulant. It should be noted that unmodified polyurethane has a high flammability
constant. The most convenient way of determining fire resistance on a small scale is to
use the limiting oxygen index test t o ASTM 2863. This test measures quantity of oxygen
necessary t o sustain burning of a small sample of the plastic foam, but it does not
pretend t o simulate what might happen in a real-life situation. Thus materials which
require a higher percentage of oxygen t o burn than the 21% present i n the atmosphere
have some fire retarding capability. Typical figures are shown i n Appendix B.
Consideration should be given t o the possibility of smoke and toxic fume generation
during a fire.
6.7
Membranes and Linings
6.7.1
General
Prolonged contact with hydrocarbon products does not have any significant
detrimental effect o n the properties or useful life of concrete, even at ambient
temperatures, and chemical and physical activity is progressively reduced as the
temperature is lowered. However, membranes, linings and barrier systems are
commoniy included i n the design of concrete components for RLG storage systems for
the following purposes:
-
-
t o make the component gas tight a n d o r liquid tight;
to prevent the ingress of water vapour into the tank; if admitted, this would form
ice within the insulation, thereby reducing the effectiveness of that insulation.
A lining or liner is here defined as an impervious barrier which is i n contact with, and
usually acts compositely with, the concrete. A membrane, by contrast, is an impervious
barrier which is separated from the concrete by some o r all of the insulation, and which
transmits transverse loading t o the insulation and thence t o the concrete; it does not
act compositely with the concrete.
The requirements which the membrane or lining must meet depend upon the design
philosophy, the location of the liner (on the internal or external face, or embedded), its
temperature conditions and its initial state of stress. Liners have usually been of steel
and membranes of metals or reinforced plastics. Investigations of coatings of various
types such as butyl rubber, polyurethane foam, mastics, and glass reinforced plastic
are continuing and some are being tested i n service, but in these recommendations
only metallic membranes and liners are considered.
6.7.2
Design Philosophy
This will determine the service conditions, and the abnormal or accident conditions,
which the membrane or lining must resist.
The service conditions may include (but are not limited to):
(a)
degree of resistance t o permeation and diffusion of liquids and/or gases
(b)
service temperature
(c)
strain compatibility requirements
(d) limiting thermal gradients
The abnormal conditions may in addition include (but are not limited to):
(a)
thermal shock - nature, magnitude, position
(b) degree of resistance to permeation and diffusion under various accident
conditions
(c)
lower temperatures than service temperature
46
liquid loading
mechanical loading
additional gas pressure
strain compatibility requirements, perhaps under transient thermal conditions
need to bridge cracks o n concrete
resistance t o fire
resistance t o blast, flying objects and impact effects
resistance to earthquake conditions
6.7.3
Liner Design
6.7.3.1
The liner m a y b e located on the outer face o f a concrete component but in practice this
option i s available for wall components only. Floor and roof linings are constrained b y
construction considerations t o be located o n the inner face, and hence at wall to floor
and wall t o roof junctions the liner must pass through the concrete t o form a fully
continuous seal.
A liner applied t o tJe outer face of the wall is only suitable for use with wire winding
prestressing systems; the wire i s then applied to the outside face of the lining which is
thereby placed in ring compression. The close spacing of the wires eliminates any
possibility o f buckling of the liner. When used on the outer wall of a storage system it is
more vulnerable under some abnormal conditions (external fire, impact, missiles) than
an inner liner but i s more easily repaired if damaged. It is protected from thermal shock
arising from internal leaks b y the thickness of the concrete. An outer wall liner is not
suited for use with embedded tendons.
6.7.3.2
A liner applied to the inner face of the wall is suitable for a reinforced concrete tank with
an earth embankment and prestressed tanks with embedded tendons or with wire
winding. If designed t o act compositely with the concrete it must be designed t o resist
buckling during and after prestressing (including the effects of creep and shrinkage of
the concrete wall). If leaks occur from the inner tank the liner may experience
contraction and thermal shock which is sufficient t o overcome the prestress.
Consideration should also be given to the rate o f strain under these conditions. A more
expensive metal suitable for the.lower temperature may be needed. The effects of
thermal shock on any anchors, shear studs, and the like connecting the liner with the
concrete must also be considered.
At the junctions with the floor and roof, there is no need for the liner to penetrate the
concrete. However, the wall t o floor junction will be subjected to circumferential and
radial strains, due t o the effects of prestress, creep, long term shrinkage, and
temperature changes after construction, under both service and abnormal conditions.
These dimensional changes must be accommodated b y overall straining, or by means
of flexible zones at the junction, or b y other suitable means.
6.7.3.3
An embedded wall liner is protected from buckling and from thermal shock (as with an
outer liner). It partly penetrates the wall at the floor and roof junctions, and tends to
separate the wall into two concentric cylinders, so that shear studs are required on both
faces of the metal. It is not easily accessible if repair is needed, and may cause
considerable construction difficulties.
6.8
Base and Wall Heating Design
6.8.1
Tank Base and Wall
Where the tank base and wall are not exposed t o the supply of heat from the
atmosphere, heating shall be provided t o maintain the tank walls and base at the
desired temperature and t o prevent ice lensing.
47
6.8.2
Heater Layout a n d O u t p u t
The heat output and physical positioning of the heating elements shall be designed on
the basis of heat transfer calculation using preferably finite element or finite difference
methods and including a factor of safety on heat input of approximately 1.3.It should
ensure that the top of the foundation does not fall below 0°C. For tank bases, two
options exist to create a two dimensional model:
(a)
a section across a base radius perpendicular to the direction of the heater element.
(b)
assumption that elements are circular and considering axisymmetric segments.
Material heat transfer properties must be incorporated in the model for the ring beams,
insulation, bitsand, levelling concrete etc., subsoil and air around the ground surface.
Two sets of boundary conditions are required, one a t the tank base, which can be the
design temperature for the product. The second boundary condition is soil at some
depth below the tank. At a depth of 20m an assumption of a fixed temperature of 7°C
should be adequate for the purposes of base heating design in normal soil conditions.
6.8.3
Heating Control
The heating circuit output shall be controlled by a sufficient number of temperature
controllers, whose sensors shall be strategically located throughout shelf and base and
particularly located close t o any thermal discontinuity. The temperature controllers
shall be so connected that if any temperature sensor reaches the lowest set
temperature, then all heaters are switched on until all sensors reach the maximum set
temperature.
6.8.4
Spare Temperature Sensors
All temperature controllers shall have spare temperature sensors, permanently
installed and suitable for quick connection into the controller circuits, when required.
6.8.5
Electrical Failure
Electrical heating shall consist of a number of independent parallel circuits so designed
that electrical failure of any one circuit does not decrease power supply to the
remaining circuits. Heaters shall be so located that the heating deficiency caused by
failure of any one heating circuit is spread evenly throughout the heated area.
6.8.6
Electrical Failure of Main Power Supply
Electrical heating shall be so designed that in the case of electrical failure of a main
power supply cable or a power transformer, sufficient time is available to repair the
above equipment before damage occurs due to excessive cooling. Alternatively,
provision for connecting a stand-by heating power source should b e made.
6.9
Pressure and Vacuum Relief
The following guidelines are given for the design of pressure and vacuum relief
systems:
1.
Pressure relief safety valves should relieve from the inner tank.
2.
Vacuum safety valves should relieve into the space between the outer roof and
suspended roof.
3.
Safety valves to atmosphere should be adequate to relieve the worst case
emergency flows, assuming that all outlets from the tank are closed, including the
outlet to flares.
4.
The quantity of vapour to be relieved should be based on:
(a)
Heat inleak per tank.
(b)
100% of vapours generated due to circulation of the loading lines during the
holding mode.
48
(c)
(d)
100% of vapours generated due to normal product rundown.
The greater of the following quantities:
-
-
to provide for 5 mbar/hour atmospheric pressure change;
100% of vapour generated due to hot product rundown from one
process module;
full flow of hot gas into the tank;
vapours generated due to inner tank overflow, if applicable.
vapour expansion due to an adjacent tank fire.
Note: Safety valves are not normally sized to relieve vapours generated
during "roll-over". However, by providing recirculation capability and
sizing relief valves in a generous manner, the hazard of roll-over may
be reduced.
5.
Vacuum relief should be based on:
(a)
maximum liquid pump-out rate;
(b) full boil-off flows to compressor;
(c)
5 mbar/hour atmospheric pressure rise;
(d) vapour contraction after extinguishing of adjacent tank fire.
.'
6.
Relief to flare should be via a pressure control valve installed in a line connecting
the boil-off compressor suction with the main flare header. Line and control valve
should be generously sized to relieve at least vapours generated during
operational disturbances such as a trip of the boil-off vapour handling facilities. It
should also be capable of relieving the vapours generated due to circulation of
loading lines during the "holding mode" and if practicable, vapour expansion due
to an adjacent tank fire.
The pressure setting of the pressure control valve should be such that lifting of the
safety relief valves to atmosphere will not occur during these disturbances.
7.
Relief headers and lines should be free of pockets and where necessary slope
towards a knock-out drum. Where the lowest ambient temperature is below the
dew point of relief vapours (butane), or where different vapours can be relieved
simultaneously and partially condense, or where thermal relief valves also
discharge into the tank flare system, it shall have a knock-out drum. When the
amount of liquid caught will be small at all times, the knock-out drum need not be
provided with a pumping system; a heating coil will suffice.
8.
The tank flare must be a separate one since the maximum back-pressure in plant
flare systems may exceed the maximum allowable working pressure of the tank.
9.
Block valves should be located in each individual tank flare line to permit safe
maintenance. These may be the flare pressure control valve isolation valves. (See
also 3.1.1.4.)
10.
In order to avoid freezing problems, the tank flare system should not have a liquid
seal. The flare stack requires to be purged at all times to prevent ingress of air and
possible flash-back.
11.
It should be noted that for tanks which have a relatively large vapour buffering
capacity and which receive small rundown flow from e.g. process facilities, the
installation of a flare relief system may not be required, provided local
circumstances allow and adequate and reliable boil-off vapour handling facilities
are available.
For LPG and LNG export and receiving terminals, the normal flows of vapour and
energy are in general so high that a flare relief system is essential for safe
operation. (See also API RP 521, API Std. 2000 and Fig. 3.5 of this document.)
49
_.
..-
6.10
Venting and Drainage of the Annulus of Double Containment Tanks
6.10.1
Venting
For single containment tanks the venting around the tank is dependent on the
atmospheric conditions. When a small leak occurs the gas will most probably be spread
by the wind. For double containment tanks the situation is somewhat different. A
natural ventilation in the annular space may be ineffective. A heavy gas may remain in
the annular space and where applicable under the bottom of an elevated concrete
foundation. Access to the annular space is then dangerous and repair work cannot be
carried out.
The annular space may be covered by roof plates against penetration of rainwater or it
may be left open. Roof plates have the advantage that "heavy gas" cannot enter the
annular space when the emergency relief system relieves to atmosphere. The
disadvantage, however, is that the natural draught around the tank is reduced and that
the annular space is nearly closed.
It is of great importance that the gas is detected when present in the annulus. Therefore
suitable gas detection instruments shall be provided in the annular space and where
applicable under the elevated concrete foundation of the tank.
6.10.2
Drainage from the Annulus
*
Where no roof plates are installed over the annulus, rainwater will enter. Also fire water
can enter the annular space during the testing of the system and during an emergency
when the system is activated. Great quantities of water may then enter the annular
space.
There should never be a condition where liquid (liquefied gas or water) in the annular
space would cause a higher pressure than the stored liquefied gas in the inner tank, as
this could cause damage t o the inner tank.
The paving around the tank and also where applicable, under the elevated foundation,
shall be such that the water i s collected and directed to a sump pit. The water can then
be removed by means of a pump. The drainlines should preferably run over the top of
the outer wall or shell so that no wall penetrations are required. The presence of a gas
detection system is essential. In case gas is detected the pumps shall be controlled so
that no liquefied gas can be pumped instead of water.
6.1 1
Earthquake Design (See Appendix F)
6.12
Special Nozzles and Access Openings
(See also 6.2.4 and 6.2.5.)
All pipe connections shall preferably be made via the roof of the tank. If in exceptional
circumstances side or bottom entry is unavoidable, the design shall take account of the
possibility of nozzle leakage and the consequences of the following effects:
-
Differential Movement
-
Thermal Stress
-
Pipeloads
-
Foundation Heating Discontinuities
-
Vulnerability of Pipework to Damage
Stress Intensification
Difficulties of InspectionlMaintenance Problems
Nozzles through the outer tank which contain a cold medium shall be thermally isolated
from the tank structure t o prevent local cold spots.
For steel tanks and for concrete tanks incorporating a steel liner the nozzle design shall
be based on the data provided by BS 4741, BS 5387 or API 620.
50
The loads of the connected piping are to be incorporated in the design of the roof. Local
reinforcement of the roof may be required. For pipes which are Supported by t h e
bottom of the tank, e.g. level gauges, expansion facilities such as bellows are required
at the roof penetrations to allow differential movement between roof and pipe. For
access to the inside of the tank at least two manholes shall be installed, preferably on
the roof. The minimum diameter shall be 600 mm. Platforms and ladders or stairways
shall be provided for access to roof nozzles which are equipped with instruments and
valves.
During construction of the tank a temporary opening can be made in the outer concrete
or steel tank to allow easy transport of materials and equipment. For steel tanks a shell
plate can be left out and this plate can be welded in at the end of the construction. Also
shell manholes can be installed in the outer tank.
In concrete tanks a temporary opening can be made in the wall. The opening shall be
incorporated in the design of the wall. In particular, for prestressed concrete, special
attention shall be paid to the timing details of the prestressing of the concrete around
and within the subsequent infill to the opening.
Where no escape opening is possible in the outer tank, manholes can be installed in the
inner steel tank t o act as an escape route to the inner tank space during construction. A
special all-welded construction of double plate cover shall be used, so that the cover
can be air pressure tested after the water testing at the end of the construction of the
tank.
51
7.
MANUFACTURE AND CONSTRUCTION
7.1
Steel Tanks
7.1.1
Shop Fabrication
7.1 .'l
.l
Single, double and full containment tanks for temperature d o w n t o -50°C.
The steel inner tanks, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be fabricated in accordance with the requirements
specified in BS 4741.
7.1.1.2
Single, double and full containment tanks for temperatures between -50°C and
-165°C.
The steel inner tanks, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be fabricated in accordance with the requirements
specified in BS 5387.
7.1.2
Site Erection
7.1.2.1
Single, double and full containment tanks for temperatures d o w n t o -50°C.
The steel inner tanks, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be erected in accordance with the requirements
specified in BS 4741.
The erection of double and full containment tanks with prestressed or reinforced
concrete outer tanks shall be organised and scheduled in such a manner that the steel
inner tank can be erected and tested in accordance with the requirements of BS 4741.
7.1.2.2
Single, double and full containment tanks for temperatures between -50°C and
-165°C.
The steel inner tanks, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be erected in accordance with the requirements of
BS 5387.
The erection of double and full containment tanks with prestressed or reinforced
concrete outer tanks shall be organised and scheduled in such a manner that the steel
inner tank can be erected and tested in accordance with the requirements of BS 5387.
7.1.3
7.1.3.1
Welding
Single, double and full containment tanks for temperatures down t o -50°C.
The steel inner tank, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be welded in accordance with the requirements
specified in BS 4741 except that impact tests shall meet the values stated in 5.1.3 of this
document.
Where 9% nickel steel is used the welding shall be done in accordance with the
requirements specified in BS 5387 except that impact tests shall meet the values stated
in 5.1.3 of this document.
7.1.3.2
Single, double and full containment tanks for temperatures between -50°C and
- 165°C.
The steel inner tanks, the steel outer tanks and the steel parts of prestressed or
reinforced concrete outer tanks shall be welded in accordance with the requirements
specified in BS 5387 except that impact tests shall meet the requirements stated in 5.1.3
of this document.
7.1.4
Radiographic inspection
The radiographic inspection of steel inner tanks and steel outer tanks shall be carried
out according to the requirements specified in BS 5387.
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53
The vertical and horizontal shell seams of inner and outer tanks designed for liquid
containment shall be 100% radiographed by X-ray radiography. The butt welds of shell
stiffeners of liquid containing tanks shall be 100% radiographed.
7.1.5
Inspection Guidelines for Refrigerated Liquefied Gas Storage Tanks (Liquid
containing steel tanks)
It is recommended that the following inspection steps be carried out:
1.
Establish datum level readings of foundation.
2.
Material Identification.
3.
Approval and qualification of weld procedures.
4.
Qualification of welding operators.
5.
N.D.T. requirements for liquid containing steel inner and outer tanks.
Radiographic techniques and interpretation acceptance standards must be
included in the specification.
100% radiography of all bottom annular plate butt welds
100% radiography of all vertical weld seams
100% radiography of all horizontal weld seams
100% radiography of butt welds of shell stiffeners
100% crack detection shall be made at the following areas:
(i)
shell to floor fillet welds
(ii) shell t o roof annular fillet welds
(iii) all shell and roof attachments including fittings and penetrations
(iv) all ground areas after removal of welded temporary attachments.
Vacuum box testing shall be carried out at the following areas of both inner
and outer tanks prior t o and where applicable also after the hydrostatic test.
(See also 8.2).
(i) all floor lap welds
(ii) all floor butt welds
(iii) welds in outer tank floor
Leak testing of the outer roof.
7.2
Reinforced and Prestressed Concrete Construction
7.2.1
General - Construction activities should be under the control of a qualified engineer,
experienced in concrete and foundation construction.
7.2.2
Foundations - Control of construction should follow the requirements of BSCP 2004.
Particular care should be paid t o avoiding circumstances that could lead to differential
andor total settlements in excess of those anticipated by the designer.
7.2.3
Reinforced Concrete - Control of concrete materials, mix design, mixing techniques
and construction should follow the requirements of BS 81 10.
7.2.4
Prestressed Concrete - Control of concrete materials, mix design, mixing technique
and construction, and of ducting and grouting post tensioned tendons should follow
the requirements of BS 8110 and any relevant' clauses in the F.I.P. document (ref.
FIP/3/6:1982). The contractor shall issue a method statement for the casting, curing and
stressing procedures which shall be agreed with the designer and provide
comprehensive records of the stressing operations.
54
7.3
Installation of the Insulation
7.3.1
General
The selection of the insulation contractor is very important to ensure the necessary
integrity of the final insulation.
The following information must be included in the detailed specification which should
accompany every enquiry:
(i) The proposed storage temperature of the RLG and details of the external ambient
temperature ranges.
(ii)
External insulation especially when applying spray-on plastic foams should only
be installed within the range of weather conditions specified in the manufacturers
data, and under no circumstances should application be carried out at
temperatures under 10°C or relative humidities above 80%.
(iii) Minimum acceptable properties of the insulation materials to be used.
(iv) Minimum thicknesses of insulation.
(v)
The surface finish of sprayed insulation, where applicable.
(vi) Preparation of steel surfaces, including blasting to Sa
with a compatible primer system.
2’1’2
minimum and priming
(vii) The environmental conditions under which blasting and priming can take place,
and especially for spray application where this is the proposed installation
method.
(viii) For RLG duty, except where spray application is used, all slab insulants should
have staggered joints and be applied in at least two layers.
(ix) Loose fill materials, such as perlite granules, should be vibrated during installation
and include provisions in the design for automatic top-up from a reservoir whilst
in service.
(x)
Fibre blankets should be resilient, not contain phenolic binders, be of adequate
density to resist penetration of loose fill insulation, and have sufficient strength in
the longitudinal direction t o permit hanging without breaking.
The design contractor shall provide details, including manufacturer’s data, on the
following:
(i) Details of all adhesives and joint sealants.
(ii) Data on the vapour barrier to be employed, its type, specification, thickness and
surface finish and colour of the two separate coats required to ensure
impermeability of elastomeric systems.
(iii) The Quality Control Plan detailing precisely what checks will be made on-site and
what certificates should be issued for materials and workmanship.
(iv) The Progress Plan showing the advance expected in the programme of work on a
daily basis, weather permitting.
(v)
Arrangements for issue and stock checking of materials issued to laggers on a
piece basis.
(vi) Nomination of an Inspection Authority to oversee quality and progress.
(vii) The design contractor shall provide thermal calculations to BS 5422 to show that
the thicknesses of insulation to be applied are satisfactory for the application.
(viii) The design contractor shall provide detailed drawings showing how he proposes
to deal with protrusions through the insulation, terminations, around stairways, at
the bottom of tank shells to stop water penetration from the ground, attachment of
insulation, sloping for water shedding, weatherproofing details, areas and
walkways over insulation for personnel access, etc.
55
(ix) The terms and conditions of the guarantee shall be agreed between the users and
the contractor.
(x)
7.3.2
The contractor shall provide complete details of his working practices and safety
procedures.
Quality Control and Inspection
The preceding section on installation has indicated that quality control and inspection
are important aspects of RLG insulation. Once the insulating materials arrive at site,
testing is difficult due to the scarcity of facilities.
All materials should be properly packed for transportation and storage, and
warehousing in a temperature and humidity controlled environment is highly
recommended. The materials shall be supplied with certificates of conformance in
accordance with the specification, with all batch numbers identified. Only raw materials
data will be available for foam sprayed on site. In this case the tests should be agreed
between purchaser and contractor and may include the following:
(a)
density
(b)
thermal conductivity
(c)
water content
(d)
closed cell content
(e)
compressive strength
All tests to be in accordance with the standard methods of test shown in Appendix B.
For site expanded perlite the quality control test shall be agreed between the purchaser
and contractor.
7.4
Earth Embankment
For the construction of the earth embankment the designer shall specify all
requirements for materials and workmanship. Details of site preparation, dewatering or
watering, fill and compaction requrements shall be included. Also attention shall be
paid to allowable height difference- of the fill during construction as this will have an
influence on the wall loading. For details about the fill work, reference can be made to
BS 6031.
-
56
7
8.
HYDROSTATIC AND LEAK TESTING
8.1
General
For the hydrostatic test procedure reference can be made t o BS 5387.
Full hydrostatic testing ensures
-
The inner and outer tanks are well designed and constructed and have a good
margin of safety.
-
The foundation of the tank is well designed and constructed and has a good
margin of safety.
-
The inner and outer tanks are liquid tight.
Peak stresses in the steel introduced during fabrication will be reduced under
ambient temperatures.
The composition of the test water shall be determined before any hydrostatic test is
carried out and measures taken if necessary to avoid corrosion. Potable water is
preferred.
Inner Tank Testing
8 -2
The inner tank shall be filled up to the maximum design product level or the level 0.5m
below the t o p of the shell, whichever is the higher (See 4.1.8).
,
8.3
In accordance with BS 5387 all joints shall be checked for leakage. However, small leaks
in the bottom may not be readily detected. For this reason it is recommended t o repeat
the vacuum box test of the bottom plate welds after the hydrostatic testing.
Testing of Outer Steel Tanks of Double and Full Containment
A hydrostatic test is required for a steel outer tank i.e. the outer tank shall be filled t o
such a height that it contains the test liquid of a full inner tank. (See 4.1.8.)
When the outer and inner steel tank are tested simultaneously great care shall be taken
with the removal of the water, t o prevent damage to the inner tank. The liquid level in
the annular space shall always be kept equal t o o r lower than that of the inner tank, t o
prevent compressive stresses in the inner tank shell or bottom uplift. The bottom
insulation o f the inner tank must be adequately protected against the danger of liquid
penetration during testing.
8.4
Filling Rates and Level Checks
Tank filling rates and all related checks for foundation levels of the inner and outer
tanks shall be agreed between purchaser and contractor. (See BS 5387).
8.5
Outer Concrete Tank Testing
A hydrostatic test of outer tanks constructed of prestressed concrete, or reinforced
concrete i n conjunction with an earth embankment, is not necessary. (See 4.1.8).
This is because the externally applied desigdconstruction loads for both a prestressed
concrete tank and a reinforced concrete tank with an adjacent high earth embankment,
are greater than those loads due t o hydrostatic test.
8.6
Pneumatic Testing
The tank shall be pneumatically tested i n accordance with BS 5387, clause 27.2.3.
9.
COMMISSIONING AND DE-COMMISSIONING
9.1
Commissioning
See requirements indicated in BS 5387
9.2
De-commissioning
De-commissioning of refrigerated liquid storage systems is not to be regarded as a
normal operational requirement and should not be attempted on any routine basis.
However, planning for new facilities should consider the possibility of
decommissioning at least once during the lifetime of the tank.
It is considered that this activity may be necessary subsequent to a n upset or failure of a
component in the system where there is a definite need for entry.
Therefore, to ensure that decommissioning and entry of the tank can be conducted
safely, it is recommended that the original system design should include all of the
necessary equipment, instrumentation, safety facilities, etc., to permit entry by
personnel for inspection andor repair reasons.
The facilities for this activity should be designed and organised to avoid the need for an
inert atmosphere in the tank during the entry period to simplify inspection and repair.
..-
Consideration should be given t o the following points when planning shutdown, entry
to the tank and subsequent re-commissioning.
1.
Provide instrumentation for monitoring and recording of gaseous and liquid
content of the tank during emptying and purging operations.
2.
Ensure the tank purge connections are adequately designed to provide a n
effective purge based on the likely conditions for a system which has been i n
operation for a period of years. (This will be based on individual plant design
parameters).
3.
Provide sufficient monitoring and/or control devices to ensure that the inner and
outer tanks are not subjected to positive or negative pressures beyond the design
limits during the purge.
4.
Provide instrumentation to permit regular sampling and monitoring of the
atmosphere in the tank during inspection and repair to ensure freedom from
hydrocarbons or any combustible/toxic gases.
It is recommended that the contractor supplies a detailed procedure, before
construction commences, for de-commissioning of the tank.
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59
10.
RECOMMENDATIONS FOR OPERATION
Some important aspects applicable for the operation are as follows:
10.1
Cool-Down of the Tank
Refrigerated storage tanks have their operating temperature at the atmospheric boiling
temperature of the gas to be stored. This means a temperature range of -5°C for
butane tanks to -165°C for LNG tanks. Cool-down of the tanks is required and this work
starts after the drying and purging of the tank. In general purging of the tanks is
executed with nitrogen so that the cool-down proceeds with nitrogen in the tank.
A gradual and equal cool-down of the inner tank will result only in shrinkage of the
inner tank without stress generation in the tank material. A local cool-down (resulting in
temperature differences) however, will result in abnormal shrinkage and stress. These
stresses combined with those already existing from fabrication and welding may result
in cracking at a location of stress concentration. Therefore the cool-down of the tank
shall be done very carefully. Special cool-down skin thermocouples should be
connected to the inner-tank bottom and inner-tank shell. The permissible temperature
difference between adjacent thermocouples should be established by the designer.
The use of nitrogen in cool-down may result insub-cooling of the tank below its design
temperature e:g. butane tank to -45"C, propane tank to -70°C and LNG tank to -180°C.
This sub-cooling should always be avoided by the careful introduction of refrigerated
gas into the tank, a slow cool-down and frequent, proper temperature monitoring.
10.2
Prevention of an Overfill
The normal maximum operating levels are calculated by using time intervals based on
local operating conditions so that a stepwise overfill protection system exists. The
following typical levels to be noted are shown in Fig. 10.2. The distances a, b and c shall
be determined on the basis of the selected time intervals (e.g. one hour) and the
pump-in rate. (See also 3.2.5.)
The high-high level emergency alarm/trip has a trip function on the liquid supply line.
10.3
Prevention of Overpressure
Refrigerated storage tanks normally operate at a pressure considerably lower than their
design pressure, e.g. with an operating pressure in the range of 20 to 50 mbar the
design pressure would be in the order of 75 mbar gauge. The normal operating
pressure is maintained by the boil-off compressor and gadliquid supply. Should the
pressure increase to a value above the normal operating level then gas will be released
to the flare or vent. At a further increase of the pressure the emergency-relief system
will give a final protection. Where conditions allow the emergency release is generally
to atmosphere.
10.4
Prevention of Vacuum
The gadliquid supply maintains the pressure at the normal operating pressure. Should
the pressure drop, then the boil-off compressor will be tripped and liquid removal from
the tank will be stopped. In addition a vacuum breaking gas supply system may be used
but at the final stage the vacuum relief valves will be open and allow air to enter the
tank. This will typically happen at a pressure of -5 mbar gauge. This is, however, a n
emergency condition that in practice should never occur.
10.5
Prevention of Condensation
At certain locations, where the ambient temperature in winter can drop below the
atmospheric boiling point of the product, say -5°C for butane, condensation in the tank
against the underside of the roof will occur. (See figure 10.5).
Previous page
is blank
61
24000 m m
Tank rim (top of shell)
Max. allowable liquid level
a
High-high level, emergency alarmhip (LHHA (CO))
c
c
.-aCI:
Jz
Y
C
b
tu
I-
High level alarm (LHA)
C
22000 m m
Normal maximum operating level
Fig. 10.2: Typical Example for Level Alarms
/
Condensation dropping down
/
Annular
condensation
/
Outer tank
Fig. 10.5: Typical Example of Condensation in Dome Roof for Butane Gas
62
Due to the condensation the pressure in the tank will drop. All operating conditions are
to be evaluated so that regular opening of the vacuum relief Valves is prevented. Gas
injection into the dome may be considered as an active protection system and should
be carried out before each winter. During the winter period regular sampling shall be
done to check the composition of the gas in the space between inner suspended roof
and 'outer roof.
10.6
Tank Heating System
If the soil under the tank is allowed to become too cold, frost could penetrate into the
ground. Ice lenses could be formed in the soil, (mainly in clay types of soil) and the
growth Qf these ice lenses will result in high expansion forces which may lift and
damage the tank or parts of the tank (e.g. the tank bottom or shell to bottom
connection). To prevent this the heating system must operate in the foundation and
also in the vertical outer wall for tanks with an earth embankment. (See also 6.1.3.6 and
6.8.)
An automatic o d o f f switch system should activate the heating system and ensure that
the tank foundation, at its coldest location, is within a temperature range of e.g. +5"C to
+lO°C. Other areas of the tank foundation may have a'higher temperature. The
performance of the whole heating system should be monitored by a number of
sensors. A number of sensors should be evenly distributed over the whole tank base.
(See figs. 10.6a and 10.6b). If applicable, wall sensors should also be provided. One or
more of these sensors should have an alarm function. Typically the set-point for the
"low temperature alarm" is 0°C and for the "high temperature alarm" +50°C. Proper
and frequent control of the monitoring systems of base and wall is essential because it
will provide the first indication of a tank leak. In the event of a leak the sensor located
near this leak will show a sudden temperature drop. Daily recording of all bottom
sensor readings is therefore recommended.
Another indication of a n abnormal situation is a change in duty cycle or heating power
consumption which produces a change in on-off time. Normally the heating system will
be activated 40430% of the operating time and a sudden change to e.g. 100% may
indicate that there is something wrong with the system, or that a leak is present. It i s
recommended to record daily whether the heating is activated or not.
10.7
Liquid in the Annulus
Liquid may be present in the annular space adjacent to the inner tank due to one of the
following abnormal conditions:
-
spillage from the inner tank
condensation at the outside of the inner tank
a leak of the inner tank
If liquid enters the annulus there is a danger that the inner tank and the bottom
insulation will be damaged. Large quantities of liquid in the annulus may cause upward
bulging of the tank bottom and ultimatelyflotation of the tank. In this condition damage
to the lower shell courses (e.g. buckling) is also likely to occur. In addition the light foam
glass blocks located under the inner bottom will float so that the entire insulation
system will be disturbed and damaged. (See fig. 10.7).
If liquid is detected in the annulus liquid removal shall be done carefully. Pumping out
shall always start in the annulus so that the level in the inner tank is always higher than
in the annulus to prevent the possibility of buckling of the inner tank shell. Small
quantities of liquid in the annular space can be removed by the special venting system
which may be located at the bottom of the annulus. Hot gas or nitrogen can be used to
accelerate the evaporation.
Tanks with an open annulus not filled with perlite insulation may have a pump to
remove the liquid and a liquid detection system consisting of either a bubbler or a level
63
/-
\
Controller
system
heating
1
/
\
Alarm (low)
Fig. 10.6a: Sensors under Tank Bottom
- - - - - Alarm (hightemp)
One of the other sensors
\
/
/
Controller
Operating on sensor
recording lowest
temperature
- - - - - Alarm(lowtemp)
.Cool down
period
Time
64
measuring device. They should be set i n such a way that they can detect small
quantities of liquid, say 100 mm.
For tanks with a perlite filled annulus it is difficult t o install liquid detection instruments
for control of leaks and hence a pump for the removal of liquid is not feasible. Liquid
can only be removed b y evaporation. The detection and control of leaks from the inner
tank relies on monitoring of the heating system under the tank bottom.
Level in
annulus
Level in
inner tank
-I
I
Bottom bulging upwards
1
Resultant
liquid
pressure
Fig. 10.7: Floating of the Inner Tank
65
APPENDIX A
Base insulation
Base insulation
contain liquid)
Base insulation-
Bund
+
,
contain liquid)
Base insulation
Fig. A.l: Examples of Single Containment Tanks
Previous page
is blank
67
APPENDIX A
-
Roof if
required
I
External
weather
barrier
Outer tank
shell
Base insulation'
Bottom heater
(notable to
contain liquid)
Base insulation
Bottom heater
embankment
fig. A 2 : Examples of Double Containment Tanks
68
APPENDIX A
Suspended roof
(insulated)
Outer tank shell
Loose fill
insulation
or empty
depending
o n product
stored
-
Insulation on inside of
outer tank shell
Inner tank
Ik
l/-
Base insulation
Bottom heater
Reinforced
concrete roof-\
Suspended roof
(insulated)
Pre-stressed concrete
outer tank wall
Insulation on inside
of outer tank wall
Base insulation
Bottom heater
Outer steel
roof
Suspended roof
(insulated)
Reinforced concrete
outertank wall
Loose fill
insulation
orempty ,
depending
on product
Insulation on inside
of outer tank wall
Bottom and wall heater
fig. A.3: Example of full containment tanks
69
APPENDIX B
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APPENDIX 6
NOTES TO TABLES B1 TO B4
Not applicable
Parallel to direction of foam rise
Perpendicular to direction of foam rise
Method
Appendix
Dimensional change for 24 hours at -196°C x 5 cycles
Over range +20°C to -196°C
At 38°C and 88% relative humidity
7 day test with 50 mm head
Inclusive of surface water retained in cells
75
APPENDIX C
DETERMINATION OF A T FOR IMPACT TESTING STEELS
c.1
Introduction
This is not the requirement for a Weld Procedure Test as defined in 7.1.3 of this
document. This test has been included since it is recognised that Charpy V Testing is
the most widely used standardised method of testing materials, despite its limitations.
The desired value for any plate in the tank measured in the heat affected zone is 27 J at
the design temperature for double and full containment tanks and 20°C t o 30°C lower
for single containment tanks. In addition, to ensure that the material does not have a
flat energy v temperature relationship the material should demonstrate that the Cv
transition temperature is within 30°C of the test temperature, and to this end a higher
energy requirement of 120 J would give a reasonable demonstration.
To achieve the desired value of 27 J in any tank plate with a reasonable degree of
assurance, the steel shall be tested t o demonstrate the shift in temperature at the 27 J
Cv level of the HA2 location compared with the plate materials. This shift is defined as
AT.
The determination of A T for a specific steel is required t o be repeated when a steel
making process route is amended since minor micro alloy elements and
desulphurisation, deoxidation, casting and other steelmaking practices can affect the
response of the steel t o welding.
Having determined AT, each plate shall then be tested at a temperature AT below the
design temperature, hence ensuring that the 27 J will still be achieved in the degraded
HAZ, and tested on a batch basis at the higher temperature t o demonstrate the 120 J
requirement.
This Appendix defines the test method t o be used by the steelmaker t o determine AT.
c.2
Frequency of Testing
Where it is necessary t o determine AT in Table 5.1 -2, the following tests shall be carried
out on the steel and shall be repeated if any of the following changes are made.
c.3
1.
Steelmaker
2.
Steelmaking process
3.
De-oxidation practice
4.
De-sulphurisation practice
5.
Casting practice
6.
Heat treatment
7.
Change in specified chemical composition including micro-alloy additions.
Test Plate
The test plate shall be of the size and configuration specified in Figure C1 and shall be
welded in the flat position using manual metal arc welding.
The welding shall be carried out in accordance with Table C1 using an agreed suitable
electrode.
c.4
Testing
On completion of welding, Charpy impact specimens shall be removed in accordance
with Fig. C2. The HAZ and Plate Charpy specimens shall be tested at suitable
temperatures to determine the transition curves for the two sets of specimens.
Particular attention should be paid t o testing at temperatures at which 27J is obtained.
From the two curves A T shall be determined, this being the shift in temperature of the
27J transition temperature (See Fig. C3.)
previous Page
is b\ank
77
APPENDIX C
c5
Verification
This testing shall be witnessed and verified by an independent inspection authority and
full documentation should be supplied on request.
78
APPENDIX C
Typical run-out
lengthlelect rode
140 mm
Typical
amps
270
Electrode
dia.
5mm
Typical multi-run
weld
Required
heat input
3.5 to 4KJ/mm
Test plates shall be unrestricted.
Test plates shall be welded complete with maximum time between runs of 1 hour.
-
15+2
375
* 10
c-
375 & 10
-
Fig. C.l
Details of Test Plate
HAZ
100 ? 10
Minimum of 15 plate specimens from same side of
weld as HAZ.
Specimens taken at mid thickness.
Longitudinal axis of specimen t o be perpendicular
to weld axis.
Fig. C.2
-
\
i””
Minimum of 15 specimens with notch located in
HAZ.
Specimen to be etched to demonstrate that notch is
not in weld metal or parent plate.
Location of Charpy Impact Specimens
PLATE,
/
100
Energy
absorption
80
(J)
60
40
27J
20.
IFig. C.3.
A T
I
Test temperature
Shift in Temperature of t h e 27J Transition Temperature
APPENDIX D
STEELS FOR REINFORCEMENT OF CONCRETE FOR CRYOGENIC SERVICE
D.l
Ferritic Steels
The established reinforcing steels, and all other ferritic steels may be characterised by
the temperature at which they change from ductile t o brittle failure when stressed at a
section containing a stress raiser, a change in shape or a flaw.
The composition, strength and metallurgical structure of the steel govern the transition
temperature, together with the section thickness and resultant intensity of stress
developed at a stress-raiser.
The recommendations in this document have related properties of steels t o service
temperature based on the use of established specifications for the steel, but such
specifications for reinforcing steels d o not relate specifically to service at cryogenic
temperatures. It is recommended that results of work on full-scale tests of concrete
units and development in proprietary steels be considered.
Several steelmakers have developed steels t o cover different temperature ranges down
t o -196°C. The work has been based on using established steels of the carbonmanganese, low, intermediate and higher (9%) nickel types.
Recognised test methods, including the Charpy V-Notch impact test have been used in
assessing the effects of composition, steelmaking and rolling practice o n the fracture
toughness of the steels.
Purchasers are thus able t o negotiate with steelmakers on the basis of established test
methods for quality control of the steel appropriate to their service conditions.
D.2
Austenitic Steels
The established austenitic stainless steels are not subject t o the notch brittleness
behaviour shown by ferritic steels, and are accepted for service below -196°C without
need for specific fracture toughness tests.
0.3
Clad Steels
There are proprietary ferritic steels clad in austenitic stainless steel and these should be
considered as a separate case for discussion with the steel manufacturer.
APPENDIX E
DESIGN CRITERIA FOR CONCRETE STRUCTURES
E.1
General
BS 8110 covers the design of concrete structures on the basis of limit state methods.
Partial safety factors are applied t o characteristic material strengths and loads, to
provide design strengths and design loads used in the analysis of sections at relevant
limit states.
All relevant limit states should be considered in the design analysis t o ensure adequate
degrees of safety and serviceability. The normal approach is to design initially on the
basis of the most critical limit state, which is frequently the ultimate limit state, and then
t o check against the serviceability limit states which will b e mainly those imposed by
deflection and cracking limitations.
Structures will be subject t o different types of loading simultaneously i.e. there will be
various combinations of loads to be considered in the design, and critical conditions
can apply when one load is at its maximum value whilst another combined load is at its
minimum value. Hence two values are used for the partial safety factors, depending on
whether they have an "adverse" o r "beneficial" effect on the section being analysed, t o
p 6 d u c e the most onerous combination of ultimate loads.
E.2
Load Cases to be Considered
In general the tank owner will specify the load cases t o be considered by the tank
designer. However it is the responsibility of the tank designer t o check and ensure that
all appropriate load cases and combinations are incorporated t o ensure an adequate
safe design. As part of this responsibility the designer shall prepare a detailed loading
summary table, t o cover all phases of.the tank lifetime. Emergency or abnormal
loadings as listed in Section 4.2 of this document shall be evaluated and included as
necessary. Table E2 shows a typical loading summary for a concrete outer tank
incorporating an external earth embankment.
E.3
Partial Safety Factors
Adverse and beneficial partial safety factors to be applied to loads and materials for the
ultimate limit state (ULS) and serviceability limit state (SLS), for normal loads, are given
in BS 8110. Values for these factors for abnormal load cases should be as shown in
Table E3.
Previous page
is blank
83
APPENDIX E
X
X
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>
x
>
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IX
APPENDIX E
Table E.3
Partial Safety Factors for Abnormal Load Cases
I
I
Load combinations
I
I
Load Type
Imposed
Dead
Adverse
Earthquake, blast
overpressure
external impact,
fire, leakage
from inner tank
1.05
Beneficial
1.o
Adverse
Beneficial
I
1.05
(1.0 x 0.3
Values for material partial safety factors to be used when considering abnormal load cases are
quoted in BS 8110.
85
APPENDIX F
DESIGN CONSIDERATION FOR EARTHQUAKE LOADINGS
F.l
Ground motions and loading
F.l.l
In geologically active areas f a u l t movements m a y occur. They generate ground
motions travelling a l o n g t h e ground surface.
The ground m o t i o n s induce vertical and horizontal acceleration forces which
are known as seismic loads. T h e vertical accelerations are usually a significant
ratio of the horizontal accelerations. The accelerations m a y b e amplified or
d a m p e d d u e to t h e structural response. The amplification depends on natural
frequency, d a m p i n g a n d stiffness of the total structure a n d m a y range up to 5
times.
F.1.2
Seismic loads are not deterministic. Their magnitude depends on the selected
probability of occurrence.
For RLG tanks it is necessary to distinguish between two levels:
-
Operating Basis Earthquake (OBE).
The structure should resist this earthquake without any damage. It is suggested to
consider the seismic loads with a 10% probability of being exceeded during the
structure's lifetime. Allowable stresses should not be exceeded.
-
Safe Shutdown Earthquake (SSE).
The structure may be damaged by this earthquake, but it should not collapse nor
should it impose serious consequential hazards. It is suggested to use the seismic
loads with a 1% probability of being exceeded during the lifetime of the
structures. Under this load the ultimate strength should not be exceeded.
Notes: The determination of the seismic risk requires both specialist and regional
expertize. The frequency, magnitude and parameters to be considered at the
design stage need t o be thoroughly researched with due regard t o local seismic
history and geological criteria. Suggested sources for reference to assist in
determining Design Parameters are:1)
NFPA 59A (1985)
2)
3)
CPUC GC-1120 -The
4)
Seed H.B. and ldriss I.M. (1982) 'Ground Motions and Soil Liquefaction'.
Japan M.I.T.I. (1981 The Japanese Ministry of International Trade and
Industry standard for aboveground L.N.G. Storage.
5)
state of California Public Utilities Commission Code
CEGB (1982) 'Earthquake Hazard'. Civil Eng. Branch Ref:- C/JVSD/152.0/R019
F.2
Structural Response
F.2.1
The structural response is determined by the natural frequency damping and stiffness
and will also depend on the level of damage which is acceptable. The following
damping percentages are suggested for RLG tanks:
OBE-case
SSE-case
concrete
steel
liquid
3%
concrete
steel
liquid
7%
2%
0.5%
1%
0.5%
A particular type of damping is soil damping. Studies and tests indicate that it may be
as high as 50%. However, it depends on the structure of the subgrade, local
seismological and geological environment.
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87
APPENDIX F
F.2.2
Contrary to other structures, the liquid content of tanks dominates the vibration modes.
Generally the liquid is divided into an impulsive part which follows the motions of the
foundation and a convective part which sloshes at its own natural frequency.
It is recommended that account be taken of the stiffness and damping of the foundation
when determining the acceleration forces of the impulsive mass. Otherwise significant
under estimation of forces may result.
F.2.3
The acceleration forces of the impulsive and convective mass give an overturning
moment which may result in uplift of the tank wall. The uplift follows from the
deformation of the annular plate and the extensionless deformation of the tank wall.
Also the stiffness of the subgrade has a large influence on the uplift.
Uplift is always associated with an increase of vertical stresses in the opposite part of
the tank wall. In extreme cases this may lead to buckling: the so called "elephant's
foot". API 650 gives formulae to estimate the buckling strength. However tests have
shown that buckling strength may be exceeded by a factor of 3 without buckling
occurring. It is most likely that dynamic buckling strength, taking into account the
added liquid, is significantly higher and it is possible that the yield stress will be the
limiting criterion instead of the buckling strength.
F.2.4
The sloshing of liquid and the extensionless deformation associated with uplift causes
ovalisation of the top of the tank wall, it is recommended that ovalisation is limited by a
stiffening ring.
The tank should have sufficient free board to prevent overspill of the sloshing liquid.
The sloshing seems not to be influenced by deformations of the tank wall.
F.2.5
For a double and full containment, the outer tank wall may be analysed by the modal
analysis techniques. Generally the first 10 vibration modes with the lowest frequencies
are sufficient. However if substantial uplift occurs high membrane forces are likely and
many more modes need to be considered. In such cases direct integration techniques
may be more efficient.
For tanks with earth embankments the acceleration forces of the soil masses impose a
considerable load on the tank wall, also in this case a sufficiently large number of
vibration modes must be analysed for accurate results.
aa
APPENDIX G
REFERENCES
Codes, Standards and Reference Documents for Prestressed Concrete Tanks and
Reinforced Concrete Tanks with External Earth Embankment:
BS 5337: 1976 (1982)
Code of Practice for the structural use of concrete for
retaining aqueous liquids
BS 6031:
Code of Practice for earthworks
1981 (1983)
BS 81 10: 1985
Structural use of concrete
BS CP 2004: 1972 (1975)
Foundations
BS 4449: 1978 (1984)
Specification for hot rolled steel bars for reinforcement of
concrete
BS 4461: 1978 (1984)
Specification for cold worked steel bars for the reinforcement
of concrete:
BS 4482: 1969 (1976)
BS 4486: 1980
Hard drawn mild steel wire for the reinforcement of concrete
-
Specification for hot rolled and hot rolled and processed high
tensile alloy steel bars for the prestressing of concrete
FIPl3l2: 1978*
Recommendations for the design of prestressed concrete oil
storage tanks
FIPl36: 1982'
Preliminary recommendations for the design of prestressed
concrete containment structures for the storage of
refrigerated liquefied gases (RLG)
"Prestressed Concrete for the Storage of Liquefied Gases" by Prof. A.S.G. Bruggeling***
"Concrete and Cryogenics" by F.H. Turner***
Proceedings of the First International Conference on Cryogenic Concrete (1981) and Second
International Conference on Cryogenic Concrete (1983). published by the Concrete Society (UK).
List of publications on prestressed concrete (Technical Paper No. 1031, available from the Concrete
Society (UK).
Codes and Standards for Steel Tanks:
BS4741: 1971 (1980)
Specification for vertical cylindrical welded steel storage
tanks for low temperature service: Single wall tanks for
temperatures down to -50°C.
BS 5387: 1976
Specification for vertical cylindrical welded storage tanks for
low temperature service: double-wall tanks for temperatures
down t o -196°C
API 620: Appendix 0
Low pressure storage tanks for liquefied hydrocarbon gases
API 620: Appendix R
Low pressure storage tanks for refrigerated products
API 650: Appendix E
Seismic design of storage tanks
General:
BS 6656
British Standard Guide to prevention of inadvertent ignition
of flammable atmospheres by radio-frequency radiation
IP Model Code of Safe Practice: Part 9 - Liquefied Petroleum Gas (Re-draft scheduled for issue
1986).
BS CP 3: Chapter V Part 2
Wind loads
CIA Code of Practice for large scale storage of fully refrigerated anhydrous Ammonia in the United
Kingdom.
89
APPENDIX G
NFPA 59**
Standard for the storage and handling of liquefied petroleum
gas (LPG)
NFPA 59A: 1985**
Standard for the production,
liquefied natural gas (LNG)
storage and handling of
The American Federal Safety Standard 49 Code of Federal Regulations, Part 193, 1980.
CPUC GD-112D -The state of California Public Utilities Commission Code
CEGB (1982) 'Earthquake Hazard'. Civil Eng. Branch Ref:- C/JI/SD/152.O/RO19
Seed H.B. and ldriss I.M. (1982) 'Ground Motions and Soil Liquefaction'.
Japan M.I.T.I.
(1981) The Japanese Ministry of International Trade and Industry standard for
__
aboveground L.N.G. Storage.
Codes and Standards applicable to Insulation
BS 476:
Fire tests on building materials a n d structures
: Part 4: 1970 (1984)
Non-combustibility test for materials
: Part 5: 1979 (1980)
Method of test for ignitability
: Part7: 1971
Surface spread of flame tests for materials
BS 874: 1973 ( 1980)
Methods for determining thermal insulating properties, with
definitions of thermal insulating terms
BS 2972: 1975 (1984)
Methods of test for inorganic thermal insulating materials
BS 2989: 1982
Specification for continuously hot-dip zinc coated and ironzinc alloy coated steel: wide strip, sheevplate and slit wide
strip
BS 3177: 1959 (1969)
Method of determining the permeability t o water vapour of
flexible sheet materials used for packaging
BS 3533: 1981
Glossary of thermal insulating terms
BS 3927: 1965 (1967)
Phenolic foam materials for thermal insulations and building
applications
BS 3958:
Part 1 t o Part 6
Specification for thermal insulating materials
BS 4370:
Part 1 t o Part 3
Methods of tests for rigid cellular materials
BS 5111:
(Part 1)
Laboratory methods of test for determination of smoke
generation characteristics of cellular plastics and cellular
rubber materials
BS 5241 : 1975
Rigid urethane foam when dispensed or sprayed o n a
construction site
BS 5422: 1977 (1978)
Specification for the use of thermal insulating materials
BS 5608: 1978
Specification for preformed rigid urethane and isocyanurate
foam for thermal insulation of pipework and equipment
BS 5970: 1981
Code of practice for thermal insulation of pipework and
equipment (in the temperature range of -100°C to +87"C)
ASTM E 96
Water vapour transmission of materials
ANSI C 165
Compressive properties of thermal insulations
ANSl C 177
Steady-state thermal transmission properties by means of a
guarded hot plate
90
APPENDIX G
ANSl C 203
Breaking load and calculated flexural strength o f preformed
block-type thermal insulation
ASTM C 240
Cellular glass insulating block
ASTM C 303
Density o f preformed block-type thermal insulation
ANSVASTM C 547
Mineral fibre preformed pipe insulation
ASTM C 548
Dimensional stability of low-temperature thermal block and
pipe insulation
AWSIIASTM C 552
Cellular glass block and pipe thermal insulation
ANSl C 591
Rigid preformed cellular urethane thermal insulation
ANSl C 592
Mineral fibre blanket insulation and blanket type pipe
insulation (metal-mesh covered) (industrial type)
ANSVASTM D 2341
Rigid urethane foam
ANSl D 2863
Minimum oxygen concentration t o support candle-like
combustion of plastics (oxygen index)
I S 0 2896
Rigid cellular plastics-determination o f water absorption
Federation lnternationale de la Precontrainte (FIP), d o Institution o f Structural
Engineers, 11 Upper Belgrave Street, London SW1X 8BH.
**
National Fire Protection Association, Boston, Massachusetss, USA.
+++
Published by Eyre & Spottiswoode
91
SUMMARY LIST QF CURRENT EEMUA PUBLICATIONS
Introductory Note
Publications are listed in numerical order under the following headings: Electrical,
Instrumentation & Control, Mechanical Plant and Equipment, Offshore, Storage Tanks and
Vessels, Noise, and General. (For further details see website www.eemua.co.uk/publications.)
An asterisk (*) indicates a publication in preparation
Amendments Where amendments have been issued, these are listed in bracketed italics
after the title of the publication. It is intended that amendments be placed on the website
www.eemua.co.uk/publications/amendments.
Publication No.
ELECTRICAL
132 : 88
Specification for Three-phase Cage Induction Motors (Amdf No 7, Mar 02)
133 : 88
Specification for Underground Armoured Cable Protected against Solvent
Penetration and Corrosive Attack
181 : 95
A Guide to Risk Based Assessments of In-situ Large Ex
Machines
186 : 97
A Practitioner's Handbook-Electrical Installation, Inspection and Maintenance
in Potentially ExplosiveAtmospheres (Updated & reprinted 2002)
198*
Electromagnetic Compatibility A User Guide to Installations and Standards
'e' and Ex 'N'
INSTRUMENTATION & CONTROL
138 : 88
Design and Installation of On-Line Analyser Systems
138 S1 : 93
Design and Installation of On-Line Analyser Systems: A Guide to Technical
Enquiry and Bid Evaluation
155 : 88
Standard Test Method for Comparative Performance of Flammable Gas
Detectors against Poisoning
175 : 95
Code of Practice for Calibration and Checking Process Analysers-Formerly IP
Code of Practice 340
178 : 94
A Design Guide for the Electrical Safety of Instruments, Instrument / Control
Panels and Control Systems
187 : 00
Analyser Systems - A Guide to Maintenance Management
189 : 97
A Guide to Fieldbus Application for the Process Industry
191 : 99
Alarm Systems - A Guide to Design, Management and Procurement
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201: 02
Process Plant Control Desks Utilising Human-Computer Interfaces-A Guide to
Design, Operational and Human interface Issues
MECHANICAL PLANT AND EQUIPMENT
I
107 : 92
Recommendations for the Protection of Diesel Engines for Use in Zone 2
Hazardous Areas
143 : 85
Recommendations for Tube End Welding: Tubular Heat Transfer Equipment,
Part 1 - Ferrous Materials (No subsequent parts issued)
151 : 87
Liquid Ring Vacuum Pumps and Compressors
153 : 96
EEMUA Supplement to ASME B31.3 -1996
Dec 2000 & Feb 02)
164 : 93
Seal-less Centrifugal Pumps: Class 1
167 : 91
Specification for Quality Levels for Carbon Steel Valve Castings
168 : 91
A Guide to the Pressure Testing of In-service Pressurised Equipment
169 : 93
Specification for High Frequency Electric Welded Line Pipe ( Obsolescent )
170 : 91
Specification for Production Testing of Valves-Part 1 Ball Valves (Reprinted
2001 incorporating Amdt No 1 Apr 96 & other minor changes)
171 : 94
Specification for Production Testing of Valves-Part
Amdt No 1 Apr 96)
172 : 95
Specification for Production Testing of Valves - Part 3 Gate Valves (Amdt NO
1 Jan 96
173 : 95
Specification for Production Testing of Valves
Valves
179 : 96
A Working Guide for Carbon Steel Equipment in Wet H2S Service (Developed
largely from Oil Refinery experience)
182 : 95
Specification for Integral Block and Bleed Valve Manifolds for Direct Connection
to Pipework (incorporating information Sheet No 20: Application Guidelines)
(Reprinted incorporatingAmdt No 1 Nov 98)
184 : 96
Guide to the Isolation of Pressure Relieving Devices
185 : 96
Guide for Hot Tapping on Piping and other Equipment (Reprinted 2000
incorporafing Amdf No 1 Dec 97)
188 : 99
Guide for Establishing Operating Periods of Safety Valves
192 : 98
Guide for the Procurement of Valves for Low Temperature (Non-cryogenic)
Service
196 : 99
Valve Purchasers’ Guide to the European Pressure Equipment Directive
(Reprinted 2002 incorporating Amdts 1-3, Nov 00, Feb 02 & Aug 02,
respectively)
Edition, Process Piping (Amdfs
2 Plug Valves (€rata &
- Part 4
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Butterfly and Globe
199 : 00
On-Line Leak Sealing of Piping - Guide to Safety Considerations
200 : 00
Guide to the Specification, Installation and Maintenance of Spring Supports for
Piping
202 : 01
Guide to the Use of I S 0 15649 and ANSVASME 831.3 for Piping in Europe in
Compliance with the Pressure Equipment Directive (Reprinted 2002
incorporating Amdf No 7 May 02)
OFFSHORE
144 : 87
90/10 Copper Nickel Alloy Piping for Offshore Applications-Specification:
Tubes Seamless and Welded
145 : 87
90110 Copper Nickel Alloy Piping for Offshore Applications-Specification:
Flanges Composite and Solid
146 : 87
90110 Copper Nickel Alloy Piping for Offshore Applications-Specification:
Fittings
158 : 94
Construction Specification for Fixed Offshore Structures in the North Sea
(Reprinted 2000 incorporating Amdts f (Revd) & 2, Apr 97, & 3 Sep 02, and
other minor emendations)
166 : 91
Specification for Line Pipe for Offshore Pipelines (Seamless or Submerged Arc
Welded) (Obsolescent
176 : 98
Specification for Structural Castings for Use Offshore
194 : 99
Guidelines for Materials Selection and Corrosion Control for Subsea Oil and
Gas Production Equipment (Under revision, 2003)
197 : 99
Specification for the Fabrication of Non-Primary Structural Steelwork for
Offshore Installations
STORAGE TANKS AND VESSELS
147 : 86
Recommendations for the Design and Construction of Refrigerated Liquefied
Gas Storage Tanks
154 : 02
Guidance to Owners on Demolition of Vertical Cylindrical Steel Storage Tanks
and Storage Spheres (2ndEdition)
159 : 03
Users' Guide to the Inspection, Maintenance and Repair of Aboveground
Vertical Cylindrical Steel Storage Tanks (3' Edition) (In two volumes,
completely revised and expanded)
180: 96
Guide for Designers and Users on Frangible Roof Joints for Fixed Roof Storage
Tanks
183 : 99
Guide for the Prevention of Bottom Leakage from Vertical Cylindrical Steel
Storage Tanks
190 : 00
Guide for the Design, Construction and Use of Mounded Horizontal Cylindrical
Bulk Storage Vessels for Pressurised LPG at Ambient Temperatures
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104 : 85
Noise: A Guide to Information required from Equipment Vendors
140 : 85
Noise Procedure Specification
141 : 85
Guide to the Use of Noise Procedure Specification
161 : 88
Guide to the Selection and Assessment of Silencers and Acoustic Enclosures
GENERAL
101 : 94
Lifting Points-A
Design Guide
105 : 02
Factory Stairways, Ladders and Handrails (including Access Platforms and
Ramps) New edition 2002
148 : 86
Reliability Specification-Model
clauses for
specifications for equipment items and packages
149 : 97
Code of Practice for the Identificationand Checking of Materials of Construction
in Pressure Systems in Process Plants
193 : 99
EEMUA Recommendations for the Training, Development and Competency
Assessment of Inspection Personnel
195 : 99
Compendium of EEMUA Information Sheets on Topics Related to Pressure
Containing Equipment (Arndt No 7 Jan 00)
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inclusion
in
purchasing