tankdesign

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ENG: MOAMEN MOHAMED HUSSEIN ENG: MOAMEN MOHAMED HUSSEIN

Storage tank Design

4

4 Tanks

Tanks

4.1

4.1 Introduction

Introduction

At e-styrenics there are many tanks; At e-styrenics there are many tanks; three identical tanks used for styrene three identical tanks used for styrene storage, styrene day tank, EB

storage, styrene day tank, EB storagestorage tank and TBC storage tank.

tank and TBC storage tank. At this part we

At this part we will travel throughwill travel through tanks to know it different types, parts tanks to know it different types, parts and apply our knowledge by

and apply our knowledge by designingdesigning the main styrene storage tank.

the main styrene storage tank. At our travel will walk through the At our travel will walk through the following:

following: 1.

1. Tank types.Tank types. 2.

2. Tank Standards.Tank Standards. 3.

3. Material selection.Material selection. 4.

4. Shell design.Shell design. 5.

5. Roof design.Roof design. 6.

6. Wind load including windWind load including wind stiffener.

stiffener. 7.

7. Seismic loads.Seismic loads. 8.

8. Tank foundation.Tank foundation. 9.

9. Tank accessories.Tank accessories. 10.

10. Tank testing.Tank testing.

4.2

4.2 Types and Functions of

Types and Functions of

Storage Tanks

Storage tanks are used in refinery, Storage tanks are used in refinery, chemical, and petrochemical, and chemical, and petrochemical, and operations to store crude oil, operations to store crude oil, intermedia

intermediate and te and refined products, gas,refined products, gas, chemicals, and water. Such chemicals, and water. Such characteristics of the stored fluid as characteristics of the stored fluid as quantity, volatility, chemical quantity, volatility, chemical characteristics, and corrosiveness characteristics, and corrosiveness combine with such considerations as combine with such considerations as the required storage pressure to the required storage pressure to

determine the type, size, and determine the type, size, and construction material of a storage tank. construction material of a storage tank. When corrosion is expected on the When corrosion is expected on the inside of a tank, a corrosion allowance inside of a tank, a corrosion allowance is typically added to the tank is typically added to the tank component thickness as part of the component thickness as part of the original design. In extreme cases, original design. In extreme cases, internal lining or coating systems (such internal lining or coating systems (such as epoxy- or fiberglass-reinforced as epoxy- or fiberglass-reinforced plastic) may be considered in place of a plastic) may be considered in place of a very large corrosion allowance or the very large corrosion allowance or the use of alloy materials. The following use of alloy materials. The following standard

standard types of types of storage tankstorage tanks:s:

  AtmosphericAtmospheric   Low-temperatureLow-temperature   Low-pressureLow-pressure

4.2.1

4.2.1 Atmospheric Storage

Atmospheric Storage

Tanks

Atmospheric storage tanks are Atmospheric storage tanks are designed to store liquids such as crude designed to store liquids such as crude oil, gasoline, and other products, and oil, gasoline, and other products, and water. Atmospheric storage tanks water. Atmospheric storage tanks operate with the internal pressure of operate with the internal pressure of their vapor space at approximately their vapor space at approximately atmospheric pressure (an internal atmospheric pressure (an internal pressure that is less than the weight of pressure that is less than the weight of the roof). These tanks are typically of the roof). These tanks are typically of all-welded carbon steel construction; all-welded carbon steel construction; however, tanks that

however, tanks that construcconstructed beforeted before reliable welding equipment and reliable welding equipment and practices were available used bolted or practices were available used bolted or riveted

riveted constructiconstruction.on.

This course discusses only welded steel This course discusses only welded steel storage tanks, although most of the storage tanks, although most of the topics apply to any type of topics apply to any type of construction.

construction. Atmospheric Atmospheric storagestorage tanks are usually classified by the type tanks are usually classified by the type of roof that is installed. The major of roof that is installed. The major types of atmospheric storage tanks are types of atmospheric storage tanks are as follows:

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•

• Fixed roof Fixed roof

•

•Floating roofFloating roof

•

•Fixed roof with internal floating roofFixed roof with internal floating roof 4.2.1.1

4.2.1.1 Fixed Roof TanksFixed Roof Tanks

are the simplest type of atmospheric are the simplest type of atmospheric storage tank. The roof is usually in the storage tank. The roof is usually in the form of a cone or dome. Figures form of a cone or dome. Figures 4-14-1 and 2 provide examples of cone roof and 2 provide examples of cone roof and dome roof tanks.

and dome roof tanks.

Cone roof tanks can be up to 90 m (300 Cone roof tanks can be up to 90 m (300 ft.) in diameter and 20 m (64 ft.) in ft.) in diameter and 20 m (64 ft.) in height. In larger diameter tanks, height. In larger diameter tanks, internal structural members that internal structural members that consist of girders, rafters, and columns consist of girders, rafters, and columns must be used to support the roof. The must be used to support the roof. The fixed roofs of smaller diameter tanks fixed roofs of smaller diameter tanks may be designed to

may be designed to be self-supporting.be self-supporting.

Figure 4-1 Cone Roof Tank Figure 4-1 Cone Roof Tank

Figure 4-2 Dome Roof Tank Figure 4-2 Dome Roof Tank

4.2.1.2

4.2.1.2 Floating Roof TanksFloating Roof Tanks

are another common type of are another common type of atmospheric storage tank. The design of atmospheric storage tank. The design of floating roof storage tanks minimizes floating roof storage tanks minimizes breathing losses of hydrocarbon vapor breathing losses of hydrocarbon vapor when the tank is filled and emptied. when the tank is filled and emptied. The floating roof eliminates a vapor The floating roof eliminates a vapor space above the stored liquid or space above the stored liquid or maintains a small and constant vapor maintains a small and constant vapor space. The shell and bottom of floating space. The shell and bottom of floating roof tanks are similar to cone roof roof tanks are similar to cone roof storage tanks, but the roof is designed storage tanks, but the roof is designed to float on the stored liquid. The most to float on the stored liquid. The most common type of floating roof is the common type of floating roof is the annular-pontoon-type. The annular-pontoon-type. The double-deck-type floating roof is used for very deck-type floating roof is used for very large diameter tanks in order to large diameter tanks in order to increase roof stability. Figures

increase roof stability. Figures 4-34-3 andand 4-4

4-4 provide cross-sectional illustrationsprovide cross-sectional illustrations of floating roof storage tanks.

of floating roof storage tanks.

Figure 4- 3

Figure 4- 3 Double-Deck-Type FloatinDouble-Deck-Type Floating Roof Tankg Roof Tank

Figure 4-4 single-Deck-Type Floating Roof Tank Figure 4-4 single-Deck-Type Floating Roof Tank

4.2.1.3

4.2.1.3 Fixed Roof with InternalFixed Roof with Internal Floating Roof Tanks Floating Roof Tanks

Usually consist of a cone roof storage Usually consist of a cone roof storage tank with a pan-type, panel-type, or tank with a pan-type, panel-type, or pontoon-type floating roof located pontoon-type floating roof located inside. The floating roof in this case is inside. The floating roof in this case is

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called an internal floating roof. The called an internal floating roof. The internal floating roof may be internal floating roof may be constructed of materials other than constructed of materials other than steel, such as aluminum or plastic. steel, such as aluminum or plastic. Figures

Figures 4-54-5 andand 4-64-6 provide cross-provide cross-sectional illustrations of tanks with sectional illustrations of tanks with internal floating roofs.

internal floating roofs.

Figure 4-5 Pan-Types Internal Floating Roof Tank Figure 4-5 Pan-Types Internal Floating Roof Tank

Figure 4-6 Float-Types Internal Floating Roof Tank Figure 4-6 Float-Types Internal Floating Roof Tank

4.2.2

4.2.2 Low-Temperature

Low-Temperature

Storage Tanks

Low-temperature storage tanks are Low-temperature storage tanks are designed to operate at temperatures designed to operate at temperatures below the ambient temperature and below the ambient temperature and with the internal pressure of their vapor with the internal pressure of their vapor

space not exceeding 103 kPa (ga; 15 space not exceeding 103 kPa (ga; 15 psig). These tanks are of welded steel psig). These tanks are of welded steel construction.

construction.

Low-temperature storage tanks are Low-temperature storage tanks are used when economic studies show that used when economic studies show that these tanks give a higher economic these tanks give a higher economic return than can be obtained with return than can be obtained with pressurized storage, typically for pressurized storage, typically for large-volume applications. Low-temperature volume applications. Low-temperature storage tanks are used for refrigerated storage tanks are used for refrigerated product storage or for liquefied product storage or for liquefied hydrocarbon gases, such as ethane, hydrocarbon gases, such as ethane, ethylene, or methane.

ethylene, or methane. Refrigerate

Refrigerated tanks d tanks are either single-wallare either single-wall insulated tanks or

insulated tanks or double-wall insulateddouble-wall insulated tanks. A double-wall tank consists of an tanks. A double-wall tank consists of an inner tank that stores the refrigerated inner tank that stores the refrigerated liquid and an outer tank that encloses liquid and an outer tank that encloses an insulation space around the inner an insulation space around the inner tank. A double-wall tank is a composite tank. A double-wall tank is a composite tank; the outer tank is not required to tank; the outer tank is not required to contain the product that is enclosed by contain the product that is enclosed by the inner tank. In a double-wall tank, the inner tank. In a double-wall tank, differences in materials, design, and differences in materials, design, and testing apply to the inner and outer testing apply to the inner and outer tank because of their different tank because of their different functions. Figure

functions. Figure 4-74-7illustrates a cross-illustrates a cross-section of a typical double-wall tank. section of a typical double-wall tank.

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Figure 4-7 Double-Wall, Low-Temperature Storage Tank Figure 4-7 Double-Wall, Low-Temperature Storage Tank

4.2.3

4.2.3 Low-Pressure Storage

Low-Pressure Storage

Tanks

Low-pressure storage tanks are Low-pressure storage tanks are designed to operate with the internal designed to operate with the internal pressure of their vapor space over the pressure of their vapor space over the limits of atmospheric tanks but not limits of atmospheric tanks but not overover 103 kPa (ga; 15

103 kPa (ga; 15 psig). These tanks are ofpsig). These tanks are of welded steel construction and are welded steel construction and are normally fabricated from carbon steel; normally fabricated from carbon steel; however, stainless steel and nickel however, stainless steel and nickel alloys may be required for very low alloys may be required for very low temperature applications.

temperature applications.

Low-pressure storage tanks are typically Low-pressure storage tanks are typically used to store substances that have true used to store substances that have true vapor pressures over 18 kPa (ga; 2.6 vapor pressures over 18 kPa (ga; 2.6 psig) but not over 103 kPa (ga; 15 psig). psig) but not over 103 kPa (ga; 15 psig). Low-pressure storage tanks store Low-pressure storage tanks store substances such as the following:

substances such as the following:



 Light crude oilsLight crude oils 

 Light naphtha'sLight naphtha's 

 Some gasoline blending stocksSome gasoline blending stocks



 Some volatile chemicalsSome volatile chemicals

Tanks with cylindrical shells and cone Tanks with cylindrical shells and cone roofs or, more commonly, dome roofs roofs or, more commonly, dome roofs are typically used for pressures of 34 are typically used for pressures of 34 kPa (ga; 5 psig) and less. The kPa (ga; 5 psig) and less. The cylindrical-shell low-pressure storage tank is the shell low-pressure storage tank is the most common type of low-pressure most common type of low-pressure tank. The bottoms of the tanks are tank. The bottoms of the tanks are usually flat but may be shaped like the usually flat but may be shaped like the roofs. Hold- down anchorage is usually roofs. Hold- down anchorage is usually required to prevent the internal required to prevent the internal pressure from lifting the tank off its pressure from lifting the tank off its foundation.

foundation.

4.3

4.3 Storage Tank Design

Storage Tank Design

Specifications

In the case of storage tanks, the In the case of storage tanks, the contractor's responsibilities include contractor's responsibilities include specifying the required design basis. specifying the required design basis. The tank design basis includes the tank The tank design basis includes the tank

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capacity, service, design code, capacity, service, design code, materials, design conditions, external materials, design conditions, external loads, appurtenances, and connections loads, appurtenances, and connections that are needed for a particular storage that are needed for a particular storage tank application. Storage tank design tank application. Storage tank design specifications are used to specify these specifications are used to specify these requiremen

requirements. The ts. The specificatispecifications consistons consist of engineering standards and a storage of engineering standards and a storage tank design specification sheet.

tank design specification sheet.

4.3.1

4.3.1 Standards and

Standards and

Specifications

API-650 covers the material selection, API-650 covers the material selection, design, fabrication, erection, and design, fabrication, erection, and testing requirements for vertical, testing requirements for vertical, cylindrical, above ground, closed- and cylindrical, above ground, closed- and open-top, welded steel storage tanks open-top, welded steel storage tanks for internal pressures that are for internal pressures that are approximate

approximately ly equal equal to to atmosphericatmospheric pressure. If the supplemental pressure. If the supplemental requirements that are contained in requirements that are contained in Appendix F of API-650 are applied, Appendix F of API-650 are applied, storage tanks may be designed for storage tanks may be designed for internal pressures up to 18 kPa (ga; 2.6 internal pressures up to 18 kPa (ga; 2.6 psig). The entire tank bottom must be psig). The entire tank bottom must be uniformly supported. API-650 tanks uniformly supported. API-650 tanks must be in nonrefrigerated service and must be in nonrefrigerated service and they will typically have a maximum they will typically have a maximum operating temperature of 93ºC (200ºF). operating temperature of 93ºC (200ºF). A maximum operating temperature of A maximum operating temperature of 260ºC (500ºV) is permitted when the 260ºC (500ºV) is permitted when the additional requirements contained in additional requirements contained in Appendix M of API-650 are followed. Appendix M of API-650 are followed.

API-620 covers the design and API-620 covers the design and construction of large, welded, construction of large, welded, low-pressure carbon steel above ground pressure carbon steel above ground storage tanks that have a single vertical storage tanks that have a single vertical axis of revolution. The maximum axis of revolution. The maximum permitted internal pressure in the permitted internal pressure in the

vapor space is 103 kPa (ga; 15 psig), vapor space is 103 kPa (ga; 15 psig), and the maximum permitted and the maximum permitted temperature is 120ºC (250ºF). The temperature is 120ºC (250ºF). The basicbasic API-620 rules permit design to a lowest API-620 rules permit design to a lowest one-day mean atmospheric one-day mean atmospheric temperature of -46ºC (-50ºF). This temperature of -46ºC (-50ºF). This temperature corresponds to a temperature corresponds to a minimum acceptable design metal minimum acceptable design metal temperature of -37ºC (-35ºF); however, temperature of -37ºC (-35ºF); however, Appendix R covers tanks that are used Appendix R covers tanks that are used for refrigerated product services with a for refrigerated product services with a minimum design metal temperature minimum design metal temperature between +4ºC to 50ºC (+40ºF to between +4ºC to 50ºC (+40ºF to -60ºF). API-620, Appendix Q, covers 60ºF). API-620, Appendix Q, covers tanks that are used to store liquefied tanks that are used to store liquefied hydrocarbon gases that have a design hydrocarbon gases that have a design metal temperature as low as -168ºC metal temperature as low as -168ºC (270ºF). The primary additional design (270ºF). The primary additional design considerations for API-620 tanks, when considerations for API-620 tanks, when compared to API-650 tanks, relate to compared to API-650 tanks, relate to the specified design pressure and the specified design pressure and minimum design

minimum design temperature.temperature.

4.4

4.4 Floating Roof Tanks

Floating Roof Tanks

Floating roof tank was developed Floating roof tank was developed shortly after World War I by Chicago shortly after World War I by Chicago Bridge & Iron

Bridge & Iron Company (CB & I).Company (CB & I). Evaporation of the product in fixed Evaporation of the product in fixed roof caused a great loss of

roof caused a great loss of money; thismoney; this led to research to develop a roof that led to research to develop a roof that can float directly on the surface of can float directly on the surface of Product, reducing the evaporation Product, reducing the evaporation losses.

losses.

4.4.1

4.4.1 Principles of the Floating

Principles of the Floating

Roof

The floating roof is a circular steel The floating roof is a circular steel structure provided with a built-in structure provided with a built-in buoyancy which allowing it to sit/ float buoyancy which allowing it to sit/ float

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on top of the liquid product in a close on top of the liquid product in a close or open top tank.

or open top tank.

The overall diameter of the roof is The overall diameter of the roof is normally 400 mm smaller than the normally 400 mm smaller than the inside diameter of the tank, which has inside diameter of the tank, which has about 200 mm gap on each side about 200 mm gap on each side between the roof and the inside tank between the roof and the inside tank wall. This is due to the limitation on wall. This is due to the limitation on the accuracy of dimension during the accuracy of dimension during construction for the large diameter construction for the large diameter tank.

tank.

The gaps allow the floating roof to The gaps allow the floating roof to rise and fall without binding on the rise and fall without binding on the tank wall. To protect the product tank wall. To protect the product inside the tank from evaporation to inside the tank from evaporation to the atmosphere and contamination the atmosphere and contamination from the rain water through the gaps from the rain water through the gaps between the outer rim of the floating between the outer rim of the floating roof and the tank wall, the

roof and the tank wall, the gaps will begaps will be

closed or sealed up by mean of

closed or sealed up by mean of flexibleflexible sealing system. Due to environmental sealing system. Due to environmental issue, selection of the roof seal is one issue, selection of the roof seal is one of the major concerns in the floating of the major concerns in the floating roof tank design.

roof tank design.

In single deck roof, is also called In single deck roof, is also called pontoon roof, the buoyancy is derived pontoon roof, the buoyancy is derived in the pontoon, an annular circular in the pontoon, an annular circular pontoon radially divided into liquid pontoon radially divided into liquid tight compartments. The center deck tight compartments. The center deck which is formed by membrane of thin which is formed by membrane of thin steel plates are lap welded together steel plates are lap welded together and connected to the inner rim of the and connected to the inner rim of the pontoons.

pontoons.

Figure

Figure4-8 Appurtenances on Annular-Pontoon Type Floating Roof Tank4-8 Appurtenances on Annular-Pontoon Type Floating Roof Tank

Double deck roof consists of upper Double deck roof consists of upper and lower steel membranes separated and lower steel membranes separated by a

by a series of circumferential bulkheadseries of circumferential bulkhead which is subdivided by radial which is subdivided by radial bulkhead. The outer ring of the bulkhead. The outer ring of the compartments is the main liquid tight compartments is the main liquid tight buoyancy for the roof. Double deck buoyancy for the roof. Double deck roof is much heavier than single deck roof is much heavier than single deck one, hence it is more rigid. The air gap one, hence it is more rigid. The air gap between the upper and bottom plates between the upper and bottom plates of the deck has insulation effect which of the deck has insulation effect which

helps against the solar heat reaching helps against the solar heat reaching the product during the hot

the product during the hot climate andclimate and preventing heat loss of the product preventing heat loss of the product during cold climate.

during cold climate.

Figure 4-9 Double-Deck-Type Floating Roof Tank Figure 4-9 Double-Deck-Type Floating Roof Tank

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4.4.2

4.4.2 Advantages of the

Advantages of the

floating roof storage tank

As the roof floats directly on the As the roof floats directly on the product, there is no vapour space and product, there is no vapour space and thus eliminating any possibility of thus eliminating any possibility of flammable atmosphere. It reduces flammable atmosphere. It reduces evaporation losses and hence evaporation losses and hence reduction in air pollution. Vapour reduction in air pollution. Vapour emission is only possible from the rim emission is only possible from the rim seal area and this would mainly seal area and this would mainly depend on the type of seal selected depend on the type of seal selected and used.

and used.

Despite of the advantages of the Despite of the advantages of the floating roof, to design and c

floating roof, to design and construct aonstruct a floating roof tank will be much more floating roof tank will be much more complicated and costly than the fixed complicated and costly than the fixed ones. In term of tank stability and ones. In term of tank stability and design integrity, floating roof tank is design integrity, floating roof tank is never better than the fixed roof tank never better than the fixed roof tank as there are still many unknown as there are still many unknown parameters and factors in designing parameters and factors in designing the floating roof.

the floating roof.

4.5

4.5 Design Considerations

Design Considerations

4.5.1

4.5.1 Material Selection and

Material Selection and

Corrosion Assessment

Material selection study was carried Material selection study was carried out by the

out by the material specialist to reviewmaterial specialist to review the

the conceptual design basic of theconceptual design basic of the plant and assess expected longevity of plant and assess expected longevity of materials for

materials for various piping andvarious piping and equipment, he/she then proposes equipment, he/she then proposes materials suitable for the required materials suitable for the required design life of 30 years. The approach design life of 30 years. The approach of this material selection is to evaluate of this material selection is to evaluate the internal corrosivity of the fluids the internal corrosivity of the fluids with respect to utilisation of carbon with respect to utilisation of carbon steel.

steel.

Carbon Steel is considered as first Carbon Steel is considered as first choice, due to its lower cost, ready choice, due to its lower cost, ready availability and well understood availability and well understood requirements to fabrication and requirements to fabrication and testing. Material selection for the testing. Material selection for the hydrocarbon system is based on detail hydrocarbon system is based on detail evaluation of fluid properties.

evaluation of fluid properties. 4.5.1.1

4.5.1.1





Corrosion Corrosion

Carbon dioxide dissolves in water and Carbon dioxide dissolves in water and dissociates to form weak

dissociates to form weak carbonic acidcarbonic acid which

which causes corrosion on carboncauses corrosion on carbon steels. Higher partial pressures of steels. Higher partial pressures of





imply more dissolved





and hence and hence higher corrosion rate. Higher higher corrosion rate. Higher temperatures and pressure increase temperatures and pressure increase the corrosion rate, but in certain the corrosion rate, but in certain conditions, about 70 to 80°C, a conditions, about 70 to 80°C, a protective carbonate scale can form protective carbonate scale can form on the steel surface that reduces the on the steel surface that reduces the corrosion rate, compared to lower corrosion rate, compared to lower temperatures where the scale does temperatures where the scale does not form.

not form.

Corrosion resistant alloys (CRA) are Corrosion resistant alloys (CRA) are used to avoid corrosion at high used to avoid corrosion at high





contents, and in less corrosive contents, and in less corrosive condition and where required lifetime condition and where required lifetime is limited, but it would be more is limited, but it would be more economical to use carbon steel with a economical to use carbon steel with a corrosion allowance and/or chemical corrosion allowance and/or chemical inhibitor treatment. The presence of inhibitor treatment. The presence of





infers that carbon steel will have infers that carbon steel will have finite life due to the wall thinning; a finite life due to the wall thinning; a corrosion allowance is practical to corrosion allowance is practical to accommodate up to 6mm.

accommodate up to 6mm. 4.5.1.2

4.5.1.2 MercuryMercury

Mercury (Hg) is a trace component of Mercury (Hg) is a trace component of all fossil fuels. It is

all fossil fuels. It is therefore present intherefore present in liquid hydrocarbon and natural gas liquid hydrocarbon and natural gas deposits, and may transfer into air, deposits, and may transfer into air, water and soil. Materials unsuitable water and soil. Materials unsuitable

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for hydrocarbon streams in presence for hydrocarbon streams in presence of mercury due to liquid metal of mercury due to liquid metal embrittlement, which will result in embrittlement, which will result in crack, are:

crack, are:



 Aluminium and AluminiumAluminium and Aluminium

Alloys Alloys



 Titanium and Titanium AlloysTitanium and Titanium Alloys 

 Copper and Copper AlloysCopper and Copper Alloys 

 Zinc and Zinc AlloysZinc and Zinc Alloys

Recommended materials are: Recommended materials are:



 Carbon steels and low allowCarbon steels and low allow

steels steels



 Stainless Stainless steels steels (Austenitic(Austenitic

stainless steel, Duplex stainless stainless steel, Duplex stainless steel)

steel)



 Nickel Alloys (Inconel 625, 825Nickel Alloys (Inconel 625, 825

and Monel) and Monel)

4.5.1.3

4.5.1.3 EFFECT OF MATERIALEFFECT OF MATERIAL STRENGTH AND FRACTUR STRENGTH AND FRACTUREE

TOUGHNESS PROPERTIES TOUGHNESS PROPERTIES ON MATERIAL SELECTION ON MATERIAL SELECTION

The materials that are to be used The materials that are to be used for the primary structural for the primary structural components of a storage tank must components of a storage tank must first be selected before these first be selected before these components can be designed. This components can be designed. This section discusses the following section discusses the following items:

items:



 Material strength Materialstrength andand

fracture toughness fracture toughness properties

properties



 General General steps steps that that are are usedused

to select appropriate to select appropriate materials

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4.5.1.3.1

4.5.1.3.1 Fracture ToughnessFracture Toughness

Figure

Figure4-4-0101_{(USC) Minimum Permissible Design Metal Temperature for Materials Used in}_{(USC) Minimum Permissible Design Metal Temperature for Materials Used in Tank}_Tank NOTE: materials with same toughness are in group.

NOTE: materials with same toughness are in group.

Fracture toughness is the ability of Fracture toughness is the ability of a material to withstand conditions a material to withstand conditions that could cause a

that could cause a brittle fracturebrittle fracture.. Brittle fracture is characterized by Brittle fracture is characterized by the lack of deformation or yielding the lack of deformation or yielding in the material prior to failure. in the material prior to failure. When a brittle fracture occurs, When a brittle fracture occurs, there is no leak or warning prior to there is no leak or warning prior to complete failure of the component. complete failure of the component. These failure characteristics of These failure characteristics of brittle fracture are in contrast to the brittle fracture are in contrast to the the ductile type of failure that the ductile type of failure that occurs when the material strength occurs when the material strength is exceeded. Brittle fracture occurs is exceeded. Brittle fracture occurs only when the following three only when the following three conditions occur simultaneously: conditions occur simultaneously:



 The The material material hashas

insufficient fracture insufficient fracture toughness at the toughness at the temperature. temperature. 

 There There is is sufficient sufficient stressstress

in the component to in the component to cause a crack to initiate cause a crack to initiate and grow.

and grow.



 There is There is a ca critical sizritical sizee

defect in the component defect in the component that can act as a local that can act as a local stress concentration stress concentration point and site for crack point and site for crack



 Initiation such Initiation such as as at aat a

weld. weld.

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The brittle fracture occurs without The brittle fracture occurs without warning the first time that the warning the first time that the component is exposed to the component is exposed to the necessary combination of low necessary combination of low temperature, high stress, and temperature, high stress, and critical size defect; therefore, it is critical size defect; therefore, it is extremely important that material extremely important that material selection eliminate the possibility of selection eliminate the possibility of brittle fracture. The fracture brittle fracture. The fracture toughness of a material decreases toughness of a material decreases as the material temperature as the material temperature decreases (see

decreases (see Figure 4-Figure4-0101₎₎_..

Tank material fracture toughness Tank material fracture toughness is a minimum at the minimum is a minimum at the minimum temperature to which the tank will temperature to which the tank will be exposed. The

be exposed. The design metaldesign metal temperature

temperature is is the the minimumminimum temperature to which the tank will temperature to which the tank will be exposed; therefore, material be exposed; therefore, material fracture toughness considerations fracture toughness considerations are pertinent to ensure that tank are pertinent to ensure that tank components will not experience a components will not experience a brittle fracture at temperatures that brittle fracture at temperatures that are as low as the design metal are as low as the design metal temperature. The design metal temperature. The design metal temperature of the tank is specified temperature of the tank is specified on the Storage Tank Data Sheet on the Storage Tank Data Sheet (Appendix L of API-650 for (Appendix L of API-650 for atmospheric tanks).

atmospheric tanks).

4.5.1.3.2

4.5.1.3.2 Determining FractureDetermining Fracture

Toughness

The

The Charpy V-notch testCharpy V-notch test ((





) is) is commonly used to qualitatively commonly used to qualitatively determine the fracture toughness of determine the fracture toughness of steel. The test consists of steel. The test consists of performing an

performing an impact testimpact test on aon a notched specimen that is taken notched specimen that is taken from a specific location in the from a specific location in the material, and then recording the material, and then recording the impact energy

impact energy that is required tothat is required to

fracture the specimen at various fracture the specimen at various temperatures.

temperatures.

4.5.1.3.3

4.5.1.3.3 StrengthStrength

Strength is the ability of a material Strength is the ability of a material to withstand an imposed

to withstand an imposed force orforce or stress. The strength of a material is stress. The strength of a material is defined by its yield

defined by its yield strength,strength, ultimate tensile strength, and creep ultimate tensile strength, and creep strength. Material

strength. Material creep strength iscreep strength is only a design factor at only a design factor at temperatures that are

temperatures that are aboveabove approximately 427°C (800°F). approximately 427°C (800°F). Because the design

Because the design temperaturestemperatures for storage tank applications are for storage tank applications are never more than

never more than 260°C (500°F),260°C (500°F), the tensile and yield strengths are the tensile and yield strengths are the only

the only strength properties thatstrength properties that are of concern for storage tanks. are of concern for storage tanks. The yield strength and the tensile The yield strength and the tensile strength of a material

strength of a material decrease asdecrease as the material temperature increases. the material temperature increases. The tank material strength is a The tank material strength is a minimum at the maximum minimum at the maximum temperature to

temperature to which the tank willwhich the tank will be exposed. Therefore, material be exposed. Therefore, material strength

strength considerations considerations areare pertinent to ensure that tank pertinent to ensure that tank components will

components will not fracture at thenot fracture at the maximum operating temperature of maximum operating temperature of the tank.

the tank. Component fracture thatComponent fracture that is caused by exceeding the is caused by exceeding the material

material strength is ductile instrength is ductile in nature and is preceded by nature and is preceded by permanent

permanent deformation. Therefore,deformation. Therefore, there is normally time to take some there is normally time to take some form of remedial action to reduce form of remedial action to reduce the imposed loads before a the imposed loads before a component fracture occurs.

component fracture occurs. TheThe maximum operating temperature of maximum operating temperature of the tank is specified on

the tank is specified on either theeither the Storage Tank Design sheet.

(12)

Table 4-1 - (SI) Permissible Plate Materials and Allowable Stresses Table 4-1 - (SI) Permissible Plate Materials and Allowable Stresses Specification of the maximum

Specification of the maximum operating temperature ensures operating temperature ensures thatthat material strength is properly material strength is properly considered in tank design.

considered in tank design. TheThe strength of the material, as defined strength of the material, as defined by its tensile and yield

by its tensile and yield properties,properties, has a direct impact on the has a direct impact on the structural design of tank structural design of tank components. Storage tank components. Storage tank components are designed to have components are designed to have a

a margin between the maximummargin between the maximum stress that is permitted under the stress that is permitted under the imposed load conditions and both imposed load conditions and both the yield strength and tensile the yield strength and tensile strength of the material. The strength of the material. The allowable stress

allowable stress is the maximumis the maximum stress that is permitted in a stress that is permitted in a component for design purposes. component for design purposes. Because the yield strength and Because the yield strength and tensile strength define failure

tensile strength define failure limitslimits of a material, a safety factor

of a material, a safety factor is usedis used between the

between the allowable stress andallowable stress and the stress at which a tank the stress at which a tank component is

component is considered to fail.considered to fail. API-650

API-650 specifies specifies safety fsafety factors actors forfor the determination of

the determination of allowableallowable stresses. For example, when a tank stresses. For example, when a tank shell is designed

shell is designed for the loads thatfor the loads that

are imposed by the stored liquid, are imposed by the stored liquid, the allowable

the allowable stress is limited to thestress is limited to the lower of the following two values: lower of the following two values: two thirds

two thirds of the yield strength, orof the yield strength, or two-fifths of the tensile strength of two-fifths of the tensile strength of the material.

the material. API-650

API-650 specifies specifies allowableallowable stresses for each

stresses for each materialmaterial specification (see

specification (see TableTable 4-14-1) that) that

may be used to construct an may be used to construct an atmospheric storage tank. The atmospheric storage tank. The allowable stress of each specific allowable stress of each specific material is constant for all material is constant for all temperatures up to 93°C (200°F); temperatures up to 93°C (200°F); however, the allowable stress of however, the allowable stress of each material decreases for each material decreases for temperatures that are above 93°C temperatures that are above 93°C (200°F). API-650 Appendix M (200°F). API-650 Appendix M contains additional design criteria contains additional design criteria that must be followed for tanks that that must be followed for tanks that have maximum operating have maximum operating temperatures over 93°C (200°F). temperatures over 93°C (200°F).

4.5.1.4

4.5.1.4 Material SelectionMaterial Selection

Tank materials are selected to Tank materials are selected to provide the most economical provide the most economical design that is suitable for the design that is suitable for the specified design conditions. This specified design conditions. This

(13)

materials selection considers both materials selection considers both the material strength fracture and the material strength fracture and toughness properties that were toughness properties that were previously discussed.

previously discussed. Although

Although several several materials materials can can bebe technically acceptable, the ultimate technically acceptable, the ultimate choice of what materials to use is choice of what materials to use is based on current economic based on current economic conditions, material availability. As conditions, material availability. As an example of the basis for an example of the basis for material selection, the use of higher material selection, the use of higher strength steel may reduce the strength steel may reduce the thickness that is required for shell thickness that is required for shell sections, but the cost per pound of sections, but the cost per pound of the higher-strength steel may be so the higher-strength steel may be so much higher than the cost of a much higher than the cost of a lower-strength material that it could lower-strength material that it could result in a higher overall cost for result in a higher overall cost for the tank. Generally speaking, an the tank. Generally speaking, an initial material selection can be initial material selection can be made based on strength made based on strength considerations. Then, shell wall considerations. Then, shell wall thicknesses can be calculated, and thicknesses can be calculated, and a check can then be made to a check can then be made to confirm that the fracture toughness confirm that the fracture toughness of the selected material is of the selected material is acceptable for the specified design acceptable for the specified design metal temperature. Shell wall metal temperature. Shell wall thicknesses are normally kept to a thicknesses are normally kept to a maximum of 40 mm (1.5 in.) in maximum of 40 mm (1.5 in.) in order to avoid the need for any order to avoid the need for any special fabrication or heat special fabrication or heat treatment considerations.

treatment considerations.

The steps in the material selection The steps in the material selection process are explained below.

process are explained below.



 Make an initial material Make an initial material

selection for the tank selection for the tank primary components (roof, primary components (roof, shell, bottom) based on shell, bottom) based on strength. API-650 contains a strength. API-650 contains a list of acceptable material list of acceptable material specifications. Typically, first specifications. Typically, first

select the highest strength select the highest strength steel that is acceptable.

steel that is acceptable.



 Determine Determine preliminarypreliminary

thicknesses for the primary thicknesses for the primary tank components. tank components. Procedures for this Procedures for this determination will be determination will be discussed.

discussed.



 Determine Determine whether whether thethe

selected materials have selected materials have adequate fracture toughness adequate fracture toughness in the calculated thicknesses in the calculated thicknesses for the required design metal for the required design metal temperature of the tank. As temperature of the tank. As previously discussed, previously discussed, fracture toughness becomes fracture toughness becomes a more significant a more significant consideration as the design consideration as the design metal temperature of the metal temperature of the tank decreases.

tank decreases.



 Change Change the the selectedselected

materials as needed, based materials as needed, based on their fracture toughness. on their fracture toughness. Recalculate the component Recalculate the component thicknesses based on the thicknesses based on the new materials used. Also new materials used. Also determine if the thicknesses determine if the thicknesses should be reduced by using should be reduced by using stronger material to stronger material to minimize fabrication minimize fabrication difficulties. difficulties. 

 Review Review the the cost cost andand

availability of the selected availability of the selected materials, and adjust the materials, and adjust the material selections as material selections as appropriate.

appropriate.

The final materials selections are The final materials selections are specified on the Storage Tank Data specified on the Storage Tank Data Sheet (Appendix L of API-650). Sheet (Appendix L of API-650).

(14)

Table 4-2 Material Selection Guide Table 4-2 Material Selection Guide

F

OR OUR TANK

Min. design temp. is 1 Min. design temp. is 1



From API

Table 5-2a-(SI) Permissible Plate Materials and

Table 5-2a-(SI) Permissible Plate Materials and Allowable StressesAllowable Stresses Figure

Figure 4-14-1 a- (SI) Minimum a- (SI) Minimum Permissible Design Metal Temperature for MaterialsPermissible Design Metal Temperature for Materials Used in Tank Shells without Impact Testing

Used in Tank Shells without Impact Testing Table 4-4a-(SI) Material Groups

Table 4-4a-(SI) Material Groups Section 4.2.2

Section 4.2.2

MAT.





(Mpa) (Mpa)





(Mpa)(Mpa)

ASTM ASTM Specifications Specifications





(mm)(mm) acceptanceacceptance

For

group

I

max.thickness

based

on

Fracture

Toughness

=

18.643

18.643 mm

mm

A283M A283M C C 137 137 154 154 2525 A285M A285M C C 137 137 154 154 2525 A131M A131M A A 157 157 171 171 1313

(15)

A36M

A36M 160 160 171 171 4040

For

group

IV

max.

thickness

based

on

Fracture

Toughness

=27.25

mm

A573M A573M 450 450 160 160 180 180 4040 A573M A573M 485 485 193 193 208 208 4040 A516M A516M 450 450 160 160 180 180 4040 A516M A516M 485 485 173 173 195 195 4040 A662M A662M B B 180 180 193 193 4040

For

group

II

max.thickness

based

on

Fracture

Toughness

=32.7

5mm

A131M

A131M B B 157 157 171 171 2525

A36M

A36M 160 160 171 171 4040

For

group

IVA

max.thickness

based

on

Fracture

Toughness

=33.2

mm

A662M

A662M C C 194 194 208 208 4040

A573M-485

A573M-485 193 193 208 208 4040

Thickness of lower shell course based on

Thickness of lower shell course based on strength by 1-foot method

strength by 1-foot method

(1-foot method will be discussed later)

MAT.













A283M C

12.2094

10.4236

12.2094

A285M C

12.2094

10.4236

12.2094

A36M

10.6699

9.3874

10.6699

A573M 450

10.6699

8.9180

10.6699

A573M 485

9.1020

7.7175

9.1020

A516M 450

10.6699

8.9180

10.6699

A516M 485

9.9809

8.2320

9.9809

A662M B

9.6511

8.3173

9.6511

A36M

10.6699

9.3874

10.6699

A662M C

9.0628

7.7175

9.0628

A573M-485

9.1020

7.7175

9.1020

-- Compare each material thickness with its max. thickness

Compare each material thickness with its max. thickness

based

based on

on Fracture

Fracture Toughness

Toughness

-- Choose the material with closest thickness with its max.

Choose the material with closest thickness with its max.

thickness

(16)

MAT.





(mm) (mm) Based

Based on on Fracture Fracture ToughnessToughness





_acceptance

A283M C

18.643

18.643 12.2094

12.2094

yes

A285M

C

12.2094

yes

A36M

10.6699

yes

A573M 450

27.25

27.25 10.6699

10.6699

A573M

A573M 485

485 9.1020

9.1020

A516M

A516M 450

450 10.6699

10.6699

A516M

A516M 485

485 9.9809

9.9809

A662M

A662M B

B

9.6511

A36M

32.75

32.75 10.6699

10.6699

A662M C

33.2

33.2 9.0628

9.0628

A573M-485

9.1020

A573M-485

9.1020

--

Materials A283M C , A285M C & A36M are accepted

-- Select the most economical one.

Select the most economical one.

--

Material A283M C is used for shell, Roof and Bottom

plates.

-

From material

selection guid

e (

Table 4-2)Table 4-2)

select

material for

pipes, fittings, bolting and forgings

For pipes use

SA-106-B

For Forgings (Flanges) use

SA-105

For Bolting use

(17)

4.5.2

4.5.2 Mechanical Design

Mechanical Design

The basic stress analyses to be taken The basic stress analyses to be taken care in tank design are as follow:

care in tank design are as follow:



 Tank shell wall due to internalTank shell wall due to internal

and external loading and external loading



 Bottom plate/ Tank flooringBottom plate/ Tank flooring 

 Tank roofTank roof – – In this case, In this case,

floating roof floating roof



 Annular plates.Annular plates.

4.5.2.1

4.5.2.1 BOTTOM PLATESBOTTOM PLATES

When the tank foundation is done When the tank foundation is done andand ready for the tank erection, bottom ready for the tank erection, bottom plate will start laying on top of the plate will start laying on top of the foundation and welded in sequence. It foundation and welded in sequence. It is important to lay and weld the is important to lay and weld the bottom plate in correct sequence to bottom plate in correct sequence to avoid any weld distortion.

avoid any weld distortion.

According to API 650 all bottom plates According to API 650 all bottom plates shall have a corroded thickness of not shall have a corroded thickness of not less than 6mm (0.236 in.) Unless less than 6mm (0.236 in.) Unless otherwise agreed to by the Purchaser, otherwise agreed to by the Purchaser, all rectangular and sketch plates shall all rectangular and sketch plates shall have a nominal width of not less than have a nominal width of not less than 1800 mm (72 in.).

1800 mm (72 in.).

For our tank For our tank

Min Thickness of bottom plates = 6 + Min Thickness of bottom plates = 6 + 1.5(C.A) = 7.5 mm

1.5(C.A) = 7.5 mm

Nominal thickness = 8 mm

NOTE: he ordered 10 mm thi

NOTE: he ordered 10 mm thicknessckness

4.5.2.2

4.5.2.2 ANNULAR BOTTOM PLATES ANNULAR BOTTOM PLATES Annular rings are usually used on

Annular rings are usually used on larger tank

larger tanks. s. An Annular An Annular Ring is aRing is a thicker plate on the outside of the thicker plate on the outside of the bottom floor under the shell. bottom floor under the shell.

The purpose of annular ring is to The purpose of annular ring is to support the weight of the shell support the weight of the shell courses.

courses. It also heIt also helps improve lps improve thethe seismic and

seismic and wind design. wind design. Both theBoth the wind & seismic design allow for an wind & seismic design allow for an annular volume on the outside of annular volume on the outside of thethe tank to help resist the overturning tank to help resist the overturning moment.

moment. The width The width of this anof this annularnular volume depends on the bottom plate volume depends on the bottom plate thickness so having a thicker annular thickness so having a thicker annular ring increases the annular volume ring increases the annular volume resisting the overturning moments. resisting the overturning moments. According to API 650 When the According to API 650 When the bottom shell course is designed using bottom shell course is designed using the allowable stress for materials in the allowable stress for materials in Group IV, IVA, V, or VI, butt-welded Group IV, IVA, V, or VI, butt-welded annular bottom plates shall be used . annular bottom plates shall be used . When the bottom shell course is of a When the bottom shell course is of a material in Group IV, IVA, V, or VI and material in Group IV, IVA, V, or VI and the maxim product stress for the first the maxim product stress for the first shell course is less than or equal to shell course is less than or equal to 160 MPa or the maximum hydrostatic 160 MPa or the maximum hydrostatic test stress for the first shell course is test stress for the first shell course is less than or equal to 171 MPa

less than or equal to 171 MPa,, lap- lap-welded bottom plates may be used in welded bottom plates may be used in lieu of butt-welded annular bottom lieu of butt-welded annular bottom plates.

plates.

API 650 contain a table specify the API 650 contain a table specify the minimum annular plate thickness minimum annular plate thickness according to first shell stress and according to first shell stress and thickness.

thickness.

The welding sequence for bottom The welding sequence for bottom plate layout with annular plates, with plate layout with annular plates, with reference to

reference to

Figure 4-11 is as follow: Figure 4-11 is as follow: 1. Lay plates and lightly tack

1. Lay plates and lightly tack – –weldweld 2. Weld centre sump in position 1 & 2 2. Weld centre sump in position 1 & 2

(18)

3.

Weld rectangular plates togetherWeld rectangular plates together commencing at centre, welding short commencing at centre, welding short seams first 3 to 11, seams between seams first 3 to 11, seams between rows of plates shall be free of rows of plates shall be free of tack-welds before making final weld

welds before making final weld

4. Weld only outer part of radial seams 4. Weld only outer part of radial seams of annular plates before erection of of annular plates before erection of shell plates at 12a

shell plates at 12a

5. After complete assembly and 5. After complete assembly and welding of lower shell courses, weld welding of lower shell courses, weld lower shell course to annular 12b for lower shell course to annular 12b for prevention of welding distortion.

prevention of welding distortion.

6. Weld remaining part of radial weld 6. Weld remaining part of radial weld of annulars at 12c

of annulars at 12c

7. Weld rectangular and sketch plates 7. Weld rectangular and sketch plates together at 13 to 22 and finally to together at 13 to 22 and finally to annulars at 23.

annulars at 23.

Figure 4-11 bottom and annular plates Figure 4-11 bottom and annular plates

(19)

For our tank For our tank

According API 650, from table 5-1a According API 650, from table 5-1a

Plate Thickness of First Shell Plate Thickness of First Shell Course=12.5 mm

Course=12.5 mm

Stress in First Shell Course (MPa) = Stress in First Shell Course (MPa) =

((

 



_–

C.A)/ C.A)/corrodedcorroded t)t)( (





) = ) =

((12.2094-1.5)/12.5)(137)=117.375 ((12.2094-1.5)/12.5)(137)=117.375

MPa MPa

Min Thickness of bottom plates = 6 + Min Thickness of bottom plates = 6 + 1.5 (C.A) = 7.5 mm

1.5 (C.A) = 7.5 mm

Nominal thickness (





))

= 8 mm

NOTE: he ordered 12 mm thickness

Min. radial width of

Min. radial width of annular plateannular plate

L =





√ √ 



= =



√ √ 



= = 779.033 mm779.033 mm

H

H= design liquid level, in m =12= design liquid level, in m =12 G

G = Design specific gravity of the liquid= Design specific gravity of the liquid to be stored =0.914

to be stored =0.914

4.5.2.3

4.5.2.3 Tank Shell DesignTank Shell Design 4.5.2.3.1

4.5.2.3.1 Calculation of thickness byCalculation of thickness by

1-Foot Method

The 1-foot method calculates the The 1-foot method calculates the thickness required at design points 0.3 thickness required at design points 0.3 m (1 ft) above the bottom of each m (1 ft) above the bottom of each shell course.

shell course. For design shell

For design shell thicknessthickness













_

_

+C.A +C.A For hydrostatic test shell

For hydrostatic test shell thicknessthickness









_



_





= Design shell thickness, in mm= Design shell thickness, in mm





= Hydrostatic test shell thickness, in= Hydrostatic test shell thickness, in mm

mm H

H = liquid level for course, in m= liquid level for course, in m G

G = Design specific gravity of the liquid= Design specific gravity of the liquid to be stored =0.914

to be stored =0.914 C.A

C.A = Corrosion allowance, in mm=1.5= Corrosion allowance, in mm=1.5





= Allowable stress for the design= Allowable stress for the design condition, in Mpa = 137

condition, in Mpa = 137





=Allowable stress for the =Allowable stress for the hydrostatichydrostatic test condition, in MPa = 154

test condition, in MPa = 154 D

D= nominal tank diametr, m=28= nominal tank diametr, m=28

This method is shall not be used for This method is shall not be used for tanks larger than 60 m

tanks larger than 60 m in diameter.in diameter. O

OUR TANK SHELL THICKNESS CALCULATIONSUR TANK SHELL THICKNESS CALCULATIONS

ARE

ARE SUMMARIZEDSUMMARIZED AT FOLLOWING AT FOLLOWING

TABLE

(20)

course width course width

















1 1 2400 2400 12.2094 12.2094 10.4236 10.4236 12.209412.2094 1414 2 2 2400 2400 10.0126 10.0126 8.2855 8.2855 10.012610.0126 1212 3 3 1500 1500 7.8158 7.8158 6.1473 6.1473 7.81587.8158 1010 4 4 1500 1500 6.4428 6.4428 4.1473 4.1473 6.44286.4428 88 5 5 1500 1500 5.0698 5.0698 3.4745 3.4745 5.06985.0698 88 6 6 1500 1500 3.6968 3.6968 2.1382 2.1382 3.69683.6968 88 7 7 1182 1182 2.6149 2.6149 1.0851 1.0851 2.6149 2.6149 88 4.5.2.3.2

4.5.2.3.2 Calculation of thickness byCalculation of thickness by

Variable-Design-Point

Method

Design using variable-design-point Design using variable-design-point method gives shell thickness at design method gives shell thickness at design points that in the calculated stressed points that in the calculated stressed being relatively closed to the actual being relatively closed to the actual circumferential shell stress.

circumferential shell stress.

This method normally provides a This method normally provides a reduction in shell-course thickness and reduction in shell-course thickness and total material weight, but more total material weight, but more important is its potential to permit important is its potential to permit construction of large diameter tanks construction of large diameter tanks within the maximum plate thickness within the maximum plate thickness limitation.

limitation.

This method may only be used when This method may only be used when 1-foot method is not specified and 1-foot method is not specified and when the following is true:

when the following is true:



==





L =

(

())





t = bottom-course shell thickness, in t = bottom-course shell thickness, in mm

mm 4.5.2.3.3

4.5.2.3.3 Elastic Analysis methodElastic Analysis method

For tanks where L / H are greater than For tanks where L / H are greater than 1000/6, the selection of

1000/6, the selection of shell thicknessshell thickness shall be based on an elastic analysis shall be based on an elastic analysis that shows the calculated that shows the calculated circumferential shell stress to be circumferential shell stress to be below the allowable stress.

below the allowable stress. 4.4.2.1

(21)

Figure 4-12 Loading Diagram Figure 4-12 Loading Diagram

4.5.2.3.4

4.5.2.3.4 Weight LoadsWeight Loads

When designing a tank and its When designing a tank and its foundation, the design engineer must foundation, the design engineer must consider the weight loads which are consider the weight loads which are the weight of the tank and the the weight of the tank and the maximum weight of its contents.

maximum weight of its contents.

Since most petroleum products are Since most petroleum products are lighter than water, the heaviest weight lighter than water, the heaviest weight load occurs during hydrostatic testing, load occurs during hydrostatic testing, which is done using water.

which is done using water. 4.5.2.3.5

4.5.2.3.5 Total PressureTotal Pressure

4.5.2.3.5.1

4.5.2.3.5.1 Hydrostatic pressureHydrostatic pressure

The specific gravity of the liquid that is The specific gravity of the liquid that is being stored, (G), in conjunction with being stored, (G), in conjunction with the depth of the liquid, determines the depth of the liquid, determines the hydrostatic pressure of the liquid, the hydrostatic pressure of the liquid, as illustrated in

as illustrated in Figure 4-12Figure 4-12. The total. The total hydrostatic pressure at a given hydrostatic pressure at a given elevation in a tank must be considered elevation in a tank must be considered in determining the required thickness in determining the required thickness of the tank shell. The specific gravity of of the tank shell. The specific gravity of the stored liquid must be specified on the stored liquid must be specified on the Storage Tank Data Sheet (API-650 the Storage Tank Data Sheet (API-650 Appendix L).

Appendix L).

Figure 4-13 Hydrostatic Pressure in a Storage Figure 4-13 Hydrostatic Pressure in a Storage Tank

Tank

4.5.2.3.5.2

4.5.2.3.5.2 Vapor pressureVapor pressure

The internal pressure at which a The internal pressure at which a storage tank will operate determines storage tank will operate determines which API standard is to be used for which API standard is to be used for the mechanical design of the tank and the mechanical design of the tank and

its associated components. API-650, its associated components. API-650, Welded Steel Tanks for Oil Storage Welded Steel Tanks for Oil Storage, is, is the design standard for tanks that the design standard for tanks that operate at internal pressures operate at internal pressures approximating atmospheric pressure. approximating atmospheric pressure. API-650 may also be used for tanks API-650 may also be used for tanks that operate at internal pressures up that operate at internal pressures up to 17 kPa (ga; 2.5 psig); however, to 17 kPa (ga; 2.5 psig); however, additional design requirements that additional design requirements that are contained in API-650 Appendix F are contained in API-650 Appendix F must be followed if the internal must be followed if the internal pressure exceeds atmospheric pressure exceeds atmospheric pressure. The internal operating pressure. The internal operating pressure is determined by process pressure is determined by process engineers based on the operating engineers based on the operating requirements of the stored

requirements of the stored 4.5.2.3.6

4.5.2.3.6 Roof Live LoadRoof Live Load

The weights of items on the roof that The weights of items on the roof that are not a part of the permanent are not a part of the permanent structure. structure.   PersonnelPersonnel   EquipmentEquipment 

 Rainwater & dustRainwater & dust

4.5.2.3.7

4.5.2.3.7 Wind LoadsWind Loads

A strong wind can overturn or slide a A strong wind can overturn or slide a tank off its foundation or cause a tank tank off its foundation or cause a tank wall to collapse. Empty tanks are wall to collapse. Empty tanks are especially vulnerable to wind forces. especially vulnerable to wind forces. Wind forces acting on tank Wind forces acting on tank appurtenances, such as platforms and appurtenances, such as platforms and ladders, can overload these ladders, can overload these appurtenances or their attachments to appurtenances or their attachments to the tank. The pressure due to the wind the tank. The pressure due to the wind varies around the circumference of varies around the circumference of the tank from a high pressure on the the tank from a high pressure on the windward side to a low pressure windward side to a low pressure (vacuum) on the leeward side. The (vacuum) on the leeward side. The effects of wind increase with effects of wind increase with

tankdesign

Storage tank Design

Storage tank Design

Email:[email protected]

Email:[email protected]

4

4

Tanks

Tanks

4.1

4.1

Introduction

Introduction

4.2

4.2

Types and Functions of

Types and Functions of

Storage Tanks

Storage Tanks

4.2.1

4.2.1

Atmospheric Storage

Atmospheric Storage

Tanks

Tanks

4.2.2

4.2.2

Low-Temperature

Low-Temperature

Storage Tanks

Storage Tanks

4.2.3

4.2.3

Low-Pressure Storage

Low-Pressure Storage

Tanks

Tanks

4.3

4.3

Storage Tank Design

Storage Tank Design

Specifications

Specifications

4.3.1

4.3.1

Standards and

Standards and

Specifications

Specifications

4.4

4.4

Floating Roof Tanks

Floating Roof Tanks

4.4.1

4.4.1

Principles of the Floating

Principles of the Floating

Roof

Roof

4.4.2

4.4.2

Advantages of the

Advantages of the

floating roof storage tank

floating roof storage tank

4.5

4.5

Design Considerations

Design Considerations

4.5.1

4.5.1

Material Selection and

Material Selection and

Corrosion Assessment

Corrosion Assessment

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