Sulphuric Acid Storage Tank

DESIGN OF AN ABOVE GROUND SULPHURIC ACID STORAGE TANK

Final Year Project Report

Group: 53

Batch: 2009-2010

Muhammad Anas

ME-09139

S.M Ali Asad Jafri

ME-09185

Mirza Noman Baig

ME-09322

Irfan Khan Lodhi

ME-09070

Internal Advisor: Mr. Akhlaque Ahmed Assistant Professor Department of Mechanical Engineering

Reference#: 53/2013

DEPARTMENT OF MECHANICAL ENGINEERING NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY

CERTIFICATE It is to certify that the following students have completed their project “Design of an above ground Sulphuric acid tank" satisfactorily.

Group: 53

Batch: 2009-2010

Name

Seat No.

Muhammad Anas

ME-09139

S.M Ali Asad Jafri

ME-09185

Mirza Noman Baig

ME-09322

Irfan Khan Lodhi

ME-09070

Internal Advisor Mr. Akhlaque Ahmed Assistant Professor

Project Coordinator Dr. Muhammad Shakaib Associate Professor

DEPARTMENT OF MECHANICAL ENGINEERING NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY

ACKNOWLEDGEMENTS

The special thank goes to our helpful teacher, Mr. Akhlaque Ahmed -Assistant Professor Mechanical Department (NEDUET).The supervision and support that he gave truly help the progression and smoothness of the Storage Tank Design. The co-operation is much indeed appreciated.

Our grateful thanks also go to Mr. Ahmed Mustafa – Manager at Engro Polymer . A big contribution and hard worked from him during the project is very great indeed. All practical concepts and knowledge during the project would be nothing without the enthusiasm and imagination from him. Besides, this project makes us realized the value of codes & standards in designing of mechanical elements, which challenges us every minute. Not forget, great appreciation go to the rest of classmates that help us from time to time during the project. The whole project really brought us together to appreciate the true value of friendship and respect of each other.

Last but not least we would like to thank Mr. Ahmed Mustafa – Manager at Engro Polymer for providing free demo version of Etank2000 that truly helps in verification of our results. Finally, Special thanks also to Dr. Muhammad Shakaib – Project Coordinator, that have encouraged, support and help us in completing this course successfully.

ii

ABSTRACT

This project represents the designing of storage tank. It includes sufficient information and knowledge on how a storage tank is designed and which parameters are considered while designing a storage tank according to codes and standard.

Storage tanks have been widely used in many industrial particularly in the oil refinery and petrochemical industry which are to store a multitude of different product with Sulphuric acid as one of it.

There are various industrial code and standard available for the basic requirement for tank design and construction. Design and safety concern has been a great concern for the increasing case of fire and explosion due the tank failure.

Although every effort has been made to obtain the most accurate solutions, it is the nature of engineering that certain simplifying assumption is made. Solutions achieved should be viewed in this light, and where judgment is required, they should be made with due concentration.

This project describes different classification of storage tank followed by the description of major components of a storage tank. The calculations are made as per API 650 code.

iii

TABLE OF CONTENTS Contents

Page No

Acknowledgements

ii

Abstract

iii

List of figures

x

List of Tables

xii

2.2

Types of Storage Tanks………………………………….………………..5

2.2.1

Classification Based on Internal Pressure…………….………………….6

2.2.1.1

Atmospheric Tanks……………………………………………….……….6

2.2.1.2

Low Pressure Tanks………………………………………………………6

2.2.1.3

High Pressure Tanks………………………………………………………6

2.2.2

Classification Based on Roof Type………………………………………8

2.2.2.1

Fixed Roof Tanks……………………………………………...…………8

2.2.2.1.1

Cone Roof Tanks…………………………………………………………10

2.2.2.1.2

Umbrella Roof Tanks…………………………………………………….11

2.2.2.1.3

Dome Roof Tanks………………………………………………………..11

2.2.2.2

Floating Roof Tanks………………………………………….…..………12.

2.2.2.2.1

Internal Floating Roof ……………………………………………...…….12

2.2.2.2.2

External Floating Roof…………………………………………………. 13

2.3

Process Description and Requirements…………………..………………..14

2.4

Design Factors considered in the Design of Storage Tanks……..………..15

2.4.1

Metal Temperature………………………………………………………...15

2.4.2

Pressure …………………………………………………………….……..15

2.4.3

Specific Gravity…………………………………………………………….16

2.4.4

Corrosion Allowance…………………………………………….………….17

2.4.5

Other Loads…………………………………………………...…………….18

2.5

Mechanical Design………………………………………………..……..….19

2.6

Mechanical Design Considerations…….…………………………………...20

2.7

Tank Assembly………………….…….……………………………….…22

iv

2.7.1

Shell Attachments………………………………………………...………22

2.7.1.1

Permanent Attachments…………………………………………………..22

2.7.1.2

Temporary Attachments………………………………………….……....22

2.7.2

Tank Venting………………………………………….………………….22

2.7.3

Wind Girder……………………………………….…….………………..23

2.7.3.1

Secondary Wind Girder……………….………………………………….23

2.7.4

Clean-out Doors…………………………………………………...……..23

2.7.5

Stairways and Handrails.…………………………………………………24

2.7.6

Drainage arrangement….……………………………………………...…24

2.7.7

Nozzles………………….………………………………………………..25.

2.7.8

Manholes………………………………………………………...…….…25

2.7.9

Anchor Bolts……………………………………………………………..26

3.

INTRODUCTION TO API………………………….………………………..27

3.1

Introduction…………………………..………………………………………27

3.2

Standards and certification………………………………..………………….27

3.3

API 650 (Welded steel tanks for oil storage)…………………………………28

3.3.1

Scope…………………………..……………………..…………………….29

3.3.2

Materials…………………………………………….……………………..29

3.3.3.

Design………………………….………………….……………………….30

3.3.3.1 Welded Joints………………..…………………………………………….30 3.3.3.1.1 Double-welded butt joint…….………………………………………….30 3.3.3.1.2 Single-welded butt joint with backing….……………………………….30 3.3.3.1.3 Double-welded lap joint ……..……………………………….………..30 3.3.3.1.4 Single-welded lap joint…………………..……………………….…….30 3.3.3.1.5

Butt-weld……………………………….…… ………………………..30

3.3.3.1.6

Fillet weld………………………………………………….………….30.

3.3.3.1.7

Full-fillet weld………………………….……………………………..30

3.3.3.1.8

Tack weld …………………………………………………………….30

3.3.3.2

Weld Size…………………………………………………..…………..30

3.3.3.3

Restrictions on Joints………………………………………...…………30 v

3.3.3.4

Typical Joints……………………….......……………………..……31

3.3.3.4.1

Vertical Shell Joints…………………………………………………31

3.3.3.4.2

Horizontal Shell Joints………………………………………………31

3.3.3.4.3

Lap-Welded Bottom Joints……………….…………………………31

3.3.3.4.4

Butt-Welded Bottom Joints……………….………………...………31

3.3.3.4.5

Bottom Annular-Plate Joints………………………………...………31

3.3.3.4.6

Shell-to-Bottom Fillet Welds………………..………………………31

3.3.3.4.7

Wind Girder Joints…………………………………..………………31

3.3.3.4.8

Roof and Top-Angle Joints……………………….…………………32

3.3.3.5

Loads………………………………………………………………..32

3.3.3.5.1 Dead load (DL) ………………………….…………………………..32 3.3.3.5.2

Stored liquid (F)……………………………………...……………..32

3.3.3.5.3

Hydrostatic test (Ht)………………………………….……………..32

3.3.3.5.4

Minimum roof live load (Lr)………………………….……………32

3.3.3.5.5

Snow (S)………………………………….................…………….. 32

3.3.3.5.6

Wind (W) …………………………………………...……………..32

3.3.3.5.7

Design internal pressure (Pi) ………………………………………32

3.3.3.5.8

Design external pressure (Pe)………………………………………32

3.3.3.5.9

External Pressure………………………………………...…...……32

3.3.4

Marking……………………………………...……………………..33

3.3.4.1

Nameplates…………………………………..…………………….33

4.

TANK DESIGN…………………………………………………………34

4.1

Introduction………………………………………….……………..……34

4.2

Shell Design…………………………………………….………………..34

4.3

Calculating Shell Thickness…………………………………..………….35 vi

4.3.1

One-Foot Method…………………………………..…………….……35

4.3.2

Variable Design Point Method……………………………..……….…35

4.4

Shell Design by one foot method………………………………………36

4.4.1

Longitudinal Stress…………………………………………..…………37

4.4.2

Circumferential Stress …………………..……………………..………37

4.4.3

Longitudinal Stress versus Circumferential Stress…..…………………38

4.4.4

Circumferential Stress Thickness Equation and 1-Foot Method……

4.5 4.5.1

Top Stiffener and Intermediate Wind Girder Design………………..…39 Top Stiffener/ Top Wind Girder……………………………………..…39

4.5.2

Intermediate Wind Girder………………………………………………40

4.6

Bottom Plate Design…………………………………………….………43

4.7

Roof Design………………………………………………………..……44

4.8

Overturning Stability against Wind Load…………………………….…45.

4.9

Seismic Design…………………………………………………………..47

4.9.1

Overturning Stability against seismic load……………..…….…………47

4.10

Anchorage requirement………………………………………………….48

. 5. 0

DESIGN CALCULATIONS……………………………………………50

5.1

Material Selection ……………………………………………………….50

5.2

Design Specifications…………………………………………………….51

5.3

Basic Calculation…………………………………...…………………….52

5.4

Shell Design………………………………………………………………53

5.5

Bottom Plate Design ………………………………...………....…………56

5.6

Annular Plate Design………………………………...……………………56

5.7

Intermediate Wind Girder…………………………………………………58

5.8

Roof Design (Supported Conical Roof )……………..……………………61

vii

39

5.8.1 Roof Plate Design…………………………………………………………….61 5.9

RAFTER DESIGN ……………………………...………..…………….........63

5.10 COLUMN DESIGN…………………………………………………….……64 5.11

Tank Overturning Stability………………………………….…………..……68

5.12.1 RESISTANCE TO OVERTURNING (per API-650 5.11.2) …………….. 71 5.12.2 Stability of Tank against Seismic Load ………………………………….... 73 5.12.3 SEISMIC VARIABLES …………………………………………………….74 5.12.4 STRUCTURAL PERIOD OF VIBRATION………………………………..76 6.0

RESISTANCE TO DESIGN LOAD… …………………………………….77

6.1

EFFECTIVE WEIGHT OF PRODUCT ……………………………...……..77

6.1.1

DESIGN LOADS ……………………………………………………………77

6.2.1

CENTER OF ACTION FOR EFFECTIVE LATERAL FORCES …… …..78

6.2.2

CENTER OF ACTION for RINGWALL OVERTURNING MOMENT…...78

6.2.3

CENTER OF ACTION for SLAB OVERTURNING MOMENT ………….79

6.2.4

Dynamic Liquid Hoop Forces ……………………………………………….79

6.2.5

Overturning Moment …………………………………………………….…..80

6.2.6

RESISTANCE TO DESIGN LOADS…………………...…………………..80

6.3

ANCHOR BOLT DESIGN…………………………………………………..83

6.4

CAPACITIES and WEIGHTS ………………………………...……………..87

7.0 DEVELOPMENT OF STORAGE TANK DESIGN SOFTWARE & VERIFICATION OF RESULTS USING ETANK 2000…………………………….93 7.1

Overview………………………………………………………………..……..93

7.2

Design Capabilities…………………………………………………………….93

7.3

Key Features…………………………………… ……………………………93

7.4

Application Areas…………………………………………………………….93 viii

7.5

Visual Basic Programming for Shell Design………………………………….94

7.6

VERIFICATION OF RESULTS……………………………………………..101

CONCLUSION……………………………………………………………………..103 REFERENCES………………………………………………...……………………104 APPENDIX…………………………………………………………………………105 Appendix C Shell Design………………………………………………………..…..107 Appendix D Bottom and annular Plate Design…………………….………………..110 Appendix E Intermediate wind girder …………………………….………………..112 Appendix F Roof Design……………………………………………………………114 Appendix G Tank overturning stability…………………………….……………….117

ix

LIST OF FIGURES Figure 1

Types of Tank ............................................................................................. 4

Figure 2

Tanks on the basis of internal pressure ..................................................... 7

Figure 3

Fixed roof tank ........................................................................................... 8

Figure 4

Fixed roof tank ........................................................................................... 9

Figure 5

Steel tank with cone roof .......................................................................... 10

Figure 6

Cone roof tank with column supports ...................................................... 10

Figure 7

Umbrella Roof Tank……………………………………………………………11

Figure 8

Dome roof tank ........................................................................................ 11

Figure 9

Internal floating roof tank........................................................................ 12

Figure 10

External floating roof tank ....................................................................... 13

Figure 11

Storage tank capacities and levels shell .................................................. 14

Figure 12

Hydrostatic pressure in a storage tank .................................................... 16

Figure 13

Corrosion allowance in a tank shell ........................................................ 17

Figure 14

Wind and earthquake loads ..................................................................... 18

Figure 15

Tank exploding ......................................................................................... 20

Figure 16

Loading diagram on a tank shell ............................................................. 21

Figure 17

Tank Venting……………………………………………..……………………..22

Figure 18

Wind Girder placement on shell…………………………..………………… 23

Figure 19

Cleanout Door……………………………………………….…………………..23

Figure 20

Stairways and handrails………………………………….………..………..…24

Figure 21

Nozzle………………...……………………………………………….…………25

Figure 22

Manholes…………………..……………..….….………………………………25

Figure 23

Anchor Bolts………………..……………….….………………….…………...26

Figure 24

Name Plates of storage tanks…………….….………………..………………33

Figure 25

Diagramatic variation of stress in a shell.….……………………………….34

Figure 26

Thickeness of tank shell courses……………..…………….…………………35

Figure 27

Longitudinal forces acting on thin cylinder…..………………………..……37

Figure 28 Circumferential forces acting on thin cylinder ...………..………………....38 Figure 29 Stiffener rings……..………………………………………….….…………….....39 Figure 30

Wind girders…………………………………………………………………….41

Figure 31

Transformed shell and intermediate wind girder…………………………..42

Figure 32

Bottom Layout for tank…………………………………………………….......43

Figure 33

Cross joints in bottom plates…………….……………………………............44 x

Figure 34

Overturning moment against wind load.…………………………..…………45

Figure 35

Shell out of roundness caused by wind……………………………………….45

Figure 36

Roof Segments………………………………………………..……...…………..62

Figure 37

Compression ring at shell to roof joint…………………….…………………64

Figure 38

Selected Plate Size………………………………………………………………76

Figure 39

Surface development of shell ………………….……………..….……………77

Figure 40

Construction of upper shell course- inside tank..…………….……………..78

Figure 41

Construction of upper shell course- outside tank …..………………………78

Figure 42

Bottom plate arrangement on foundation……………………………………80

Figure 43

Arrangement of bottom plates…………………………………………………81

Figure 44

3D model of storage tank……………….……………….……… .……………83.

Figure 45

3D model of storage tank ……………………………..………………………..84

Figure 46

Arrangement of stiffener at roof…………………….…………………………85

Figure 47

Snapshot of software……………………………………………………………87.

Figure 48

Design report showing hydroststic and design thickness…………………..87

Figure 49

Message box indicating compeltion of calcuklations……………….……….93

Figure 50

Output Results……………………………………………………………………..94

Figure 51

Verification of results thriugh E-Tank………………………………………….95

xi

LIST OF TABLES Table 1:

Pepsi can and storage tank comparison table………………………………..19

Table 2:

Anchorage ratio criteria [API 650,2007]……………………………………..48

Table 3:

BOQ for shell arrangement………………………………………………………79

Table 4:

BOQ for bottom plate arrangement…………………………..…………………82

xii

CHAPTER 1: INTRODUCTION 1.1 Rationale Storage tanks have been widely used over the world in many industries. They are designed, fabricated and tested to code and standard. There are a variety of codes and standards stating the similar common minimum requirements and some additional requirements from company standards or specifications. Engineer or tank designer who do the preliminary and detail design are normally not familiar or not exposed to the actual site condition. Their designs are basically based on the code and standard requirements and basic theory from reference book. Some would only rely on the commercial software for the basic design, they have limited knowledge on the actual tank operation which limit them on cost effectiveness and even safety detail design. There is limited procedure and rules in design the fixed and floating roof tanks. These had resulted lots of roof failure in the industry. Hence industry, tank owner and also the tank designer or engineer need to have a simple rules and formula to ensure the roof is adequately designed and strong enough for the various loading during operation. Beside of the procedures and rules, understanding of the stresses behave in the tank material is essential for a complete safe design. Hence it is essential for the engineers or tank designer to know how and what effects each inter discipline design would have on one’s tank that affected the tank integrity, and taking all these consideration into his design.

1.2 Project Goal 1.2.1Project Aim The aim of this project is to follow basic rules and procedures, highlighting the concerns in designing of a fixed roof tank.

1.2.2Project Objective The main objective of this project is “To design an above ground Suphuric acid storage tank.

1

1.3 Project Methodology 1.3.1 Literature Review Literature review is conducted to study the basic design and requirement of the fixed roof storage tank in the storage tank design code (API 650 – Welded Steel Tanks for Oil Storage).

1.3.2Design Approach Upon completion of the literature review, design approach is then developed. The storage tank design consists of two major designs, that is (1) the shell design analysis and (2) the roof design. In the shell design analysis, shell stress design will be performed taking into consideration of all the considerably loading including hydrostatic pressure, wind loading and seismic loading. In the roof design, it consists of two sections, that is (1) roof stress design and the (2) roof fitting and accessories design.

1.4 Perspective view on Standards and Codes Industries that require the storage of flammable and combustible liquids face a complex array of codes and standards with which they must comply. Besides adhering to environmental regulations, underground and aboveground tank systems must be sited and operated in accordance with local building and fire codes.

1.4.1 What is a standard? A standard is a series of requirements that tell you how to do something. A standard tends not to have any enforcement requirements. A standard becomes an enforceable document when it is adopted by reference in a code.

1.4.2 What is a code? A code is a set of regulations that tells you when to do something. A code will have requirements specifying the administration and enforcement of the document.

1.4.3How Does a Code or Standard Become Enforceable? A code or standard becomes enforceable when it is adopted by reference through local, state, or federal government legislative process, such as an ordinance, statute, or bill. The law must adopt a specific edition (year of publication) of a code or standard, and may include amendments to specific portions of the code or standard being adopted.

2

CHAPTER 2: LITERATURE REVIEW 2.1 Introduction Storage tanks have been widely used in many industrial established particularly in the processing plant such as oil refinery and petrochemical industry. They are used to store a multitude of different products. They come in a range of sizes from small to truly gigantic, product stored range from raw material to finished products, from gases to liquids, solid and mixture thereof. Liquids and vapors in the petroleum industry, usually called petroleum liquids or vapors generally are mixtures of hydrocarbons having dissimilar true vapor pressures. Examples would include jet fuel diesel, gasoline and crude oil. Liquidsandvaporsinthechemicalindustry,usuallycalledvolatileorganicliquidsand vapor, are composed of pure chemicals or mixtures of chemicals with similar true vapor pressures. Examples would include benzene, styrene, and alcohols. There are a wide variety of storage tanks, they can be constructed above ground, in ground and below ground. In shape, they can be in vertical cylindrical, horizontal cylindrical, spherical or rectangular form, but vertical cylindrical are the most usual used. In a vertical cylindrical storage tank, it is further broken down into various types, including the open top tank, fixed roof tank, external floating roof and internal floating roof tank. The type of storage tank used for specified product is principally determined by safety and environmental requirement. Operation cost and cost effectiveness are the main factors in selecting the type of storage tank. .

.

3

2.2 Types of Storage Tanks

Types Of Storage Tanks

Based On Internal Pressure

Based On Roof type

Atmospheric Tanks

Fixed Roof Tanks

Floating Roof Tanks

Low Pressure Tanks

Cone Roof

Internal Floating Roof

High Pressure Tanks

Umbrella Roof

External Floating Roof

Dome Roof

Figure 1Types of storage tank

4

2.2.1 Classification Based on Internal Pressure In the case the internal pressure reacts on the tank during storage, it is possible to classify the tanks based on this level of pressure. This pressure effect depends directly of the size of the tank. The larger the tank, the more severe effect of pressure is on the structure. This classification is commonly employed by codes, standards and regulations all over the world.

2.2.1.1

Atmospheric Tanks

These tanks are the most common. Although they are called atmospheric, they are usually operated at internal pressure slightly above atmospheric pressure. The fire codes define an atmospheric tank as operating from atmospheric up to 3.5 kN/m2above atmospheric pressure.

2.2.1.2 Low-Pressure Tanks Within the context of tanks, low pressure mean that tanks are designed for a pressure higher than atmospheric tanks. Tanks of this type are designed to operate from atmospheric pressure up to about 100 kN/m2.

2.2.1.3 Pressure Vessels (High-Pressure Tanks) Since high-pressure tanks are really pressure vessels, the term high-pressure tank is not frequently used; instead they are called only vessels. Because these kinds of tanks are usually built underground, they are treated separately from other tanks by all codes, standards, and regulations.

5

Figure 2Tanks on the basis of Internal Pressure

6

2.2.2 Classification based on Roof Type 2.2.2.1 Fixed Roof Tanks Fixed Roof Tanks can be divided into cone roof, umbrella roof and dome roof types. They can be self-supported or rafter/ trusses supported depending on the size. Of currently used tank designs, the fixed-roof tank is the least expensive to construct and is generally considered the minimum acceptable equipment for storing VOL's (volatile organic liquids).A typical fixed-roof tank consists of a cylindrical steel shell with a cone- or domeshaped roof that is permanently affixed to the tank shell. Most recently built tanks are of allwelded construction and are designed to be both liquid-and vapor-tight. For fixed-roof tanks, the nominal capacity is the geometric volume from the bottom of the tank up to the cur bangle, which is a metallic angle that is welded along the periphery at the top of the cylindrical portion of the tank.

Figure3FixedRoofTank

7

Figure4FixedRoofTank

8

2.2.2.1.1Cone Roof Tanks Cone-roof tanks have also cylindrical shells in the lower part. These are the most widely used tanks for storage of relatively large quantities of fluid. They have a vertical axis of symmetry; the bottom is usually flat land the top is made in the form of shallow cone. They are economical to build and the economy supports a number of contractors capable of building them. Cone-roof tanks typically have roof rafters and support columns excepting very small-diameters tanks.

Figure5Steel Tank with cone-roof

Figure 6Cone-rooftankwithcolumnsupports 9

2.2.2.1.2 Umbrella-Roof Tanks They are very similar to cone-roof tanks, but there of looks like an umbrella. They are usually constructed with diameters not much larger than 20 m. Another difference is that the umbrella-roof does not have to be supported by columns to the bottom of the tank, so that they can be a self-supporting structure.

Figure7UmbrellaRoofTank

2.2.2.1.3 Dome-Roof Tanks This type has almost the same shape of the umbrella type except that the dome approximate a spherical surface more closely than these gentled sections of an umbrella-roof. There are several ways to fabricate such tanks. One of the known as the tank airlift method, "in which the roof and the upper course of shell are fabricated first, then lifted by air that is blown in to the tanks as the remaining lower courses of steel shell are welded into place”.

Figure8DomeRoofTank 10

2.2.2.2 Floating Roof Tanks Floating roof tanks is which the roof floats directly on top of the product. There are 2 types of floating roof:

2.2.2.2.1 Internal Floating Roof Internal floating roof tank is the one in which the roof floats on the product in a fixed roof tank.

Fixed-roof center vent

Peripheral roof vents

Fixed roof column supported

Rim seal

Tank shell

Sample port Vacuum breaker Gage head

Ladder

Fixed roof Supported column

Deck leg

Deck drain

Access hatch

Figure9InternalFloatingRoof Tank

11

2.2.2.2.2External Floating Roof External floating roof tank is the one in which the roof floats on the product in an open tank and the roof is open to atmosphere.

Figure10ExternalFloatingRoofTank

12

2.3 Process Description and Requirements Capacity determination is the one of the first steps in designing the tank. Only after the capacity is known, the tank can be sized up. The definition of the maximum capacity can be explained easily in figure below.

Figure 11 Storage Tank Capacities and Levels shell

The maximum or total capacity is the sum of the inactive capacity (minimum operating volume remaining volume in tank), actual or net-working capacity and the-overfill protecting capacity. The net-working capacity is the volume of available product under normal operating conditions, which is between the low liquid level (LLL) and the high liquid level (HLL).

13

2.4 Design Factors that are considered in the Mechanical Design of Storage Tanks This section discusses the primary factors that are considered in the mechanical design of storage tanks. These factors are as follows: 1. Metal temperature 2. Pressure 3. Specific gravity of the stored liquid 4. Corrosion allowance 5. Other loads

2.4.1 Metal Temperature The metal temperature of storage tank components is determined by the operating requirements of the stored liquid, and by the ambient temperature at the tank location. The operating requirements and operating conditions of the stored liquid are determined by process engineers. The mechanical design of storage tank components must consider both the highest and the lowest temperatures to which the tank can be exposed. The maximum operating temperature determines the allowable stress that is used for the mechanical design of storage tank components. The allowable stress of each specific material is constant for all temperatures up to 93°C (200°F); however, the allowable stress of each material decreases for temperatures that are above 93°C (200°F). API-650 Appendix M contains additional design criteria that must be followed for tanks that have maximum operating temperatures over 93°C (200°F). The tank could experience a permanent deformation or a ductile fracture if the design requirements of API-650 Appendix M are not followed.

2.4.2 Pressure The internal pressure at which a storage tank will operate determines which API standard is to be used for the mechanical design of the tank and its associated components. API-650, Welded Steel Tanks for Oil Storage, is the design standard for tanks that operate at internal pressures approximating atmospheric pressure. API-650 may also be used for tanks that operate at internal pressures up to 17 kpa; however, additional design requirements that are contained in API-650 Appendix F must be followed if the internal pressure exceeds atmospheric pressure.

14

2.4.3 Specific Gravity of Stored Liquid The specific gravity of the liquid that is being stored, (G), in conjunction with the depth of the liquid determines the hydrostatic pressure of the liquid. The total hydrostatic pressure at a given elevation in a tank must be considered in determining the required thickness of the tank shell.

Figure 12 Hydrostatic Pressure in a Storage Tank

Storage tanks must be designed for the specific gravity of water (1.0), because the tanks are filled with water for testing purposes after they are constructed. If the specific gravity of the liquid that is to be stored exceeds 1.0 (water), the tank must be designed for the higher specific gravity. The required shell thickness is directly proportional to the specific gravity of the stored liquid. If the specific gravity is not correctly specified, the calculated shell thickness will be incorrect. In extreme cases, the shell can become permanently deformed if it is too thin, and a ductile fracture may occur. It may be desirable for operational reasons to change the liquid that is being stored after the tank has been in service for some period of time. In situations where the stored liquid is changed, the tank must be evaluated based on the specific gravity of the new liquid.

15

2.4.4 Corrosion Allowance The components of a storage tank may lose metal due to corrosion that is caused by the stored liquid. To compensate for this metal loss, a "corrosion allowance" (CA) may be added to the metal thickness that is required for strength. This "corrosion allowance" offsets the expected deterioration of the tank components while they are in service. When needed, the corrosion allowance is typically added to the calculated required thicknesses of the shell, internal components, and structural members that may be used to support a fixed roof. A corrosion allowance is typically not added to the required thicknesses of the roof itself or the bottom.

Figure 13 Corrosion Allowance in Tank Shell Where t = Minimum required shell thickness T = Total required shell thickness CA = Corrosion allowance

16

2.4.5 Other Loads The mechanical design of a storage tank must also consider loads other than pressure. These other loads include wind and earthquake, loads that are imposed by connected piping systems (and other attachments) on nozzles, and rainwater accumulation on the roof of tanks.

Figure 14Wind and Earthquake Loads

Where Fw= Base shear force due to wind M = Overturning moment due to wind or earthquake

17

2.5 Mechanical Design Stress design and analysis of the storage tank is the greatest concern to engineer as it provides the basic for the tank stability and integrity. The basic stress analyses to be taken care in tank design are as follow:  Tank shell wall due to internal and external loading  Bottom plate/ Tank flooring Storage tanks always look big and strong, and there are also often being referred as ‘tin can’. Some simple comparison in term of their sizes and strength is made here.

Table 1 Pepsi Can and Storage Tank Comparison Table

From the Table 1, it can be seen found the tank ratio (t/D) is 4 times less than the typical bean can which show that how relatively flimsy the shell of the tank it would be if it is subjected to partial vacuum. Figure 19 shows tank exploding due to vacuum loading.

18

Figure 15Tank Exploding

2.6 Mechanical Design Consideration The principal factors in determine the shell thickness is the loads, the primary loading to determine the basic shell thickness is as follow:  The internal loading due to the head of liquid  The pressure in the vapor space Other external loading shall be taken into consideration are:  External pressure-Vacuum condition  Wind loading  Seismic Loading  Localized loads resulting from nozzles, attachments, ladder/ stair and platform etc.

19

Figure 16Loading Diagram on a Tank Shell

The internal pressure exerted on the tank shell is the product liquid head; the pressure is at the highest at the tank shell bottom and decreases linearly along its height. External loading of wind and seismic act on the tank shell and create an overturning moment about the shell to bottom joint, this result in the uplift reaction of the tank and affected the tank stability. The various stresses to which the shell of a tank is subjected are:  Hoop tension This is caused by the head of product in the tank, together with any over pressure in the roof space of a fixed roof tank.  Axial compression This comes from the tank self-weight, internal vacuum, wind and seismic loading acting on the shell which causes an overturning effect.  Vertical bending This is due to the expansion of shell under normal service loading.

20

2.7 TANK ASSEMBLY 2.7.1 Shell Attachments 2.7.1.1 Permanent Attachments Permanent attachments are items welded to the shell that will remain while the tank is in its intended service. These include items such as wind girders, stairs, gauging systems, davits, walkways, tank anchors, supports for internal items such as heating coils and other piping supports, ladders, floating roof supports welded to the shell, exterior piping supports, grounding clips, insulation rings, and electrical conduit and fixtures. Items installed above the maximum liquid level of the tank are not permanent attachments.

2.7.1.2 Temporary Attachments Temporary attachments are items welded to the shell that will be removed prior to the tank being commissioned into its intended service. These include items such as alignment clips, fitting equipment, stabilizers, and lifting lugs.

2.7.2 Tank Venting Suitable vents shall be provided to prevent overstressing of the roof deck or seal membrane. Vents, bleeder valves, or other suitable means shall be adequate to evacuate air and gases from underneath the roof during initial filling Tanks designed in accordance with this standard and having a fixed roof shall be vented for both normal conditions (resulting from operational requirements and atmospheric changes) and emergency conditions (resulting from exposure to an external fire). Normal venting shall be adequate to prevent internal or external pressure from exceeding the corresponding tank design pressures. Emergency venting requirements are satisfied if the tank is equipped with a weak roof-to-shell attachment (frangible joint).

Figure 17 Tank Venting

21

2.7.3 Wind Girder Tank shall be provided with stiffening rings to maintain roundness when the tank is subjected to wind loads. The stiffening rings shall be located at or near the top of the top course, preferably on the outside of the tank shell. Stiffening rings may be made of structural sections, formed plate sections, sections built up by welding. The outer periphery of stiffening rings may be circular or polygonal Rings that may trap liquid shall provided with adequate drain holes.

Figure 18 Wind girder placement on shell

2.7.3.1 Secondary wind girders Tank may require secondary rings to maintain roundness over the full height of the tank shell under wind and/or vacuum conditions. There are basically, additional stiffening rings. Continuous welding (full penetration butt welds) shall be used for all connections of the secondary wind girders.

2.7.4 Clean-out doors If required for tanks made of carbon steel, clean out doors shall be designed and fabricated. This is more for sludge removal and to allow entry of a conveyor belt, if required.

Figure 19 Clean-out doors 22

2.7.5 Stairways and handrails Vertical tanks should be provided with spiral stairways. An exception may be made for groups of tanks of less than 12.5 m diameter sited close together and connected by walkways at roof level. In such groups, two tanks at opposite ends of each group shall be provided with stairways, so that each tank in that group will then have at least two escape routes from the roof. Handrails shall be provided at the edge of the roof for full circumference of all fixed roof tanks and to the center of the roof on all tanks exceeding 12.5 m diameter. Handrails shall be provided on the outside of all spiral stairways. For open top tanks, the inside of the staircases shall also be provided with a handrail in the immediate vicinity of the top landing. Handrails shall be provided on both sides of all walkways between tanks. Stairways shall be provided with the specified lighting facilities.

Figure 20Stairways and handrails 2.7.6 Drainage arrangement – Water draw (Center drains or side drains) In operation, tank bottoms should normally slope down towards the center and be fitted with center sumps. Large tanks (>50 m diameter) may also be provided with additional side drain sumps, the nozzles of which may be blinded off after the water test. However, for products with temperature exceeding 100 , the tank bottom slope up towards the centre in order to prevent corrosion caused by rain water penetrating under the bottom.

23

2.7.7Nozzle When considering the nozzle, one might think that it has to do something with change in velocity and pressure which is the application of Bernoulli’s equation and continuity equation as well. In storage tanks, the nozzle is nothing but just an opening through which either the fluid can enter or leave the storage tank.

Figure 21 Nozzle

2.7.8Manholes Manholes are nothing but big nozzles of sizes more than 16 inch .Usually the pipe section used for manholes will be fabricated pipe from plate. Therefore, for vessels with joint efficiency 1, the long seem weld is category A butt, and hence calls for 100% radiography prior to fit up of the circumferential joint between the flange and the neck. For manholes with fabricated neck, the reinforcement pad is essential and will be provided as per design. In case there is any practical difficulty and placement of reinforcement pad prior to the welding manhole to the shell, it can be inserted into halves provided there are at least two tapped telltale holes on both halves of the pad. A part from these, manufactures of manhole is the same as that of the nozzle.

Figure 22Manholes 24

2.7.9Anchor bolts An anchor bolt is used to attach objects or structures to concrete. There are many types of anchor bolts, consisting of designs that are mostly propriety to the manufacturing companies. All consist of a threaded end, to which a nut and washer can be attached for the external load. Anchor bolts are extensively used on all types of projects, from standard building to dams and nuclear power plants. The simplest anchor bolt is a cast-in-place anchor. Most designs consist of standard bolt with a hexagonal head , which is cast in the wet concrete before it sets .There are other designs, some consisting of a bent bolt with a hook on the end, or some other sort of bending.

Figure 23 Anchor bolts

25

CHAPTER 3: INTRODUCTION TO API STANDARDS

3.1 INTRODUCTION American Petroleum Institute (API) Standards 650, 653 and 620 are the primary industry standards by which most aboveground welded storage tanks are designed, constructed and maintained. These standards address both newly constructed and existing aboveground storage tanks used in the petroleum, petrochemical and chemical industries. API Standards 650, 653, 620, and some related Recommended Practices that have been made over the years or are being developed to improve the standards with respect to leak detection and spill prevention. API and other standards and practices that should be followed to reduce the risk of spills and leaks. API has published standards for the construction of aboveground storage tanks since the mid- 1930’s. API Standards for aboveground storage tanks designed for atmospheric pressures, up to a maximum of 2.5 psig. API Standard 620 is applicable to tanks and vessels designed for low-pressure storage, ranging from about 2.5 psig to 15 psig. The First Edition of API 650 was published in 1961, but its predecessor, API 12C, had been in use since 1936, when welding began to replace riveting as the preferred construction method. Both API 12C and API 650 address only newly constructed tanks. It was not until the late 1980’s that API began development of a new standard to address specific maintenance and inspection issues for existing aboveground storage tanks. This standard is API 653, “Tank Inspection, Repair, Alteration and Reconstruction.” Since the publication of API Standard 653 in 1991, the tank inspection, repair, alteration and reconstruction methods prescribed therein have - when properly applied – significantly improved the safety and reliability of existing tanks. This standard and other API standards are continuously being improved to incorporate new technology and to reflect the actual experiences of owners and operators of aboveground storage tanks.

3.2Standards and Certification The publications, technical standards, and online products are designed, according to API itself, to help users improve the efficiency and cost-effectiveness of their operations, comply with legislative and regulatory requirements, and safeguard health, ensure safety, and (perhaps most controversially) "protect the environment". Each publication is overseen by a committee of industry professionals, mostly member company engineers. These technical standards tend to be uncontroversial. For example, API 610 is the specification for centrifugal pumps, API 675 is the specification for controlled volume positive displacement pumps, both packed-plunger and diaphragm types are included. Diaphragm pumps that use direct mechanical actuation are excluded. API 677 is the standard for gear units and API 682 governs mechanical seals.

26

API provides vessel codes and standards for the design and fabrication of pressure vessels that help safeguard the lives of people and environments all over the world. API also defines and drafts standards for measurement for manufactured products such as:  Precision thread gauges  Plain plug and ring gauges  Thread measuring systems  Metrology and industrial supplies  Measuring instruments  Custom gauges  Precision machining and grinding

3.3 API 650 (WELDED STEEL TANKS FOR OIL STORAGE) API 650 covers material, design, fabrication, erection and testing requirements for aboveground, vertical, cylindrical, closed and open-top, welded steel storage tanks in various sizes and capacities. This standard applies to tanks with internal pressures approximating atmospheric pressure, but ranging as high as 2.5 psig. This standard applies to newly constructed tanks before they have been placed in service. General contents are: 1. 2. 3. 4. 5. 6. 7.

Scope Materials Design Fabrication. Erection Methods Of Inspecting Joints Welding Procedure And Welder Qualifications

8. Marking

27

3.3.1 Scope  This standard covers material design, fabrication, erection, and testing requirements for vertical, cylindrical, aboveground, closed- and open-top, welded steel storage tanks in various sizes and capacities.  Internal pressures approximating atmospheric pressure (internal pressures not exceeding the weight of the roof plates), but a higher internal pressure is permitted when additional requirements are met.  This standard applies only to tanks whose entire bottom is uniformly supported and to tanks in no refrigerated service that have a maximum design temperature of 93°C.  This standard is designed to provide the petroleum industry with tanks of adequate safety and reasonable economy.  This standard does not present or establish a fixed series of allowable tank sizes; instead, it is intended to permit the purchaser to select whatever size tank may best meet his needs.  This standard has requirements given in two alternate systems of units, that is SI Units and US Customary Units. System can be choose by the mutual agreement between manufacturer and purchaser but the condition is that units must be consistent.  The appendices of this standard provide a number of design options requiring decisions by the purchaser, standard requirements, recommendations, and information that supplements the basic standard.  An appendix becomes a requirement only when the purchaser specifies an option covered by that appendix.

3.3.2Materials  Materials used in the construction of tanks shall conform to the specifications listed in this standard.  Conditions of usage of material i.

Approved by the purchaser.

ii.

Material should certify to meet all of the requirements of a material specification listed in this standard.

 New or unused plates should be completely identified by records.

28

 Materials of construction are used that are certified to two or more material specifications.  Plates for shells, roofs and bottoms may be ordered on an edge thickness basis or on a weight(kg/m2 or lb/ft2)  Shell plates are limited to a max thickness of 45mm (1.75in).  Plates used as flanges may be thicker than 45mm (1.75in).

3.3.3Design 3.3.3.1 Welded Joints 3.3.3.1.1 Double-welded butt joint :A joint between two abutting parts lying in approximately the same plane that is welded from both sides. 3.3.3.1.2 Single-welded butt joint with backing :A joint between two abutting parts lying in approximately the same plane that is welded from one side only with the use of a strip bar or another suitable backing material. 3.3.3.1.3 Double-welded lap joint: A joint between two overlapping members in which the overlapped edges of both members are welded with fillet welds. 3.3.3.1.4 Single-welded lap joint: A joint between two overlapping members in which the overlapped edge of one member is welded with a fillet weld. 3.3.3.1.5 Butt-weld: A weld placed in a groove between two abutting members. Grooves may be square, V-shaped (single or double), or U-shaped (single or double), or they may be either single or double beveled. 3.3.3.1.6 Fillet weld: A weld of approximately triangular cross section that joins two surfaces at approximately right angles, as in a lap joint, tee joint, or corner joint. 3.3.3.1.7 Full-fillet weld: A fillet weld whose size is equal to the thickness of the thinner joined member. 3.3.3.1.8 Tack weld: A weld made to hold the parts of a element in proper alignment until the final welds are made.

3.3.3.2 Weld Size: The size of a groove weld shall be based on the joint penetration (that is, the depth of chamfering plus the root penetration when specified).

3.3.3.3 Restrictions on Joints: There are also some restrictions in welded joints mentioned in standards according to the thicknesses and position of sheets/plates. 29

3.3.3.4 Typical Joints 3.3.3.4.1 Vertical Shell Joints: Vertical shell joints shall be butt joints with complete penetration and complete fusion attained by double welding or other means that will obtain the same quality of deposited weld metal on the inside and outside weld surfaces. Vertical joints in adjacent shell courses shall not be aligned but shall be offset from each other a minimum distance of 5t. Where, t is the plate thickness of the thicker course at the point of offset. 3.3.3.4.2 Horizontal Shell Joints: Horizontal shell joints shall have complete penetration and complete fusion; however, as an alternative, top angles may be attached to the shell by a double-welded lap joint. Unless otherwise specified, abutting shell plates at horizontal joints shall have a common vertical centerline. 3.3.3.4.3 Lap-Welded Bottom Joints: Lap-welded bottom plates shall be reasonably rectangular. Additionally, plate may be either square cut or may have mill edges. Mill edges to be welded shall be relatively smooth and uniform, free of deleterious deposits, and have a shape such that a full fillet weld can be achieved. Lapping of two bottom plates on the butt-welded annular plates does not constitute a three-plate lap weld. 3.3.3.4.4 Butt-Welded Bottom Joints: Butt-welded bottom plates shall have their parallel edges prepared for butt welding with either square or V grooves. Butt-welds shall be made using an appropriate weld joint configuration that yields a complete penetration weld. 3.3.3.4.5 Bottom Annular-Plate Joints: Bottom annular-plate radial joints shall be butt-welded in accordance with 3.1.5.5 and shall have complete penetration and complete fusion. The backing strip, if used, shall be compatible for welding the annular plates together. 3.3.3.4.6 Shell-to-Bottom Fillet Welds: For bottom and annular plates with a nominal thickness 12.5 mm (1/2in.), and less, the attachment between the bottom edge of the lowest course shell plate and the bottom plate shall be a continuous fillet weld laid on each side of the shell plate. 3.3.3.4.7 Wind Girder Joints: Full-penetration butt-welds shall be used for joining ring sections. Horizontal bottom-side joints shall be seal-welded if specified by the purchaser. Seal-welding should be considered to minimize the potential for entrapped moisture, which may cause corrosion.

30

3.3.3.4.8 Roof and Top-Angle Joints: Roof plates shall, as a minimum, be welded on the top side with a continuous full-fillet weld on all seams. Butt-welds are also permitted. Roof plates shall be attached to the top angle of a tank with a continuous fillet weld on the top side only.

3.3.3.5 Loads Loads are defined as follows: 3.3.3.5.1 Dead load (DL): corrosion allowance.

The weight of the tank or tank component, including any

3.3.3.5.2 Stored liquid (F): The load due to filling the tank to the design liquid level with liquid with the design specific gravity. 3.3.3.5.3 Hydrostatic test (Ht): The load due to filling the tank with water to the design liquid level. 3.3.3.5.4 Minimum roof live load (Lr): 1kPa (20 lbf/ft²) on the horizontal projected area of the roof. 3.3.3.5.5 Snow (S): The design snow load shall be 0.84 times the ground snow load. Alternately, the design snow load shall be determined from the ground snow load in accordance with ASCE 7. 3.3.3.5.6 Wind (W): The design wind speed (V) shall be 190 km/hr (120 mph), the 3 second gust design wind speed determined from ASCE 7. 3.3.3.5.7 Design internal pressure (Pi): Shall not exceed 18 kPa (2.5lbf/in2). 3.3.3.5.8 Design external pressure (Pe): Shall not be less than 0.25kPa (1 in. of water) and shall not exceed 6.9 kPa(1.01 lbf/in2). 3.3.3.5.9 External Pressure: Tanks that meet the requirements of this standard may be subjected to a partial vacuum of 0.25 kPa (1 in. of water), without the need to provide any additional supporting calculations.

31

3.3.4 Marking 3.3.4.1 Nameplates  A tank made in accordance with this standard shall be identified by a nameplate.  The nameplate shall be attached to the tank shell adjacent to a manhole or to a manhole reinforcing plate immediately above a manhole.  A nameplate that is placed directly on the shell plate or reinforcing plate shall be attached by continuous welding or brazing all around the nameplate.  When a tank is fabricated and erected by a single organization, that organization’s name shall appear on the nameplate as both fabricator and erector.  When a tank is fabricated by one organization and erected by another, the names of both organizations shall appear on the nameplate, or separate nameplates shall be applied by each.

Figure 24 Name plate for a tank 32

CHAPTER 4: TANK DESIGN 4.1 Introduction Storage tank design consists of 2 main sections – Shell Design and Roof Design. The shell design include the shell stress design which is to size up the shell wall thickness, top and intermediate stiffener ring, stability check against the wind and seismic load and sizing up the anchor bolt. The roof design will consist of roof stress design, and the roof accessories and fitting design.

4.2 Shell Design For practical reasons, it is necessary to build up the shell from a number of fairly small rectangular pieces of plate, butt welded together. Each piece will be cylindrically curved and it is convenient to build up the shell in a number of rings, or courses, one on top of the other. This technique provides, at least for deeper tanks, a convenient opportunity to use thicker plates in the lower rings and thinner plates in the upper rings. The lowest course of plates is fully welded to the bottom plate of the tank providing radial restraint to the bottom edge of the plate. Similarly, the bottom edge of any course which sits on top of a thicker course is somewhat restrained because the thicker plate is stiffer.

Figure 25Diagrammatic variation of stress in a shell

33

4.3Calculating Shell Thickness API 650 gives two methods for calculating the required plate thickness for each shell course :the “one-foot method” and the “variable design point method”.

4.3.1 One-Foot Method The one-foot method is based on limiting the approximate membrane stress to the allowable stress at a location that is 1 ft. above the bottom of the course being considered. The required shell thickness is then determined based on that stress. A distance of 1 ft. above the bottom of the course is assumed to be the location of maximum membrane stress. Thismethodshallnotbeusedfortankslargerthan200ft.indiameter.Anassumptionismadetha teachshellcourseisstiffenedeitherbythetankbottomorthethicker shellcourseimmediatelybelow.Therefore,ineffect,eachshellcourseisreinforcedatitslower circumferentialseam,andthemaximumstressthatoccursinashell courseisshiftedabovethecircumferentialseam.Thedistancethatthemaximum stressisshiftedisconservativelysetatonefoot,whichgivesthedesignmethodits name.

4.3.2 Variable Design Point Method Design by the variable design point method gives shell thicknesses at design points that result in the calculated stresses being relatively closed to the actual circumferential shell stresses this method may only be used when the purchaser has not specified that the onefoot method be used and when the following is true.

Whereas per API 650 sec 5.6.4 L = (500Dt)0.5, in mm D = tank diameter, in m t = bottom course shell thickness excluding any corrosion allowance, in mm H = design liquid level ,in m

Figure 26 Tank Shell Courses thicknesses 34

4.4 Shell Design by One foot method The required minimum thickness of shell plates shall be the greater of the value computed as followed [API 650, 2007 sec 5.6.3]: Design shell thickness td 

4.9 D( H L1  0.3)G  CA Sd

Hydrostatic test shell thickness tt 

Where

4.9 D( H L1  0.3) St

td = design shell thickness, mm tt = hydrostatic test shell thickness, mm D = nominal tank diameter, m H = design liquid level, m G = design specific gravity of the liquid stored C.A = corrosion allowance, mm Sd = allowable stress for the design condition, MPa St = allowable stress for the hydrostatic test condition, MPa

The equation in the API 650 (2007) 1-Foot Method can be derived from the basic membrane theory, the two main stresses exerting on the cylindrical shell due to the internal pressure are longitudinal stress and circumferential stress. Let’s look into each stress individually by analyzing the stresses in the thin-walled cylindrical shell which an internal pressure exerted on it.

35

4.4.1 Longitudinal Stress Figure shows a thin walled cylindrical in which the longitudinal force FL resulted from the internal pressure, Pi, acting on the thin cylinder of thickness t, length L, and diameter D.

Figure 27 Longitudinal forces acting on thin cylinder under internal pressure

Longitudinal force =

Area resisting Fl , A =

as shaded in above diagram

Longitudinal stresses =

Sl = =

36

4.4.2Circumferential Stress Similarly Figure 2.2 considers the circumferential stresses caused by internal pressure, Pi, acting on the thin cylinder of thickness t, length L, and diameter D.

Figure 28 Circumferential forces acting on thin cylinder under internal pressure

Circumferential force =

Area resisting Fc , A =

as shaded in above diagram

circumferential stress Sc =

Sc= = 4.4.3Longitudinal Stress versus Circumferential Stress Comparing the both thickness equations due to the longitudinal stress and circumferential stress, with a specific allowable stress, pressure and fixed diameter, the required wall thickness to withstand the internal pressure, Pi, for circumferential stress will twice that required for the longitudinal stress. Circumferential stress in the thin wall will be the governing stress and hence the Circumferential Stress Thickness Equation (tc) is used.

37

4.4.4 Circumferential Stress Thickness Equation and 1-Foot Method From the Circumferential Stress Thickness Equation, replace the internal pressure, pi to the hydrostatic pressure due to product liquid head , consider the effective head at 0.3 m height (H – 0.3), and consider the corrosion allowance (C.A) by adding in to the equation of circumferential stress. The minimum required thickness from the 1-Foot method can be now be derived.

Circumferential Stress Thickness equation to 1-Foot method equation

4.5Top Stiffener and Intermediate Wind Girder Design 4.5.1 Top Stiffener/ Top Wind Girder Stiffener rings of top wind girder are to be provided in an open-top tank to maintain the roundness when the tank is subjected to wind load. The stiffener rings shall be located at or near the top course and outside of the tank shell. The girder can also be used as an access and maintenance platform. There are five numbers of typical stiffener rings sections for the tank shell given in API 650 (2007) and they are shown in Figure 30 [API 650, 2007].

Figure 29 Stiffener ring 38

The requirement in API 650 (2007) stated that when the stiffener rings or top wind girder are located more than 0.6 m below the top of the shell, the tank shall be provided with a minimum size of 64 x 64 x 4.8 mm top curb angle for shells thickness 5 mm, and with a 76 x 76 x 6.4 mm angle for shell more than 5 mm thick. . The top wind girder is designed based on the equation for the minimum required section modules of the stiffener ring [API 650, 2007, sec 5.9.6].

Where Z = Minimum required section modulus, cm³ D = Nominal tank diameter, m H2= Height of the tank shell, in m, including any freeboard provided above themaximum filling height V = design wind speed (3-sec gust), km/h

4.5.2 Intermediate Wind Girder The shell of the storage tank is susceptible to buckling under influence of wind and internal vacuum, especially when in a near empty or empty condition. It is essential to analysis the shell to ensure that it is stable under these conditions. Intermediate stiffener or wind girder will be provided if necessary. To determine whether the intermediate wind girder is required, the maximum height of the un-stiffened shell shall be determined. The maximum height of the un-stiffener shell will be calculated as follows [API 650, 2007,sec 5.9.7.1]:

Where H1 = Vertical distance, in m, between the intermediate wind girder and top wind girder t = Thickness of the top shell course, mm D = Nominal tank diameter, m V = design wind speed (3-sec gust), km/h As stated in earlier section, the shell is made of up diminishing thickness and it makes the analysis difficult. The equivalent shell method is employed to convert themulti39

thickness shell into an equivalent shell having the equal thickness as to the top shell course. The actual width of each shell course in changed into a transposed width of each shell course having the top shell course thickness by the following formula [API 650, 2007,sec 5.9.7.2]:

Where W tr= Transposed width of each shell course, mm Wt = Actual width of each shell course, mm tuniform= Thickness of the top shell course, mm tactual= Thickness of the shell course for which the transpose width is being calculated, mm

Figure 30 Wind Girders Situations exist where just a top wind girder alone will not provide enough shell stiffness for a given combination of tank height, tank diameter, and tank shell course thicknesses. Put in simple terms, the distance between the top wind girder and the tank bottom is too large, in 40

these situations, to resist wind-induced shell deformation. Installation of an intermediate wind girder at a location between the top wind girder and the tank bottom reduces the un stiffened length of the shell, and is required in order to prevent shell deformation in these cases. Intermediate wind girder design calculations in accordance with API-650 requirements consist of the following general steps:  Determine if an intermediate wind girder is needed, based on design wind velocity, tank diameter, and shell course thicknesses.  Locate the intermediate wind girder.  Calculate the minimum required section modulus of the intermediate wind girder and select a standard structural shape that provides this section modulus. The API-650 procedure for locating the intermediate wind girder considers the variation in shell course thickness. As illustrated in Figure 32, the API-650 procedure mathematically converts the actual tank shell height to a "transformed shell" height. As detail in design calculation chapter the shell transformation is done by accounting for the actual individual course thicknesses. The transformed shell then has the same stiffness throughout its height Locating the intermediate wind girder at the mid-height of the transformed shell results in equal shell stiffness both above and below the intermediate wind girder. The intermediate wind girder is then located on the actual tank shell in the same course and in the same relative position within that course as it is on the transformed shell. Using this approach, the intermediate wind girder is located much higher than the mid-height on the actual tank shell.

Figure31 Transformed shell and intermediate wind girder

41

4.6 Bottom Plate Designing For oil storage tanks, steel bottom plates are specified, laid and fully supported on a prepared foundation. Since it is in common practice if the diameter of tank is greater is than 12m than we have to incorporate annular plate in bottom plate to make it more strengthen. According to API 650 5.4 all bottom plates shall have a minimum nominal thickness of 6mm exclusive of any corrosion allowance specified by the purchaser for the bottom plates. The bottom is made up of a number of rectangular plates, surrounded by a set of shaped plates, called sketch plates, to give a circular shape, as shown in Figure 33. The plates slightly overlap each other and are pressed locally at the corners where three plates meet (see Figure 34). Lapped and fillet welded joints are preferred to butt welded joints (which must be welded onto a backing strip below the joint) because they are easier and cheaper to make.

See figure 34 details A and B

Figure 32Bottom layout for tank

42

Figure 33 Cross joints in bottom plates

4.7 Roof Design We have selected conical roof with self-supported at its periphery since it is easy to construct and design comparing with other types of roof. But it is strongly dependent to customer that what type of roof selected for storage tank. Fixed roofs of cylindrical tanks are formed of steel plate and are of either conical or domed (spherically curved) configuration. The steel plates can be entirely self-supporting (by 'membrane' action), or they may rest on top of some form of support structure. Membrane roofs are more difficult to erect - they require some temporary support during placing and welding – and are usually found only on smaller tanks. Permanent support steelwork for the roof plate may either span the complete diameter of the tank or may in turn be supported on columns inside the tank. The use of a single central column is particularly effective in relatively small tanks (15-20 m diameter), for example. The main members of the support steelwork are, naturally, radial to the tank. They can be simple rolled beam sections or, for larger tanks, they can be fabricated trusses. Roof plates are usually lapped and fillet welded to one another. For low pressure tanks, they do not need to be welded to any structure which supports them, but they must normally be welded to the top of the shell.

43

4.8 Overturning Stability against Wind Load The overturning stability of the tank shall be analyzed against the wind pressure, and to determine the stability of the tank with and without anchorage. The wind pressure used in the analysis is given as per API 650 (2007, sec 5.11). The design wind pressure on the vertical projected areas of cylindrical surface area shall be 0.86 kPa (V/190)² and 1.44 kPa (V/190)² uplift on horizontal projected area of conical surface. These design wind pressure are in accordance with American Society of Civil Engineer - ASCE 7 for wind exposure Category C [ASCE 7, 2005]. The loading diagram due to the wind pressure on the roof tank is shown in following Figures.

Figure 34 Overturning moment against wind load

Figure 35 Shell Out of Roundness Caused By Wind 44

The wind load (Fs) on the shell is calculated by multiplying the wind pressure (ws) to the projected area of the shell. As per API 650 (2007), the tank will be structurally stable without anchorage when the below uplift criteria are meet [API 650, 2007, sec 5.11.2].

Where Mpi= moment about the shell-to-bottom from design internal pressure (Pi) and it can be calculated by the formula

Mw= Overturning moment about the shell-to-bottom joint from horizontal plus vertical wind pressure and is equal to Fr. Lr + Fs. Ls. Fr and Fs is the wind load acting on the roof and shell respectively and Lr and Ls is the height from tank bottom to the roof center and shell center respectively. MDL= Moment about the shell-to-bottom joint from the weight of the shell and roof supported by the shell and is calculated as 0.5 D.WDL.

MF= Moment about the shell-to-bottom joint from liquid weight and is equal to

45

4.9 Seismic Design The seismic design of the storage tank is accordance to API 650 (2007) – Appendix E. There are two major analyses to be performed in the seismic design, and they are: i)Overturning Stability check - The overturning moment will be calculated and check for the anchorage requirement. The number of anchor bolt required and the anchor bolt size will also be determined based on the overturning moment. ii)Maximum base shear

4.9.1Overturning Stability against seismic load The seismic overturning moment at the base of the tank shall be the square root of sum of squares (SRSS) summation of the impulsive and convective components multiply by the respective moment arms to the center of action of the forces. For tanks supported by the concrete ring wall, the equation for calculating the ring wall moment, Mrw is as follow [API 650, 2007, sec E.6.1.5]:

Where Ai = Impulsive design response spectrum acceleration coefficient, %g Ac = Convective design response spectrum acceleration coefficient, %g Wi = Effective impulsive portion of liquid weight, N Ws = Total weight of the tank shell and appurtenances, N Wr = Total weight of fixed tank roof including framing, knuckles, any permanent attachments and 10% of the roof design snow load, N Wc = Effective convective (sloshing) portion of liquid weight, N Xi = Height from the bottom of the tank shell to the center of action of the lateral seismic force related to the impulsive liquid force for ring wall moment, m Xs = Height from the bottom of the tank shell to the shell’s center of gravity, m Xr = Height from the bottom of the tank shell to the roof and roof appurtenances center of gravity, m Xc = Height from the bottom of the tank shell to the center of action of the lateral seismic force related to the convective liquid force for ring wall moment, m 46

This overturning moment is important for the mechanical to design the anchorage requirement and determine the minimum the number and size of the anchor bolt for the storage tank. It is also important to the civil engineer to design the tank foundation in which the tank is being supported.

4.10 Anchorage requirement The resistance to the design ring wall overturning moment at the base of the shell will be provided by the weight of the tank shell, weight of the roof reaction, Wrs, by the weight of a portion of the tank contents adjacent to the shell for unanchored tanks or provided by the mechanical anchorage devices. The anchorage requirement is checked by the Anchorage Ratio, J, and the anchorage ratio criteria in Table will determine whether the tank can be self-anchored or mechanically anchored.

Table 2Anchorage Ratio Criteria [API650, 2007, table E-6]

47

The anchorage ratio, J is determined as follow [API650, 2007, sec E.6.2.1.1.1]:

Where wt = Weight of tank shell & portion of roof supported by shell and is define as

wa = Resisting force of annulus which is defined as

Where Fy= Min. specified yield strength of bottom annulus H = Maximum design product level Ge = Effective specific gravity including vertical seismic effect = G(1 - 0.4 Av) ; G = 1, Specific gravity Av = Vertical earthquake acceleration coefficient Wint= Uplift due to product pressure wrs= Roof load acting on shell, including 10% of specified snow load

48

CHAPTER:05 DESIGN CALCULATIONS

5.1 Material selection The first step is to select material for shell, bottom plate, annular plate, roof plate etc. The factors that govern that material selection are as follows:    

Cost Availability Strength Inertness

ASTM 283 Grade C is selected as shell, bottom, annular and roof plate material. The yield strength of the material is given as 205 MPa. it belongs to group 1 material as listed in table 4-3a of API 650. Material used in the construction of tanks shall conform to the specification listed in the API sec 4, subject to the modification and limitation indicated in this standard material produced to specification other than those listed in this section may be employed, provided that the material is certified to meet all of the requirements listed in this standard and the material is approved by the purchaser the manufacturer proposal shall identify the material specification to be used.

49

5.2 Design specifications Design Code

API 650, 11th Edition

Fluid

Sulphuric acid

Material

SA 283 Gr. C(ρm = 7850 kg/m3)

Specific Tank Diameter

5.6 meters

Tank Height

11.0 meters

Geometrical Capacity

270 m3

Design Liquid Level

10.49 m

gravity of contents

G = 1.94

Material’s yield strength

dy = 205 MPa

Design Pressure (+ve)

3.0 IN WC (0.1083 psig

Design Pressure (-ve)

1.0 IN WC (0.036 psig)

Design Temperature (max)

50oC

Design Temperature (min)

5 oC

Roof Type

Structurally Supported Fixed Cone Roof

Roof Slope

1:16

Bottom Type

Flat non-annular with center sump

Bottom Slope

1:48

Allowable Product Design stress

Sd = 137.0 Mpa

Allowable Hydrostatic test stress

St = 154 MPa

Corrosion allowance Bottom = 1.5mm Shell = 1.5 mm Roof = 1.5mm Joint Efficiency

0.85

Wind Speed

120 mph

Seismic Zone

2B

Plate Size

1500 mm x 6000 mm

Modulus of Elasticity

E

Yield strength of steel structure (Stiffeners)

Fy = 250 MPa

50

= 199000 MPa

Material Shell Material

HR-235

Roof Material

HR-235

Bottom Material

HR-235

Structure Material

ASTM A-36

Pipe Material

A-106 Gr. B

Flange Material

A-105, 150#, Welding Neck

Gasket Material

Spiral Wound

Anchor Bolt Material

ASTM A-36

Venting Type

Vent to closed loop/ vapor return

Painting

Yes (Only External)

Internal Lining

Yes (Rubber lining 3mm thick compatible with H2SO4)

Insulation

Yes

Insulation Thickness

2 Inch

Insulation Density

50 kg/m3

Tank Foundation

Ring Wall

51

5.3 Basic Calculations Height = H= 11.0 m (Given) Diameter =D = 5.6 m (Given) Aspect Ratio =

=

= 1.96 Total working capacity =

= = 270 = 9567.84

5.4 Shell Design As per API 650 5.6.3 Calculations of Shell Thicknesses The required shell plates thickness shall be greater of the values computed by following formulas. 4.9 D( H L1  0.3)G  CA Design Shell Thickness (As tper d API 5.6.3) Sd Hydrostatic Test Thickness t t 

4.9 D( H L1  0.3) (As p (as per API 5.6.3) St

Height for each shell course HLi= HL(i-1) - (i-1)W G = Specific Gravity of fluid to be stored D = Nominal dia. of tank (m) HL1 = Design liquid level (m) for course under consideration. CA = Corrosion allowance. = 1.50 mm td = Design shell thickness (mm)

52

tt= Hydrostatic test shell thickness (mm) HLo = Total Height of the Tank Shell = 11.00 m W = Width of the Plate (Course) = 2.45 m i = Shell Course Number = 1 to 7 1st Shell Course Width of 1st. Course

W1 =1.5 m

Design height for 1st shell Course

HL1 = 11.0 m

Required Shell Thickness

tt =2.15mm


td= 3.92mm

Shell thickness selected

t1= 6.00 mm

2nd Shell Course Width of 2nd Course

W2 =1.50 m

Design height for 2nd shell Course

HL2=9.5 m


tt =1.84mm


td= 3.57mm


t2= 6.00 mm

3rd Shell Course Width of 3rd Course

W3 =1.50 m

Design height for 3rd shell Course

HL3 =8.0 m


tt =1.52 mm


td= 3.21mm


t3

53

= 6.00 mm

4th Shell Course Width of 4th Course

W4 =1.50 m

Design height for 4th shell Course

HL4 =6.5 m


tt =1.21 mm


td= 2.86 mm


t4

= 6.00 mm


W5 =1.50 m


HL5 =5.0 m


tt =0.89 mm


td= 2.50 mm


t5

= 6.00 mm


W6 =1.50 m

Design height for 6thshell Course

HL6 =3.5 m


tt =0.58 mm


td= 2.15 mm


t6

= 6.00 mm


W7 =1.50 m


HL7 =2.0 m


tt =0.26mm


td= 1.79 mm


t7

54

= 6.00 mm


W8 =0.50 m


HL8 =0.5 m


tt = 0 mm


td= 1.49mm


t8

= 6.00 mm

Shell Thickness & Weight Summary Shell Course #

1

2

3

4

5

6

7

8

Shell width (m)

1.5

1.5

1.5

1.5

1.5

1.5

1.5

0.5

Shell Thick, corroded (mm)

6.0

6.00

6.00

6.00

6.00

6.00

6.00

6.00

Shell Weight (KN)

12.17 12.17 12.17 12.17 12.17 12.17

12.17 4.05

Shell Weight(corroded) (KN)

9.13

9.13

9.13

9.13

9.13

9.13

Total Shell Weight

= 12.17(7)+4.05=89.24KN

Total Shell Weight (corroded)

= 9.13(7)+ 3.04=66.95KN

55

9.13

3.04

5.5 Bottom Plate Design As per API 650 5.4.1 All bottom plates shall have minimum nominal thickness of 6mm, exclusive of any corrosion allowance as per API 650 5.4.1 Required Bottom Plate Thickness tr= 6 + CA mm = 6+1.5 = 7.5 mm Selected bottom plate thickness

tb = 8.0 mm

 D  0.1  Wact 2  tb   m     tb   m D  0.12  D  0.1  Wact 2   4 4    



Weight of Btm. Plate +Annular plate  



For corroded weight  D  0.1  Wact 2  (tb  CA)   m     (tb  CA)  m Weight of Btm. Plate +Annular plate    D  0.12  D  0.1  Wact 2   

4

 

4



Weight of Btm. Plate +Annular plate = 7907.57 kg =>15.72 KN Weight of Btm. Plate +Annular plate = 64.24.90 kg =>12.78KN (Corroded)

5.6 Annular Plate Design (As per API 650 Sec. 5.5) Product stress

137.00Mpa

Hydrostatic test stress

154.00 MPa

Annular bottom plate thickness

t = 6 mm (As per API 650 Table 5-1 a)

Including corrosion allowance

7.50 mm

Used annular plate thickness

tb = 8.00 mm

Max. design liquid level

HL1= 10.5 m

56





5.7 Intermediate Wind Girder Design (As per API 650 Sec. 5.9.7) The maximum height of the Un-stiffened shell shall be calculated as follows:

H1 = 9.47 t( )

⁄

(

)

(As per API 650 Sec. 5.9.7)

Where H1= Vertical distance, in m, between the intermediate wind girder and the top angle of the shall or the top wind girder of an open top tank. t = Thickness of the top shell course = 6 mm D = Nominal tank diameter (m) = 5.76 m H1 =30.68 m Modification as per API 650 (5.9.7.1 Note 2, a)

H1 = (

)xH1

= 17.64 m

Transformed Shell thicknesses

Wtr(i)

=

Wi x (

)

(As per API 650 Sec. 5.9.7)

Where, Wtr(i)

= Transformed

Shell Thickness

Wi =Width of Course’s (W1 to 7= 1.50 m ; W8 = 0.50 m) ttop = Shell Thickness of 8thCourse ti = Thickness Of the Course that is consider i = Shell Course Number = 1 to 8

57

1st Course Thickness of first course

t1= 6.00 mm

Wtr1 = W1 x(

) = 1499.61 mm

2nd Course Thickness of 2nd course

t2= 6.00 mm Wtr2 = W2 x (

)

= 1499.61mm 3rd Course Thickness of 3rd course

t3 = 6.00 mm Wtr3 = W3 x (

)

= 1499.61 mm

4th Course Thickness of 4th course

t4= 6.00 mm Wtr4 = W4 x (

)

= 1499.61 mm 5th Course Thickness of 5th course

t5 = 6.00 mm Wtr5 = W5 x (

)

= 1499.61 mm 58

6th Course Thickness of 6th course

t6 = 6.00 mm Wtr6 = W6 x (

)

= 1499.61mm 7th Course Thickness of 7th course Wtr7 = W7 x (

t7 = 6.00 mm

) = 1499.61mm

8th Course Thickness of 7th course Wtr7 = W7 x (

t7 = 6.00 mm

) = 489.87mm

Height of transformed shell, Htr = Wtr1+Wtr2+Wtr3+Wtr4+Wtr5+Wtr6+Wtr7+ Wtr8 Height of transformed shell, Htr =10987.14 mm or 10.98 m As Htr< H1 10.98 < 17.64 Intermediate Wind Girder is Not Required.

59

5.8 Roof Design (Supported Conical Roof) As per API 650(5.10.5) Minimum roof thickness is 5mm

(As per API 650(5.10.5)

Roof plate thickness = 6.5 mm (with corrosion allowance) Selected Roof Plate thickness= th= 7 mm θ = slope of roof = 3.57 Do= Outer Diameter= 5.6 m ρ = 850 kg/m3 Vertical Projected Area of Roof =

pt = 0.75 in/ft (Cone Roof Pitch) Horizontal Projected Area of Roof (Per API-650 5.2.1.f): Xw = Moment Arm of UPLIFT wind force on roof = = Ap = Projected Area of roof for wind moment =

R = 9.184 ft Dead Load = Insulation + Plate Weight + Added Dead Load

Roof Loads (per API-650 Appendix R)

60

e.1b = DL + MAX(Sb,Lr) + 0.4 Pe

e.2b = DL + Pe + 0.4 MAX(Sb,Lr)

T = Balanced Roof Design Load (per API-650 Appendix R) = MAX(e.1b,e.2b)

e.1u = DL + MAX(Sb,Lr) + 0.4 Pe

e.2u = DL + Pe + 0.4 MAX(Su,Lr)

U = Unbalanced Roof Design Load (per API-650 Appendix R) = MAX(e.1u,e.2u) = 33.833

P = Max. Design Load = Lr1

l = Maximum Rafter Spacing (Per API-650 5.10.4.4) –

61

MINIMUM # OF RAFTERS FOR OUTER SHELL RING: l = 84 in. since calculated l > 84 in. (7 ft)

Minimum roof thickness based on actual rafter spacing:

RLoad

= Maximum Roof Load based on actual rafter spacing

Let Max = RLoad P

(Vacuum limited by actual rafter spacing)

= -0.3336 PSI or -9.25 IN. H2O Pa

=P = -0.3336 PSI or -9.25 IN H2O.

t

=0.2465 in.

62

5.9 RAFTER DESIGN Maximum Rafter Span = 9.184 ft Average Rafter Spacing on Shell = 6.282 ft Average Plate Width= M

=3.141 ft

= Maximum Bending Moment

M

=

where,

l

= (9.184)(12) = 110.21 in.

Mmax = (9.66)(110.21)

Z req'd = Mmax/23,200

W

(Max. stress allowed for each rafter in ring 1)

Max (Max. Load allowed for each rafter in ring 1)

63

Let Max

= Max

P

144

(Vacuum limited by Rafter Type)

= -1 PSI due to Rafter Type Pa2

=P (limited by Rafter Type)

5.10 COLUMN DESIGN : CENTER COLUMN l = Column Length

r = Radius of gyration if l/r must be less than 180, then

Actual r = 2.93 in. using Pipe 8 Inch Sch. 40

64

Fa = Allowable Compressive Stress (Per API-650 5.10.3.4) R = L/r = 150.2 (actual)

Per API-650 5.10.3.3,

Cc = Column Slenderness Ratio

FS = Factor of Safety = 5/3 + 3 (150.2)/(8 (125.7)) - (150.2) /(8 (125.7) 3) = 1.9015 Since R <= 120, Using AISC Specification Formulas Section E2, (let K = 1)

Fa is not modified Since Design Temp. <= 200 °F. (API-650 M.3.5 N.A.)

= 6574 PSI

65

A

= P/Fa = [4,791 + (440/12)(28.55)]/6,574 = 0.89 in

F = actual induced stress for the column = P/A [

W

(

)

]

(Max. weight allowed for each column in ring 1)

Max (Max. Load allowed for each column in ring 1) Let

P

(Vacuum limited by Column Type)

= -1 PSI due to Column Type

Pa

=P (limited by Column Type)

66

ROOF WEIGHT Weight of Roof Plates

Weight of Roof Plates supported by shell

67

5.11 Tank Overturning Stability

WIND MOMENT (Per API-650 SECTION 5.11) vs = Wind Velocity = 120 mph vf = Velocity Factor = (vs/120) = (120/120) =1

API-650 5.2.1.k Uplift Check

68

Ap

= Vertical Projected Area of Roof

Horizontal Projected Area of Roof (Per API-650 5.2.1.f) Xw = Moment Arm of UPLIFT wind force on roof

Ap = Projected Area of roof for wind moment

M

(Moment Due to Wind Force on Roof)

Xs (Moment Arm of Wind Force on Shell)

As (Projected Area of Shell)

69

(

M

)

(Moment Due to Wind Force on Shell)

Mw (Wind moment)

W = Net weight (PER API-650 5.11.3) (Force due to corroded weight of shell and shell-supported roof plates less 40% of F.1.2 Uplift force.)

70

5.12.1 RESISTANCE TO OVERTURNING (per API-650 5.11.2)

An unanchored Tank must meet these two criteria: 1) 0.6 Mw + MPi < MDL/1.5 2) Mw + 0.4MPi < (MDL + MF)/2

Mw = Destabilizing Wind Moment = 365,138 ft-lbf

Mpi = Destabilizing Moment about the Shell-to-Bottom Joint from Design « Pressure.

MDL = Stabilizing Moment about the Shell-to-Bottom Joint from the Shell and « Roof weight supported by the Shell.

tb = Bottom Plate thickness less C.A. = 0.2559 in. wl = Circumferential loading of contents along Shell-To-Bottom Joint.

wl = 0.9

H

Do (lesser value than above) 71

MF = Stabilizing Moment due to Bottom Plate and Liquid Weight. = (Do /2) wl PI Do

Criteria 1

Since 257,035 >= 106,528, Tank must be anchored.

Criteria 2

Since 380319 >= 230758 Tank must be anchored.

RESISTANCE TO SLIDING (per API-650 5.11.4)

F

= vF

F

18 As

= Maximum of 40% of Weight of Tank

72

Bolt Shear Area Req'd = 0.055 in

Anchorage Requirement Anchorage required since Criteria 1, Criteria 2, or Sliding are NOT acceptable. Bolt Spacing = 10 ft, Min # Anchor Bolts = 6

5.12 .2Stability of Tank Against Seismic Load Seismic design provide minimum requirements for the design of welded steel tanks that may be subjected to seismic ground motion, since seismic loads are strongly dependent on geography condition of site therefore we assumed a lot of factors that are related to the site of the storage tank for detail of coefficient used under this section see API 650 E.2.2 Check against Seismic Failure as stated by UBC 97 & appendix E of API 650 D = 5.6 m H =11 m D/H = 0.50 H/D = 1.96

WEIGHTS Ws = Weight of Shell (Incl. Shell Stiffeners & Insul.)

Wf = Weight of Floor (Incl. Annular Ring)

Wr = Weight Fixed Roof, framing and 10% of Design Live Load & Insul.

73

5.12.3 SEISMIC VARIABLES SUG = Seismic Use Group (Importance factor depends on SUG) =I Site Class = E Sp = Design level peak ground acceleration parameter for sites not addressed by ASCE methods

Ss = Design Spectral Response Param. (5% damped) for Short Periods (T=0.2 sec)(Ss = 2.5 Sp per E.4.3 formula E.4.3-1)

S1 = Design Spectral Response Param. (5% damped) for 1-Second Periods (T=1.0 sec)(S1 = 1.25 Sp per E.4.3 formula E.4.3-2)

T = Regional Dependent Transition Period for Long Period Ground Motion (per API-650 E.4.6.1 for regions outside the USA)

Av = Vertical Earthquake Acceleration Coefficient

Q = Scaling factor from the MCE to design level spectral accelerations

Fa = Acceleration-based site coefficient (at .2 sec period)(Table E-1)

Fv = Velocity-based site coefficient (at 1 sec period)(Table E-2)

I = Importance factor defined by Seismic Use Group

74

Rwi = Force reduction factor for the impulsive mode using allowable stress design methods.

Rwc = Force reduction factor for the convective mode using allowable stress design methods.

Ci = Coefficient for impulsive period of tank system (Fig E-1)

tu = Equivalent uniform thickness of tank shell

Density = Density of tank product. SG 62.4

E = Elastic modulus of tank material (bottom shell course) Sds = The design spectral response acceleration param. (5% damped) at short periods (T = 0.2 sec) based on ASCE7 methods.

Sd1 = The design spectral response acceleration param. (5% damped) at 1 second based on ASCE7 methods. = Q Fv S1

75

5.12.4 STRUCTURAL PERIOD OF VIBRATION E.4.5.1 Impulsive Natural Period

E.4.5.2 Convective (Sloshing) Period Ks = 0.578/SQRT(TANH(3.68 H/D))

Tc = Ks SQRT(D)

E.4.6.1 Spectral Acceleration Coefficients Ai = Impulsive spectral acceleration parameter

K = Coefficient to adjust spectral acceleration from 5% - 0.5% dampin

Ac = Convective spectral acceleration parameter

76

Chp:06 RESISTANCE TO DESIGN LOADS

6.1 EFFECTIVE WEIGHT OF PRODUCT D/H = Ratio of Tank Diameter to Design Liquid Level

Wp = Total Weight of Tank Contents based on S.G.

Wi = Effective Impulsive Portion of the Liquid Weight

Wc = Effective Convective (Sloshing) Portion of the Liquid Weight

Weff = Effective Weight Contributing to Seismic Response = Wi + Wc

Wrs = Roof Load Acting on Shell, including 10% of Live Load

6.1.1 DESIGN LOADS Vi = Design base shear due to impulsive component from effective weight of tank and contents = Ai (Ws + Wr + Wf + Wi)

77

Vc = Design base shear due to convective component of the effective sloshing weight = Ac Wc

V = Total design base shear

6.2.1 CENTER OF ACTION FOR EFFECTIVE LATERAL FORCES

Xs = Height from Bottom to the Shell's Center of Gravity

RCG = Height from Top of Shell to Roof Center of Gravity

Xr = Height from Bottom of Shell to Roof Center of Gravity

6.2.2 CENTER OF ACTION for RINGWALL OVERTURNING MOMENT

Xi = Height to Center of Action of the Lateral Seismic force related to the Impulsive Liquid Force for Ring wall Moment

Xc = Height to Center of Action of the Lateral Seismic force related to 78

the Convective Liquid Force for Ring wall Moment

6.2.3 CENTER OF ACTION for SLAB OVERTURNING MOMENT Xis = Height to Center of Action of the Lateral Seismic force related to the Impulsive Liquid Force for the Slab Moment =

=

Xcs = Height to Center of Action of the Lateral Seismic force related to the Convective Liquid Force for the Slab Moment = (1-(cosH(3.67×H/D)-1.937)/((3.67×H/D)×sinH(3.67×H/D)))×H = =

6.2.4 Dynamic Liquid Hoop Forces

79

SHELL SUMMARY Shell

Width Ft

Y ft

Ni

Nc

Nh lbf

Sig(+)

Sig(-)

1 2 3 4 5 6 7 8

4.92 4.92 4.92 4.92 4.92 4.92 4.92 1.64

33.44 28.52 23.6 18.68 13.76 8.84 3.92 -1

3.28 3.28 3.28 3.28 3.27 2.85 1.6 -0.49

0.003 0.004 0.011 0.029 0.078 0.208 0.558 1.495

1935 1659 1382 1106 829 553 276 0

10951 9391 7826 6267 4702 3140 1569 9

10914 9354 7789 6230 4665 3108 1550 -9

6.2.5 Overturning Moment Mrw = Ring wall moment—Portion of the total overturning moment that acts at the base of the tank shell perimeter Mrw = ((Ai (Wi Xi+Ws Xs+Wr Xr)) + (Ac Wc Xc) )

Ms = Slab moment (used for slab and pile cap design) Ms = ((Ai (Wi Xis+Ws Xs+Wr Xr)) + (Ac Wc Xcs) ) =

80

6.2.6 RESISTANCE TO DESIGN LOADS

E.6.2.1.1 Self-Anchored Fy = Minimum yield strength of bottom plate = 29732 psi Ge = Effective specific gravity including vertical seismic effects

wa = Force resisting uplift in annular region

wa = 810 lbf/ft (reduced to 1.28 H D Ge because that is the max allowable per E.6.2.1.1)

wt = Shell and roof weight acting at base of shell

wint = Uplift Load due to design pressure acting at base of shell

81

E.6.2.1.1.1 Anchorage Ratio J = Mrw/(D

[wt (1-0.4 Av)+wa-0.4 wint])

= 59,140/(18.368

[436.6302 (1-0.4 0)+810-0.4 28.6453])

= 0.1419 The tank is self anchored.

E.6.2.2 Maximum Longitudinal Shell-Membrane Compressive Stress E.6.2.2.1 Shell Compression in Self-Anchored Tanks ts1 = Thickness of bottom shell course minus C.A. = 0.177 in. Sig C = Maximum longitudinal shell compression stress

E.6.2.2.3 Allowable Longitudinal Shell-Membrane Compression Stress Fty = Minimum specified yield strength of shell course

Fc = Allowable longitudinal shell-membrane compressive stress

82

6.3 ANCHOR BOLT DESIGN

Bolt Material : A-36 Sy = 36000 PSI

Uplift Load Cases, per API-650 Table 5-21b

D (tank OD) = 18.368 ft P (design pressure) = 3 INCHES H2O Pt (test pressure per F.4.4) = P = 3 INCHES H2O Pf (failure pressure per F.6) = N.A. (see Uplift Case 3 below) t (roof plate thickness) = 0.2755 in. Mw (Wind Moment) = 365138 ft-lbf Mrw (Seismic Ring wall Moment) = 59140 ft-lbf W1 (Dead Load of Shell minus C.A. and Any Dead Load minus C.A. other than Roof Plate Acting on Shell) W2 (Dead Load of Shell minus C.A. and Any Dead Load minus C.A. including Roof Plate minus C.A. Acting on Shell)

W3 (Dead Load of New Shell and Any Dead Load other than Roof Plate Acting on Shell)

For Tank with Structural Supported Roof, W1 = Corroded Shell + Shell Insulation

83

W2 = Corroded Shell + Shell Insulation + Corroded Roof Plates Supported by Shell + Roof Dead Load Supported by Shell

W3 = New Shell + Shell Insulation

Uplift Case 1: Design Pressure Only

Uplift Case 2: Test Pressure Only

Uplift Case 3: Failure Prssure Only Not applicable since if there is a knuckle on tank roof, or tank roof is not frangible.

84

Uplift Case 4: Wind Load Only

85

Uplift Case 5: Seismic Load Only

Uplift Case 6: Design Pressure + Wind Load

-

Uplift Case 7: Design Pressure + Seismic Load

86

Uplift Case 8: Frangibility Pressure Not applicable since if there is a knuckle on tank roof, or tank roof is not frangible.

6.4 CAPACITIES and WEIGHTS

Maximum Capacity (to upper TL)

:

Design Capacity (to Max Liquid Level)

71214 gal :

67975 gal

Minimum Capacity (to Min Liquid Level) : NetWorking Capacity (Design - Min.) Weight of Tank, Empty Weight of Tank, Full of Product

:

0 gal 67975 gal

:

29644 lbf

(SG=1):

623953 lbf

Weight of Tank, Full of Water

:

623953 lbf

Net Working Weight, Full of Product

:

596923 lbf

Net Working Weight, Full of Water

:

596923 lbf

Shell Roof plates Rafters Girders Columns Bottom Stiffeners Nozzle Wgt Misc Roof Wgt Insulation Total

New condition 20064 lbf 2983 lbf 793 lbf 0 lbf 1047 lbf 3536 lbf 0 lbf 0 lbf 0 lbf 1221 lbf 29644 lbf

87

Corroded 15055 lbf 2344 lbf 793 lbf 0 lbf 1047 lbf 2,874 lbf 0 0 0 1221 lbf 23334 lbf

STORAGE TANK DESIGN FLOW CHART A START

RAFTER DESIGN Quantity+spacing

SHELL DESIGN Thickeness + weight (corroded + uncorroded) As per 5.6 of API 650

STIFFENER DESIGN Length+quatity+spacing +weight As per IPE 200

BOTTOM PLATE DESIGN Thickeness + weight (corroded + uncorroded) As per 5.4 of API 650

ANNULAR PLATE DESIGN Thickeness + weight (corroded and uncorroded) If D≤12 As per 5.5 of API 650

No

COMPRESSION RING DESIGN At shell to roof junction As per appendix F of API 650

Annular Bottom Plate is NOT required

Improve Roof Design

Yes

CHECK FRANGIBILITY CONDITION If max area reqd for frangibility condition> Areqd

Yes

Annular Bottom Plate is Neccessary No

WIND GIRDER DESIGN If unstiffened shell height H1>transposed height i.e H1>Htrans As per 5.9 of API 650

Find FAILURE pressure Pf + Max DESIGN pressure Pmax As per appendix F of API 650 No

Intermediate wind girder is required

No

Yes

If Pmax ≤ Pf

Find Min. no of Wind girder Yes

Intermediate wind girder is NOT required Find Location of wind girder

ROOF DESIGN Plate thickeness+weight,radius, (corroded+uncorroded) As per 5.10 of API 650

NO

Recheck shell Thickeness against Pf If tprov > treqd

Yes

1

A

88

STORAGE TANK DESIGN FLOW CHART

1

TANK OVERTURNING STABILITY

Check against WIND load As per 5.11.2 of API 650

satisfactory

Anchorage Against wind pressure is NOT required

Satisfactory

Anchorage against sliding is NOT required

Unsatisfactory Anchorage against wind pressure is Required

Check for SLIDING FAILURE as per 5.11.4 of API 650

unsatisfactory

Anchorage against Sliding is required

Stability check Against SEISMIC LOAD as per Appendix E of API 650

Anchorage Ratio If ≤ 1.54

No

Yes

Tank is SelfAnchored

END of Calculations

89

Mechanical Anchorage is required (Not self anchored)

6.5 2D and 3D Drawings The arrangement of stiffeners at roof of the tank and location of stairs and some other attachments’ is shown in 2D diagram. 3D modeling of storage tank that is develop with the help of Pro E wildfire 5.0 is shown below:

Figure 45. 3D Model of storage tank

90

Figure 46. 3D Model of storage tank

91

CHAPTER # 07: DEVELOPMENT OF STORAGE TANK DESIGN SOFTWARE & VERIFICATION OF RESULTS USING ETANK 2000

7.1 Overview FYP-Storage Tank Design software is developed by using Microsoft Excel Visual Basic Programming Technique. It is comprehensive, easy-to-use software program for the design, and evaluation of welded steel oil storage tanks according to American Petroleum Institute (API) Standards 650. It provides owners, operators and engineering firms with quick easy and comprehensive design for new tank construction and evaluation of existing tanks.

7.2 Design Capabilities      

Steel Oil Storage Tank Design Design Output detailed & semi detailed Reports API 650 Standards, 10th edition Allowable Fluid Height & diameter Shell course thickness using one foot method Up to 60 m shell height& 60 m internal diameter  Intermediate Wind girder requirements  Bottom plate + annular Plate minimum thickness evaluation  Design of Self supported cone roof

7.3 Key Features  Built for Real World Applications  Designed for fast input  Recheck of the Design input Data  Detailed and semi-detailed output Results  Just one click Design

7.4 Application Areas Can be use to design all welded oil storage Tank that incorporates API 650 Standards.

Welded oil Storage Tank Design Software

92

Figure 48 Snap shot of software Input is fast because each input item includes an edit box with the units displayed & Read Values provides the rechecking of the design data input

Figure 49 Design report showing design & hydrostatic testthickness

7.5Visual Basic Programming for Shell Design 93

The coding started with the calculation of number of shell courses. For this purpose user must define the height of the shell and width of shell course.

n = H1 / W Where n = number of courses required H1 = height of shell W = width of shell course provided Dim MyDoubleAs Double Dim Temp As Double

MyDouble = Int(n) Debug.Print "MyDouble: " &MyDouble

Temp = n - MyDouble

If Temp > 0 Then MyDouble = MyDouble + 1 End If n = MyDouble Dim J As Integer J = 1

Now, Using the formulae for design thicknesstd, hydrostatic test thickness tt, width of each course iwand weight of each shell course wt by considering each shell course

Dim I As Integer

94

For I = 0 To n - 1 Step 1

td(J) = ((4.9 * D * (HL1 - ((I) * W) - 0.3) * G) / Sd) + CA tt(J) = ((4.9 * D * (HL1 - ((I) * W) - 0.3)) / St) iw(J) = (n + 1) * W - (n) * W Wt(J) = (3.142 * 9.81 * D * td(J) * iw(J) * Sm) / (1000000)

J = J + 1 Next I

Now the next step is to print out the calculated result into respective cells and the code is: Sub shelldesign22_Click()

Dim rg As Range Set rg = ThisWorkbook.Worksheets(1).Range("B52:B65")

rg.CurrentRegion.ClearContents Set rg = ThisWorkbook.Worksheets(1).Range("C53:F61") Range("C53:F61").UnMerge rg.ClearContents Set rg = Nothing

Dim Para As String

95

Para = " SHELL DESIGN as stated by 5.6 API 650" &vbCr& _ "The minimum design shell thickness and hydrostatic test shell thickness are calculated by" &vbCr& _ "1 foot method are given below:" &vbCr& _ "The selected / Provided shell thickness must be greater of the values than calculated shell thickness as a factor of safety" &vbCr& _ ". "

Range("C53:F61").Merge Range("C53:F61").Value = Para Set rg = Nothing

' ---------------------------------Dim I As Integer Dim J As Integer J = 1 Dim rg2 As Range Set rg2 = ThisWorkbook.Worksheets(1).Range("C64")

Range("B62").Font.Size = 15 Range("B62").Font.Color = RGB(25, 25, 255) Range("B53").Font.Size = 15 Range("B53").Font.Color = RGB(25, 25, 255) Range("B53").Value = " SHELL DESIGN " Range("B54").Value = " As stated by 5.6 of API 650 " Range("B62").Value = " - DESIGN SHELL THICKNESS (td), HYDROSTATIC TEST THICKENESS (tt),WIDTH(iw) and WEIGHT (wt) of each uncorroded Shell are summerized as: - " 96

For I = 1 To n Step 1

' Transfer values to the worksheet

rg2.Value = "td(" & J & ")" & " = " rg2.Offset(0, 1).Value = td(J) rg2.Offset(0, 2).Value = "mm"

rg2.Offset(0, 3) = "tt(" & J & ")" & " = " rg2.Offset(0, 4).Value = tt(J) rg2.Offset(0, 5).Value = "mm"

rg2.Offset(64 + n - 62, 0).Value = "iw(" & J & ")" & " = " rg2.Offset(64 + n - 62, 1).Value = iw(J) rg2.Offset(64 + n - 62, 2).Value = "m"

rg2.Offset(64 + n - 62, 3).Value = "Wt(" & J & ")" & " = " rg2.Offset(64 + n - 62, 4).Value = Wt(J) rg2.Offset(64 + n - 62, 5).Value = "KN"

' Move down to next row

97

Set rg2 = rg2.Offset(1, 0)

J = J + 1

Next I

' Print Sum Set rg2 = rg2.Offset(1, 0) rg2.Offset(2 + n, 3).Value = "WEIGHT TOTAL: " rg2.Offset(2 + n, 4).Value = Sum rg2.Offset(2 + n, 5).Value = "KN"

' ----------------------------------

End Sub

The following output result appeared first pressing start button and then selecting shell design as:

98

Figure50. Message Box Indicating the completion of calculation

99

Figure 51Output Result

7.6 VERIFICATION OF RESULTS

100

A large number of software is available for designing and evaluation of welded oil storage tank as per codes and standards. E-tank 2000 is the most dedicated and extensively used software. In order to verify our design calculations we contacted Mr. Jeffcott Smith-CEO Etank2000, who was kind enough to give us a student version of the software for the final year project. Unfortunately the working of this version is quite limited and we can only verify the shell design & hydrostatic test thickness from it. The results are in good agreement with our developed software & our calculated results.

Figure 52Verificationthrough E-TANK Software

101

CONCLUSION The API 650 provides extensive information for designing, erection, fabrication, inspecting of joints, and welding procedure & welder qualifications for the above ground storage Tanks for oil storage. It also contains dedicated appendixes for special design parameters such as seismic design floating roof etc. it also includes the appendixes for shop-weld storage Tanks that are built at workshop and transferred to desired locations. However in seismic design it does not include the structural loading requirements and criteria for soil selection and settlement technique for which Uniform Building Code (UBC) had to be used as a supplement material. Both of the standards deal only with the Mechanical aspects of the design. Thus it can be concluded that designing of storage Tank for oil storage is an extensive and difficult task for which information from within as well outside the standards has to be used. It is also concluded that a tank is designed for the most severe combination of the various possible loadings. Storage tanks carry the hydrostatic pressure by simple hoop tension. The cylindrical shell has to carry both its own weight and the weight of the supported roof by axial stresses. Wind loading on the tank influences the axial stress. For open tanks, primary wind girders are required to maintain the roundness of the tank when it is subject to wind load. Secondary wind girders are needed in tall tanks.

102

REFERENCES [1] API 650 standards 11th edition [2] Bob Long and Bob Garner “Guide to storage tank and equipment” [3] Mohammad A El-Reedy Ph.D. “Construction management and Design of industrial concrete and steel structures” [4] http://kolmetz.com/pdf/EDG/ENGINEERING_DESIGN_GUIDELINE__storag e_tank_rev_2.pdf [5] www.etank.com [6] Okpala, Alexander N. and Jombo, P.P., Design of Diesel Storage Tank in Consonance with Requirements of American Petroleum Institute (API) Standard 650 Industrial engineering Letters, volume II, No 04, 2012. [7] Esdep Lecture Note [Wg15] www.fgg.uni-lj.si/kmk/…/l0100.htm [8] Zhi Lu “Evaluation Of Design Criteria For Storage Tanks With Frangible Roof Joints” B.S., Tianjin University, 1982 M.S., Tianjin University, 1984

[9] Praveen K. Malhotra, Senior Res. Scientist Factory Mutual Research, Norwood, MA, USA ” Simple Procedure for Seismic Analysis of Liquid-Storage Tanks”

103

APPENDIX

104

105

Appendix C Shell Design

106

107

108

Appendix DBottom and annular Plate Design

109

110

Appendix E Intermediate wind girder

111

112

Appendix F Roof Design

113

114

115

Appendix G Tank overturning stability

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

Sulphuric Acid Storage Tank

Recommend Documents