Design and Stability of Large Storage Tanks and Tall Bins

DESIGN AND STABILITY OF LARGE STORAGE TANKS AND TALL BINS

PREPARED BY : MUKESH M. CHAUHAN BE-IV CHEMICAL ROLL NO. 803 EXAM NO. 341

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THE MAHARAJA SAYAJIRAO UNIVERSITY OF BARODA

DEPARTMENT OF CHEMICAL ENGINEERING FACULTY OF TECHNOLOGY & ENGINEERING, BARODA.

Certificate This is to certify that Mr. CHAUHAN MUKESH MOHANLAL., a student of B.E-IV Chemical has work on the Project entitled “Design and Stability of Large Storage Tanks and Tall Bins” under my guidance and herewith submits his report in partial fulfillment of the degree of B.E. (Chemical) for the year 2011-12.

Dr. R. A. Sengupta Head and Professor, Chemical Engg. Deptt. Faculty of Technology & Engineering M.S.university of Baroda.

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Acknowledgement I am extremely thankful to Dr. R. A. Sengupta, Head of Department of Chemical Engineering and my guide for his excellent guidance, encouragement and support throughout my dissertation work. His profound knowledge that he readily shared with me has helped me overcome many difficulties. I cannot forget the innumerable time and effort to teaching me both in this seminar and in writing it, that my work will never be able to match. His constant support, encouragement, never ending enthusiasm and confidence in me has been a source of motivation for me. I would also like to express my heartfelt gratitude to Ms. N. H. Tahilramani, who have personally paid attention in the progress of this work Special thanks to library staff of T. K. Gajjar and A.C.E.S library for their kind cooperation. Finally, I express my deepest gratitude to all my family members for their constant love and support and “God”.

Mukesh M Chauhan

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Contents Chapter 1 Introduction to Storage tanks and Bins 1.1 Function of Storage Tanks and Bins …………………………………………………..01 1.2 Types of Storage Tanks and Bins……………………………………………………... 01 1.3 Design codes and Standards ………………………………………………………….04 Chapter 2 Design of Liquid Storage Tanks 2.1 Shell Design …………………………………………………………………………..05 2.2 Roofs …………………………………………………………………………………..09 2.3 Bottom plate …………………………………………………………………………...12 Chapter 3 Design and Stability of Storage Bins 3.1 Introduction ……………………………………………………………………………14 3.2 Functional Design of Bins ……………………………………………………………..14 3.3 Design of Bins-Loadings……………………………………………………………….17 3.4 Structural Design of bins……………………………………………………………….21 Chapter 4 Stability of Storage Tanks 4.1 Provisios for seismic loading…………………………………………………………..29 4.2 Overturning Stability against Wind Loads……………………………………………..41

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List of Figures Figure 1.1 - Types of storage tanks Figure 2.1 – Column supported framed roof Figure 2.2 – Floating roof Figure 2.3 – Joints in floor plates Figure 2.4 – Bottom plate layout Figure 3.1 – Flow patterns of materials in bins Figure 3.2 – Graphical method for calculation of flow pattern Figure 3.3 – Distribution of horinzontal and vertical pressure against depth of stored material Figure 3.4 – Bin dimensions for use in Reinbert‟s and Janssens‟s equation Figure 3.5 – Critical values of axial stresses for cylinders subjected to axial compression Figure 3.6 – Cylinder to cone transition Figure 3.7 – Forces on suspended bottoms Figure 4.1 – Impulsive hydrodynamic pressure on wall Figure 4.2 - convective hydrodynamic pressure on wall Figure 4.3 – Typical stiffener ring section for ring shell Figure 4.4 – Overturning check on tank due to wind load

List of Tables Table 2.1 – Minimum thickness based on Diameter of the tank Table 4.1 – Expressions for parameters of spring mass model Table 4.2 – Importance factor-I

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Chapter 1

Introduction To Storage Tanks & Bins

1.1 Fuction of Storage tanks and Bins 1.1.1 Storage tanks Storage tanks had 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. 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. 1.1.2 Storage Bins The storage of granular solids in bulk represents an important stage in the production of many substances derived in raw material form and requiring subsequent processing for final use. These include materials obtained by mining, such as metal ores and coal; agricultural products, such as wheat, maize and other grains; and materials derived from quarrying or excavation processes, for example sand and stone. All need to be held in storage after their initial derivation, and most need further processing to yield semi- or fully-processed products such as coke, cement, flour, concrete aggregates, lime, phosphates and sugar. During this processing stage further periods of storage are necessary.

1.2 Types of Storage tanks and bins 1.2.1 Storage tanks

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1.2.1.1 Open Top Tanks This type of tank has no roof. They shall not be used for petroleum product but may be used for fire water/ cooling water. The product is open to the atmosphere; hence it is atmospheric tank. 1.2.1.2 Fixed Roof Tanks Fixed Roof Tanks can be divided into cone roof and dome roof types. They can be self supported or rafter/ trusses supported depending on the size. Fixed Roof are designed as  Atmospheric tank (free vent)  Low pressure tanks (approx. 20 mbar of internal pressure)  High pressure tanks (approx. 56 mbar of internal pressure) Figure 1.1 illustrates various types of storage tank that are commonly used in the industry today.

Figure 1.1 Types of storage tank 7|Page

1.2.1.3 Floating Roof Tanks Floating roof tanks is which the roof floats directly on top of the product. There are 2 types of floating roof: Internal floating roof is where the roof floats on the product in a fixed roof tank. External Floating roof is where the roof floats on the product in an open tank and the roof is open to atmosphere. Types of external floating roof consist of:  Single Deck Pontoon type ( Figure 1.4)  Double deck ( Figure 1.5)  Special buoy and radially reinforced roofs 1.2.2 Storage bins Regarding descriptive terminology applicable to containment vessels, it should be noted that the word "bin" as used in this text is intended to apply in general to all such Containers, whatever their shape, ie whether circular, square or rectangular in plan, Whether at or above ground level, whatever their height to width ratio, or whether or not They have a hopper bottom. More specific terms, related to particular shapes or Proportions, are given below, but even here it must be noted that the definitions are not Necessarily precise. a) A bin may be squat or tall, depending upon the height to width ratio, Hm/D, where Hm is the height of the stored material from the hopper transition level up to the surcharged material at its level of intersection with the bin wall, with the bin full, and where D is the plan width or diameter of a square or circular bin or the lesser plan width of a rectangular bin. Where Hm/D is equal to or less than 1,0 the bin is defined as squat, and when greater as tall. b) A silo is a tall bin, having either a flat or a hopper bottom. c) The hopper transition level of a bin is the level of the transition between the vertical side and the sloping hopper bottom. d) A bunker is a container square or rectangular in plan and having a flat or hopper bottom.

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e) A hopper, where provided, is the lower part of a bin, designed to facilitate flow during emptying. It may have an inverted cone or pyramid shape or a wedge shape; the wedge hopper extends for the full length of the bin and may have a continuous outlet or several discrete outlets. f) A multi-cell bin or bunker is one that is divided, in plan view, into two or more separate cells or compartments, each able to store part of the material independently of the others. The outlets may be individual pyramidal hoppers (ie one per cell) or may be a continuous wedge hopper with a separate outlet for each cell. g) A ground-mounted bin is one having a flat bottom, supported at ground level. h) An elevated bin or bunker is one supported above ground level on columns, beams or skirt plates and usually having a hopper bottom.

1.3 Design Codes and Standards The design and construction of the storage tanks are bounded and regulated by various codes and standards. List a few here, they are: 

American Standards API 650 (Welded Steel Tanks for Oil Storage)



British Standards BS 2654 (Manufacture of Vertical Storage Tanks with Butt welded Shells for the Petroleum Industry



The European Standards - German Code Din 4119 – Part 1 and 2 (Above Ground Cylindrical Flat Bottomed Storage Tanks of Metallic Materials) - The French Code, Codres – (Code Francais de construction des reservoirs cylindriques verticauz en acier U.C.S.I.P. et S.N.C.T.)



The EEMUA Standards (The Engineering Equipments and Materials Users Association)

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Company standards such as shell (DEP) and Petronas (PTS)

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Chapter 2

Design of liquid Storage tanks

The design of vertical, cylindrical tanks for the storage of liquids can be divided into three basic areas: 

The shell



The bottom



The roof

The design of each of these is discussed in detail in this Chapter.

2.1 Shell Design The cylindrical region of the tank is made up of a number of cylindrical shell courses or tiers, each usually of same height. The courses are usually butt-welded although lap joints are occasionally used. Each course is made up of number of equal length plates. For calculating the thickness of courses two methods are available which are discussed below. 2.1.1 Calculation of Thickness by the 1-Foot Method The 1-foot method calculates the thicknesses required at design points 0.3 m (1 ft) above the bottom of each shell course. This method shall not be used for tanks larger than 60 m (200 ft) in diameter. The required minimum thickness of shell plates shall be the greater of the value computed as followed [API 650, 2007]: Design shell thickness:

Hydrostatic test shell thickness:

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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 2.1.2 Calculation of Thickness by the Variable-Design-Point Method Note: This procedure normally provides a reduction in shell-course thicknesses and total material weight, but more important is its potential to permit construction of larger diameter tanks within the maximum plate thickness limitation. Design by the variable-design-point method gives shell thicknesses at design points that result in the calculated stresses being relatively close to the actual circumferential shell stresses. This method may only be used when it is not specified that the 1-foot method be used and when the following is true:

L = (500 D t)0.5, in mm, D = tank diameter, in m, t = bottom-course shell thickness, excluding any corrosion allowance, in mm, H = maximum design liquid level, in m. Complete, independent calculations shall be made for all of the courses for the design condition, exclusive of any corrosion allowance, and for the hydrostatic test condition. The required shell thickness for each course shall be the greater of the design shell thickness plus any corrosion allowance or the hydrostatic test shell thickness, but the total shell thickness shall not be less than the shell thickness required by following condition. 

The required shell thickness shall be the greater of the design shell thickness, including any corrosion allowance, or the hydrostatic test shell thickness, but the shell thickness shall not be less than the following:

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Nominal Tank Diameter

Nominal Plate Thickness

(m)

(mm)

D