Engineering Presentation-STORAGE TANKS_Part-3_1.pptx

7/30/2019 Engineering Presentation-STORAGE TANKS_Part-3_1.pptx

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DESIGN OF STORAGE TANKS

MECHANICAL DEPARTMENT

Design Of Tanks Sunday, 28 April 2013


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FLOATING ROOF

SAFETY MOMENT

If you discover a fire:

1. Shout FIRE and immediately break the glass in front of a red

PUSH BUTTON ALARM ACTIVATION POINT (by all fire exit

doors). This will sound the fire alarm.

2. On hearing the fire alarm ring continuously for more than 20

seconds, all of us must immediately evacuate the building by the

nearest available fire exit. As we have two fire exits, DO NOT PANIC ;walk and do not run.

3. The Fire Wardens INSTRUCTIONS MUST BE OBEYED.

4. All of us should go to the Muster Point located on the grass lawn

opposite side of the road to the main entrance.

5. Do NOT leave the Muster Point until you are advised that it is safe to

do so.

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Design Of Tanks

Design of Tanks (API-650) Part-2

Sunday, 28 April 2013

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Design Of Tanks

Tank Stability Check For Seismic Load.

Design of Tanks with Internal Pressure.

Design of Tanks with External Pressure.

Design of Anchorage For Tanks

INDEX

Sunday, 28 April 2013

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Design of Tanks

Tank Stability Check For Seismic Load

Sunday, 28 April 2013Design Of Tanks

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Seismic Design of TankSeismic Parameters


The procedure for finalizing the seismic design parametersare explained below:

For sites located in USA or where ASCE-7 method is the

regulatory requirement, the maximum considered

earthquake ground motion shall be defined as the motion

due to an event with 2% probability of exceeding within aperiod of 50 years, where:

SS = the mapped maximum considered earthquake (MCE),

5% damped, spectral response acceleration at short

period (0.2 second).S1 = the mapped maximum considered earthquake (MCE),

5% damped, spectral response acceleration at a

period of 1 second.

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S0 = the mapped maximum considered earthquake (MCE),5% damped, spectral response acceleration at a period

of 0 second, usually referred to as peak ground

acceleration. Unless otherwise specified or determined,

S0 shall be defined as 0.4SS. S0 is same as the seismic

zone factor Z as specified in UBC 97. SS & S1 can obtained from ASCE for sites located in USA.

For sites located outside USA, these values shall be

specified by client.

For locations outside USA, if only the peak groundacceleration S0 is specified, SS & S1 can be calculated as

below:

SS = 2.5 x S0 & S1 = 1.25 x S0

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Seismic Design of Tank

Seismic Parameters

SMS = MCE spectral response acceleration at short period (0.2second), adjusted for site class effect = Fa x SS

SM1 = MCE spectral response acceleration at 1 second,

adjusted for site class effect = Fv x S1.

Fa & Fv can be taken from table E1 & E2 of API 650

based on the site class as specified by Client.

SDS = Design spectral response acceleration at short period

(0.2 second)

= SMS x (2/3) for locations inside USA;

= SMS for locations outside USA

SD1 = Design spectral response acceleration at 1 second.

= SM1 x (2/3) for locations inside USA;

= SM1 for locations outside USASunday, 28 April 2013Design Of Tanks

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Oncethe values of SDS & SD1 are known, use API 650 Appendix Eequations to find seismic shear and moment.

When the ground moves under seismic activity, the body of the

tank and a portion of the liquid (Wi) will be excited (vibrating) in

the impulsive mode (corresponding to 5% damped spectra)

whereas the remaining part of the liquid (Wc) will be excited in theconvective mode (corresponding to 0.5% damped spectra). Each

of these parts will be vibrating at its natural frequency-f (where

time period = 1/f).


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The natural frequency of the tank (and the part of liquid vibratingwith it- Wi) is such that, its time period will always will be less than

Ts (0.2 seconds), and hence its spectral response acceleration is

SDS.

The time period of the liquid moving in convective mode is:

Where


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Where,

Ai = Response spectrum acceleration coefficient for impulsive

mode.

Ac = Response spectrum acceleration coefficient for convective

mode.

I = Importance factor = 1 unless otherwise specified.

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Seismic Design of TankSeismic Shear Force

Rwi = Response modification faction for impulsive mode= 4 for mechanically anchored tanks; 3.5 for self

anchored tanks.

Rwc = Response modification faction for convective mode

= 2 for mechanically anchored tanks & self anchored

tanks.

TL = Long period transition period, as listed in ASCE-7; =

4 for regions outside USA.

TC = Time period for the sloshing mode.

K = Coefficient to adjust spectral acceleration from 5%to 0.5% damping = 1.5


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The seismic shear force is:

Where,

V = total shear force in Newton

Vi = shear force from the part in impulsive mode.Vc = shear force from the part in convective mode.

Wp = total weight of tank content. N.


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Wi = Weight of tank content in impulsive mode . N.Wc = Weight of tank content in convective mode . N.

Ws = Weight of tank shell & Appurtenances . N.

Wr = roof load including 10% of design snow load . N.

Wf = Weight of tank floor . N.


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Seismic Design of TankSeismic Shear Force & Moment

Wc = Weight of tank content in convective mode

Where,D = tank diameter in M

H = Design Liquid height in M


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The centers of action of these shear forces (required to calculatethe ring wall moment) are :


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Where,Xi = Height from the bottom of shell to Centre of action of lateral

seismic force related to impulsive liquid force for ring wall

moment . m.

Xc = Height from the bottom of shell to Centre of action of lateral

seismic force related to convective liquid force for ring wall

moment . m.

Xs = Height from the bottom of shell to Centre of gravity of tank

Shell. m.

Xr = Height from the bottom of shell to Centre of gravity of tankroof. m.


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Seismic Shear Force & Moment

The centers of action of impulsive & convective shear forces, tocalculate the slab moment are :

Xis = Height from the bottom of shell to Centre of action of lateral

seismic force related to impulsive liquid force for slab moment. m.


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Seismic Shear Force & Moment

Xcs = Height from the bottom of shell to Centre of action of lateralseismic force related to convective liquid force for slab moment .

m.


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Seismic Design of TankDynamic liquid Hoop Stress

Dynamic Liquid Hoop Forces.


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Ni = Impulsive hoop membrane force N/mm

Nc = Convective hoop membrane force N/mm

Nh = hydraulic hoop membrane force N/mm

= (h x t) = 4.9 x D x Y x G

Y = Distance from liquid surface to analysis point. (Note: For

each shell course, the analysis point may be one foot above the

base of the shell course.Av = Vertical Earthquake acceleration coefficient =0.14*SDS

h = Hoop stress due to liquid head


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s = Hoop stress due to hydro-dynamic effect of Seismic load.t = Corroded thickness of shell at analysis point.

The calculated values of hoop stress shall be less than 1.33 times

the allowable stress as specified in table 5.2 of API-650


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Seismic Design of TankCheck for Anchorage

To check if tank requires mechanical anchorage to resist seismicoverturning moment (Mrw), calculate the weight of liquid

available to resist overturning as below:

Wa =

Where

Wa = weight of liquid available to resist overturning N / m

ta = corroded thickness of bottom plate under shell in mm

Fy = minimum specified yield strength of the bottom plate in Mpa.

H = the design liquid level in M

Ge = effective specific gravity including vertical seismic

acceleration = G (1-Av).


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If the annular bottom plate is thicker than the remaining part ofthe bottom plate, the internal projection (L) of the thicker annular

plate shall be greater than or equal to the value calculated as

below if the benefit of Wa in resisting overturning is to be

considered.


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To check, if tank requires mechanical anchorage, calculate the

anchorage ration, J :

Where,

wt = (Weight of shell, Roof and appurtenances) / (D). N/M

wint = (D * Pi * 1000 / 4). N/M


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Seismic Design of TankCompressive stress in shell

If J is < 0.785, there is no net uplift; mechanical anchorage is notrequired.

If 0.785 < J < 1.54, tank is still self anchored; Check the shell for

compressive stress.

If J > 1.54 tank requires mechanical anchorage to resist seismic

overturning.

Compressive stress in the bottom shell course of a self anchored

tank :

For J < 0.785

Mpa


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For J > 0.785

Mpa

Compressive stress in the bottom shell course of a mechanicallyanchored tank :

Mpa


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Allowable compressive stress:

t in the above equation is the required thickness of bottom shell

course excluding any corrosion allowance.

If the calculated compressive stress is more than allowable

compressive stress, increase the bottom shell course thickness

such that the calculated compressive stress is less than theallowable stress.


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Seismic Design of TankSloshing Height

Corroded shell thickness for all other shell course shall also beincreased from the required thickness in the same ratio as the

bottom shell course.

The method for calculating the sloshing height and the

requirement of free board to contain the sloshing liquid are

specified in clause E.7.2 of the code.


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Design of Tank

Design of Tanks with Internal Pressure


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Design of Tank For Internal Pressure


API 650 tanks can be designed for a maximum of 18 kPa internalpressure in the vapor space, when additional requirements as

specified in Appendix F are met.

When the uplift due to internal pressure is less than the weight of

roof plate & attached roof structure if any, additional requirements

of appendix F need not be followed.

When the uplift due to internal pressure is more than the weight

of roof plate & attached roof structure if any, but less than the

weight of roof, roof structure, shell & shell attachments, apply the

requirements of clause F3 through F6.

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When the uplift due to internal pressure is more than the weightof roof, roof structure, shell & shell attachments, apply the

requirements of clause F3 through F7, and anchor the tank to a

counter balancing weight.

Requirement of clause F7 is applicable only if anchorage is

required due to internal pressure alone. For, tanks requiringanchorage to resist the combined uplift due internal pressure plus

wind or seismic, clause F7 is not applicable if anchorage is not

required for internal pressure alone.

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The above is explained in a decision tree in Figure F-1


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The basic requirement of Appendix F is that the roof to shelljunction is to be adequately stiffened to withstand the hoop

compressive stress generated from the horizontal component of

the tensile force in the roof plate due to internal pressure.

The participating area of

the roof to shell junction

to resist this hoop stress

is marked in Fig. F2.


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The provided area in the compression ring in the corrodedcondition shall be more than or equal to the required area as

calculated from equation F.5.1.

Eqn F.5.1

Back calculate the (maximum) design pressure of the tank on the

basis of the as-built area of the compression ring using equation

F4.1 Equation F.4.1.


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Clause F.4.2 defines the maximum permitted design pressurePmax for an un anchored tank under the combined effect of

internal pressure and wind. If the specified design pressure is

more than Pmax, anchorage shall be provided.

Calculation of Failure pressure is to be done on the basis of the

pressure calculated as per clause F.4.1 using the as-built area ofthe compression ring.

Also as per clause F.4.3, Pmax < = 0.8 Pf


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If the net uplift (uplift weight) at the bottom of the shell ispositive, tank shall be anchored to a counter balancing weight

and additional requirements of clause F.7 shall be met.

These additional requirements are:

In calculating the thickness of shell, shell manhole & clean out

door, the design liquid head H shall be increased by the quantityP/(9.8G).

Design & welding of roof and design, reinforcement and welding

of roof manholes & nozzles shall be completed with consideration

of both API 650 & API 620. The design rules shall be as follows:


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The thickness of self supporting roof shall not be less than thatrequired by API-620 5.10.2 & 5.10.3, using allowable stress as

defined in table 5.2 of API 650. The thickness of self supporting

roof shall not be less than that required by API 650 clause 5.10.5

& clause 5.10.6.

1. Roof Plate, manway & nozzle material shell be as per API 650section 4.

2. Roof manway and roof nozzle shall meet the requirement API

650 clause 5.51 through 5.7.6 for shell manway and nozzles.

When designed details for API 650 vary by height of liquid

head, the values for the lowest liquid level may be used.

Alternatively, manways and nozzles may be designed as per

API 620 (Provided the design temperature is less than 250o F)


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The wording of the above clause (F.7.3) the design rules shall beas follows: is followed by a clause related to self supported roof

only. Many vendors interpret this clause to mean that thickness

calculation as per API 620 is required only for self supported roof.

This interpretation is wrong. Required thickness for all types of

roof (except stiffened roof) shall be calculated using API 620procedure.

The above requirement shall be spelt out in the Inquiry

Requisition to avoid conflicts in future.


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The counterbalancing weight shall be designed so that theresistance to uplift at the bottom of the shell will be greatest of the

following:

1. Uplift produced by 1.5 times the design pressure of the corroded

empty tank plus the uplift from the design wind velocity on the

tank.2. Uplift produced by 1.25 times the test pressure applied on empty

tank (with nominal thickness)

3. Uplift produced by 1.5 times the failure pressure applied to the

tank with the design liquid. Effect of weight of liquid shall belimited to the inside projection of the ring wall from the tank shell.


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Design of Tank

Design of Tank For External Pressure


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API 650 Appendix V defines the procedure for designing Tankshells & roof for external pressure.

All Tanks designed as per Section 5 of API 650 can take external

pressure (partial internal vacuum) corresponding to 0.25 KPa.

The design external pressure can be increased to 6.9 KPa, by

applying the rules of Appendix V

This appendix does not cover the requirement of design of

bottom plates. The minimum liquid level inside the tank shall be

decided in such a way as to have no external pressure on the

bottom plate.


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Equations for calculating the required thickness of self supportingcone & dome roofs are listed. As these equations are slightly

different from the corresponding equations in section 5.10.5.1, &

5.10.6.1., the required thickness is the higher of the two

thicknesses calculated.

The equation for calculating the required area of the roof to shelljunction and the participating area of roof to shell junction are

listed. These equations are also slightly different from the

corresponding equations in section 5.10.5.1, & 5.10.6.1. Hence

the required area is the higher of the two areas calculated.


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Equations for calculating the required thickness of supported roofplates are not listed. However, roof plate with minimum specified

thickness ( 5 mm + CA) is adequate, when the spacing between

supporting rafters are as per clause 5.10.44 of API 650. If the

spacing calculated as per the above equation is too low, increase

the thickness of roof plate.


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Design of shell for external pressure: The rules in this section are applicable only if the following

criterion is fulfilled. (tanks with very small diameter and very high

thickness may not meet this criterion)

For an un-stiffened shell, the following criterion shall be fulfilled.

Where Ps = Greater of Pe & (W + 0.4Pe).


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If the above criterion is not fulfilled, stiffeners are to be provided. The maximum spacing between the stiffeners can be calculated

as below:

If the transformed height of the shell, based on minimumthickness of shell, calculated in the same way as for design of

secondary wind girders are more than Hsafe, Stiffener rings are to

be provided, such that the spacing between the stiffener on the

transformed shell is less than Hsafe.

Apply the same procedure as in the case of intermediate wind

girders for fixing the location of the stiffener ring on the actual

shell.

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Where,

For Ps < 0.25 KPa

For 0.25 < Ps < 0.7 KPa

For Ps > 0.7 KPa


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Design of Tank For External PressureDesign of Stiffener

The number of waves N into which the shell will theoreticallybuckle under external pressure is defined by:

The radial load imposed on the intermediate stiffener:

Q = 1000 PS LS

The required Moment of Inertia & area of the stiffeners are :

The area of the stiffener ring excluding the area of the

contributing shell shall be > half the required area as calculated

above


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Stiffener rings are to be sized to meet the above criteria. In calculating the available MOI and area of the stiffener region, a

height of shell equal to above and below the

attachment of the ring may be considered as contributing.

The area of the stiffener ring excluding the area of the

contributing shell shall be > half the required area as calculatedabove


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k l


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D i f T k F E l P


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Design of end stiffener The required Moment of Inertia & cross-sectional area of the end

stiffener regions are defined as below.

Where, V1 is the radial load imposed on the end stiffener

H is the shell height.

In calculating the available moment of Inertia of the end region, a

distance of Wshell can be considered as participating where,


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D i f T k F E l P


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In calculating the available moment of Inertia and area of the endstiffeners, no benefit shall be taken from the roof plate. A

participating width corresponding to 16*tb on the bottom plate can

be considered as participating, where tb is the thickness of the

bottom plate.


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D i f T k


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Design of Tanks

Design of Anchorage for Tanks


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D i f A h f T k


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The requirements for designing the anchor bolts and anchor chairare defined in table 5.12

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D i f A h f T k


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D i f A h f T k


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The required area of the anchor bolt shall be calculated for eachof the applicable load combination in the table 5.12 using the

specified bolt allowable stress.

The details of anchor chair shall be finalized considering the rules

of AISI E-1 Vol. II, Part VII.

The stresses in the anchor chair and shell from the bolt load shallbe checked for each of the load case as listed in table 5.12, and

shall be less than the specified allowable stress.


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FLOATING ROOF

Design of Storage Tanks

Questions ?

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D i f St T k


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FLOATING ROOF

Design of Storage Tanks

Thank You For Your Patience

Team Members

Ashok Kumar

Rakesh Saxena

Rajesh Choudhury

Jaya Narayanan

Documents

Engineering Presentation-STORAGE TANKS_Part-3_1.pptx