Bpcl Project Completed !!!

ABSTRACT

This project titled “Designing of storage tank for storing furnace oil” gives

and insight into the designing of a storage tank for storing furnace oil. Storage tanks

are constructed to store huge quantities of various petroleum products. Volatile

petroleum products are stored in floating roof tanks. In this project we intend to do

the design of floating roof tank for storage of crude oil.

The tank is designed according to API 650 (11TH Edition) Standards. Furnace

oil comes under Class B category; hence a cone roof type storage tank was selected.

The shell of the tank was designed in the most cost effective manner.

The height of the tank is 16m and Diameter is 12 m. Due to stability problem

the Height of the tank is restricted. The shell plates were designed according to their

availability. The wind guiders are provided for providing stiffness to the shell. The

roof was designed according to API 650 Standards.

The project deals with the design features of a fixed cone roof namely bottom

and annular plates, shell plates, wind girder, cooling water system, roof drain and

firefighting equipment.

KARPAGAM COLLEGE OF ENGINEERING 1

INTRODUCTION

COCHIN REFINERIES LIMITED was incorporated in the joint sector as a public

limited company in September 1963 at Ernakulam with technical collaboration and financial

participation from Philips Petroleum Company of USA and Duncan brothers of Kolkata.

Former Indian Prime Minister Mrs. Indira Gandhi dedicated KRL to the nation on 23

September 1966.

The name of the company was changed to Kochi Refineries Limited in May 2000.

KRL became a subsidiary company of Bharath Petroleum Corporation limited in April 2002.

Philips Petroleum International Corporation was the prime contractor for the

construction of our refinery. They entrusted the work to Pacific Procon Limited. Construction

work started in March 1964 and the first unit came on stream just after 29 months in

September 1966.

From the commissioning to date, the refinery under took three expansions in the

refining capacity and the installation of secondary processing facilities .The refinery then had

a design capacity of 2.5 metric million tons per annum (mmtpa) which was increased to 3.3

mmtpa in 1973. Production of liquefied petroleum gas (LPG) and aviation turbine fuel (ATF)

commenced after this expansion. Mumbai high court was first processed in 1977.

Refining capacity was further enhanced to 4.5 mmtpa in November 1984 when a

fluidized catalytic cracking unit (FCCU) was added. The secondary processing facilities (fpu,

fccu, lpg and gasoline merox unit) with a capacity of processing 1 mmpta VGO was

commissioned in 1985. It entered the petrochemical sector in 1989 when an aromatic

production facility with a design capacity of 87,200 tons per annum of benzene and 12,000

tons per annum of toluene was commissioned.

In Dec 1994, refining capacity was increased to 7.5 mmtpa (150,000 bpsd). A

fuel gas de-sulphurisation unit was installed as part of this project to minimize sulphur

dioxide emission. A captive power plant of 26.3 MW was commissioned in 1991. An

additional captive power plant of 17.8 MW was commissioned in 1998. KRL is now self -

sufficient in power


Bharat Petroleum Corporation Limited acquired the Government of India's shares in KRL in

March 2001. With this the company has become a subsidiary of BPCL.

PROJECTS COMPLETED

CEMP PHASE-1

The phase 1 of the capacity-expansion-cum-modernization project (CEMP) that

envisaged refinery modifications required to meet BS-II Product Specifications, has met the

target. Supply of auto fuels like petrol and diesel confirming to Bharath Stage-II

specifications began in April 2005.

Rainwater Harvesting

Kochi Refinery has one of the largest rainwater reservoirs in the state with a

detention pond of 1, 25,000 KL capacity to collect surface run off water from around 8.0

lakhs.sq.m of land. The integrated rainwater harvesting system to collect, conserve and

protect rainwater for effective utilization has been constructed and commissioned.

The project will enable (i) using rainwater collected from roof- top during the monsoon for

the process and drinking requirement and thereby reducing the intake of water from Periyar

river, (ii) charging the ground water table using the collected roof rainwater (iii) harvesting

around 1, 25,000 KL of rainwater per annum falling on the land area by collecting the surface

runoff and thereby augmenting the quality of existing water bodies and to replenish the

ground water table.

Eco Park

The Ecological Park within Kochi Refinery premises spreads over a land area of 5.50

acres with a view to restore the healthy ecosystem, control pollution, develop clean

environmental condition and prevent soil erosion. Around 3750 numbers of wide ranges of

forest species, ornamental trees, fruit trees and attractive flowering plants along with

medicinal herbs have found a place in the Eco Park. Treated effluent water is being utilized to

feed the dry land plants. Available resources is also being used to develop scrap land to green

belts which in-turn would promote environmental awareness, enhance the environmental

quality of region, develop habitat for rare migratory species and also increase tree coverage.


ONGOING/UPCOMING PROJECTS

CEMP PHASE-II PROJECT

The object of the project is to upgrade auto fuels i.e. Motor spirit diesel from the

present BS-II specifications to Euro-III specification and to increase the capacity of the

refinery from 7.5 MMTPA to 9.5 MMTPA. Consent to establish the project facilities have

been obtained from State Pollution Control Board and clearance from Ministry of

Environment & Forests. The investment clearance for the project has also been obtained.

Estimated cost of the project is Rs.2592crores.

The major project facilities include revamp of CDU-II for capacity expansion by 2.0

MMTPA, VGO HDS unit, CCR Reformer unit and a GT for power generation. The project is

scheduled to be completed by September 2009.

Single Point Mooring Project

This project is to set up Crude Oil Receipt Facilities (CORF) consisting of Single

Point Mooring (SPM) for berthing Very Large Crude Carriers (VLCC). Shore Tank Farm and

associated pipelines and facilities. The job is progressing as per scheduling. Pilling jobs for

tank foundations are in progress. Orders have been released for Single Point Buoy. SPM

Project is scheduled for completion by May 2007.Community development schemes have

been activated along with the construction activities of the SPM. As part of its commitment

towards community development in the region, KRL has agreed to undertake schemes that

include; development of roads, drainage facilities and Fish landing Centre, improvement of

Health Care Centers including the deployment of an ambulance at Puthuvypeen, assistance

for educational facilities, augmentation of Water supply and street lighting.

Gas Task Force

The Gas Task Force (GTF) formed by BPCL and erstwhile KRL have been

signing Heads of Agreement (HOA) with major industrial customers in the States of Kerala,

Tamil Nadu, Karnataka. The HOA contains principal terms and conditions viz., term Sheet,

for the sale and purchase of Regasified Liquefied Natural Gas (RLNG) between the customer

and BPCL. The HOA shall be in force till such time a long term Gas Sales agreement is

entered in between the parties. As the gas availability is limited, the HOA acts as a formal


document by which the quantity of RLNG required by the customer is reserved in advance.

Ti is anticipated that PLL and would be able to supply RLNG from its Kochi terminal by

2009 end.

The GTF intends to market the RLNG in the state of Kerala and adjoining areas of the States

of Tamil Nadu and Karnataka, amongst major industrial customers whose Gas requirement is

more than 12,500 TPA. Distribution of Gas in the city of Kochi, Compressed Natural Gas

(CNG) for automotive sector, Piped Natural Gas (PNG) for domestic use and Regasified

Natural Gas (RNG) for industrial/commercial customers whose usage is below 12,500 TPA

would be done by a separate Joint Venture Company to be formed by BPCL & GAIL.

Propylene Recovery Unit

LPG from Fluidized Catalytic Cracking Unit is a major source of propylene and

separating this propylene form LPG is a proven route to value addition. A detailed feasibility

report on setting up Propylene recovery unit at KRL was prepared with the help of

consultants. The investment approval for the same was received from the KRL Board and

action has been initiated for implementation of the project.

FUTURE PLANS

In the view of the declining market for furnace oil with high sulphur content and

reducing availability/increasing prices of light and low sulphur crudes, a suitable residue up

gradation facility has been found essential for Kochi Refinery. The proposed capacity

expansion of the refinery by the year 2010 will result in generation of additional quantities of

high sulphur heavy residue.

Delayed coking has been identified as an option for up gradation of refinery residue to

value added distillate products. A detailed feasibility study for refinery bottoms up gradation

is being carried out with the help of consultants. The possibility of transporting and

processing some short residue from BPCL-Mumbai Refinery is also being studied.


UTILITIES

Utilities section provides the utilities such as steam. Compressed air and cooling

water required for various process units and other facilities in the refinery. A

demineralization plant treats and supplies feed water to boilers and water for process

requirement facilities and for power generation also come under this section. Power

requirements of the entire refinery can be met by the internal generation.

Steam- It is generated and consumed in the refinery is classified into three

depending on the pressure i.e., low-pressure @ 5kg/cm2, medium pressure @ 18kg/cm2 and

high pressure having pressure above 18kg/cm2.Medium pressure and low pressure steam are

used for various process requirements. Medium pressure steam is used for driving turbines

used as prime movers in the process units and other facilities. High pressure steam is mainly

used for power generation.

CPP-1: It has capacity of 26.3 MW. The unit was commissioned in 1991.It consists of

gas turbine for power generation and heat recovery steam generator.

CPP-2: The 17.8 MW steam turbo generator was commissioned in 1998.Refinery fuel oil

is used as fuel for generating high pressure steam in the boiler. UB7 and steam is used for

driving the-turbine.

COMPRESSED AIR: It is used as instrument air and plant air. Instrument air is required

for operating the instruments and plant air is used for general cleaning, blowing, and

operating pneumatic tools and other process requirement. The supply of plant air and

instrument air is done by separate air compressor.

COOLING WATER: - Water serves for various purposes such as cooling medium for

process steam, making boiler feed water to produce steam etc. Total consumption of water is

about 2.5 million gallon per day. Water is received from Periyar river basin. Water is stored

in two quarries from where it is pumped to process area and colony after treatment.


DEMINERALISATION PLANT

The natural water obtained from various sources contains a member of dissolved salts

such as bicarbonates, carbonates, sulphates, chlorides, and nitrates of calcium, magnesium,

and sodium. For high-pressure boilers, steam is put to use in condensing turbines and for

laboratory purpose the dissolved impurities in water are objectionable and complete removal.

The complete demineralization or de-mineralization is carried by passing water

through a series of ion exchange beds where all the dissolved ions are removed. The essential

steps followed are: dosing of Na2SO3 to remove excess chlorine, filtration through a strong

acid cation exchanger, weak base anion exchanger in series, and removal of free carbon

dioxide in the decationised water in a mixed bed containing a mixture of cation and anion

resins.


SULPHUR RECOVERY UNIT

Petroleum products are finding increasing use in the day to day activities of mankind

includes personnel and commercial needs. Coupled with the increasing demand for fuels is

the problem of deteriorating quality of air in the environment. One of the largest contributors

to the poor quality of air is vehicular exhaust. Due to the increased pressure on the

environment from various exhaust gases significant reduction in emissions of SO2 and NO2

are required. There is a general agreement that reducing sulphur content is an effective means

of improving air quality.

It is in this context that the sulphur recovery unit comes into perspective. The sulphur

recovery unit is the process unit setup for the removal hydrogen sulphide from the refinery

fuel gas steam. KRL has setup a diesel desulphurization unit of 2 mmtpa capacity to reduce

the sulphur content in diesel from 1 weight % to 0.25 weight %. The input of fuel gas to the

SRU comes in two streams. High pressure steam comprising of gas from CC discharge,

sponge gas from naphtha stabilizer in PU –2 and merge streams from NHDS and KHDS.

Overhead non-condensable of visbreaker along with gas from LV1 constitute steam. The high

pressure gas steam out of SRU has various consumption points of fuel gas.

LIGHT END FEED PREPATION UNIT

A Light End Feed Preparation Unit (LELPU) to supply polybutenes was

commissioned in March 1993. BPCL also commissioned a raffinate purification unit for the

manufacture of petroleum hydrocarbon solvent in January 1994. BPCL started production of

mineral turpentine oil in March 1996 and mixed aromatic solvent in March 1996.

The main areas of concern for BPCL are

Water requirement

Crude oil receipt facilities

Pollution control and environment care

The organizational structure of BPCL consists of various departments as follows:


Manufacturing

Stock and oil department

Maintenance

Technical service department

Projects

Materials & Services

Quality Control

Research & Development

Oil Economics

Vigilance

Power and utilities

Computer and automation

Corporation planning

Marketing

Finance and accounts

Secretarial

Human Resource Management

Security

Each department is performing certain specific objectives in coordination with the

others in achieving the organizational goals.

BPCL'S MISSION

To strengthen the presence in petroleum refining and marketing of

petroleum products and to grow into the energy and petrochemical sectors.

To realign orientation of thinking and philosophies to become a market

driven and customer friendly organization with focus on total quality

management.

To enhance shareholder value and maximize returns through the best use

of resources.

To recognize employees as the most valuable asset of the organization and

foster a culture of participation and innovation for employee growth and

contribution.


To achieve global standards of excellence through R & D efforts,

technology up-gradation, safety management and environmental

protection.

To be a major contributor towards community development and welfare of

the society at large.

ENVIRONMENTAL POLICY

BPCL engaged in petroleum refining activity is committed to:

» Strive for continual improvement of the environment performance at

BPCL and prevent pollution

» Comply with regulatory & legal requirements of oil industry

o Respect the interests of customers, employees and other interested parties

o Promotion and development of greenery in the surrounding areas

o Select cleaner technologies & avoid environmental degradation

o Conserve natural resources and reduce energy consumption

o Print and distribute BPCL's environmental policy to all employees

and make them available to public

o Safe disposal of hazardous waste

Our environmental objectives:

Treatment and disposal of 10000 MT of accumulated oily sludge after

mechanical recovery of oil by December 2003.

Decommissioning of equalization pond at ETP-I by Dec 2002 to

reduce fugitive emissions at KRL.

De-silting of water channel from outlet `B` to outlet `C` during the year

2002-03.

Reduce specific energy consumption of BPCL from the present level.

Conducting training programs on ISO 14001 EMS awareness.

ISO 14001


The company has been awarded the prestigious ISO 14001 certificate in

recognition of the company’s environment management measures.

Environment auditors M/s Bureau Veritas Quality International (BVQI) certified

that the management system of the company had been assessed and found it to be in

accordance with the requirements of the environmental standards ISO 14001.

ISO 14001 is an international standard for environment management system,

(EMS), issued by the International Organization for Standardization, Geneva. It provides a

systems approach to handling the impact of an organization’s activities and the use of its

product services on the environment.

This standard requires formation of short-term and long-term environmental

policy, environmental objectives, and compliance with legislative requirements and

addressing significant environmental impacts with solutions.

BPCL is the first company in Kerala to get this environment management standard

BPCL took the road of quality and responsibility. And it paid rich dividends of goodwill

and progress. It was thirty-five years back that BPCL, formerly known as Cochin Refineries

Ltd, started as a refinery with a capacity of 2.5 million metric tons per annum. Now we

refine more than 7.5 million metric tonnes every year.

Its turnover was Rs. 104802 million. Its profit for the year 2002-03 was

Rs. 6965 million. We have been paying rich dividends consistently.

BPCL AT A GLANCE

Location: Ambalamugal in Kochi

Refining capacity: 7.5 million metric tonnes per annum

Products: LPG, petrol, diesel, kerosene, naphtha, benzene, toluene,

LSHS, furnace oil, ATF, specialty solvents, bitumen,

rubberized bitumen etc.

Turnover: Rs.104802 million (2002-2003)

Profit before tax: Rs.6965 million (2002-2003)


KRL is the only company in Kerala with a turnover of over Rs.10000 million. We

have been paying rich dividends to our shareholders consistently. The Board of Directors

has recommended a Dividend of Rs.10/- per share (100%) for the year 2002-03 as against

Rs. 2.20 per share during 2001-02.

Government of India has rated our performance for the year 2002-2003 as

'Excellent'. The turnover during 2002-2003 was Rs 104802 million. The profit before tax

was Rs.6965 million.

New proposals are:

Capacity Expansion Project (CAPEX) for expanding capacity from 7.5

MMTPA to 13.5 MMTPA

500 MW power generation project.

Kochi – Karur products pipeline project

A mandatory crude oil tankage project


INTRODUCTION TO STORAGE TANKS

Petroleum storage tank are an indispensable part of petroleum refining industries.

They are used for intermediate and final product storage in a process plant or for storing

petroleum products and chemicals at terminals. They can also be used as process equipment

in non-ferrous plants where open top tanks are used for mixing, blending, precipitation and

settling process or as chemical reactor vessels.

Tanks are classified according to their construction, and the construction is on the

basis of the product which is to be stored in them.

CLASSIFICATION OF PETROLEUM PRODUCTS

Petroleum products are classified on the basis of their Flash Points.

FLASH POINT

"Flash point" of any petroleum liquid is the minimum temperature at which the liquid

yields vapour in sufficient concentration to form an ignitable mixture with air and gives a

momentary flash on application of a small pilot flame under specified conditions of test.

Petroleum products are classified according to their flash points as follows:

Class A Petroleum: Liquids which have flash point below 23 degree C - crude (Bombay

High), gasoline, naphtha, low aromatic naphtha, high aromatic naphtha.

Class B Petroleum: The Liquids that have flash point of 23 degree and above but below 65

degree C . E.g.: superior kerosene oil, high speed diesel, light diesel oil, aviation turbine fuel,

and jet propulsion-5.

Class C Petroleum: The Liquids that have flash point of 65 degree C and above but below


93 degree C. E.g. Furnace oil, low sulphur heavy stock, asphalt, seal oil, plant fuel.

Excluded Petroleum: The liquids that have flash point 93 degree C and above. E.g.

Liquefied gases including LPG do not fall under this classification but form separate

category.


TYPES OF STORAGE TANKS

I. Cone roof tanks

2. Floating roof tanks

3. Floating cum cone roof tanks

4. Spherical vessels

1. CONE ROOF TANKS

Fig:1 cone roof tank

The cone roof tanks have fixed roof and are in a sense closed vessels. They are

vertical cylindrical vessels having a conical top and made of welded steel plates and used

mainly for storing less volatile products. The fixed cone roofs have truss suppOl1S. Tanks

meant for storing products like asphalt, vacuum gas oil etc. at high temperature is fully

insulated externally. There are 32 cone roof tanks in KRL at present. Depending on the

service the cone roof tanks will have the following accessories:

Man ways to go in- on the shell and roof

Vent with flame alerter or mesh roof vents

Pressure cum vacuum relief vents with flame arrestor to prevent excessive

pressure build up of vacuum pulling inside.

Gauging datum plate

Gauge hatch with reference mark


Auto gauges

Dial thermometer

Mixing devices

Steam heating coils with inlet and outlet nozzles

Product inlet or outlet headers, the inlet header with jet nozzles

Gas fired burners with steam heating coil for heating the product (asphalt

/LSHS)

Water draw

Stairway

Earthing facilities


2. FLOATING ROOF TANKS

Fig:2 Floating roof tank

Floating roof tanks are intended for storing products having high vapour pressure like

HSD and gasoline. They have a movable roof that floats on the surface of the tank contents.

Thus the vapour space is kept constant and minimum. Roofs are pontoon type having

enclosed air chambers. Foam type neoprene seal is used to seal off the clearance between the

rim of the roof and the tank shell in these tanks. As long as the pontoons do not leak the roof

will not sink.

The roof is supported when it is not afloat by a number of adjustable legs with low

and high position. Normally roofs are kept on low legs. When a tank is to be taken out of

service for cleaning or repairs, the roof will be put on high legs to provide space for people to

work inside. Pump out vents in the roof permit the escape of air when an empty or near-


empty tank is filled and the roof is afloat. Roof drains are provided to drain water that is

collected on the roof during rains. This is done by providing hoses or pipes with swivel joints

from the roof to the outside of the tank shell near the bottom. A non-return valve on the

hose/pipe at the roof end and a gate valve at the bottom prevent escape of oil from the tank in

case the hose develops leak. In certain cases the roof is also provided with an emergency

drain having water seal. In cases the rainwater does not flow freely through the roof drain it

can get into the tank through the emergency drain. Access to the floating roof is by an inside

stairway, one end if which is hinged at the gauge’s platform at the top of the outside stairway

and the other end is free to move on rollers on a runway fixed to the roof as the roof moves

up and down To maintain the shape of the tank when it is subjected to wind loads the tank is

reinforced with stiffening rings called wind girders.

There are 51 floating roof tanks in KRL at present. The following arc the accessories

provided on floating roof tanks:

Man ways to go in - on the shell and roof.

Gauging datum plate.

Gauge hatch with cover and reference mark.

Auto gauges (in certain tanks).

Dial thermometer.

Mixing devices.

Water draw.

Roof drain.

Inlet pipe header with jet nozzle and outlet.

Gas fired burners with steam heating coil for heating the product.

(Asphalt /LSHS).

Outside stairway.

Inside stairway.

Gauging platform.

Roof legs and pump-out vents.

Roof guides to keep the roof in position.

Roof shoe with neoprene seal.

Metal conductors over the roof seal to dissipate electric charge to the

earthing.


Earthing facilities.

3. FLOATING CUM CONE ROOF TANKS

They have fixed cone roof in addition to a floating roof and they are intended for

storing toxic products having high vapour pressure. Products like benzene and toluene are

carcinogenic and should be prevented from escaping into the atmosphere. So they are stored

in floating cum cone roof tanks. These tanks prevent product from contamination and are

used to store class A and class B products. There are 13 floating cum cone roof tanks in KRL

at present.


LAYOUT OF STORAGE TANKS BASED ON OISD

DYKED ENCLOSURES

Petroleum storage tanks shall be located in dykes enclosures with roads all

around the enclosure. Aggregate capacity of tanks located in one dyked

enclosure shall not exceed following values:

For a group of floating roof tanks: 120000cu.m.

For a group of fixed roof tanks: 60000cu.m.

If a group of tanks contains both fixed and floating roof tanks then it shall

be treated as a group of fixed roof tanks for the purpose of above limits.

Dyked enclosure should be able to contain the complete contents of the

largest tank in the tank farm in case of any emergency. Enclosure capacity

shall be calculated after deducting the volume of the tanks (other than the

largest tank) up to the highest of the enclosure. A free board of 200mm

above the calculated liquid level shall be considered for fixing the height

of the dyke.

However for excluded petroleum, the capacity of the

dyked enclosure should be based on spill containment but not

for containment on tank rupture.

The height of tank enclosure dyke shall be at least one meter and shall not

be more than 2.0m above average grade level; inside. However, for

excluded petroleum the minimum height of dyke wall shall be 600mm.

Inter-distance between the nearest tanks located in two dykes shall be

equivalent to the largest tank diameter or 30m, whichever is more.

The dykes should be of earthen construction havl11g trapezoidal cross -

section. The dyke shall not have slope steeper than 1.5 horizontal to 1.0

ve11ical. The top flat surface of dykes up to 1m and up to 2m height, top

flat surface shall have 1000mm width. Brick or stone masonry wall may be

provided where space does not permit construction of earthen dykes.

Pump stations should be located outside dyke areas by the side of roads.


Tanks located overhead for process considerations shall meet safety

distance and shall also have dyked enclosure of RCC construction and

provided with drain valves at suitable height for easy operation.

Grouping of Tanks

Grouping of petroleum products for storage shall be based on product

classification. Class A and/or class B petroleum can be stored 111 the same

dyked enclosure. Class C petroleum should be stored separate enclosure.

However, where class C petroleum is stored in a common dyke along with

class A and / or class B petroleum, all safety stipulations applicable for class

A and/or class B respectively shall apply.

Excluded petroleum shall be stored in a separate dyked enclosure and shall

not be stored along with class A, B or C petroleum.

Tanks shall be arranged in maximum 2 rows so that each tank is

approachable from the road surrounding the enclosure. However, tanks

having capacity 50000cum and above shall be laid in single row.

Fire Walls

In an enclosure where more than one tank is located, firewalls of 600mm should be

provided as explained below:

Any tank having a diameter more than 30m should be separated with fire

walls from other tank

Firewalls should be provided by limiting the aggregate capacity of group of

tanks within, to 20000cu.m.

General

The tank height should not exceed one and a half times the diameter of the


tank or 20m whichever is less.

Piping from/to any tank located in a single dyked enclosure should not pass

through any other dyked enclosure. Piping connected to tanks should run

directly to outside of dyke to the extent possible to m1l11mise piping withll1

the enclosures.

No fire water/foam ring main shall pass through dyked enclosure.

The minimum distance between a tank shell and the inside toe of the dyke

wall shall not be less than one half the height of the tank

Inter distances for tanks/offsite facilities

The following stipulations shall apply for the inter-distances for above ground tanks

storing petroleum:

Inter distances for storage tanks

Sl.no Item FRT

CRT(Class A&B

Petroleum)

Class C

Petroleum

1 All tanks with

diameter upto

50m

(D+d)/4 (D+d)/4 (D+d)/6

2 All tanks with

diameter

exceeding 50m

(D+d)/4 (D+d)/3 (D+d)/4

Table:1

This table is applicable for installations where aggregate storage capacity of class A&B

petroleum stored above ground exceeds 5000cu.m or where the diameter-of any such

tank for the storage of petroleum exceeds 9m.

Distances given are she!] to shell in the same dyke

Notation

o FRT: Floating roof tank


o CRT: Cone roof tank

o D: diameter of larger tank in meters

o d: diameter of smaller tank in meters

If the inter-distance (for class A&B) calculated as above is less than 15m, then

minimum of 15m or 0.50 or d shall be followed.

Inter-distance between class A/B storage tanks and class C storage tanks shall not be

less than 6m.


PARTS OF STORAGE TANK

BOTTOM PLATES AND ANNULAR PLATES

Bottom plates are those plates which are laid at the bottom of the tank. These plates

are lap welded to each other. All bottom plates have a nominal thickness of 6 mm excluding

of corrosion allowance specified by the purchaser.

Bottom plates get corroded rapidly if the fluid is having sea water content (crude

petroleum). Bacterial corrosion of the bottom plates is generally observed in crude and HSD

tanks having high sulphur content. The bottom plates develop deep isolated pits which

eventually puncture and bottom starts leaking. So the proper corrosion allowance should be

provided.

Annular plates are those bottom plates on which the shell plates rest. Annular bottom

plates should be capable of withstanding the weight of the shell plates and the appurtenance.

According to API 650 (3.5.2), annular bottom plates shall have a radial width that

provides at least 600 mm between the inside of the shell and any lap welded joint in the

remainder of the bottom and at least a 50 mm projection outside of the shell.

The projecting out portion of the annular bottom plates are prone to corrosion at the

edges due to accumulation of water between the foundation and the annular bottom plates. So

here also appropriate corrosion allowance should be given.

DRAW OFF SUMP

A draw off sump is provided at the bottom of the tank such that a sl11a'll inclination

is given to the bottom plates towards the sump. Sump shall be placed in foundation before

bottom placement. A neat excavation shall be made to conform to the shape of the draw off

sump. The sump shall be put in place, and the foundation shall be compacted around the

sump after placement and the sump shall be welded to the bottom.


Draw off sump is provided in order to collect the water particles in the oil. A draw

off nozzle is provided on the shell plate to remove the water collected in the draw off sump.

The sump and nozzle are connected by means of an internal pipe.

SHELL

Shell is the major portion of the tank which is exposed to the atmosphere. The

major problem that may arise is corrosion. Shell plates generally get corroded internally

where liquid-vapour is maintained. Internal corrosion in the vapour space is most commonly

caused by hydrogen sulphide vapour, water vapour and oxygen giving pitting type corrosion.

Atmospheric corrosion can occur on all external parts of the tank. This type of corrosion may

range from negligible to severe depending on upon the atmospheric condition of the locality.

All vertical and horizontal shell joints shall be full penetration and full fusion welds. Shell

joints shall be double welded butt joints. . Wind girders shall be welded to the tank at the

location designed. Welding shall be of the same quality as used for the shell. The necessary

shell openings such as manholes, nozzles, drain holes etc. shall be provided to the horizontal

plates.

SHELL OPENINGS

The important shell openings are shell man hole, yield and suction nozzles, water

drain and rain drain.

1. SHELL MANHOLE

One manhole is provided to the tank shell at the bottom shell course for the entry of

humans into the tank for maintenance or other purposes. Here a 600mm dia. manhole is

provided.


Fig:3 shell manhole

2. YIELD AND SUCTION NOZZLES

Three yield nozzles and one suction nozzle arc provided for the tank. These nozzles

are also fixed at the bottom shell course. Yield nozzle is provided for receiving finished,

intermediate or unfinished products into the tank. This nozzle is designed according to the

velocity of yielding and need for agitation. Suction nozzle is designed according to capacity

of the tank and according to place to where the oil is transferred.

3. WATER DRAIN AND ROOF DRAIN

Three nozzles for water draw off and two nozzles for roof drain are provided. The

three water drains are fixed at 120 degree apart on the bottom shell course.

Even though one roof drain is sufficient for proper working two roof drains are

provided. As per the API standards the other is provided as a 100% Standby. Roof drain

outlets are provided at the opposite sides of the bottom shell course.


WIND GIRDER

Wind girder or stiffening rings are provided on storage tanks to prevent the buckling

of tanks against wind loads. Wind girders are usually constructed as walkways to facilitate

the inspection and repair of storage tank.

SEAL

The space between the outer rim of roof and shell should be sealed by an approved

sealing device and sea1ing material should be resistant to the stored product and durable

against friction due to roof movement. Sealing system should exert sufficient sealing pressure

in all directions to prevent any evaporation losses and the arrangement should touch the

product during the operation.

Fig:4 seal

Foam seals have excellent flexibility and recovery from compression and at the same

time permit the roof movement up and down freely with the level of tank contents.

AUTOMATIC TANK GAUGING

Automatic Tank Gauging (A TG) is carried to obtain information about the total

volume or weight of the product in the tank. This information is obtained from four

parameters i.e., liquid level, tank capacity table, average temperature and relative density of


individual tank.

ADVANTAGE'S OF TANK GAUGING

1) Accurate and better inventory control

2) Reduction of work load

3) Tank level is displayed at the tank site and at the central monitoring unit for

prompt attention

4) Accurate level measurements even under turbulent product condition

5) Accurate water bottom level detection

6) It can be used in high safety hazards environments

7) Remote repeatability tests

COOLING SYSTEM

Storage tanks are equipped with water cooling system to bring down the temperature

of the tank shell & protect them from damage when a fire hazard occurs to a neighboring

tank. The system consists of rings fitted around the tank. Numerous nozzles are fixed into the

rings through which water is sprayed to the tank shell at a particular pressure. Water is

supplied to the cooling rings by means of 2 risers which arc placed diametrically opposite to

each other.

FOAM SYSTEM


Fig:5 foam system

Foam for firefighting purposes is an aggregate of air filled bubbles formed from aqueous

solutions and is 100ver in density than the lightest flammable liquid. It is principally used to

form a coherent floating blanket on flammable and combustible liquids lighter than water and

prevents or extinguishes fire by excluding air and cooling the fuel it also prevents re-ignition

by suppressing formation of flammable vapour. It has the property of adhering IO surfaces,

providing a degree of exposure protection from adjacent fires.

The foam generally used in modem tanks is AFFF (Aqueous Film Forming Foam). It

is a synthetic film forming concentrate and is based on fluorinated surfactants plus foam

stabilizers and is diluted with water to a 3% to 6% solution. The foam formed acts as 'a

barrier to exclude air or O2 and to develop an aqueous film on the fuel surface capable of

suppressing the evolution of fuel vapour. The foam produced with AFFF concentrate is dry

chemically compatible and thus is suitable for combined use with dry chemicals.

MATERIAL SPECIFICATION FOR STORAGE TANKS

The materials used in the construction of storage vessels are usually metals, alloys,

clad-metals, or materials with linings that are suitable for containing the fluid. Where no

appreciable corrosion problem exists the cheapest and most easily fabricated construction

material is usually hot rolled mild (low carbon) steel plate.


Low carbon steels are rather soft and ductile and are easily rolled and formed into the

various shapes used in fabricating vessels. These steels are also easily welded to give joints of

uniform strength relatively free from localized stresses. The ultimate tensile strength is

usually between 380Mpa and 450Mpa and the carbon content between 0.15% and 0.25%.

The material generally used for manufacturing storage tanks in India is IS2062 grade

A. It is a low carbon, hot rolled steel with the following specifications.

Carbon (max.) 0.23%

Manganese (max.) 1.50%

Sulphur (max.) 0.050%

Phosphorous (max.) 0.050%

Silicon (max.) 0.40%

Table:2

It has a minimum ultimate tensile strength of 410.6 Mpa and yield strength of 247.6

Mpa.

The pipe material used for making roof legs is AI 06 grade B. The chemical

composition is given below:

Carbon (max.) 0.03%

Manganese (max.) 1.06%

Phosphorous (max.) 0.048%

Sulphur (max.) 0.058%

Silicon(min.) 0.1%

-


Table:3

The minimum tensile strength is 414 Mpa and the minimum yield strength is 241 Mpa


DESIGN OF STORAGE TANK

Design and construction of storage tank for storing furnace oil.

1. Tank selection

The furnace oil is a highly volatile; the flash point of furnace oil is 66ºC. So it

comes under class C of petroleum products and has to be stored in a fixed cone roof tank.

2. Height and Diameter

For fixing the height and the diameter of the tank, the criterion to be maintained as

per API 650 is that the ratio of the total height of the tank to the internal diameter must be

less than 1.5.

Height of the tank/Diameter of tank <1.5

i.e.; H/D<1.5

Height and diameter mostly depends upon the space available on the site, distance between

two consecutive tanks etc. It also depends on the judgment of the designer, by studying the

H/D ratio of the existing tanks in refinery. We selected the diameter as

Height of the tank = 14m

Diameter of the tank = 36m

Here H/D ratio = 14/36=.3889<1.5

(Hence condition H/D < 1.5 is satisfied)


So it is possible according to API 650.

Volume, V=πR2H

V = 3.14*(18*18)*14

= 14243.04 m3

BOTTOM PREPERATION

Cone penetration test

To assess the soil bearing capacity of soil at locations under the bottom plate

penetration test was conducted by IIT Madras. Cone penetration resistance (CPR) was

calculated by determining the number of blows required to attain a 300 mm penetration by

test cone.

The cone penetration resistance is found to vary between 20 and 40 which indicates

that the maximum settlement to be less than 100mm which is permitted for large diameters.

(Present tank being of 50m diameter)

Soil testing

The test sample of soil is collected from various positions of tank bottom and is sent

to IIT Madras. It was tested and certified OK for the construction of the above mentioned

tank.

Bitumen carpeting


Sieved river sand is mixed with 8-10 % volume of Bitumen (80/100 grade) and is

laid on the site and consolidation, rolling, tamping etc. are done. A slope of 1:100 is

maintained towards the shell from the core of the tank.


DESIGN DATA

Design code: API 650 (11th edition)

Diameter: 36 m

Height: 14 m

Product stored: Furnace oil

Specific gravity of product: 0.95

Design specific gravity: 0.95

Corrosion allowance: 2 mm for annual and bottom plate

: 2 mm for shell plates

: 2 mm for roof plates

Design pressure: Atmospheric pressure

Material specification: ASTM A537 grade 1 (As per API 650 Table 3.2). ASTM A537 grade

1 is the Pressure Vessel Plates, Heat-Treated, Carbon-Manganese-Silicon Steel and also it

has got an acceptable value of yield strength (50,000 psi or 345 Mpa) and tensile strength

(70,000 psi or 485 Mpa)

Wind speed: 185 kmph (max)

Maximum rain fall intensity: 57 mm in one hour or 254 mm in 24 hours

DESIGN OF BOTTOM PLATES

According to API 650 standards, bottom plates shall have a minimum nominal

thickness of 6mm exclusive of any corrosion allowance.

So the bottom plate thickness = 6 + 2 = 8 mm

So the thickness of bottom plate is selected as 8mm. (Since the thickness of shell plates

available in market are of sizes 6, 8, 10, 14, 12, 18, 20, 24 mm etc.)

Bottom plates of sufficient size shall be ordered so that when trimmed at least a 25 mm width

will project beyond the outside edge of the weld attaching the bottom to the shell plate. The


commonly available sizes of plates in market are off length 6m to 10 mm and of width I- 5m,

2m, 2.5m etc. Bottom plate preparation involves shot blasting and Bituminized painting.

DESIGN OF SHELL PLATES

Tank is made of plates. Plates of same width have been welded together to form a

course of equal diameter. The course contains a number of vertical joints of length = plate

width. A number of courses are welded together horizontally to form the total height of the

tank.

According to API 650, the shell thickness for a tank of diameter in the range of 36-60 m

should not be less than 8 mm. (For tank diameter less than 36 m, the shell thickness should

not be less than 6 mm).

The shell thickness is calculated taking into account the material specification and allowable

stresses. The maximum allowable product design stress Sd (API 50 CI.3.6.2.1), shall be either

two-third the yield strength or two-fifth the tensile strength whichever is less, the maximum

allowable hydrostatic test stress St (API 50 CI.3.6.2.1), shall be either three-fourth the yield

strength or three-seventh the tensile strength whichever is less.

Yield strength of selected material (IS2062) = 247.60 Mpa


Tensile strength of selected material l= 410.6 Mpa

Maximum allowable design stress (Sd)

Sd=2/3* yield strength

Sd=2/3*247.60 = 165 Mpa

Or

Sd = 2/5*Tensile strength

Sd = 2/5*410.6=164.24 Mpa

So design stress is taken as 165 Mpa

Maximum allowable hydrostatic stress (St)

St = 3/4*yield strength

S = 3/4*247.60=185.70 Mpa

Or

St = 3/7*Tensile strength

St = 3/7*410.6=175.9 Mpa

So Hydrostatic stress is taken as 176 Mpa

According to API 650 thicknesses of tanks less than 60 m in diameter is calculated using


1-foot method, and if the diameter is above 60 m, the thickness is found out using variable

design point method. So here I-foot Method is used.

I-foot method calculates the thickness required at the design point 0.3 m (1 ft) above the

bottom of each shell course. In this method we find out the design shell thickness (td) and the

hydrostatic test shell thickness (tt) and the maximum of the two values is taken.

Here,

Td =4 .9*D*(H-0.3)*G/Sd + CA

Tt = 4.9*D*(H-0.3)/St

Td = Design shell thickness in mm

Tt = Hydrostatic shell thickness in mm

D = Nominal tank diameter in m=36 m

H = height from the bottom of the course under consideration to the top of the shell.

G = Design specific gravity of the liquid to be stored=0.95

CA = Corrosion allowance in mm =1.6 mm

Sd = Allowable design stress=165 Mpa

St = Allowable hydrostatic stress=176 Mpa

Since the height of the tank is 14 m, we have to divide it into a number of courses considering

the economic conditions. This is done by trial and error method. It is to be noted that the

standard thickness available in market are 6, 10, 12, 14, 16, 20, 25 mm. Values of thickness


obtained by calculation are rounded off to the nearest size of the metal plate available in the

market.

We select a number of random cases with varying number of courses and course width. The

total weight of the metal used and cost in each case is also calculated to determine the most

economical case of shell structure.

Case 1

We divide the total Height 14 m to 6 courses of 2, 2, 2.5, 2.5, 2.5, and 2.5 m respectively.

From the above formula shell thickness is calculated.

Shell thickness.

1 st Course

Nominal Tank Diameter in meters D = 36.00 m

Height from bottom of the course under

consideration to the top of shell H

= 14.00 m

Design stress to be considered Sd = 194 Mpa

Corrosion Allowance = 2.00 mm

Specific Gravity G = 0.95 Kg/mm3

Max hyd stress to be considered = 208 Mpa

Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 13.80 mm

Tt =(4.9D(H – 0.3))/St = 11.60 mm

Max thickness = 13.80 mm

Thickness selected t = 14 mm

= 0.014 m

Width of shell course W = 2.00 m

Volume of Shell course V1 = 3.14 *D*W* t = 3.17 m3


2 nd Course


Height from bottom of the course under consideration to

the top of shell H

= 12.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 12.08 m

Tt =(4.9D(H – 0.3))/St = 9.91 m



= 0.014 m


Volume of Shell course V2 = 3.14 * D * W * t = 3.17 m3

3 rd Course



the top of shell H

= 10.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 10.36 m

Tt =(4.9D(H – 0.3))/St = 8.21 m




= 0.012 m



4 th Course



the top of shell H

= 7.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 8.20 m

Tt =(4.9D(H – 0.3))/St = 6.10 m



= 0.010 m



5 th Course



the top of shell H

= 5.00 m






Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 6.05 m

Tt =(4.9D(H – 0.3))/St = 3.98 m



= 0.008 m



6 th Course



the top of shell H

= 2.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 3.90 m

Tt =(4.9D(H – 0.3))/St = 1.86 m



= 0.008 m



Total Volume V = V1+ V2 + V3+V4+V5+V6 = 17.07 m3

Case 2


We divide the total Height 14 m to 6 courses of 1.5, 1.5, 2.5, 2.5, 2.5 and 3.5 each

respectively.

Shell Thickness

1 st Course



the top of shell H

= 14.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 13.80 m

Tt =(4.9D(H – 0.3))/St = 11.60 m



= 0.014 m



2 nd Course



the top of shell H

= 12.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 12.51 m


Tt =(4.9D(H – 0.3))/St = 10.33 m



= 0.014 m



3 rd Course



the top of shell H

= 11.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 11.22 m

Tt =(4.9D(H – 0.3))/St = 9.06 m



= 0.012 m



4 th Course



the top of shell H

= 8.50 m




Specific Gravity G = 0.95


Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 9.07 m

Tt =(4.9D(H – 0.3))/St = 6.94 m



= 0.010 m



5 th Course



the top of shell H

= 6.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 6.91 m

Tt =(4.9D(H – 0.3))/St = 4.83 m



= 0.008 m




6 th Course



the top of shell H

= 3.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 4.76 m

Tt =(4.9D(H – 0.3))/St = 2.71 m



= 0.008 m



Total Volume : V1+V2+V3+V4+V5+V6 = 16.39 m3

Case 3

We divide the total Height 16 m to 6 courses of 1, 1.5, 2.5, 2.5, 3, and 3.5 respectively.

Shell Thickness

1 st Course


Height from bottom of the course under consideration to = 14.00 m


the top of shell H





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 13.80 m

Tt =(4.9D(H – 0.3))/St = 11.60 m



= 0.014 m



2 nd course



the top of shell H = 13.00 m




Max hyd stress to be considered St = 208 Mpa

Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 12.94 m

Tt =(4.9D(H – 0.3))/St = 10.75 m



= 0.014 m




3 rd course



the top of shell H

= 11.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 11.65 m

Tt =(4.9D(H – 0.3))/St = 9.48 m



= 0.012 m



4 th course

Nominal Tank Diameter in meters D

=

36.0

0 m


the top of shell H

= 9.00 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 9.50 m


Tt =(4.9D(H – 0.3))/St = 7.37 m



= 0.010 m



5 th course


Height from bottom of the course under consideration

to the top of shell H

= 6.50 m





Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 7.34 m

Tt =(4.9D(H – 0.3))/St = 5.25 m



= 0.008 m



6 th course


Height from bottom of the course under consideration

to the top of shell H

= 3.50 m






Td=((4.9*D*(H-0.3)*G)/Sd))+CA = 4.76 m

Tt =(4.9D(H – 0.3))/St = 2.71 m



= 0.008 m



Total Volume V1+V2+V3+V4+V5+V6 = 16.05 m3


ECONOMIC CONSIDERATION

For selecting the optimum combination we are considering the material cost and

fabrication cost for each case

Case 1

The total volume of shell plate required = 17.07m³

The total weight of shell plates = volume*density

= 16.05 * 9.50

= 162.16 tonnes

Material cost per metric tonne = Rs 40,000

So overall material cost of shell plates = 40,000 * 162.16

= Rs 64.86 lakhs

Case 2



= 16.39* 9.50

= 155.71 tonnes




= Rs 62.29 lakhs

Case 3



= 16.05* 9.50

= 152.49 tonnes



= Rs 60.99 lakh


TABLE

CASE NO OF SHELL

COURSES

TOTAL VOLUME

OF SHELL PLATE

TOTAL MATERIAL

COST (lakhs)

1 6 1

64.86

2 6 16.39 62.29

3 6 16.05 61.00

Table:4

SELECTION OF SHELL

Here we are selecting case 3 because case 2 and case 1 are more expensive.


So taking the case 3 conditions :

1st shell course thickness = 14.00 mm

2nd shell course thickness = 14.00 mm

3rd shell course thickness = 12.00 mm

4th shellcourse thickness = 10.00 mm

5th shell course thickness = 8.00 mm

6th shellcourse thickness = 8.00 mm



14mm

12 mm

10 mm

8 mm

14 mm

2.5m

2.5 m

1.5 m

1 m

3.5 m

8mm

3 m

DESIGN OF ANNULAR PLATE

As per table 3.1 of API 650 the minimum annular plate thickness is 6 mm.

So minimum thickness required = 6 + 2.0(C.A) = 8 mm

Here we provide 8 mm thick plate for annular plate, since it has to withstand the entire load

carried from the shell.

RADIAL WIDTH OF BOTTOM PLATE

Radial width is calculated using 2 methods and the greater value is selected.

1 st method

According to API 650, the minimum radial width is the sum of the projection from outer

surface of the shell plate, dimension between the inner surface of the shell plate and lap

joint, lap of the annular and bottom plate and the 1st shell course thickness.


Minimum radial width = minimum projection from outer surface of the shell plate

+ Minimum dimension between surfaces of shell plate to lap joint

+ lap of annular and bottom plate + 1st shell course

thickness

From API 650 standards,

The minimum projection from outer surface of the shell plate = 65 mm (min50mm)

Minimum dimension between inside surface of shell plate to lap joint =

610mm (min600)

Lap of annular and bottom plate = 65 mm (standard)

1st shell course thickness =14 mm

So required minimum radial width = 65 + 610 + 65 + 14 = 744 mm

2 nd method

The minimum radial width is given by the formula R = (215tb)/ (HG) 0.5

Tb - thickness of annular plate in mm = 8mm

H- Maximum design liquid level in m = 12.5 m

G- Design specific gravity of liquid to be stored =0.95

So radial width = (215*8)/ (14*0.95)0.5 )= 471.63 mm


As per the above 2 methods the greater of required radial width = 754mm


DESIGN OF WIND GIRDER

Basic wind speed

It is based on peak guest velocity averaged over a short time interval of about 3 seconds and

corresponds to mean heights above ground level in an open terrain.

Design speed of wind, V = 185 km/hr

Section modulus required for primary girder =D2H2/17 * (V/160)2 cm³ (API 650

3.9.6.1)

D = Nominal tank diameter in meters = 36 m

H = Height of tank shell, including any free board provided above the maximum

filling height = 14 m

Section modulus Z = 1426.88 cm³

Portion of tank shell to be considered for calculating L=13.4(D*t) ^0.5 mm

D = nominal diameter of tank =36 m

t = shell thickness at the attachment = 8 mm

Portion of tank shell to be considered for calculating L=13.4(D*t) ^0.5

=13.4* (36*8) ^0.5 = 227.41 = 227mm (approx)

(The section is taken as per cl 3.9.7.6.2 and cl 3.9.7.7 of API 650.pg 3-44)

Centre of lamina = Ʃax/Ʃa


= (a1x1 + a2x2 + a3x3)/ a1 + a2 + a3

= 333 mm

Moment of inertia

Moment of inertia (Ixx) = (Ah²+bd³)/12

Ixx = (BD3/12) – [(B-b) (D-d)3/12] {B = 227 mm, D = 666 mm, b = 8 mm,

d = 16 mm}

=66777.57 cm4

Distance from neutral axis to extreme fiber, Y = 33.3 cm

Section modulus of the above I section Zxx=Ixx/Y

Zxx = 66777.57 /33.3 = 2005.33 cm3

Zxx = 2005.33 cm3 > 1426.88 cm3

So design is feasible (as per API requirements Zxx should be greater than

section modulus Z


Figure

Location of Primary Wind Girder

The primary wind girder is provided as a walkway at a distance of 1000 mm from the top.

Requirement of Second wind girder (According to API 650, cl3.9.7.1)

Maximum height of the unstiffened shell = Hi=9.47*t *[(t/d)3]0.5 *(V/160)2

T=Thickness of top shell course =8 mm

D = Nominal tank diameter = 36 m

HI = 9.47 *8 * [(8/36)³]0.5 * (185/160)2 = 10.61 m


650 mm

227 mm

666 mm

8 mm 8 mm

(According to API 650 code 3.9.7.1 pg 3-40)

Transformed shell

As per API codes the transformed shell shall be calculated as the change in actual width of

each shell course into a transformed width of shell course having a top shell thickness by

the equation.

(API 650 01.3.9.7.2)

Where;

Wtr = transformed shell course in mm

W = Actual width of each shell course in mm

tuniform = Thickness of top shell course in mm excluding the corrosiom allowance.

= 8 - 2 = 6 mm

Tactual = Ordered shell course thickness excluding the corrosion allowance in mm for which

Wtr is being calculated.


Shell course

No

Provided

thickness –CA

mm

Course width

w mm

Transformed

width wtr mm

Cumulative

transformed

width mm

6 6.00 3500 3500 3500

5 6.00 3000 3000 6500

4 8.00 2500 1217.848224 7717.848224

3 10.00 2500 697.1370023 8414.985226

2 12.00 1500 265.1650429 8680.150269

1 12.00 1000 176.7766953 8856.926965

Table:5

Since cumulative transformed width is not greater than maximum unstiffened height an

intermediate wind girder is not required( 8.86 < 10.61 )

DESIGN OF FOAM SYSTEM

Foam application rate = 5ir/min/m2 as per (OISD166)

Foam area = ᴨ D2/4

When D = tank diameter = 36

Foam area = 1017 m3

Total foam flow required = Foam area * 5 lpm = 5087 lpm

No of foam makes provided = 4

Foam maker capacity required = 5087/4

= 1272 lpm

DIAMETER OF RISER PIPE

Capacity of each foam maker = 1272

Maximum velocity allowed = 5 m/s

Discharge Q = ᴨd2v/4

=5087

Diameter of riser pipe = (Q * 4)*(ᴨ *V * 60000)

= 21.6 mm

Diameter of riser pipe provided = 2 inch


SHELL OPENINGS

MAN HOLE (SHELL)

One-man hole is provided to the tank shell at the bottom shell course. It is enough to provide

600mm manhole.

Dimensions required for the manhole according to API 650

Minimum thickness of cover plate, tc = 14mm

Thickness of bolting flange tf = 11mm [API 650 table 3.3]

Bolt circle diameter, Db = 756 mm

Cover plate diameter, Dc = 820 mm [API 650 table 3.5]

Neck thickness, tn = 6 mm [API 650 table 3.4]

Distance from shell to flange face, J = 300 mm.

Distance from bottom of tank to centre of manhole, Hn = 700 mm [API 650 table 3.6]

BOLTS

Number of bolts = 28 mm

Diameter of bolts = 20 mm

Diameter of hole = 24 mm

NOZZLE

One yield nozzle and one suction nozzle are provided for the tank. They are fixed in the

bottom shell courses. Also three nozzles for water draw off and two nozzles for roof drain are

provided. According to BPCL requirements, the size of nozzle are selected as

Yield nozzle size = 200mm

Suction nozzle size = 350 mm

YIELD NOZZLE

Size of nozzle mm 200

Nominal thickness of flange nozzle pope wall, tn mm 12.7

Diameter of reinforcing plate, Do mm 222

Diameter of hole of reinforcing plate, Dr mm 485


Distance from shell to flange face, J mm 200

Width of reinforcing plate W 590

Distance from bottom of tank to centre of nozzle, Hn mm 325

Thickness of flange, Q mm 28

Outside diameter of flange, A mm 345

Diameter of raised face, D mm 270

Diameter of bolt circle, C mm 300

No of holes 8

Diameter of holes mm 23

Diameter of bolts mm (API 650 table 3.8) 20

SUCTION NOZZLE

Size of nozzle mm 350

Nominal thickness of flange nozzle pope wall, tn mm 12.5


Diameter of hole in reinforcing plate Dr 359


Distance from shell to flange face, J mm 250

Distance from bottom of tank to centre of nozzle, Hn mm 450

Thickness of flange, Q mm 35


Diameter of bolt circle, = C mm 475

No of holes 12


Diameter of bolts mm(API 650 table 3.8) 24

WATER DRAIN


Two water drains are provided to the tank. These are fixed at 180 degrees apart

on the bottom shell course.

Size of drain hole mm is feasible 150

Nominal thickness of flanged nozzle pipe wall, tn mm 10.97

Diameter of hole in reinforcing plate Dr mm 171



distance from bottom of tank to centre of nozzle, Hn mm 275

Minimum thickness of flange, Q mm 25


Deameter of raised face, D mm 216

Diameter of bolt circle mm 240

No of holes 8


Diameter of bolts mm 20

DRAW OFF SUMP

One or two draw off sumps are provided at the bottom plate in order to stop the

water content in the product and to remove it

Diameter of nozzle for draw off mm 75

Diameter of sump for draw off, A mm 910

Depth of sump for draw off , B mm 450

Minimum internal pipe thickness mm 6.35

Minimum nozzle neck thickness mm 7.62

Size of drain hole mm is feasible 10

Nominal thickness of flanged nozzle pipe wall, tn mm 10.97


Minimum distance from shell to flange face, J mm 200

distance from bottom of tank to centre of nozzle, Hn mm 275


Minimum thickness of flange, Q mm 25

Outside diameter of flange, Amm 280

Deameter of raised face, D mm 216

Diameter of bolt circle mm 240

No of holes 8


Distance from Centre pipe to shell m

Thickness of Plates in Sump mm

Diameter of bolts mm (API 650 t5able 3.8)

1.5

10

20

DESIGN OF COOLING-WATER SYSTEM

Cooling water system is provided with the tank as per OISD codes. The cooling

water is sprayed onto the tank with the help of nozzles.

INPUT DATA

Type of tank: Fixed cone roof

Diameter of tank: 36m

Height of tank: 14m

Height of wind girder from bottom: 10.61m

Maximum operating height = 14m

Design code OISD 116

CALCULATIONS

D, diameter of the tank = 36m

Height below the top wind girder H1=10.61m

The cooling water is sprayed on the tank with the help of nozzles on two sets of pipelines

around the shell as per the new design aspects.

Total surface area of the tank: 3.14DH


= 3.14*36*14=1583m

Since OISD specifies a minimum of 3 liters has to be sprayed per minute per unit area of the

shell, the total amount of water required = 1583 * 3

= 4748 lr/min

Considering pressure losses in the pipes connecting the rig and the water tank,operating

pressure of the nozzle is calculated to be between 1.5 to 3.5 kgicm^2.

Ring no:1

Surface area to be cooled by the water from top ring= ᴨ*D*h

D = Diameter of the tank =36m

H = Distance between the two wind girders = 9m

Surface area = ᴨ*36*9 = 1017m^2

Water required = 3*1017 = 3052 lpm

Ring no:2

Surface area to be cooled by the water from top ring= ᴨ*D*h

D = Diameter of the tank =36m

H = Distance between the two wind girders = 9m

Surface area = ᴨ*36*9 = 1017.36m2

Water required = 3*1017 = 3052 lpm


Selection of nozzles

The nozzles are provided around the shell in an identical manner above top set of nozzle , but

just below the secondary wind grider. Nozzle is separated by a distance of 2.4m on the ring.

No. of nozzles per ring = 3.14*(36+2)/2.4=49.72

Working pressure = 1.5 kg/cm2

Average flow per nozzle = 3052/50

= 61.8 lr/min/nozzle

K- factor of nozzle = flow per nozzle / (working pressure)0.5

= 61.8/(1.5)0.5

= 50.52 = 51

Orifice diameter = 7.5mm

Deflection angle = 120ᵒ

Let the nozzle be provided at a distance of 1m from shell

DIAMETER OF FIRST RING

Max. velocity allowed V =5m/sec

Discharge through the top ring, Q =3052 lr/min

Since water is provided to the ring by two tubes, discharge in one quadrant is calculated as,

Q/4 = 3052/4

= 763 lr/min


Area A = ᴨd2/4

Let d = diameter of the ring

Also Q/4 = area * velocity

= (ᴨ d2* V)/4

763 = (ᴨ * d2 * 5 * 60000)/4

d = 770.3 mm

So pipe of d = 770.3mm is required

DIAMETER OF SECOND RING

Discharge through the second ring, Q =3052 lr/min

Since water is provided to the ring by two tubes, discharge in one quadrant is calculated as,

Q/4 = 3052/4

= 763 lr/min

Area A = ᴨd2/4

Let d = diameter of the ring

Also Q/4 = area * velocity

= (ᴨ d2* V)/4

763 = (ᴨ * d2 * 5 * 60000)/4

d = 770.3 mm

ie a pipe having diameter of 770.3mm is required.

DESIGN OF ROOF


Total weight of roof = ᴨ/4 * d2 * 0.005 * 7.85

= ᴨ/4 *36 * 0.005 * 7.85

= 39.93 MT

Live load = 0.46 KPA

Dead load = 4.43 * 0.133 = .589

For designing the roof the combination of live load + dead load < 2.2

i.e. 0.46 + 0.58919 < 2.2

1.04919 < 2.2

So the design is feasible

The slope of the roof shall be 19 mm in 300mm (3/4 in 12 inch) or graeater.

Roof plates shall have a minimum nominal thickness of 5 mm (3/6 inch) 7-gauge

sheet . Thick roof plates are needed for self- supporting roof. Corrosion allowance should

be added with minimum nominal thickness. All internal and external structure members

have a minimum nominal thickness of 4.3mm (0.17 inch).roof plates shall be attached to

the top angle of the tank with a continuous fillet weld on the top side only.

INSPECTION PROCEDURE

Before commencing the inspection of a tank, all detail given in its history card

and records shall be gone thoroughly.

VISUAL INSPECTION


Visual external inspection of each tank shall be made once a year. During the visual

inspection, following shall be checked:

1. Protective coatings

Condition of paint shall be checked visual for rust spots, mechanical damage, blisters

and film lifting.

2. Roof plates

Roof plates shall be inspected for defects like pin holes, weld cracks, pitting etc., at

water accumulated locations.

3. Ladder, Strairways, Platforms and Structural

These shall be examined for corroded or broken parts. Free movement and alignment

of wheels on rolling ladder shall be checked. Ladder and staircase steps shall be checked for

wear and corrosion. In addition to loss of strength caused by loss of metal, treads becomes

slippery when the surface is worn. Hand rails shall be checked for firmness. Platform and

walkways shall be inspected for thinning, water accumulation areas and general corroded

areas.

4. Tank pads

i) Tanks pads shall be visually checked for settlement, sinking, tilting, spalling, cracking and

general deteriorations.

ii) Proper sealing of opening between tank bottom and the concrete pad shall be checked (no

water shall flow under the tank bottom).

iii) Slops of tank pad shall be checked to ensure water drainage.

5. Anchor Bolts

Anchor bolts where ever provided shall be checked for tightness, and integrity by

hammer testing. These shall also be checked for thinning/bending. Deterioration of bolts is an

indication of excessive settlement. Concrete foundation at anchor bolt shall be checked for

cracks.


6. Fire Fighting System

General condition of fire fighting facilities and sprinkler systems provided on the tank

with respect to clogging of spray nozzle, perforation of foam connections, etc., shall be

checked. Frequency and procedure for checking shall be as per OSID –Std-142 (Inspection of

Fire Fighting Equipment).

7. Vents & Pressure Relieving Devices

All open vents, flame arrestors and breather valves shall be examined to ensure that the

wire mesh and screens are neither torn or clogged by foreign matter or insects. Rim and

bleeder vents for floating roof tanks shall be examined for proper working. All vents and

pressure relieving devices shall be inspected as per the frequency and procedure outline in

OSID-Std-132 (Inspection of Pressure Relieving Devices).

8. Insulation

If a tank is insulated ,the insulation and weather proof sealing shall be visually inspected

for damage.The water proof sealing of the insulation shall be examined every year, since the

entry of moisture will greatly reduce the insulating properties and may also result in serious

un detected corrosion of the tank plates underneath the insulation. Cracks in the water proof

sealing are apt to occur and wind may enlarge small tears rapidly. It is suspected that

moisture has penetrated through the cracks, a small area of the plates shall be uncovered and

examined for signs of corrosion.

9. Grounding Connection

Grounding connection shall be visually checked for corrosion at the points where they

enter earth and at the connection to the tank. The resistance of grounding connection shall be

annually before monsoon. The total resistance from tank to earth shall not exceed the value

given in OSID-Std-137 (Inspection of Electrical Equipment).

10. Leaks

The tanks shall be inspected for any obvious leakage of the product. Valves and fitting

shall be checked for tightness and free operations.

EXTERNAL INSPECTION


The detailed external inspection of the tank shall be carried out as per the frequency

mentioned while the tank is in commission.

The following should be checked/inspected during external inspection, besides the visual

inspection.

1. Tank fittings, Accessories and Pipe Connections

All nozzles shall be visuall inspected for corrosion / distortion.

Thickness measurements shall be taken with ultrasonic thickness meter. On

nozzles of 50 mm and above, minimum four readings should be taken.

2. Tank Shell

The tank shell shall be visually examined for external corrosion,

seepage, crack, bulging and deviation from the vertical. Cracks mostly occur

at the welded connections of nozzles to the tank, in welded seams, at the weld

connections of brackets or other attachments to the tank and fillet welds of

shell to the bottom plates.

Shell wall thickness survey should be carried out using ultrasonic

thickness meter. External thickness survey shall be carried out all around for

the first and second bottom shell courses. For the rest of the shell courses,

thickness survey shall be done along the staircase and three compass

directions. An extensive scanning shall be done if there is an indication of

appreciable thickness loss.

The following minimum requirement for thickness survey is

recommended on all tanks:

All the plates of first and second course of the shell thickness should

be surveyed.

On the first course, 3 to 4 readings should be taken on each plate

diagonally. The bottom, middle and top positions of the plate must be

checked.


On the second course, two readings should be taken on each plate.

One reading shall be near the lower weld joint and other at

approachable height.

Three readings should be taken on one plate on all the courses along

the staircase and three compass directions. Bottom, middle and top

portion of the plates should be covered.

For tanks having light produces services like gasoline and naphtha,

pitting generally observed in the middle courses of shell. In such

cases, thickness survey should be more extensive on middle courses.

If significant internal corrosion of roof is observed, then top shell

courses should be examined for thickness. In case of eternally

insulated tanks, suitable inspection windows shall be provided to

facilitate wall thickness survey. For the tanks which are likely to have

water at the bottom, the bottom shell courses near the annular ring

welding joint should be thoroughly checked ultrasonically within 150

mm of the bottom plate.

3. Water Draw-off

Water draw-off is subjected to internal to internal and external

corrosion as well as cracking. They shall be visually inspected and

hammer tested along with thickness survey as feasible. Bottom plate

under dip hatch shall be checked for dents etc.

The bottom plates of tank having water at bottom (such as crude oil)

shall be inspected visually in details for internal corrosion or pitting.

The bottom plates where bacterial corrosion may be suspected (such

as crude oil and HSD tanks) shall be gauged in more detail.

Drain sumps shall be carefully checked for cracks, pitting, leak in the

weld and measured in particular when corrosion at the underside of

the tank bottom plate has been suspected or found.

4. Linings


When the inside surface of a tank are lined with corrosion

resistant material such as sheet lead, rubber, organic and

inorganic coatings, or concrete inspection shall be made to

ensure that the lining is in good condition, that is in proper

position and it does not have holes or cracks in the rubber

lining as evidenced by bulging.

Hardness testing of the rubber lining shall be carried out

while inspecting the tank internally. Care shall be taken

while cleaning the painted surface so that no mechanical

damage takes place.

5. Roof Drains

Roof drains on the floating roof can be designed in many ways.

They can be simple open drain pipes, swivel joints or flexible hose

drains that keep the water from contaminating the contents. Proper

functioning of the roof drains shall be ensured otherwise this may

lead to sinking or over-turning of the floating roof. The drain lines

shall be checked for blockage before pressure test. All swivel

joints shall be thickness surveyed and serviced during every

outage and individually hydro tested. After assembly of the roof

drain system, complete system shall be hydro tested. In fixed cone

roof tanks slope of the roof should be checked and blockages

should be removed.


TESTING METHODS

1. DYE PENETRANT TESTING

Used for detecting discontinuities open to the surface.

Basic Process

Surface penetration and pre-cleaning.

Applying a visible or fluorescent liquid penetrant to surface.

Wait for the penetrant to enter surface breaking discontinuities.

Removing excess penetrant from the surface.

Applying a developer to the examination surface.

Interpretation of indication.

Advantages

Easy to apply and cheap.

Interpretation is easier.

Can be used for any metal.

Disadvantages

Can detect only surface discontinuities.

2. MAGNETIC PARTICLE TESTING

Use to detect surface and subsurface discontinuities.

Basic Process

Magnetic field is included in the specimen.

The discontinuities lying in a direction transverse to the field will cause a leakage flux

to develop around it.


Fine magnetic powder is sprinkled on to this will adhere on the vincity of leakage

flux.

Materials Required

Magnetic yoke

Fluorescent iron powder

Backlight source

Both AC and DC current can be used for producing magnetic field.

Permanent magnets can be used for the same.

Advantages

Can be used for surface and subsurface discontinuities up to 5 mm.

Interpretation easy

Disadvantages

Can be used only for ferrous metals.

Residual magnetism is a problem.

Power requirement.

3. ULTRASONIC TESTING

Ultrasonic waves are sound waves with frequency above the audible

range i.e. above 20000 Hz.

This method is used to detect all types of defects.

Basic Process

Ultrasonic wave is propagated through the material.

Any change of medium reflects the waves due to change in acoustic impedance.

Defects or change of materials are known by change in acoustic impedance.

The reflected waves are detected using cathode ray tube.

The amplitude and distance in the CRT will give an indication on the type and

position of defect.


4. RADIOGRAPHIC TESTING

Used to detect all kinds of defects

Basic Process

It is a volumetric examinations using X-ray radiation or nuclear radiation that

penetrates through the specimen and produces an image on the film.

Radiation is absorbed as it passes through the material.

The absorption depends on the amount, density and atomic number of the material.

A discontinuity causes a condition of less material of lesser density.

The image depends on the amount of transmitted rays that strikes the film.

Radiographic source can be either X-ray tubes or gamma radiation source.

X-ray gives better quality of image.

Gamma ray sources contain radioactive isotopes of iridium 192 or cobalt 60.

Advantages

Any kind of defects can be detected.

Gives a permanent record.

Defect location and positioning is more accurate.

One of the widely used methods in construction sites.

Disadvantages

Radiation safely is an area of concern especially in case of gamma ray sources.

The operation is likely to be exposed to radioactive radiation and need constant

monitoring.

.


CONCLUSION

As per the requirement of BPCL (Kochi Refinery), tank for storing furnace oil was

designed. The design was based on API 650 codes. Our design of tank include all main

parts such as fixed supported cone roof , shell plates , bottom and annular plates , wind

girder and the various accessories like foam system and cooling system. The design

calculations were verified and necessary corrosion allowances were provided to the tank

parts. The tank meets all required safety standards.


REFERENCE

API 650 STANDARDS (11th EDITION)

BOOK OF ABOVE GROUND STORAGE TANKS

API STANDARDS FOR CONE ROOF TANKS

www.bpcl.co,in

OISD 115


Documents

Bpcl Project Completed !!!