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 storing furnace oil. Storage tanks are are constr construct ucted ed to store huge quanti quantitie tiess of variou variouss petrol petroleum eum products. products.

Volati Volatile le

petroleum petroleum products products are stored in floating floating roof tanks. In this project project we intend to do the design of floating roof tank for storage of crude oil.

The tank is designed according to API 650 (11 TH Edition) Standards. Furnace oil comes under Class B category; hence a cone roof type storage storage tank was selected. 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

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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 Former Indian Prime Minister Minister Mrs. Mrs. Indira Indira Gandhi Gandhi dedicated 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 fccu,, lpg lpg and and gaso gasolin linee mero merox x unit unit)) with with a capac capacit ity y of proc proces essi sing ng 1 mmpt mmptaa VGO VGO was was commis commissio sioned ned in 1985. 1985. It entered entered the petroc petrochem hemica icall sector sector in 1989 1989 when when an aromat aromatic ic productio production n facility with a design design capacity capacity of 87,200 87,200 tons per annum of benzene benzene and 12,000 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 dioxid dioxidee emissi emission. on. A captiv captivee power power plant plant of 26.3 26.3 MW was commissi commissione oned d in 1991. 1991. An additional captive power plant of 17.8 MW was commissioned in 1998. KRL is now self -sufficient in power


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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-expa capacity-expansion nsion-cum-mo -cum-moderni dernization zation project (CEMP) (CEMP) that envisaged refinery modifications required to meet BS-II Product Specifications, has met the targ target et.. Supp Supply ly of auto auto fuel fuelss like like petro petroll and and dies diesel el conf confir irmi ming ng to Bhara Bharath th Stag Stage-I e-III 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. lakhs.sq. sq.m m of land. land. The integr integrate ated d rainwa rainwater ter harves harvestin ting g system system to collect collect,, conser conserve ve 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 acre acress with with a view view to rest restor oree the the heal health thy y ecos ecosys yste tem, m, cont contro roll poll pollut utio ion, n, deve develo lop p clea clean n environmen environmental tal condition condition and prevent prevent soil erosion. Around Around 3750 numbers numbers of wide ranges of forest forest specie species, s, orname ornamenta ntall trees, trees, fruit fruit trees trees and attract attractive ive flower flowering ing plants plants along along with with medicinal medicinal herbs have found a place in the Eco Park. Treated effluent effluent water is being utilized to feed the dry land plants. Available resources is also being used to develop scrap land to gree green n belt beltss whic which h in-t in-tur urn n woul would d prom promot otee envi enviro ronm nmen enta tall awar awaren enes ess, s, enha enhanc ncee the the environmental quality of region, develop habitat for rare migratory species and also increase tree coverage.


3

ONGOING/UPCOMING ONGOING/UPCOM ING 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 bee been n obta obtain ined ed from from Stat Statee Poll Pollut utio ion n Cont Contro roll Boar Board d and and clea clearan rance ce from from Mini Minist stry ry of Environment & Forests. The investment clearance for the project has also been obtained. Estimated cost of the project is Rs.2592crores. The The major major projec projectt facilit facilities ies includ includee revamp revamp of CDU-II CDU-II for capaci capacity ty expans expansion ion 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 activated along with the constructio construction n activities of the SPM. As part of its commitment 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 Centers including including the deploymen deploymentt of an ambulance ambulance at Puthuvypee Puthuvypeen, n, assistance 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


4

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.


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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/cm 2, medium pressure @ 18kg/cm 2 and high pressure having pressure above 18kg/cm 2.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.


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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.


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SULPHUR RECOVERY UNIT

Petroleum products are finding increasing use in the day to day activities of mankind includes includes personnel personnel and commercial needs. Coupled with the increasing increasing demand for fuels is the problem of deteriorating quality of air in the environment. One of the largest contributors to the the poor poor qual qualit ity y of air air is vehi vehicu cula larr exha exhaus ust. t. Due Due to the the incr increa ease sed d pres pressu sure re on the 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 recovery unit is the process process unit setup for the removal removal hydrogen sulphide 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 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 Ligh Lightt End End Feed Feed Prep Prepar arat atio ion n Unit Unit (LEL (LELPU PU)) to supp supply ly poly polybu bute tene ness was 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:


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

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 BPCL 'S MISSION MISSI ON

•

To stre streng ngth then en the the pres presen ence ce in petr petrol oleu eum m refin refinin ing g and and mark market etin ing g of petroleum products and to grow into the energy and petrochemical sectors.

•

To realign orientation of thinking and philosophies to become a market driven driven and custom customer er friendl friendly y organi organizati zation on with with focus focus on total total qualit quality y management.

•

To enhance shareholder shareholder value and maximize maximize returns returns through through the best use of resources.


9

•

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 achi achiev evee glob global al stan standa dard rdss of exce excell llen ence ce thro throug ugh h R & D effo efforts rts,, tech techno nolo logy gy

up-g up-gra rada dati tion on,,

safet safety y

mana manage geme ment nt

and and

envi enviro ronm nmen enta tall

protection. •

To be a major contributor towards community development and welfare of the society at large.

ENVIRONMENTAL 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

o

Respect the interests of customers, employees and other interested parties 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 Treatment and and dispos disposal al of of 10000 10000 MT of of accumulat accumulated ed oily oily sludge sludge

after

mechanical recovery of oil by December 2003. •

Decommissioning of equalization pond at ETP-I by De c 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.


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ISO 14001

The The comp compan any y has has been been award awarded ed the the pres presti tigi giou ouss ISO ISO 1400 14001 1 cert certifi ifica cate te 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 This standa standard rd requir requires es format formation ion of short-t short-term erm and long-t long-term erm enviro environme nmenta ntall polic policy, y, enviro environm nment ental al object objective ives, s, and compli complianc ancee with with legisl legislati ative ve requir requireme ements nts and addressing significant environmental impacts with solutions.

BPCL BPCL is the the firs firstt comp compan any y in Keral Keralaa to get get this this envi enviro ronm nmen entt mana manage geme ment nt 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.


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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


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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


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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.


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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


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•

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


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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 nearKARPAGAM COLLEGE OF ENGINEERING

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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


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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.


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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.


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

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


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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

Class C

Petroleum) 1

Petroleum

All tanks with diameter

upto (D+d)/4

(D+d)/4

(D+d)/6

(D+d)/3

(D+d)/4

50m All tanks with

2

diameter

(D+d)/4

exceeding 50m 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 22

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.


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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.


24

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.


25

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 KARPAGAM COLLEGE OF ENGINEERING

26

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. KARPAGAM COLLEGE OF ENGINEERING

27

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


28

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%


29

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


30

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)


31

So it is possible according to API 650.

Volume, V=πR 2H

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


32

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.


33

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


34

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 S d (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


35

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


36

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 f ind 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/S d + CA

Tt = 4.9*D*(H-0.3)/S t

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


37

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.

1st Course

Nominal Tank Diameter in meters D Height from bottom of the course under

= =

36.00 14.00

m m

Design stress to be considered Sd

=

194

Mpa

Corrosion Allowance

=

2.00

mm

Specific Gravity G Max hyd stress to be considered

= =

0.95 208

Kg/mm3 Mpa

Td=((4.9*D*(H-0.3)*G)/Sd))+CA Tt =(4.9D(H – 0.3))/St

= =

13.80 11.60

mm mm

Max thickness

=

13.80

mm

Thickness selected t

=

14

mm

=

0.014

m

= =

2.00 3.17

m m3

consideration to the top of shell H

Width of shell course W Volume of Shell course V1 = 3.14 *D*W* t


38

2nd Course

Nominal Tank Diameter in meters D Height from bottom of the course under consideration to

= =

36.00 12.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

12.08 9.91

m m

Max thickness

=

12.08

mm


=

14

mm

=

0.014

m

= =

2.00 3.17

m m3

the top of shell H

Width of shell course W Volume of Shell course V2 = 3.14 * D * W * t 3rd Course


= =

36.00 10.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

10.36 8.21

m m

Max thickness

=

10.36

mm


=

12

mm

=

0.012

m

= =

2.50 3.39

m m3

the top of shell H

Width of shell course W Volume of Shell course V3 = 3.14 * D * W * t


39

4th Course


= =

36.00 7.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

8.20 6.10

m m

Max thickness

=

8.20

mm


=

10

mm

=

0.010

m

= =

2.50 2.83

m m3

= =

36.00 5.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

6.05 3.98

m m

Max thickness

=

6.05

mm


=

8

mm

=

0.008

m

= =

2.50 2.26

m m3

the top of shell H


5th Course

Nominal Tank Diameter in meters D Height from bottom of the course under consideration to the top of shell H



40

6th Course


= =

36.00 2.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

3.90 1.86

m m

Max thickness

=

3.90

mm


=

8

mm

=

0.008

m

= =

2.50 2.26

m m3

the top of shell H


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

1st Course


= =

36.00 14.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm

the top of shell H


41


= =

0.95 208

Kg/mm3 Mpa


= =

13.80 11.60

m m

Max thickness

=

13.80

mm


=

14

mm

=

0.014

m

= =

1.50 2.37

m m3


2nd Course


= =

36.00 12.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

12.51 10.33

m m

Max thickness

=

12.51

mm


=

14

mm

=

0.014

m

= =

1.50 2.37

m m3

the top of shell H

Width of shell course W Volume of Shell course V2 = 3.14 * D * W * t 3rd Course


= =

36.00 11.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm

the top of shell H


42


= =

0.95 208

Kg/mm3 Mpa


= =

11.22 9.06

m m

Max thickness

=

11.22

mm


=

12

mm

=

0.012

m

= =

2.50 3.39

m m3

= =

36.00 8.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Mpa


= =

9.07 6.94

m m

Max thickness

=

9.07

mm


=

10

mm

=

0.010

m

= =

2.50 2.83

m m3

= =

36.00 6.00

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


4th Course


Width of shell course W Volume of Shell course V4 = 3.14 * D * W * t 5th Course



43


= =

6.91 4.83

m m

Max thickness

=

6.91

mm


=

8

mm

=

0.008

m

= =

2.50 2.26

m m3



44

6th Course


= =

36.00 3.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

4.76 2.71

m m

Max thickness

=

4.76

mm


=

8

mm

=

0.008

m


= =

3.50 3.17

m m3

Total Volume : V1+V2+V3+V4+V5+V6

=

16.39

m3

the top of shell H

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

1st Course


= =

36.00 14.00

m m

=

194

Mpa

the top of shell H Design stress to be considered Sd


45

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

13.80 11.60

m m

Max thickness

=

13.80

mm


=

14

mm

=

0.014

m

= =

1.00 1.58

m m3


2nd course


=

36.00

m

the top of shell H

=

13.00

m


=

194

Mpa

Corrosion Allowance

=

2.00

mm

Specific Gravity G Max hyd stress to be considered St

= =

0.95 208

Mpa


= =

12.94 10.75

m m

Max thickness

=

12.94

mm


=

14

mm

=

0.014

m

= =

1.50 2.37

m m3


3rd course


46


= =

36.00 11.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

11.65 9.48

m m

Max thickness

=

11.65

mm


=

12

mm

=

0.012

m

= =

2.50 3.39

m m3

the top of shell H


4th course

Nominal Tank Diameter in meters D 36.0 = Height from bottom of the course under consideration to

0 =

m 9.00

m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Mpa


= =

9.50 7.37

m m

Max thickness

=

9.50

mm


=

10

mm

=

0.010

m

= =

2.50 2.83

m m3

the top of shell H

Width of shell course W Volume of Shell course V1 = 3.14 * D * W * t 5th course


47

Nominal Tank Diameter in meters D Height from bottom of the course under consideration

= =

36.00 6.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

7.34 5.25

m m

Max thickness

=

7.34

mm


=

8

mm

=

0.008

m

= =

3.00 2.71

m m3

to the top of shell H


6th course

Nominal Tank Diameter in meters D Height from bottom of the course under consideration

= =

36.00 3.50

m m


=

194

Mpa

Corrosion Allowance

=

2.00

mm


= =

0.95 208

Kg/mm3 Mpa


= =

4.76 2.71

m m

Max thickness

=

4.76

mm


=

8

mm

=

0.008

m


= =

3.50 3.17

m m3

Total Volume V1+V2+V3+V4+V5+V6

=

16.05

m3

to the top of shell H


48


49

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



= volume*density

= 16.39* 9.50

= 155.71 tonnes


50


= Rs 40,000

So overall material cost of shell plates

= 40,000 * 155.71

= Rs 62.29 lakhs

Case 3



= volume*density

= 16.05* 9.50

= 152.49 tonnes


= Rs 40,000

So overall material cost of shell plates

= 40,000 * 152.49

= Rs 60.99 lakh


51

TABLE

CASE

NO OF SHELL

TOTAL VOLUME

TOTAL MATERIAL

COURSES

OF SHELL PLATE

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.


52

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


53

3.5 m

8mm

3m

8 mm

10 mm

2.5m

12 mm

2.5 m

14mm

1.5 m

14 mm

1m


54

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.

1st 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 1 st shell course thickness.


55

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 + 1 st 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

2nd 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


56

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


57

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


58

= (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


59

Figure

8 mm

8 mm 650 mm

227 mm

666 mm

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)


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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

(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


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

Wtr is being calculated.

Shell

course Provided

Course

No

thickness –CA w mm

6 5 4 3 2 1

mm 6.00 6.00 8.00 10.00 12.00 12.00 Table:5

width Transformed

3500 3000 2500 2500 1500 1000

Cumulative

width wtr mm

transformed

3500 3000 1217.848224 697.1370023 265.1650429 176.7766953

width mm 3500 6500 7717.848224 8414.985226 8680.150269 8856.926965

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


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=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, t c = 14mm Thickness of bolting flange t f = 11mm [API 650 table 3.3] Bolt circle diameter, Db = 756 mm Cover plate diameter, D c = 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, H n = 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


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YIELD NOZZLE Size of nozzle mm

200

Nominal thickness of flange nozzle pope wall, t n 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, H n 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


750

Diameter of hole in reinforcing plate Dr

359


915

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


415

Diameter of bolt circle, = C mm

475

No of holes

12


27

Diameter of bolts mm(API 650 table 3.8)

24


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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


495


400

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

275

Minimum thickness of flange, Q mm

25


280

Deameter of raised face, D mm

216

Diameter of bolt circle mm

240

No of holes

8


23

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


400

Minimum distance from shell to flange face, J mm

200

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

275


65

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


23

Distance from Centre pipe to shell m

1.5

Thickness of Plates in Sump mm

10

Diameter of bolts mm (API 650 t5able 3.8)

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 H 1=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


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= 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


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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/cm 2

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 = 120

ᵒ

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


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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


69

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


70

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.


71

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


72

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.


73

•

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. KARPAGAM COLLEGE OF ENGINEERING

74

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 KARPAGAM COLLEGE OF ENGINEERING

75

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.


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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.


77

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


78



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.


79



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


80

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.


81

Bpcl Project Completed !!!

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