DESIGN AND MAINTAINANCE OF FLOATING ROOF STORAGE TANK IN PETROLIUM REFINERY

1 Design & Maintenance of storage tank for HSD

DESIGN AND MAINTAINANCE OF STORAGE

TANKS

FOR HSDMAIN PROJECT REPORT

Submitted by:MUHAMMED SHAFEEQUE

PRASOON KUMAR K.PMUHAMMED JAWAD

ABINRAJ P.KSHADIL N.K

GUIDE: Mr.BALAGOPAL Sr. Engineer Maintenance Department BPCL KOCHI

DEPARTMENT OF MECHANICAL ENGINEERING

AWH ENGINEERING COLLEGE

KUTTIKKATOOR, CALICUT, KERALA

2013

AWH Engg. College Calicut Dept. of Mechanical Engg.


ACKNOWLEDGEMENT

First of all we would like to thank God the Almighty for the divine grace

bestowed on us to complete this project successfully on time.

We express our sincere thanks to Prof. JUSTIN DICOTTU (Head of the

Department of Mechanical Engineering, AWH ENGG. COLLEGE) for

giving us this opportunity to present this project and for the facilities

offered to us throughout this endeavor.

The main motivation and driving force behind this project is our external

guide Mr.BALAGOPAL (Sr. Engineer E&C Department of Department

of BPCL). We are unboundedly grateful to him for the timely corrections

and scholarly guidance, which made us confident enough to come out

successfully.

We also thank Mr. SARUN (Asst. Engg. E&C Department of BPCL) for

his support and guidance throughout the completion of our project.

We extend our hearty thanks to our internal guide Sir. JITHU

PAUL(Lecturer, Department of Mechanical Engineering, AWH ENGG.

COLLEGE) for his enterprising attitude and support that made our

project fruitful. We express our sincere thanks to all the faculty members

of the Mechanical Engineering Department for their co-operation.



ABSTRACT

Petroleum storage tank is an indispensable part of petroleum refining

industries. They are used for intermediate and final product storage in

process plant or for storing petroleum products and chemicals at terminals.

They are used for mixing, blending, precipitation and setting process or as

chemical reactor vessels. Storage tanks are different types such as cone roof,

floating roof, floating cum cone roof and spherical vessels . For storing

motor spirit/ High Speed Diesel (HSD) we use floating roof tanks. As safety

has the prime importance in a refinery different fire fighting equipments are

designed and installed. Along with this thorough inspection procedures and

maintenance are necessary to ensure better safety. All the petroleum

refineries are mainly concentrating on the storing of various products

because of efficient storage and better safety, the designing of storage tank is

highly important.



CONTENTS

1. Company Profile……………………………… 1

2. Introduction to Storage Tanks………………... 4

3. Types of Storage Tanks………………………. 5

4. Parts of Storage Tanks………………………. 12

5. Material Specifications for Storage Tank…… 20

6. Design of Storage Tank……………………... 22

7. Inspection of Storage Tank…………………. 55

8. Testing of Storage Tank……………………. 63

9. Conclusion………………………………….. 67

10. References……………………………………68



COMPANY PROFILE

Kochi Refinery, a unit of Bharat Petroleum Corporation Limited (BPCL), embarked on its journey in 1966 with a capacity of 50,000 barrels per day. Formerly known as Cochin Refineries Limited and later renamed as Kochi Refineries Limited, the refinery was originally established as a joint venture in collaboration with Phillips Petroleum Corporation, USA. Today it is a frontline entity as a unit of the Fortune 500 company, BPCL.

Kochi Refinery, located at Ambalmugal near the city of Kochi in Kerala, is one of the two Refineries of BPCL, presently having a crude oil refining capacity of 9.5 Million Metric Tones per Annum (MMTPA). The product portfolio of the 190,000 barrels per day refinery today includes petrochemical feedstock and specialty products in addition to its range of quality fuels.

Fuel products of this fuel based refinery includes Liquefied Petroleum Gas, Naphtha, Motor Spirit, Kerosene, Aviation Turbine Fuel, High Speed Diesel, Fuel Oils and Asphalt. Specialty products for the domestic markets include Benzene, Toluene, Propylene, Special Boiling Point Spirit, Poly Iso Butene and Sulphur.

The refinery has implemented world class technology and systems for operations and enterprise resource planning. It is an ISO 14001 Environmental Management Systems (EMS) and ISO 9001:2000 Quality Management System (QMS) accredited company and has also obtained the ISO 17025 (Testing Methods in Quality Control) certification from NABL (National Accreditation Board for testing & Calibration of Laboratories). The refinery has successfully implemented the Occupational Health and Safety Management System (OHSAS) 18001:2007 in the year 2009.

With the prestigious Crude Oil receipt facilities consisting of the Single Point Mooring (SPM) and the associated shore tank farm in place since December 2007, the refinery is equipped to receive crude oil in Very Large Crude Carriers (VLCCs). This facility helps Kochi refinery in reducing the freight charges to a great extent, over and above increasing flexibility in crude oil selection. This, thereby, is a major infrastructure facility to accelerate the future growth of Kochi Refinery.

The refinery has facilities to evacuate products to the consuming centers through road, rail, ships and through pipelines. All the major industries in the area are connected to the refinery for product receipt. The BPCL installation at



Irumpsanam, to which the refinery is connected by pipelines, is the major product distribution centre of the refinery. Petronet CCK, a joint venture company of BPCL looks after the 300 km long pipeline that connects the refinery to various consumption points in Tamil Nadu such as Coimbatore and Karur.

Of the two-part Capacity Expansion cum Modernization Project (Phase–II), the capacity expansion to 9.5 MMTPA has been successfully completed and refinery modernization slated for completion in August 2010 would equip the refinery to produce auto-fuels conforming to Euro-III and partly Euro-IV specifications.

The refinery’s foray into direct marketing began since 1993 through marketing of its aromatic products - Benzene and Toluene. The entry into the international petroleum business stream began with its first parcel of Fuel Oil exported in January 2001. Since then the refinery, has earned the reputation as a reliable player in the international trade, by virtue of superior product quality and customer service. Moreover, the Fuel Oil has been benchmarked in the Singapore and Dubai Fuel Oil markets.

Kochi Refinery is situated in Kochi, the most happening city in Kerala that is rightly called God’s own country. The refinery has a unique bond with its environment which is evident in the green blanket so carefully nourished right around it. The refinery has been blessed with a fine topography and the entire complex, spreading across over thousand two hundred acres has been so constructed as to blend naturally with it. Upcoming expansions and developments would also adhere to this philosophy of blending with nature. The most recent addition to the refinery architecture is the rainwater harvesting pond and eco-park that has been converted to a must-see spot with sprawling landscaped lawns and thatched canopies for conferences and get-togethers. Year after year the refinery has been bagging accolades for its commitment to the environment; for the all round care for the environment, the judicious storage, use and reuse of water, the efficiency in managing solid wastes and effluents and the care taken to keep the atmosphere clean.

The recent achievement of 24 million accident free man-hours stands testimony to the fact that the prime focus of Kochi Refinery is on safety in everything we do. From training to retraining, and adhering to international standards in safety practices, both, offsite and onsite, Kochi Refinery has taken it as a mission to make safe living and working a natural mantra of its employees, contract workers, customers and the general public. Several awareness programs have been successfully conducted to this effect with the results for all to see.



As a socially responsible corporate citizen, the community welfare initiatives of the refinery concentrate on developing the weaker sections of society, particularly, the scheduled castes and scheduled tribes and people below the poverty line in important sectors like health, education, housing and women empowerment. Most of the programs falling under the categories of medical and educational assistance turned out to be poverty alleviation measures also. This is since the programs like universal health insurance, scholarship to SC/ST students and medical camps for poor have helped the poor villagers in the refinery vicinity to save money over their medical expenses and educational expenses of children. Various people intensive small-scheme community development programs have brought new life for many; be it poor villagers in need of medical treatment; poor students in government schools or differently abled children!

Thus, apart from maintaining its world class standards in operational excellence, the singular objective of Kochi Refinery is to uphold the BPCL vision of energizing lives by continued excellence in all round performance with new ideas, added vigor and sustained commitment to its social, cultural, organizational and natural environment.

Process

Kochi Refinery presently has a crude oil processing capacity of 9.5 MMTPA (Million Tons per Annum) in its two Crude Distillation units (CDU-1 and CDU-2). The refinery currently processes about 30% of Indigenous and 70% Imported crude oils. Crude oil is transported in ships from the point of origin to Kochi and is received through a Single Point Mooring (SPM) facility. Kochi SPM, located approximately 20 kms off the shore of Puthuvypeen, is capable of handling Very large Crude Carriers (VLCC) with crude oil carrying capacities upto 3.0 Lakh Tons. Crude oil from SPM is received in offshore tanks in Puthuvypeen and is then pumped to the refinery.

Apart from the Crude Distillation Units, major processing facilities in the refinery include a Fluidized Catalytic Cracking (FCC) unit, Diesel Hydro Desulphurization (DHDS) unit, Kerosene Hydro Desulphurization (KHDS) unit, Sulphur Recovery Unit (SRU) and an Aromatics Block consisting of a Naphtha Splitter Unit (NSU), Naphtha Hydro Desulphurization (NDHS), Catalytic Reformer Unit (CRU) and Aromatics Recovery Unit (ARU).



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 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 setting 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 liquids the minimum temperature at which the

liquid yields vapor in sufficient concentration to form an ignitable mixture with air

and gives a momentary flash on application of a smell pilot flame under specified

conditions of test.

Petroleum products are classified according to their flash pints 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

Liquids that have flash point of 23degree and above but below 65 degree C-

superior kerosene oil , high speed diesel, light diesel oil, aviation turbine fuel, and

jet propulsion -5.



Class C Petroleum

Liquids that have flash point of 65 degree C and above but below 93 degree C-

furnace oil, low sulphur heavy stock, asphalt, seal oil, plant fuel.

Excluded Petroleum

Liquids that have flash point of 93 degree C and above liquefied gases including

LPG do not fall under this classification but from separate category.

CLASSIFICATIONOF STORAGE TANKS

1. Cone roof tanks

2. Floating roof tanks

3. Floating cum cone roof tanks

4. Spherical vessels

1. CONE ROOF TANKS

9 March 2009BPCL Kochi Refinery 13

FIXED ROOF TANK

FOUNDATION

SHELL

BOTTOMPLATE

CONE ROOFVENT

The cone roof tanks have fixed 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. Tanks meant for storing products like



asphalt, vacuum gas oil etc. at high temperature is fully insulated externally. There

are 43 cone roof tanks in BPCL at present. Depending on the service the cone roof

tanks will have the following accessories.

FLOATING ROOF TANKS

Floating roof tanks are intended for storing products having high vapor pressure

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

tank contents. Thus the vapor space is kept constant and minimum. Roofs are

pontoon type having enclosed air chambers. Foam type neoprene seal off the

clearance between the rim of the roof and the tank shell 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 has to be

put on high legs toprovide 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 t0 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 case 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 71 floating roof tanks in BPCL at present. The following are the

accessories provided on floating roof tanks:

Man ways to go inside the shell and over the roof

Gauging datum plate

Gauge hatch with cover and reference mark

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

Outside stairway

Inside stairway



9 March 2009BPCL Kochi Refinery 19

FLOATING ROOF TANK

FOUNDATION

SHELL

BOTTOMPLATE

PONTOON

ROOF DECK

SUPPORT LEG



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 vapor 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 BPCL at present

9-Mar-09 13FOUNDATION

SHELL

BOTTOMPLATE

CONE ROOF

ROOF DECK

SUPPORT LEG

FLOATING CUM FIXED ROOF FLOATING CUM FIXED ROOF TANKTANK



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 in the same

type of tanks. 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 dike 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 form the road surrounding the enclosure. However, tanks

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

Inter-distances for tanks/offsite facilities

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

tanks storing petroleum:

Inter distance for storage tanks



Sl.N

o

Item FRT CRT (ClassA&B

Petroleum)

Class

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



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 6mm 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 plates on which the shell plates rest. Annular plates

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

appurtenance.

According to API 650 (3.5) 11th edition 2007, annular plates shall have a radial

width that provides at least 600mm between the inside of the shell, any lap welded

joint in the remainder of the bottom shall have at least a 36mm projection outside

from the shell. The projecting out portion of the annular plates is prone to

corrosion at the edges due to accumulation of water between the foundation and

the annular 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 shell’s

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-vapor is maintained. Internal corrosion in the vapor space

is not commonly caused by hydrogen sulphide vapor, water vapor-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.

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.

2. YIELD & SUCTION NOZZLES

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

nozzles are also fixed at the bottom shell course. Yield nozzle is provided fro

receiving finished, intermediate or unfinished products into the tank. This nozzle

is designed according to the velocity of yielding and need for agitation.

3. WATER DRAIN AND ROOF DRAIN

Nozzles for water draw off and roof drain are provided in storage tanks. The water

drains are fixed at 120 degree apart on 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 tanks.

FLOATING ROOF

Floating roof are installed in oil storage tanks primarily to reduce evaporation &

handling losses, to decrease corrosion and to reduce fire hazards. Floating roofs

may be of pan type, single deck pontoon type or double deck pontoon type.

WHY USE FLOATING ROOF?

1. Floating roof tank reduces breathing loss

When a volatile product is stored in a freely ventilated fixed roof tank the

concentration of volatile vapour in the vapour space will vary depending on the

tank operation conditions. During holding periods, when no liquid is added or

removed the vapour space will come to the equilibrium based on product

temperature and vapour pressure. Emissions during holding are generated by the

vapour space breathing process. As a result of daily ambient heating and cooling

processes, the air-vapour mixture in the vapour space expands and contracts.

During the daily heating process, some of the air vapour mixture is expelled from

the tank, resulting in the evaporative emissions. During the product cooling air is

drawn into the product space that helps to dilute the concentration. This initiates

further evaporation that continues until the space again reaches equilibrium.

2. Floating roof reduces filling loss

Normal tank filling and send out operations also affect the vapour space of a fixed-

roof tank when product is removed from the tank air is drawn to the vapour space.

Unless the tank is completely emptied, the air in the new, larger vapour space will

become saturated with product vapour. During the holding period before the next

tank filling operation, evaporative breathing losses will increase due to the



increased volume of the vapour space. When product is added to tank the

increasing liquid volume displaces the air-vapour mixture through the tank vent,

resulting in significant evaporative emissions than any other tank operation in a

fixed-roof tank.

3. Safety

Crude and refined petroleum products are volatile in nature and will readily

evaporative at normal storage and handling conditions producing vapour that are

combustible over a range of concentrations with air. It has been shown that the

addition of a welded floating roof to an open roof tank can produce the

evaporative emissions by more than 98%. Properly designed, the floating roof,

floating roof seals and floating roof deck fittings can control the quantity and

release of product emissions to the environment. To prevent the roof from

bottoming and failing access pipes etc located in the tank bottom and also to

[provide under roof access for cleaning and inspection, vertical leg supports are

provided for holding the roof about I or 2m above the bottom.

To enable the free movement of the roof up and down in the shell I the normal

floating condition, a flexible seal is installed between the roof and the shell.

The buoyancy of the roof is supplied by the pontoons which cover approximately

25% of the total area. The codes stipulate that the minimum pontoon volume shall

be sufficient to keep. The roof floating on the liquid with specific gravity not

exceeding 0.7. if the single deck and two pontoon compartments are punctured and

the primary roof drain in considered inoperative.

ROOF LEGS

To prevent damage to the fittings located beneath the flouting roof, clearance for

tank cleaning and repair, roof legs are provided to hold the flatling roof at a

predetermined distance above the tank bottom when the tank is emptied. The

larger the diameter of the tank, the greater the number of legs required. Roof legs

generally consist an adjustable pipe leg that passes through a slight larger diameter

vertical pipe sleeve. The sleeve is welded to the floating roof, extending both



above and below it. Steel pins passed through the holes in the sleeve and leg to

permit height adjustment.

ROOF OPENINGS

Various roof openings generally [provided are

1. Deck manhole

2. pontoon manhole

3. roof drain opening

4. opening for bleeder vent

5. opening for gauging

Deck Manhole

A manhole is provided on the deck which facilities the inspection and checking by

allowing the worker inside the tank.



Pontoon Manhole

A manhole is provided on each compartment of the pontoon for checking and

inspection. It also facilitates the repair work of the pontoon.

Opening for Gauging

An opening of about 15 inch dia. is made on the pontoons for the installment of

gauge pipes.

ROOF DRAIN

Roof drains are made such that minimum size drain shall be capable of preventing

roof from accumulating a water level greater than design at the maximum rain fall

rate, when the roof is floating at minimum operating legal. Roof drain shall be

made of flexible hose or may be joined type. A check valve shall be provided near

the roof end on the drain pipe to prevent backflow stored product if leakage

occurs. In joined type the drain pipes are connected using swivel joints.



SEAL

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

sealing device and sealing material should be resistant top the stored product and

durable against friction due to roof of 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.



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 (ATG) is carried to obtain information about the total

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

four parameter ie, liquid level, tank capacity tale, average temperature and relative

density of individual tank.

ADVANTAGES 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

COOLING SYSTEM

Storage tanks are equipped with water cooking 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 through which

water is sprayed to the tank shell at a particular pressure.

FOAM SYSTEM

Foam for fire fighting purposes is an aggregate of air filled bubbles formed from

aqueous solutions and is higher 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.The foam generally used in modern 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 SPECIFICATIONS 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 materials 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 fabrication 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 380 Mpa and 450 Mpa

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 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%

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

247.6Mpa.The pipe material used for making roof legs is AI 06 grade B. the chen”

composition is given below:



Carbon (max) 0.03%

Manganese (max) 1.06%

Sulphur (max) 0.048%

Phosphorous (max) 0.058%

Silicon (max) 0.1%

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

Mpa.

PROCEDURE

Assume the values of Height of tank (H) and the diameter of tank (D)

Divide the height into number of courses

Find out the maximum allowable design stress and the maximum allowable

hydrostatic stress for each course

Also find out the volume of shell course

Then find out the total volume of the shell

Find out the total cost of shell plate in that case

Repeat the procedure in 2 or 3 cases

Design the wind girder based on API standards

Location of wind girders based on API standards

Data of shell openings based on API standards

Data of man hole based on API standards

Data of Bolts based on API standards

Data of floating roof based on API standards

Data of Pontoon based on API standards

Data of Rolling ladders and spiral stairways based on API standards



FOUNDATION

BITUMEN CARPETING

Sieved river sand is mixed with 8-10 % by volume of bitumen (80/100grade) 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.

LAYING OF SHELL COURSE

The laying of shell course from top to bottom. The topmost shell course is laid

first. Then the whole course is lifted with the aid of hydraulic jack. The next shell

course is laid and so on. In case of a roof type tank, the roof may be erected on top

most shell course in the beginning as later installing of roof at such great height

may be difficult. The metal plates used for making the shell course need to be

rolled depending on the required curvature. Welding is performed to join the

rolled plates. Vertical welding is performed to join metal in a same course and

horizontal to join adjacent shell courses. The welding procedure and methods

performed are mentioned as below:

DESIGN AND CONSTRUCTION OF STORAGE TANKS

The design and construction of tanks is based on API 650 (11 th edition 2007)

standards

Deign and construction of storage tank number 350 for storing High speed diesel

(HSD).

Tank Selection

High speed diesel (HSD) highly volatile product. Its flash point is of 23

– 65o C. So it comes under class B of petroleum products and has to be stored in

an internal floating roof tank.

Height and diameter



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

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

less than 1.5

Height of tank (H)

Diameter of tank (D)

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 BPCL.

Design Capacity of the tank

Diameter of the tank = 36.58m

Height of the tank = 14.2m

Volume of tank = π4

× D2 H

=π4

×¿

= 3.14

4× ¿

=14915.76057

≈14000 KL

Here,

H/D ratio = 14.2/36.58 = 0.38< 1.5

So it is possible according to API650. (Also the economic condition is maintained).

BOTTOM PREPARATION

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)


<1.5


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

penetration by a test cone.

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

indicates that the maximum settlement to be less than 10mm which is permitted

for large diameters (present tank being of 36.58 dia).

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% by volume of bitumen (80/100grade) 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 June 2007)

Internal diameter : 36.58m

Height: 14.2m

Product stored: High Speed Diesel (HSD)

Specific gravity of product : 0.85

Design specific gravity:0.85

Corrosion allowance: 1.6mm for annular and bottom plate

: 3mm for shell plates

: 1.5mm for roof plates

Design pressure : atmospheric pressure

Material specification : IS 2062 grade A (As per API 650 Table 2.2&

CI2.2.5)



IS 2062 is the metal plate readily available in Indian markets and

also it has got an acceptable value of yield strength (36236 psi or 247.6Mpa) and

tensile strength (59428 psi or 410.6 Mpa).

Wind speed : 100 mph (max) or 160.93 km/h

Maximum rainfall intensity: 57mm in one hour or 254 mm in 24 hours.

I. DESIGN OF BOTTOM PLATES

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

thickness of 6mm exclusively of any corrosion allowance.

So the bottom plate thickness = 6+1.6 = 7.6mm

So the thickness of bottom plate is selected as from API 650. (Since the thickness

of steel plates available in market are sizes 8,10, 12mm etc.

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

25mm width will project beyond the outside edge of the wed attaching the bottom

to the shell plate. The commonly available size of plates in markets are of length

6m, 8m, 10m and of width 1.5m, 2m, 2.5m, etc. bottom plate preparation involves

shot blasting and bituminized painting.

II. DESIGN OF ANNUAL BOTTOM PLATES

Radial width of annular plates depends upon the shell course thickness. So annular

bottom plate designing is done after the shell designing.

III. 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

equal to 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 from the tank of diameter in the range of

36m-60m should not be less than 8mm. (For tank diameter less than 36m, the shell

thickness should not be less than 6mm).



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

allowable stresses. The maximum allowable product design stress Sd (API

650Cl.5.6.2.1), 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

650Cl.5.6.2.2), shall be either three-fourth the yield strength or three-seventh the

tensile strength whichever is less.

Yield strength of selected material (IS 2062) = 247.6MPa (Mega Pascal-

Newton/mm2)

Tensile strength of selected material = 410.6MPa

Maximum allowable design stress, (Sd)

API 650 cl 5.6.2.1

Sd = 2/3* 247.6 = 165MPa

Sd = 2/5* 410.6 = 164.24 MPa

So design stress is taken as 165 MPa (the maximum of 165MPa & 164.24MPa)

Maximum allowable hydrostatic stress, (St)

API 650 cl 5.6.2.2

St = ¾* 247.6 = 185.7MPa Or

St = 3/7* 410.6= 175.97MPa ≈ 176MPa

So hydrostatic stress is taken as 176MPa (the minimum of 175.MPa& 185.7MPa)

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

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

using variable design point method. So here 1-foot method is used.

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

the bottom of each shell course. In this method we find out the design shell


Sd = 2/3* yield strength

Sd = 2/5* tensile strength

St = 3/4* yield strength

St =3/7* tensile strength


thickness (td) and hydrostatic test shell thickness (tt) and the maximum of

the two values is taken.

Where,

td – design shell thickness in mm

tt – hydrostatic shell thickness in mm

D – nominal tank diameter in m = 36.58m

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

shell = 14.2m.

G – Design specific gravity of the liquid to be stored = 0.85

CA- Corrosion allowance in mm = 3mm

Sd – Allowable design stress = 165MPa

St – Allowable hydrostatic stress = 176MPa

Since the height of the tank is 14.2m, we have divided it into numbersof courses

considering the economic condition. It is to be noted that standard thickness

available in the market are 8, 10, 12, 14, 16, 20, 25 mm. values of thickness

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

in the market. We select a number of random cases with varying no. of courses

and course widths.

CASE 1

We divide the total height 14.2m to 6 courses 3, 3, 3, 2, 2 &1.2m respectively.

From the above formula shell thickness is calculated.


td =(4.9D* (H-0.3)* G)/Sd + CAtt = 4.9D* (H-0.3)/St


Shell thickness

1st Course

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

shell,

= 14.2m

D = nominal tank diameter in meters

= 36.58m

Design shell thickness td = (4.9D* (H-0.3)*G)/Sd+CA

Hydrostatic shell thickness tt = 4.9D* (H-0.3)/St

td = (4.9*36.58*(14.2-0.3)* 0.85)/165+ 3

= 15.8348mm

tt = 4.9*36.58* (14.2-0.3)/176

= 14.156mm

Design condition is to select max of td or tt. In this case max value is15.8348mm.

Thickness selected (as per market size) t = 16mm = 0.016m

Width of the shell course (W) = 3m

Volume of shell course = *D*W*t = x36.58x3x0.016 = 5.516m3

2nd Course

H = 14.2-3= 11.2m (total height – 1st course height)

D = 36.58m

td= (4.9D* (H-0.3*G)/Sd + CA = 4.9x36.58x(11.2 – 0.3)x0.85

165

= 13.064 mm

tt = 4.9D* (H-0.3)/St = 4.9x 36.58x(11.2-0.3)

176

= 11.1mm


+ 3


Design condition is select max of td andtt . In this case max value is 13.064mm.


Width of shell course, W = 3m

Volume of shell course V = *D*W*t = x 36.58x3x0.014

V = 4.826m3

3rd Course

H = 11.2 -3 = 8.2m

D = 36.58m

td =( 4.9D* (H-0.3)*G)/Sd + CA= 4.9x36.58x(8.2-0.3) x 0.85

165

= 10.29mm

tt = 4.9D* (H-0.3)/st = 4.9x36.58x(8.2-0.3) 176

= 8.045mm

Design condition is to select max of td or tt. In this case max value is 10.29mm.



Volume of shell course V = *D*W*t = x 36.58x3x0.012

V = 4.137m3

4th Course

H = 8.2-2 = 6.2m

D = 36.58m

td = (4.9D* (H-0.3)*G)/Sd + CA = 4.9x36.58x(6.2-0.3) x 0.85 165

= 8.447mm

tt = 4.9D* (H-0.3)/St = 4.9x36.58x(6.2-0.3) 176

=6.008 mm


+ 3

+ 3


Design condition is to select max of tdortt.In this case max value is 8.447mm.


Width of the shell course, W = 2m

Volume of the shell V = *D*W*t = x36.58x2x0.010 = 2.298m3

5th Course

H = 6.2 -2 = 4.2m

D = 36.58m

td = (4.9D* (H-0.3)* G)/Sd + CA= 4.9x36.58x(4.2-0.3)x 0.85

165

= 6.601mm

tt = 4.9D* (H -0.3)/St = 4.9x36.58x(4.2-0.3)

176

= 3.97mm

Design condition is to select max oftd ortt. In this case max value is 6.601mm.



Volume of shell course V = *D*W*t = 1.13

= x36.58x2x0.008 = 1.8387m3

6th Course

H = 4.2-1.2 = 3m

D = 36.58M

td = (4.9D* (H-0.3)* G)/Sd + CA= 4.9x36.58x(3 -0.3)x 0.85 165

= 5.493mm

tt = 4.9D* (H -0.3)/St = 4.9x36.58x(3 -0.3) 176

= 2.749 mm


+ 3

+3


Design condition is to select max of td ortt. In this case max value is 5.493mm.

Thickness selected (as per market size) t = 6mm

Therefore, thickness selected, t = 6mm = 0.006 m

Width of the shell course, W = 1.2m

Volume of shell course V = *D*W*t = x36.58x1.2x0.006

= 0.8274m3

CASE 2

We divide the total height 14.2m to 5 courses 4, 3, 2.5, 2.5& 2.2 m respectively.

From the above formula shell thickness is calculated.

1st course

H = 14.2m

D = 36.58m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(14.2 -0.3)x 0.85

165

= 15.834 mm

tt = 4.9D* (H - 0.3)/St = 4.9x36.58x(14.2 -0.3)

176

= 14.156 mm

Design condition is to select max of td or tt. In this case max value is15.834 mm.

Thickness selected (as per market size) t = 16 mm = 0.016 mm


Volume of shell course V = *D*W*t = x36.58x4x0.016

V = 7.354 m3


+ 3


2nd Course

H = 14.2 -4 = 10.2 m

D = 36.58m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(10.2 -0.3)x 0.85

165

= 12.14mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (10.2 -0.3)

176

= 10.082mm

Design condition is to select max of td or tt. In this case max value is 12.14 mm.

Thickness selected (as per market size) t = 14 mm = 0.014 mm

Width of shell course, W = 4 m


V = 6.435 m3

3rd Course

H = 10.2 – 3 = 7.2m

D = 36.58m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(7.2 -0.3)x 0.85

165

= 9.37 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (7.2 -0.3)

176

= 7.027 mm


Thickness selected (as per market size) t = 10 mm = 0.010 m

Width of shell course, w = 3m


+ 3

+ 3



V = 3.447 m3

4th Course

H = 7.2 – 2.5 = 4.7m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(4.7 -0.3)x 0.85

165

= 7.0628 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (4.7 -0.3)

176

= 4.48mm

Design condition is to select max of tdortt. In this case max value is 7.0628 mm.

Thickness selected (as per market size) t =8 mm = 0.008

Width of shell course, W = 2.5 m


V = 2.298 m3

5th Course

H = 4.7 -2.5 = 2.2 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(2.2 -0.3)x 0.85

165

= 4.564 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (2.2 -0.3)

176

= 1.935 mm


+ 3

+ 3






V= 1.7237 m3

Case 3

We divide the total height 14.2 to 7 courses of 2, 2, 2.125, 2.425, 2.425, 2.425,

0.790 are respectively.

Shell thickness

1st Course

H = 14.2m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(14.2 -0.3)x 0.85

165

= 15.8348 mm

tt = 4.9D* (H - 0.3)/St = 4.9x36.58 x (14.2 -0.3)

176

= 14.156 mm

Design condition is to select maxof td ortt. In this case max value is 15.8348 mm.

Thickness selected (as per market size) t = 16mm = 0.016 m



V= 3.677 m3

2nd Course


+ 3


H = 14.2 -2 = 12.2 m

D = 36.58m

td =( 4.9D* (H - 0.3)* G)/Sd+ CA= 4.9x36.58x(12.2 -0.3)x 0.85

165

= 13.98 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (12.2 -0.3)

176

= 12.119 mm



Width of shell course, W = 2 m

Volume of shell course V = *D*W*t = x36.58 x2 x 0.014

V = 3.217 m3

3rd Course

H = 12.2– 2.125 = 10.075 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x(10.075 -0.3)x 0.85

165 = 12.026 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (10.075 -0.3)

176

= 9.955 mm


Thickness selected (as per market size) t = 12 mm = 0.012


Volume of shell course V = *D*W*t = *36.58*2.125*0.012

V = 2.9304 m3

4th Course


+ 3

+ 3


H = 10.075 – 2.425 = 7.65 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9x36.58x (7.65 – 0.3)x0.85 +3165

= 9.786 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (7.65 -0.3)

176

= 7.48 mm


Thickness selected (as per market size) t = 10 mm = 0.010m


Volume of shell course V = *D*W*t = x36.58 x2.425x 0.010

V = 2.786 m3

5th Course

H = 7.65 – 2.425 = 5.225 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA= 4.9∗36.58∗(5.225−0.3 )∗0.85

165 +3

= 7.547 mm

tt = 4.9D* (H - 0.3)/St = 4.9x36.58 x (5.225 -0.3)

176

= 5.0157 mm


Thickness selected (as per market size) t = 8 mm = 0.008


Volume of shell course V = *D*W*t = x36.58x2.425x 0.008



V = 2.229 m3

6th Course

H = 5.225 – 2.425 = 2.8 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA=4.9∗36.58∗(2.8−0.3 )∗0.85

165 +3

= 5.308 mm

tt = 4.9D* (H - 0.3)/St = 4.9x36.58 x (2.8 -0.3)

176

= 2.547 mm




Volume of shell course V = *D*W*t = x36.58x2.425x.008

V = 2.229 m3

7th Course

H = 2.8 – 0.790 = 2.01 m

D = 36.58 m

td = (4.9D* (H - 0.3)* G)/Sd + CA=4.9∗36.58∗(2.01−0.3 )∗0.85

165 +3

= 4.578 mm

tt = 4.9D* (H - 0.3)/St = 4.9x 36.58 x (2.01 -0.3)

176

= 1.7414 mm






Volume of shell course V = *D*W*t = x36.58x 0.790x0.008

V =0.726 m3

ECONOMIC CONSIDERATION

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

fabrication cost for each cases.

Case 1

The total volumeof shell plate required = 19.4431m3

Total weight of the shell plates = volume * density

= 19.4431 x 7.85 x 103

= 152.968ton

Material cost per metric ton = Rs35000

So overall material cost of the shell plates = 152.628 x 35000

= Rs 0.534 crores

Case 2

The total volume of shell plate required = 21.2577 m3

Total weight of the shell plates = volume* density

= 21.2577 x 7.85x 103

= 166.872ton

Material cost per metric ton = Rs35000

So over all material cost of the shell plates = 35000 x 166.872

= 0.5840 crores

Case 3

The total volume shell plate required = 17.7944 m3

Total weight of the shell plates = volume * density



= 17.7944 x 7.85x103

= 139.686ton

Material cost per metric ton = Rs.35000

So over all material cost of the shell plates = 35000 x 139.686

= 0.4889 crores

Case I

It (m) Td

(mm)

Tt

(mm)

Calculated thickness (mm)

Standard thickness (mm)

Total weight

(ton)

Total cost

(crores)

3 15.8348 14.156 15.8348 16

152.628 0.534

3 13.064 11.1 13.064 14

3 10.29 8.045 10.29 12

2 8.447 6.008 8.447 10

2 6.601 3.97 6.601 8

1.2 5.493 2.749 5.493 6

Case II

It (m) Td

(mm)

Tt

(mm)

Calculated thickness (mm)


Total weight

(ton)

Total

cost

(crores)

4 15.834 14.156 15.834 16

166.872 0.584

3 12.14 10.082 12.14 14

2.5 9.37 7.027 9.37 10

2.5 7.0628 4.48 7.0628 8

2.2 4.564 1.935 4.564 6



Case III

It (m) Td (mm) Tt(mm) Calculated thickness (mm)


Total weight (ton)

Total cost

2 15.8348 14.156 15.8348 16

139.686 0.4889

2 13.98 12.119 13.98 14

2.125 12.026 9.955 12.026 12

2.425 9.786 7.48 9.786 10

2.425 7.547 5.0157 7.547 8

2.425 5.308 2.546 5.308 8

0.790 4.578 1.7414 4.578 8

Here we take case 3 because of less material consumption and less total cost

comparing than the other cases.

The shell course fig. Of the most economic case is shown below


2m2m

2.125m2.425m

2.425m2.425m

m0.790m

m

Course 7 8mm

Course 6 8mm

Course 5 8mm

Course 4 10mm

Course 3 12mm

Course 2 14mm

Course 1 16mm

14.2m




ANNULAR PLATE

Annular plates are plates on which the shell rest and connects shell plates with

bottom plates.

As per table 3.1 of API 650, for 16 mm 1st shell course thickness, the minimum

annular plate thickness is 6mm.

So minimum thickness required = 6 + 1.6 (C.A) = 7.6 mm8 mm

Here we provide 10 mm thick annular plate, since annular plate thickness should

be greater than bottom plates.

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

the outer surface of shell plate, dimension between the inner surface of the shell

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

thickness.



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

minimum dimension between surface 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 shell plate = 65 mm (min50mm)

Minimum dimension between inside surface of shell plate to lap joint, = 610 mm

(min 600)

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

1st shell course thickness = 16mm

So required minimum radial width = 65 + 610 + 65 + 16 = 756 mm

2nd Method

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

tb – thickness of annular plate in mm = 10 mm

H – maximum design liquid level in m = 14.2m

G – design specific gravity of liquid to be stored = 0.85

So radial width = 215 x10/(14.2 x 0.85)0.5

= 618.845mm

As per the above 2 methods the greater of required radial width = 756 mm. So we

provide annular plate of radial width 1000 mm (to be on safer side)

IV. DESIGN OF WIND GIRDER

Basic wind speed

It is based on peak gust 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 = 100 mile/hr= 160.93 km/hr



Section modulus required for primary wind girder, Z = D2 H 2

17 ( V

190 )2 cm3

(API 650 11th edition 2007)

t = Shell thickness at the attachment = 8 mm

Portion of tank shell to be considered for calculating L = 32 * ts + t

= 32 * 8 + 8

= 264 mm

Locating the centre of gravity of primary wind girder

Centre of gravity (x) = (A1 X1 + A2 X2 + A3X3) / (A1+A2+A3)

X = (8∗264 )∗4+ (6∗800 )∗408+(8∗264 )∗812

(8∗264 )+(6∗800 )+(8∗264) = 408 mm

8 mm 8 mm

6 mm 264 mm

800 mm

Moment of inertia about C.G

Where,


Ixx = (bd3 / 12 ) + Ah2


A = Area of the various sections (A1, A2, A3)

h = Distance from centre of gravity to centre of various sections (h1, h2, h3)

b = Vertical length of various cross sections (b1, b2, b3)

d = Horizontal width of various cross sections d1, d2, d3

Ixx = ((b1*d13/12)+A1*h12) + (( b2 * d23/12)+A2*h22)+((b3 * d33/12) +A3*h32)

Ixx = ( 264∗83

12 )+( 264∗4042 )+( 6∗8003

12 )+( 264∗83

12 )+(264∗4042)

= 3.42 * 108 mm4

Distance from neutral axis to extreme fiber , X = 408 mm

Section modulus of the above ‘I’ section (calculated value) Zxx = Ixx / X

Zxx = 3.42∗108

408 = 8.382 * 103 cm3 > 1658

So design is feasible [as per API 650 requirements, calculated value of section

modulus (Zxx) should be greater than required section modulus (Z)]

Location of Primary Wind Girder

The primary wind girder is provided as a walk way at a distance 1067 mm

from the top. Here there is no change in design and location of primary wind

girder, because of there is no maintenance work. So we take the existing data from

the previous design data according to API 650 – 11th edition 2007.

Design calculation of secondary Wind girder

Requirement of Second wind Girder

Maximum height of the un stiffened shell = H1 = 9.47 x t (r/D)3 * 190 2

V

(According to API 650, cl5.9.7.1)

t = Thickness of top shell course = 5mm



D = Nominal tank diameter = 36.58m

H = 9.47 *5*(5/36.58)3* (190

160.93¿2

H= 3.370 m

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 each shell course having a

top shell thickness by the equation.

Wtr = W {(t uniform / t actual)5} [API 650 cl 5.9.7.3]

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 corrosion

allowance.

tuniform = 5 mm

tactual = Ordered shell course thickness excluding the corrosion allowance in

mm for which Wtr is being calculate.

First,second and third courses

Tactual = 8mm - 3mm C.A=5mm

W=5640mm

So Wtr=5640*[(5/5)5]0.5 = 5640mm

Fourth course

tactual=10mm - 3mm C.A=7mm

W=2425mm

So Wtr=2425*[(5/7)5]0.5=1045.7mm

Fifth course



Tactual=12mm - 3mm C.A=9mm

W=2125mm

So Wtr=2125*[(5/9)5]0.5 =488.8mm

Sixth course


W=2000mm

So Wtr=2000*[(5/11)5]0.5 =278.59mm

Seventh course


W=2000mm

So Wtr=2000*[(5/13)5]0.5 =183.48mm

Transformed width wtr =5640+1045.7+488.8+278.59+183.48

= 7636.57mm

According to API 650 (11th edition 2007, [3.9.7.3]), if height of transformed shell

is greater than maximum unstiffened height,H1. an intermediate wind girder is

required.

No: of secondary wind girders required =height of transformed shell

Maximum un stiffened height

= 7636.57/3370 = 2.26> 1

Since ratio is greater than one, one number of secondary wind girders is required.

Location of intermediate wind girder

As per clause No.5.9.7.3, 5.9.7.3.1, &5.9.7.3.4 the secondary wind girder shall

be provided, the girder should be located at the middle of transformed

shell(7636.57/2=3818mm),The existing wind girder at a height of 3320mm from

primary wind girder.


0.790m2.425m

2.425m2.425m

2.125m2m

2m

1067mm

3818 mm


The previous wind girder was too small for a walk way (200mm) there for we

changed the dimension and constructed a new secondary wind girder of width

600mm, which made inspection around the tank possible.

V. SHELL OPENINGS

1. MAN HOLE (SHELL)

One -man hole provided to the tank shell at the bottom shell course.



It is enough to provide 600 mm manhole.

Minimum thickness of cover plate, tc = 16 mm

Thickness of bolting flange tf = 11 mm (API 650 table 3.3)

Man hole diameter, Dm = 914.4 mm

Cover plate diameter, Dc = 820 mm (API 650 table 3.5 page 5-18)

BOLTS

Number of bolts = 42

Diameter of bolts = 22 mm

Diameter of bolt hole= 24 mm (API 650 3.4 A)

e. DRAW OFF SUMP

Two draw off sumps is provided at the bottom plate in order to store the water

content in the product and to remove it. (Note: Two is selected according to Tank

no: 019KR)

Diameter of sump, A = 1220 mm

Depth of sump, B = 610 mm

Distance from center pipe to shell, C = 150 mm

Thickness of plates in sump = 10 mm

Minimum internal pipe thickness = 114.3 mm

Minimum nozzle neck thickness = 3 mm



VI. COOLING WATER SYSTEM DATA

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

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

INPUT DATA

Type of tank: floating roof tank

Diameter of the tank: 36.58m

Height of the tank: 14.2m

Wind girder from bottom: 13.2m

Design code: OISD 116

The cooling water is sprayed on to the tank with the help of nozzles on

three set of pipe rings around the shell as per the new design aspects.

Area below primary wind girder (AI)= x36.58x13.2

Total surface area = 1556.16m2



Since OISD specifies that a minimum of 3 liters has to be sprayed per

minute per unit.

Area of the shell, the total amount of water required = 1556.16 x 3

= 4668.48 (1p – liters per minute)

Considering the pressure losses in the pipes connecting the ring and the water

tank, the operating pressure of the nozzle is calculated to be between 1.5 to

3.5kg/cm2. Two sets of cooling water rings are provided, one above the primary

wind girder, and the other below the secondary wind girder.

Ring no;1

Surface area to be cooled by the water from top ring = Dh

D = dia of the tank= 36.58m

H = distance between two wind girders = 6 m

Surface area = x 36.58 x 6= 689.16 m2

Water required = 3 x surface area

= 3 x 689.16 = 2067.50lpm

VII. FOAM SYSTEM PROVIDED

Foam recommended = AFFF

Foam application rate = 12 liters/min/m2 of seal area. (As per

OISD 116)

Foam dam width = 1 m

D, diameter of the tank = 36.58m

Height of the foam dam = 600mm= 0.6 m



VII. FLOATING ROOF

The roof and accessories shall be designed and constructed so that the roof is

allowed to the float to the maximum designed liquid level and then return to a

liquid level that floats the roof well below the top of the tank shell without damage

to any part of roof and accessories.

Deck plate data

As per the API 650 standards deck plate shall have a minimum thickness of 5 mm

(Cl – C.3.3.2, pg C-1, API 650)

So the thickness of deck plate selected = 5 mm

Dimensions= 6300x1500x5thk

Total weight=31527.56kg

The deck plate shall be provided with a roof manhole, rain-drains, support legs etc.

Pontoon data

No.of components(N)= 38+1=39Qty

Pontoon bottom plate= 6300x1500x5thk

Pontoon material= IS 2062 Gr A

Weight of single pontoon= 39.25 kg

Total weight of pontoon=15318.17kg


3.06m

Pontoon

Deck

36.58 m


110

1050

1000.57 1000.57 1000.57


3066.69

200600

600

Pad

Deckplate


Data of Rolling ladder and spiral stairways

Rolling ladder rolls over a certain path with the help of wheels which are made of

steel and having a brass cap to prevent spark.

Length of ladder = 17960 mm.

Track slope = 1 : 100

Supporting legs

The floating roof shall be provided with support legs. The length of support

legs shall be adjustable from the top side of the roof. According to API 650

standards the length and attachment shall be designed to support the roof and

uniform live load at least 1.2 KPa.



INSPECTION OF STORAGE TANKS

INSPECTION PROCEDURES

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

and record shall gone through. Inspection of tank is needed to be carried out at

different staged of its making. The tank is inspected for its roundness, proper

curvature, the welding carried out, local deviations.

Inspection shall include:

Study of all technical specifications and the code to which the tank is to be

built.

Checking the foundation pad and slope

Identification of plate materials

Qualification of welding procedure and welding operator

Checking of painted underside of the bottom plate prior to these being laid

Checking of each batch of electrodes as per specifications and assurance of

its use as per suggested methods of their manufactures and codes.

Checking of proper welding sequence

Evaluating spot radiology of butt welded annular (radial) joints and vacuum

box test of the portion of the weld on the bottom plate in which shell is to

be erected

Checking of fits ups and noting of curvature and plumb readings before and

after welding of the shell courses



Inspection of Welds

Butt-Welds

Complete penetration and complete fusion are required for joining shell plates to

shell plates. Inspection for quality of welds shall be made using either

radiographic methods or ultra sonic method. Visual examination may also be

done.

Fillet-Welds

Fillet welds shall be inspected by visual method of examination. The final weld

shall be cleaned to slag and other deposits prior to inspection.

Inspection of Tank bottom

Upon completion of welding of tank bottom, bottom welds and plates shall be

examined visually for any potential defects and leaks. In addition to it can be done

by vacuum test tracer gas test.

Inspection of Reinforcement –plate welds

After fabrication is completed but before the tank is filled with test water, the

reinforcement plates shall be tested by applying up to 100 kPa gauge pneumatic

pressure between the tank shell and the reinforcement plate on each opening using

the tell-tale hole specified.

Testing of shell

After entire tank and roof structure is completed, the shell shall be made tested by

one of the following methods.

(i) If water is available for testing shell, the tank shall be filled with water as follows

(ii) To maximum design liquid level, H

(iii) For a tank with a tight roof, to 50mm above the weld connecting the roof plate or compression plate to top angle or shell

(iv) To a level lower than specified in sub items i) or ii) when restricted by

over flows.



a. If sufficient water is not available to fill the tank, tank may be tested by

painting all of the joints on inside with a highly penetrating oil and

carefully examining the outside of joint for leakage.

b. Applying vacuum top either side of joints or applying air pressure as

specified in roof test.

Testing of Roof

It can be done by

Applying internal air pressure not exceeding the weight of roof plates and

applying to weld joints a soap solution or other material suitable for

detection of leak.

Vacuum testing of weld joints

VISUAL INSPECTION

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

visual inspection, following shall be checked.

Protective Coatings

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

blisters and film lifting.

Roof Plates

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

water accumulation locations.

Ladder, Stairways, Platform and Structures

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

(trends) shall be checked fro wear and corrosion.



Tank Pads

Tanks pads shall be visually checked for settlement, sinking, tilting, sapling

cracking and general deterioration.

Proper sealing of opening between tank bottom and the concrete pad shall

be checked (no water shall flow under the tank bottom).

Slope of tank pad shall be checked to ensure water drainage

Anchor bolts

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

hammer testing. These shall also be checked for thinning/bending. Distortion of

bolts is an indication of excessive settlement. Concrete foundation at anchor bolt

shall be checked for cracks.

Fire Fighting System

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

tank with respect to clogging of spray nozzles, perforation of foam connections,

etc, shall be checked. Frequency and procedure for checking shall be over as per

OISD-Std-142 (Inspection of Fire Fighting Equipment).

Vents and 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 nor 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 outlined in OISD-Std-132 (Inspection of Pressure

Relieving Devices).



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 undetected corrosion of the tank plates underneath

the insulation.

Grounding Connections

Grounding connections shall be visually checked for corrosion at the points where

they enter earth and at the connections to the tank. The resistance of grounding

connections shall be checked annually before monsoon.

Leaks

The tank shall be inspected fro any obvious leakage of the product. Valves and

fittings 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.

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

visual inspection.

1. Tank fittings, Accessories and Pipe Connection

All nozzles shall be visually inspected for corrosion/distortion. Thickness

measurements shall be taken with ultrasonic thickness meter. On nozzle of size 50

mm NB above, minimum 4 readings should be taken.

2.Tank Shell

The tank shell be visually examined for external corrosion, seepage, cracks,

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 the fillet welds of the shell to bottom

plate.

The following minimum requirement for the thickness survey is recommended in

all tanks.

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

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

covered.

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

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

height.

3. Tank Roofs

Floating Roofs

On a floating roof, during visual inspection, the following shall also be thoroughly

checked.

Paint condition

Depressions

Pontoon boxes and buoys from leakages, indications/marks of seepage

and corrosion

Roof and emergency drain

Drain shall be checked for breakages and blockages on the check valve fitted on to

the roof drain inlet end. Emergency drains shall be checked for water level oil

spillage on roof deck.

Floating roof seals

Before making a regular inspection of floating roof seals, the drawings of seals

shall be studied so that operation and possible damages are well understood.



Floating roof seals shall be visually inspected every year. All seals shall be

inspected visually for corroded, eroded or broken parts and deteriorated sealing

materials. Exposed mechanical parts such as springs, hanfers, counter-balance,

pantographs and shoes are susceptible to mechanical damage, in addition to

mechanical wear and atmospheric or vapour space corrosion.

The rubber seal have fairly close contact with tank shell plates.

a. Hinge bolts at the top of ladder and its rollers

b. Earthing of the ladder

c. Lateral movement, rotation and titling of roof

d. Electrical continuity between the floating roof and tank shell.

5. Projecting out portion of bottom plates

The projecting out portion of the bottom plates (annular plates) shall be visually

examined for any corrosion/thinking ultrasonically gauged.

INTERNAL INSPECTION

Prior to internal inspection, an external inspection of the tank shall be done as specified

earlier. Before commencing the internal inspection, the tank must be emptied of liquid,

freed of gases and cleaned out.

Roof and Structural Members

Floating Roof

The underside and internal of floating roof shall be inspected for corrosion and

deterioration. The floating roof seals shall be inspected from the underside. The

legs and sleeved of floating roof shall be checked for deterioration, bowing and

shifting. Thickness survey of the pontoon boxes and check shall be carried out.

Any suspected pontoon/buoy compartment shall be checked with air and suds.

II. Tank Shell

Entire tank shell shall be visually scanned for signs of corrosion, pitting, cracking

etc. Finding of external inspection, service condition and history shall be guiding



factors for such observations. All weld joints shall be examined carefully. The

vapour space and liquid level line are likely areas of corrosion. However, if the

walls are alternately wet and dry or the concepts are corrosive chemicals, the

entire can be attacked.

III. Tank Bottom

After the tank has cleaned of its sludge, it shall be visually inspected to obtain the

first indication of the condition of the bottom. The tank bottom plates shall be

visually inspected for pitting, corrosion and weld cracks. The weld joints shall be

thoroughly cleaned and visually inspected for cracks or defects by magnifying

glass wherever joints of shell and annular ring and inspected for any leakage.

Depressions in the bottom and in the areas around or under the roof supports and

pipe coil supports shall be checked closely. Corrosion on the underside of flat

bottom tanks resting on soil or on pads cannot be checked from outside. From

ultrasonic thickness instrument are also indications of underside corrosion. To

carry out a positive inspection and accurate check, it is recommended to cut out

representative sections of coupons (at least 30mm in least dimension) of bottom

plate.

IV. Water draw-off

Water draw off subjected 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.

Drain sumps shall be carefully checked for crack, pitting, leak in the weld, and

measured in particular when corrosion at the underside of the tank bottom plates

has been suspected.

V. 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.

VI. 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.

TESTING METHODS

1. Dye-penetrating testing

It is used for detecting discontinuities open to the surface

Basic process

1. Surface penetration and pre cleaning

2. Applying a visible or fluorescent liquid penetrant to surface

3. Wait for the penetrant to enter surface breaking discontinuities

4. Removing excess penetrant from the surface

5. Applying a developer to the examination surface

6. Interpretation of indication

7. Dye penetrant testing

Advantages

i. Easy to apply and cheap

ii. Interpretation easier

iii. Can be used for any metal

Disadvantages

i. Can detect only surface discontinuities



2. Magnetic Particle Testing

Used to detect surface and sub surface discontinuities

Basic process

1. Magnetic field is induced in the specimen

2. The discontinuities lying in a direction transverse to the field will cause

a leakage flux to develop around it.

3. Fine magnetic powder if sprinkled on this will adhere to in the vicinity

of leakage flux.

4. Magnetizing yoke

5. Florescent iron powder

6. Black light source

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

permanent magnets are also used for the same

Advantages

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

ii. Interpretation easy

Disadvantages

i. Can be used for only ferrous metals

ii. Residual magnetism is a problem

iii. Power requirement

3. Ultra sonic Testing

Ultrasonic waves are sound waves with frequency above the audible range ie,

above 20000 Hz. This method is used to detect all types of defects ie, volumetric

NDT.



Basic process

1. Ultrasonic waves propagated through the material

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

impedance

3. Defects of material are change of acoustic impudence

4. The reflected waves are detected using cathode ray tubes

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

and position of the defect

4. Radiographic test (Applicable only at shell, annular plate joints)

Used to detect all kinds of defects

Basic process

It is a volumetric examination 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 no. of the

material

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

The image depends on the amount on the amount of transmitted rays that

strike 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



Disadvantages

Radiation safety is an area of concern especially in case of gamma ray

sources

The operators are likely to be exposed to radioactive radiation and needs

constant monitoring

The test results will take some time- processing time of film

.



CONCLUSION

Introducing a floating type roof for the storage would mean increased

safety level. The given parameters were to design and store HSD in a tank of

diameter 36.58 m to height of 14.2m of plate of IS-2062A was used. The tank was

designed to store 14000 KI. The designing was done according to the full design

specification as required by the industry using American Petroleum Institute (API

650-11th edition, 2007) design data. After the designing was completed the design

was checked with the existing parameters. The inspection of tank was also studied

at different stages of its construction.



REFFERENCES

1. AMERICAN PETROLEUM INSTITUTE (API) 650, 11TH

EDITION, 2007.

2. OIL INDUSTRIES SAFETY DIRECTORATE (OISD)116.

3. Text Book of “Introduction to Storage Tank “.

4. Guide to Storage Tank and Equipments

5. API 653 – 2009 (Only for repair)


DESIGN AND MAINTAINANCE OF FLOATING ROOF STORAGE TANK IN PETROLIUM REFINERY

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Transcript of DESIGN AND MAINTAINANCE OF FLOATING ROOF STORAGE TANK IN PETROLIUM REFINERY