If you’re planning a new facility or upgrading existing infrastructure, Wisdom Design Consultancy is here to provide cutting-edge design services for your Floating roof storage tank systems.

With over 22 years of specialized experience in Floating roof storage tank design,

Wisdom Design Consultancy is a trusted name in the industry for delivering high-quality, efficient, and code-compliant solutions tailored to your project needs

22+ Years of Expertise in Floating roof Tank Design
One-Point Contact for the Entire Project.
All engineers and draftsmen on our team have over 15 years of experience in Floating roof roof tanks design
Every design document is thoroughly reviewed and approved by a Senior Design Manager to ensure technical accuracy and quality before delivery.
We strictly follow agreed schedules, ensuring on-time delivery without compromising on quality.
Compliance with International Codes & Standards, applicable global standards.
From concept to commissioning, we ensure complete coordination with the client, consultants, and stakeholders at every stage
Our solutions strike the right balance between cost-efficiency and safety, without compromising long-term reliability

OUR SERVICES

Design Calculations Preparation
GA drawings preparation
Fabrication drawings preparation
Tank Form & Tank Terminal design
Vendor documents review
Cost Estimation for tenders
FEED front end design engineering
Basic design engineering
Tender documentation preparation
Tank selection and sizing
Material selection
P & ID drawing preparation
Storage tank pumps selection and sizing
Tanks piping design and sizing
Overall plant layout preparation
Plate cutting drawings preperation
Tank design standards.
Maintenance manual preparation

FLOATING ROOF- STORAGE TANK DESIGN- CONSULTANCY SERVICES

Design services

for single-deck pontoon-type

and double-deck-type external floating roofs,

Internal floating roof in a tank with a fixed roof at the top of the tank shell

API 650 refers to a standard published by the American Petroleum Institute (API)

API 650 refers to a standard published by the American Petroleum Institute (API) for the design, construction, and inspection of welded storage tanks used in the petroleum and chemical industries. These tanks are typically aboveground and cylindrical, with fixed roofs, floating roofs, or other types of covers.

Floating Roof Tanks (FRTs) – API 650 Overview

Floating roof tanks are storage tanks with a roof that floats directly on the surface of the stored liquid, reducing vapor space and minimizing evaporation losses. They are widely used in storing volatile liquids such as crude oil, gasoline, and other petroleum products.

API 650 covers both external and internal floating roof tanks through different sections and appendices.

External Floating Roof Tank (EFRT)

✅ Design Highlights

Open-top with a floating deck
Typically includes:
- Pontoon-type or double-deck floating roof
- Roof seals (primary and secondary) to close the gap between the roof and shell
- Drainage system for rainwater
- Guides and anti-rotation devices
Designed to reduce VOC emissions and comply with environmental regulations

📏 Considerations

Roof type: Pontoon or double-deck
Shell design: Includes wind and seismic loads (API 650, Appendix F & E)
Drainage: Flexible hose or articulated drain system
Accessories: Roof legs, gauge poles, shunts (for lightning protection)

Internal Floating Roof Tank (IFRT)

✅ Design Highlights

Has a fixed roof (cone or dome type)
Floating deck is inside the tank
Used where external floating roofs are not suitable (weather conditions, contamination, emissions regulations)

📚 API 650 Reference: Appendix H

Roof Types in IFRTs:

Full contact (aluminum honeycomb, foam-filled)
Pontoon type
Hybrid types

📏 Design Elements

Fixed roof: Designed as per API 650 (e.g., cone or dome)
Internal floating roof: As per Appendix H
Sealing system: Primary and optionally secondary seals
Ventilation: Required to prevent pressure build-up
Access and inspection: Hatches, manways, gauge hatches

BS EN 14015. This is the British and European standard

BS EN 14015: Specification for the design and manufacture of site-built, vertical, cylindrical, flat-bottomed, above-ground, welded steel tanks for the storage of liquids at ambient temperature and above

📌 Key Features

FeatureDescription

📅 First Published2004 (current version may be updated – let me know if you want latest via web)

🌍 RegionUK & Europe (based on EN standards)

🏗️ ApplicationSimilar to API 650 — for atmospheric or low-pressure liquid storage

⚙️ Tank TypeCylindrical, vertical, welded, above-ground, flat-bottomed tanks

🌡️ TemperatureAmbient to slightly elevated temps

🔧 Key Design Topics

1. Materials

Includes both carbon steel and stainless steel
More aligned with European steel grades (e.g., S235, S355)

2. Design Loads

Wind, snow, seismic, and internal pressures
Seismic per Eurocode 8
Wind per EN 1991-1-4

3. Tank Bottom & Shell Design

Includes guidance on annular plates, corrosion allowances, etc.
Bottom can be single plate or annular ring-based depending on diameter

4. Welding and NDT

Strict welding procedures
Requires Welding Procedure Specification (WPS), PQRs, and welder qualifications
NDT: Radiographic, ultrasonic, magnetic particle, and dye penetrant testing as applicable

5. Inspection and Testing

Hydrostatic testing required
Includes leak testing of bottom plates
Visual and dimensional inspections

🇯🇵 Storage Tank Design Standards in Japan

🏗️ Primary Japanese Standard:

🔹 JIS B 8501 – "Welded Steel Tanks for Oil Storage"

This is the closest equivalent to API 650 in Japan.

📌 Key Features of JIS B 8501

Feature Details

📘 Title Welded Steel Tanks for Oil Storage

🏗️ Type Field-erected, vertical, cylindrical, flat-bottomed steel tanks

🌡️ Temperature Ambient or slightly elevated

📏 Pressure Low-pressure, atmospheric tanks

🧯 Applications Crude oil, petroleum products, chemicals

🔧 Design Elements in JIS B 8501

Tank Shell & Bottom
- Design stresses and allowable stress similar to API 650
- Plate thickness, welding joints, corrosion allowance
Seismic Design
- Japan is highly seismic, so this is critical
- Earthquake design must follow Japan’s Building Standards Law and Notification No. 593 (Ministry of Construction)
Wind Loads
- Based on Japan Meteorological Agency data
- Specific formulas for design wind speed & pressures
Materials
- Japanese steel grades (e.g., SS400, SM490, similar to ASTM A36 or A516)
- Material testing & certification required
Roof Types
- Cone, dome, and floating roofs are supported
- Design of internal and external floating roofs follows similar logic to API 650, but with Japanese safety codes
Welding & NDT
- Detailed requirements for welding procedures and testing
- Radiographic testing, ultrasonic testing, visual inspections
Testing & Inspection
- Hydrostatic testing is mandatory
- Includes leak testing of bottom plates
- Seismic safety inspections may be required post-installation

Japanese Industrial Standards (JIS).

Storage Tank Design Standards – China

he main standard for aboveground welded steel tanks in China is:

🔹 GB 50128 – "Code for Construction and Acceptance of Vertical Cylindrical Welded Steel Oil Tanks"

This standard is often used alongside GB 50341 – Code for Design of Vertical Cylindrical Welded Steel Oil Tanks.

These two together cover the design, fabrication, construction, inspection, and testing of oil storage tanks, much like API 650 or BS EN 14015.

🏗️ Key Chinese Standards for Storage Tanks

Standard Title Description

GB 50341Design Code for Vertical Cylindrical Welded Steel Oil Tanks Main design standard (similar to API 650)

GB 50128Code for Construction and Acceptance Covers fabrication, welding, inspection, and testing

GB 50009Load Code for the Design of Building Structures Wind and snow load

GB 50011Code for Seismic Design of Buildings Seismic design (very important in high-risk areas)

GB 12348Emission Standard for Noise at Boundary of Industrial Enterprises May be referenced for operational compliance

HG/T 20570.1~3Floating Roof Tank Accessories Specifics on floating roof seals, vents, etc. (from chemical industry standards)

🔧 Design Scope of GB 50341

Vertical, cylindrical, aboveground, flat-bottomed, welded steel tanks
Diameter range: Generally from 5 meters to over 100 meters
Fluid: Oil and oil products (can be extended to chemicals with similar properties)
Temperature: Ambient to mildly elevated
Pressure: Atmospheric or very low pressure

🛢️ Floating Roof Tank Design (Internal & External)

Chinese standards recognize both internal and external floating roof tanks, but like BS EN 14015, they're less prescriptive than API 650.

🔄 Floating Roof Design Coverage (GB Standards)

Roof Type Included in GB? Notes

External Floating Roof (EFR)✅ Yes Common in large oil depots

Internal Floating Roof (IFR)✅ Yes Increasingly used for emission control

Fixed Roof✅ Yes Cone or dome style, often with IFR below

👇 Design Based on:

HG/T 20570 (Part 1-3) – Chemical industry standard, used for:
- Floating roof accessories (vents, manways, seals)
- Pontoon vs full-contact IFRs
Enterprise standards or project-specific specs often supplement with API 650 Appendix H principles

🧪 Construction & Testing (GB 50128)

Hydrostatic testing
Radiographic, ultrasonic, and magnetic particle testing for welds
Dimensional tolerance checks
Foundation settlement checks
Welding qualification procedures per GB/T 3323 or GB/T 11345

⚖️

Wisdom is one of the leading design Service provider for oil & Gas, Petrochemical & process Industries

GLOBAL PRESENCE

CHOICE OF SELECTION OF CONE ROOF TANKS VS FLOATING ROOF TANKS? FLAMBLE LIQUIDS

Example benzine storage tanks

When storing benzene or other volatile liquids, it’s essential to choose the right type of storage tank to ensure safety, efficiency, and environmental protection. The two most common types of tanks used for volatile liquids like benzene are cone roof tanks and floating roof tanks.

benzene is considered a volatile liquid.

Volatility refers to the tendency of a substance to evaporate or vaporize at a given temperature and pressure. Volatile liquids have high vapor pressures and low boiling points, which means they can easily transition from a liquid to a gas (vaporize), even at room temperature.

Boiling Point: Benzene has a boiling point of about 80.1°C (176.2°F), which is relatively low compared to many other liquids. This means that at room temperature, a significant portion of benzene can exist in the vapor phase.

The vapor pressure of benzene is approximately 13.3 kPa

(kilopascals) at 20°C (68°F).

This means that at room temperature (around 20°C), benzene has a relatively high tendency to evaporate into the air, forming vapor. The vapor pressure is an important property when considering the volatility of a substance because it indicates how easily the liquid will transition into a gas phase.

Fire Point:

As mentioned, the fire point of benzene is -4°C (24.8°F), which is just above freezing. This is the temperature at which benzene will continue to burn after being ignited. It's important to note that benzene's fire point is still quite low, reinforcing its flammability hazard.

Cone Roof Tanks

Advantages:

Simple and Cost-Effective: Cone roof tanks are generally simpler and cheaper to build than floating roof tanks.
Better for Low-Volume Storage: Cone roof tanks are often used for smaller to medium-volume storage needs.
Robust for Stable Conditions: Cone roof tanks work well for liquids with moderate volatility (like benzene, although it requires some level of vapor control).

Disadvantages:

Higher Evaporation Loss: Since the roof is fixed and does not move, the vapor space increases as the liquid level decreases, leading to more evaporative losses.
No Floating Mechanism: There is no floating roof to minimize the vapor space, so benzene vapors may accumulate above the liquid.

Floating Roof Tanks

Advantages:

Reduced Evaporative Losses: Since the floating roof moves with the liquid level, the vapor space above the liquid is minimized, reducing the amount of evaporative loss.
Lower Emissions: Floating roofs significantly lower the emissions of volatile organic compounds (VOCs), which is particularly important for hazardous substances like benzene.
Safer for Volatile Liquids: Floating roof tanks are more suitable for the storage of highly volatile liquids, including chemicals like benzene, as they provide better control over vapor space.

Disadvantages:

Higher Initial Costs: Floating roof tanks are more expensive to construct and maintain due to the complexity of the design and materials used.
Maintenance: Regular maintenance and inspections are required to ensure that the floating roof is functioning correctly and not damaged by corrosion or other factors.
Less Suitable for Small Storage: Floating roof tanks are typically used for larger volumes of storage because of their cost and complexity.

Cost vs. Performance Trade-Off:

Cone Roof Tanks are cheaper and simpler to construct than floating roof tanks. However, the cost-efficiency of a cone roof tank comes at the expense of higher evaporative losses and emissions, which may not be acceptable when storing volatile liquids like benzene. The higher operating and environmental compliance costs associated with these emissions may make a floating roof tank a better long-term investment.

Although floating roof tanks are more expensive, their superior performance in minimizing evaporative losses and reducing emissions makes them a more suitable choice for storing benzene in compliance with safety and environmental regulations

Conclusion:

Cone Roof Tanks are more cost-effective and simpler but are less efficient at minimizing evaporative losses, which can lead to higher emissions of benzene vapors. They are suitable for low- to medium-volume storage of volatile liquids but may not be ideal for volatile liquids like benzene in large volumes.

Floating Roof Tanks, on the other hand, are designed for more volatile liquids, offering much better control of evaporative losses and emissions. They are more expensive but are the better choice when dealing with large quantities of benzene or when environmental and safety regulations are stricter.

Storing volatile liquids in cone roof tanks is technically possible, but due to high volatility and flammability, several safety precautions must be taken to minimize the risks associated with its storage following

Vapor Recovery Systems: Since cone roof tanks allow for more vapor space and greater potential for evaporative losses compared to floating roof tanks, it's crucial to install an efficient vapor recovery system to capture and condense the benzene vapors. This prevents benzene vapor from escaping into the atmosphere and reduces the risk of fire or explosion.

Pressure Relief/Vent Systems: These systems ensure that the tank does not build up excessive pressure due to vapor expansion or thermal changes. It is important to design and maintain pressure relief valves, vents, and flame arrestors to prevent over-pressurization and minimize the release of flammable vapors.

Install flame arrestors on all vents to prevent the ignition of vapors in the event of a spark or flame near the tank. This is especially critical when storing flammable liquids like benzene.

Flame arrestors allow vapors to be vented safely without the risk of combustion.

Inerting gas such as nitrogen the tank involves displacing the oxygen inside the tank with an inert gas such as nitrogen. This is particularly important if the tank is to be opened for maintenance or if there is a risk of flammable vapors accumulating. Inerting reduces the likelihood of explosion in the presence of a spark or ignition source.

Firefighting and Emergency Response Plans: Fire Extinguishers: Install suitable fire extinguishers (such as Class B for flammable liquids) in areas surrounding the tank and ensure that they are regularly checked and maintained.

Emergency Response Plans: Establish and regularly test an emergency response plan for dealing with benzene leaks, spills, or fires. This should include evacuation routes, firefighting protocols, and spill containment procedures.

Corrosion Protection: Tank Coatings: Apply appropriate corrosion-resistant coatings to the interior and exterior of the tank to prevent the degradation of the tank structure, especially in areas where benzene vapors may condense and lead to rusting.

Tank Sizing and Overfill Prevention: Ensure that the tank has sufficient capacity to prevent overfilling, which could result in spills or leaks. Install high-level alarms and automatic shutoff valves to alert operators and stop the filling process when the tank reaches a predetermined level.

Personnel Training and Safety: Employee Training: Ensure that personnel working with benzene or around the storage tank are well-trained in the specific risks of benzene exposure (e.g., through inhalation), emergency procedures, and safe handling practices.

19-tank-project-api-650-open-top-floaters-crude-storage-large-diameter-250 X 71.jpg

api-650-tank-self-supporting-umbrella-roof-110 X 48.jpg

Mechanical
Engineering

Electrical
Engineering

Structural
Engineering

Process
Engineering

Instrumentation
Engineering

--As the name suggests, a floating roof tank is armed with a floating roof.
Floating roof tank is the most economical and efficient solution for reducing emission and product loss.
Provides flexible use of storage capacity and reduces evaporation loss.
Floating roof tanks reduce the risk of explosion and fire in above ground storage tanks for extremely volatile organic liquids

This floating roof floating up and down in shell, by adjusts its height by depending on the product level.

The factors influencing the product evaporation are:
a) temperature of the liquid;
b) the presence and the dimension of the vapor space above the liquid;
c) the possibility for ventilating of the vapor space;

d) the presence of the free surface of the product

The safety from fire is increased which is a result of the decreased evaporation of the volatile stuff hence the lower risk from compound between the air and evaporating product which can be easily detonated.

Floating roof tanks keeps the stored oil pollution-free against rain, wind, sand, snow, or dust.

Conclusion

Floating roof tanks are used for storing a variety of different products across the globe. Most of them are extremely flammable products with low flashpoints.

Floating roof tanks are nearly ignition-proof. It is the rim of a tank that is most likely to catch fire. It is advisable to keep rim seals well maintained and check rim seals for deficiencies to help prevent ignition and fires.

External floating roofs.
The floating roofs projected and used for open on the top tanks.
They are made from steel and are welded.

Loadings
a) weather conditions (rain, snow, wind);
- 250 mm rain water for the period of 24 hours.
With tank owner agreement the real values for geographical area can be accepted for calculating the rain loading;
- the normal snow loading for consider is st = 2,0 kN/m2. Depends on location of country.

b) live loading on the roof;
- 2,2 kN movable concentrated loading of two persons upon 0,1 m2, who can stay on each one point on the roof, which is floating or is in the lower position upon its supports;
c) loading from rolling ladder and supporting truss;
d) loading from additional manholes, nozzles, roof drain, and seal;
e) loading of the product upon the roof;
f) single deck roof – membrane and two neighboring compartments are punctured.
double deck roof - two neighboring compartments are punctured.

Internal floating roof tanks
They appear because of the increased requirements of environment safety and to decrease the loss of oil product. These floating roofs are fit inside under the fixed roof itself. They can be fit even in the tanks with supported cone roof.
They can be made from steel,.

Loadings:
a) 2,2 kN live concentrated load from two persons upon the 0,1m2, who can stay upon any point on the roof, when it is floating or is in its lower position supported by its supports;
b) if there are not other conditions, all project calculation must be done when the product density is 0,7t/m3;

single deck, with outsider ring of pontoons on the periphery and a membrane in the middle.
a) in the regions with small wind pressure where it is not possible to tear the membrane from the product;
b) in the regions with small sun shining where the lower temperature of the membrane helps the decrease of evaporation of the product;

Double deck floating roof, with two membranes covering all surface of the roof and structure between them.
a) in regions with increased wind pressure, where it is possible to tear the membrane from the product and it must be prevented;
b) in regions with increased sun shining when it is necessary to decrease temperature of the membrane which contacts with the product;
c) more often when the tank has diameter D > 50 m.

Criteria for determining the type of the floating roof
The purpose of the tank, kind and the characteristics of the stored product, the conditions of the site must be taken into account when the type of floating roof is being chosen. The correct determination of its kind and the facilities connected with it can assures easer maintenance and quick return of the investments

a) Stability of the floating roof:
It is one of the most important conditions for the correct work. Moving loads which are not balanced upon the roof can cause inclination of the roof and floating with slope. There is the higher risk for the roof to sink there. It is necessary to assure the work of the roof in the projected position by means of correct.

b) Product
- aggressiveness of the stored product. It is necessary to take care of chemical characteristic of the liquid and the possibility to damage the roof equipment which is not metal. Some chemical products can destroy the seals of the roof in several weeks of exploitation;
- density of the product. According to the API Std. 650 volume weight of the product which are used when the calculations for the buoyancy are made is ρf = 0,7 t/m3. It is not likely to store product with smaller density but it is possible to happen. The information for the minimal values of the ρf allows the designer

CASE STUDY OF PROJECT:

Client ; NUMALIGARH REFINERY LIMITED (INDIA)
Consultant : TECHNIP INDIA LIMITED
Scope of Work : Design, Analysis and Detail Engineering for External floating roof tank.
Tank Design Code : API 650 ‐ 13th Ed.2020, Annex C, E, P
SERVICE : LIGHT SLOPE TANK
Type : EXTERNAL FLOATING ROOF TANK
FLOATING ROOF TYPE : SINGLE DECK ANNULAR PONTOON
OPERATING TEMPERATURE : 40-45 0 C
SPECIFIC GRAVITY OF LIQUID : 0.700‐0.995 (AT 40°C )
Material of construction : A36.

Wisdom provided design & Engineering services to NUMALIGARH REFINERY LIMITED (INDIA) ,Calculations, GA, Detail drawing services for External floating roof tank,

tank diameter 23.5 m and tank height is 15 m. tank instillation location Haryana ,INDIA. The major challenging for this design services is in this location Seismic effect (Earthquake} is very high compare to the rest of India. So client provided 15 m height of tank, We checked tank height extra 1.5 m height is require for free board for seismic effect. So final height of tank 16.5 m provided.

And have provided major items like total weight of tank, weight of floating roof, all thickness, sizing of normal vent, bleeder vent, and flexible pipe for rain fall, clean out door design, stability checking for floating roof, supporting legs design etc--

Wisdom provide Design & Engineering of this storage tank , based on requirements for material, design, fabrication, erection, and testing according to Design code API 650.

Considered Vertical shell joints are , single –V butt joint or double –V butt joint , butt joints with complete penetration and complete fusion . Vertical joints in adjacent shell courses shall not be aligned, but shall be offset from each other a minimum distance of 5t, where t is the plate thickness of the thicker course at the point of offset. Horizontal weld joints are considered single bevel butt joint with complete penetration and double bevel butt joints with full penetration.. Bottom plate joints are lap welded and annular plates are but-welded. Shell to bottom plate or annular plate joints are fillet weld. Wind girder ring section are but-weld , continuous weld on top side and seal weld on bottom side .

Nozzles design

Where nozzle necks are fabricated from pipe, the pipe shell be seamless. Where nozzles are 10” nominal bore and larger may be fabricated from rolled steel plate and butt welded using full penetration welds.

Man-ways

For storage tank, man-ways with DN600 (24”) size shall be used.

GA drawing

GA drawing covering all details shown in data sheets like list of appurtenances, lists of standards and specifications, material of construction, tank design data, General notes including details of test to be conducted on tank,

Details of spiral stairway and extension stairway, roiling ladder to still well platform/LT platform, landing and handrails with bill of materials. Details of wind girders with bill of materials..