Structural Engineering for API 650 Storage Tanks
Large steel storage tanks may appear relatively simple, but structurally they can be complex engineered systems.
Whether a project involves a water storage tank, process tank, chemical tank, fuel tank, industrial storage tank or large welded steel tank, the structure must safely withstand far more than simply the weight of the liquid contained inside it.
Wind, settlement, attached pipework, platforms, equipment, foundations, operating conditions and even an empty tank can create important structural load cases.
For many large welded steel storage tanks, API 650 (API650) provides an internationally recognised framework for design and construction. However, achieving a safe and practical tank design also requires an understanding of structural engineering, mechanical engineering and the way the tank interacts with its supporting foundation and surrounding plant.
Does My Storage Tank Need Structural Engineering?
Almost every large industrial storage tank involves structural engineering to some degree.
Depending on the application, engineers may need to consider:
Tank shell strength and stability
Roof structures
Wind loading
Seismic loading
Tank foundations
Differential settlement
Anchor bolts and uplift
Nozzle reinforcement
Pipe loads
Platforms and access structures
Mixers and mechanical equipment
Local stresses and buckling
These issues apply whether the tank is being designed from scratch, modified, relocated, repaired or assessed for continued operation.
Structural Design of Large Steel Tanks
One of the interesting characteristics of a large storage tank is the efficiency of its structure.
The tank shell can be relatively thin compared with its diameter and height.
While this makes welded steel tanks economical to construct, it also means engineers need to understand shell stability, local stresses, buckling and load distribution.
An empty tank exposed to high winds, for example, presents a completely different structural condition from a tank filled with water or product.
Structural engineering may therefore consider multiple operating, maintenance, testing and environmental load cases rather than simply designing for the weight of the stored liquid.
API 650 and API650 Tank Design
API 650 – Welded Tanks for Oil Storage is widely used internationally for large welded steel storage tanks and is applicable to many applications beyond traditional petroleum storage.
Depending on the project, API650 may be used for tanks associated with:
Water
Mining and mineral processing
Industrial process liquids
Chemicals
Fuel and petroleum products
Manufacturing
Agricultural processing
Water and wastewater infrastructure
Importantly, a client does not necessarily need to know that they require an API 650 tank before speaking with an engineer.
Part of the engineering process is determining the appropriate design basis, applicable standards and structural requirements for the proposed tank and its intended service.
Tank Foundations Are Part of the Structure
A storage tank cannot be considered independently from the ground supporting it.
Large tanks can impose substantial loads over a wide area, while uneven settlement can introduce stresses that were never intended in the original tank design.
Depending on the project, tank foundation engineering may involve:
Reinforced concrete ring beams
Concrete slabs
Sand or granular pads
Bearing pressure assessment
Settlement considerations
Differential settlement
Anchor bolt design
Uplift resistance
Drainage and surrounding civil works
Relevant requirements may extend beyond API 650 to Australian Standards such as AS 3600 – Concrete Structures and AS/NZS 1170 – Structural Design Actions, together with project-specific geotechnical requirements.
This is where Civil, Structural and Mechanical Engineering increasingly overlap.
What About Existing Tanks?
Structural engineering is equally important for existing storage tanks.
A tank may require assessment because of:
Corrosion
Settlement
New pipework
Additional platforms
New nozzles
Changed operating conditions
Mixer installation
Roof modifications
Increased capacity
Relocation
Damage or deterioration
An existing tank may have been designed decades ago, and original drawings or calculations may no longer be available.
In these situations, engineers can investigate the existing structure, determine its likely load paths and assess whether it remains suitable for its proposed use.
For existing API tanks, API 653 may also become relevant to inspection, repair, alteration and reconstruction requirements.
Tank Certification and Structural Verification
Clients sometimes approach Trang seeking tank certification, structural certification, engineering verification or confirmation that an existing storage tank is safe for a proposed application.
These terms can describe different engineering requirements.
Depending on the situation, appropriate engineering work may involve:
Review of existing drawings and calculations
Site inspection
Measurement or 3D laser scanning
Material verification
Structural calculations
Foundation assessment
Review against applicable standards
Design verification
Repair or strengthening recommendations
The important first step is understanding the tank, its history, intended service and what the client needs the engineering assessment to demonstrate.
When Is FEA Used for Storage Tanks?
Not every tank requires Finite Element Analysis.
However, FEA can be extremely useful for complex storage tank structural problems where simplified calculations do not adequately represent the actual behaviour of the structure.
Typical applications can include:
Large nozzle openings
Heavy pipe loads
Platform attachments
Mixer supports
Local shell stresses
Complex roof structures
Non-standard modifications
Lifting and transportation
Existing tank repairs
FEA allows engineers to investigate stresses and deformation within specific areas of the tank and develop practical strengthening or modification solutions where required.
Mechanical and Structural Engineers Working Together
Storage tanks are a particularly good example of why Mechanical and Structural Engineers should work together.
The mechanical engineer considers the process requirements, pipework, nozzles, equipment, operation and functionality of the tank.
The structural engineer considers how the tank shell, roof, supports, foundations and attachments respond to the resulting loads.
Neither exists independently.
A pipe connected to a tank creates structural loads. A mixer introduces loads into the tank shell or roof. A platform adds weight and wind area. A foundation influences tank settlement and shell behaviour.
Considering these interactions early can produce a safer, simpler and more economical design.
Engineering for New and Existing Storage Tanks
Trang Imagineering provides engineering support for a broad range of industrial tanks, water tanks, process tanks and welded steel storage tanks, including:
Storage tank structural engineering
Tank certification and verification
Tank foundation design
Existing tank assessment
API 653 engineering
Tank modifications and repairs
Nozzle and pipe load assessment
Structural steel and access platforms
3D laser scanning
Brownfield tank upgrades
By combining Mechanical, Structural and Civil Engineering within the same team, we can consider the storage tank as part of the complete industrial facility rather than as an isolated piece of equipment.
Need Engineering Advice for a Storage Tank?
You don't need to know whether your project requires API 650, API650, API 653 or another design standard before contacting an engineer.
You may simply need a new water tank designed, an existing steel tank certified, a foundation checked, a tank modified or confirmation that an existing storage vessel remains structurally suitable.
The first step is understanding the application and determining the appropriate engineering pathway.
At Trang Imagineering, our engineers provide practical advice for new and existing industrial storage tanks, combining tank engineering with Structural, Mechanical and Civil Engineering expertise.
If you need a storage tank designed, assessed, modified or structurally verified, contact Trang Imagineering to discuss the application and the engineering requirements for your project.