Pressure tanks are essential components in a wide range of industrial systems—from compressed air and water treatment units to chemical processing and storage applications. Designing a pressure tank requires careful consideration of working pressures, material performance, structural integrity, and compliance with relevant codes and regulations. In this article, we outline the key factors that influence pressure tank design and highlight best practices to ensure safety, efficiency, and longevity.
Understanding the Purpose of the Pressure Tank
Before beginning any design work, it is vital to understand the role the pressure tank will serve within the system. Some pressure tanks are used for storage, while others act as pulsation dampeners or energy accumulators. Common types include:
- Air receivers – used in compressed air systems to store and stabilise pressure.
- Hydropneumatic tanks – used in water systems to reduce pump cycling.
- Process tanks – found in chemical and food industries, often requiring resistance to corrosion or temperature extremes.
- Surge tanks – designed to absorb sudden changes in fluid velocity or pressure.
Each application presents its own design requirements relating to volume, pressure cycles, flow characteristics, and environmental conditions.
Internal Pressure and Wall Thickness
The internal pressure of the tank is the primary factor influencing its structural design. Most tanks are designed to operate within a defined working pressure, with an appropriate margin of safety built in.
The basic formula for determining wall thickness in cylindrical tanks is derived from the hoop stress equation:
t = (P × D) / (2 × σ × E)
Where:
t = required wall thickness
P = internal pressure
D = internal diameter
σ = allowable stress of material
E = weld efficiency factor
This formula is based on thin-wall assumptions. In cases where the wall is not thin relative to the tank diameter, thick-wall equations must be used, which account for radial stress variation through the wall. The calculated thickness must also include allowances for corrosion, manufacturing tolerances, and additional mechanical loads where applicable (e.g. vacuum loads, external pressures, wind loads).
Shape and Geometry
The shape of a pressure tank plays a crucial role in its strength. Cylindrical shells with hemispherical or dished ends are the most efficient configuration for internal pressure. This form distributes stress evenly and reduces the likelihood of failure at high pressure.
Flat heads, while more cost-effective to fabricate, require increased thickness to handle the same internal pressure. Unsupported flat surfaces are generally avoided in pressure tank design unless specifically reinforced.
Vertical or horizontal orientation is dictated by space, function, and support requirements. Supports and mounting points must be designed to handle the full weight of the tank (including fluid contents), wind or seismic loads (if applicable), and vibration from nearby machinery or pipework.
Material Selection
Material choice is dictated by the application, pressure, and contents of the tank. The most common materials include:
- Carbon steel – widely used for air receivers and general-purpose storage tanks.
- Stainless steel – preferred in corrosive environments, food and pharmaceutical applications.
- Aluminium or composite materials – used in lightweight or portable pressure tanks.
- High-performance alloys – required in extreme pressure, temperature or chemical environments.
Material properties such as yield strength, corrosion resistance, and weldability must be balanced with fabrication costs and long-term maintenance requirements. In all cases, the selected material must be suitable for the design pressure and compatible with the contents of the tank.
Design Codes and Compliance
In the UK and Europe, pressure tank design must adhere to recognised codes such as:
- PD 5500 – UK standard for unfired pressure vessels.
- EN 13445 – European standard for unfired pressure vessels.
- ASME Section VIII Div. 1 or 2 – American codes often used for international projects or specific client requirements.
Designers must also consider compliance with the Pressure Equipment (Safety) Regulations 2016 (PE(S)R), which apply to pressure tanks with a pressure × volume (PS × V) product above certain thresholds. The design process must include: Calculation of pressure ratings, Material certification, Welding procedure specifications, Non-destructive testing (NDT), CE or UKCA marking (if applicable) and Manufacturer’s Data Report (MDR)
Corrosion Allowance and Protective Coatings
Most pressure tanks include an additional corrosion allowance in their wall thickness to account for long-term degradation. This is particularly important where the contents are chemically aggressive or where moisture is present.
Protective coatings, linings, or cathodic protection systems may also be used. For example:
- Epoxy linings in water tanks
- Rubber or PTFE linings in chemical tanks
- Hot-dip galvanising or powder coating for external protection
The selection of corrosion protection must consider compatibility with tank contents, maintenance procedures, and the environment where the tank will be located.
Inspection and Testing
Before commissioning, all pressure tanks must undergo inspection and testing to verify integrity and safety. Typical procedures include:
- Hydrostatic pressure testing – to check the strength of the tank under pressure.
- Leak testing – using air, gas, or liquid to detect microleaks.
- Visual weld inspection – both internal and external.
- Non-destructive testing – such as radiographic or ultrasonic testing, where required.
- Post-installation, the tank may require periodic inspection in line with written schemes of examination, depending on the application and pressure classification.
Conclusion
Pressure tank design is a multidisciplinary task that requires engineering precision, material knowledge, regulatory compliance, and an understanding of the application environment. Whether used for storing compressed air, absorbing surges, or holding process fluids, a well-designed pressure tank ensures long-term performance, operational safety, and ease of maintenance.
At Holdens Engineering, our pressure vessel design and fabrication team offers full support from concept through to manufacture and testing. We design to PD 5500, ASME and EN standards, and provide tanks across a wide range of sizes, pressures, and materials
For project support or technical guidance on your pressure tank requirements, contact Holdens Engineering today.
