Tank storage facilities
The Health and Safety Executive publication, Storage of flammable liquids in tanks, provides information on topics including:
- Location and layout of tanks
- Design and construction
- Loading and unloading facilities
- Fire protection and precautions
The storage facilities in chemical processing sites and the petrochemical industries can house liquid and solid feed, intermediate chemicals, by-products and process products.
Products stored in many facilities are required for other processes. Storage may also be required for dilutants, solvents or other process materials. All these materials are generally stored in above ground storage tanks (ASTs).
Underground storage tanks (UST) are still used in some locations, but use is limited due to access problems and limited capacity.
In addition, potential leaks in a UST present environmental problems if leaks contaminate groundwater. General earth contamination can lead to potential atmospheric exposures if there is a higher vapour-pressure materials leak. Leaked materials can be a potential exposure problem during ground remediation efforts.
UST leaks have resulted in stringent environmental regulations in many countries, such as requirements for double-walled tanks and underground monitoring.
Types of above ground storage tanks include:
- Fixed roof tank (FRT)
- External floating roof tank (EFRT)
- Internal floating roof tank (IFRT)
- Converted (or closed) floating roof tank (CFRT)
Vertical ASTs can be:
- Cone- or domed-roof tanks
- Floating roof tanks that are covered or non-covered
- Floating roof or external floating roof tanks (EFRTs)
Converted or closed roof tanks are EFRTs with covers installed on the tanks; covers are frequently geodesic type domes. Since EFRTs do not maintain a perfectly circular shape over time, sealing the floating roof is difficult and a covering is installed on the tank.
A geodesic dome design eliminates the roof trusses needed for cone roof tanks (FRTs). The geodesic dome is more economical than a cone roof and, in addition, the dome reduces the loss of materials to the environment.
Normally, the tanks are limited to liquid storage where the liquid vapour pressure does not exceed 77kPa. Where the pressure exceeds this value, spheroids or spheres are used, since both are designed for pressure operation. Spheroids can be quite large but are not installed where the pressure may exceed certain limits defined by the mechanical design.
For most higher-vapour pressure storage applications, spheres are normally the storage container and are equipped with pressure relief valves to prevent overpressuring.
Tank separation and location considerations
- Separation based on shell-to-shell distances can be based on calculating the thermal radiation distance in the event of fire in an adjacent tank
- Tanks should be separated from process units
- A tank location, preferably downwind from other areas, minimises ignition problems in the event of a tank releasing a significant vapour quantity
- Storage tanks should have bunds to contain leaks and spillages
Bunds are required and are nominally sized to hold the volume of a tank. Where multiple tanks are in a bund, the minimum bund capacity should be equivalent to the volume of the largest tank plus 10% (i.e. 110% of the largest tank capacity).
The bund walls can be constructed of earth, steel, concrete or solid masonry. However, earth bunds should be impenetrable and the soil within the bunded area should also have an impenetrable layer to prevent any chemical or oil leakage into the soil.
Hazards (for further information refer to National Operational Guidance: Utilities and fuel, National Operational Guidance: Hazardous materials, National Operational Guidance: Environmental protection, and National Operational Guidance: Fires and firefighting)
- Restricted access
- Environmental damage
- Fire phenomena
- Hazardous material
References and further reading