Types of Tanks
Fixed Roof Tank
These are conical roof or dish roof type. Vent with a flame arrestor is required on these tanks. There are tank breathing losses associated with this type of tank.
Floating Roof Tank
Floating roof tank minimize vapor loss and fire hazard.
- NFPA 30
- Local Standards.
Dyke Wall Height Calculation
Dyke heights range from 3ft to 6ft (900mm to 1800mm) above internal grade. Top dike width minimum 600mm. A free board of 200mm above calculated liquid level required. Dyke height shall be minimum 1 meter and maximum 2 meters.
Tanks shall be arranged in maximum of two rows so that all tanks can be approached by road around the dyke. Roads shall be on all four sides of dyke, and they shall be interconnected with roads of other dykes.
Spacing Between Tanks
- Use table 3 of OISD-118 for separation distance between tanks and offsite facilities for large installations.
- Use table 4 of OISD-118 for separation distance betweens storage tanks in same dyke.
- Use table 5 of OISD-118 for separation distance betweens tanks and offsite facilities for smaller installations.
- Use table 6 of OISD-118 for separation distances for LPG Facilities.
Platforms, Ladders and Stairs
The maintenance vehicle ramp to have maximum grade of 15%. Do not use stairways for tanks of diameter less than 4.7m.
Process and Utility Piping
Piping extraneous to a group of tanks shall not be located within a firewall. The number of pipelines in the tank dyke shall be kept minimum and shall be routed in the shortest practicable way to main pipe track outside the tank dyke, with adequate allowance for expansion. Within one tank dyke the piping connected to that tank shall only be routed. Manifolds shall be located outside the tank dyke & by the side of the roads, easily accessible by the walkway.
Consideration shall be given to the need of thermal relief valves on long fill and drain lines. Plug valves whenever specified shall be of pressure balance type.
Special consideration shall be given as regards to spacing of nozzles while installing special item like hammer blind, MOV etc.
Pipes passing Through Dike
Where a pipe is routed through an earthen dike or firewall, the pipe shall be coated and wrapped. Where the firewall is concrete, the pipe shall be sleeved.
Tank Farm Settlement
Piping shall be laid out to ensure sufficient flexibility to provide for settlement of tanks relative to pipe supports or anchors and differential settlement between tanks. If exceptionally high settlement is expected “dressers coupling” or “flexible ball joint” may be provided. Tank connections to be done after tank hydro testing.
All lines connected to nozzles on tanks below the maximum fill levels must be supplied with a steel block valve.
Longitudinal axis of bullets shall not point process area or other vital installations. Use protection berm for high pressure bullet tank near process tank.
Storage Tanks within Process Unit
No other tankage except day tanks / process chemicals shall be provided within battery limits of any process unit. Process chemicals storage tanks should be provided with kerb wall of minimum 300-mm height. Hydrocarbons day tanks shall be provided with dyke as per OISD Standard.