Equipment and Piping Layout : Tankfarm

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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.

Applicable Codes

  1. NFPA 30
  2. OSHA
  3. OISD-108
  4. OISD-118
  5. Local Standards.

Layout

When initially trying to establish a tank farm layout, the designer should consult NFPA codes and local codes and regulations.

Rules for spacing between tanks and all adjacent facilities usually can be found in the latest issue of the Industrial Risk Insurers “General Recommendation for Spacing’ pamphlet.

The NFPA will indicate what the designer should consider when grouping several tanks within a single dike or whether the tanks should be individually diked because of large capacities.

There is no simple answer to this layout problem. Each plant site is unique, with different products, tank capacities, fireprevention
requirements, terrain, and adjacent commercial or residential
property.

After the diking arrangement has been established, there are a few additional factors to plan for. The grade sloping away from the tanks to a sump must be determined; minor spills and rainwater may have to be pumped from the sump to a treating pond. Dike heights must also be established on the basis of inventories and available
real estate.

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.

Roads

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.

Nozzle Layout

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.

Most of the times, pumps are located outside the earthen dike, lines penetrating concrete dike …Read More..

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.

Block Valves

All lines connected to nozzles on tanks below the maximum fill levels must be supplied with a steel block valve.

LPG Bullets

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.

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