A tank farm is a bund, a pipe bridge and a fire plan
A tank farm is a group of storage tanks surrounded by containment. The steel on the site is pipe racks, walkways, stair towers, and the small buildings that support the operation.
That makes it a different kind of project from a factory: the layout is driven by containment and separation, and the steel has to fit around those constraints rather than define them.
The bund decides where the steel can stand
Each tank group sits inside a bund with a capacity sized to the largest tank in it. The bund wall is a barrier, and the area inside it is where a spill will collect.
Putting a pipe rack column inside a bund means putting a steel section where liquid will pool. That is a corrosion decision and a fire decision at the same time, and the usual answer is to route the rack outside the bund and cantilever or bridge across it.
If the rack must cross, the column base detail has to survive immersion, and the foundation has to be designed for the load without penetrating the bund liner.
Pipe racks are the site's main structure
A rack carries pipes at several levels, with walkways for access and, in hot service, room for expansion loops. The loads are not large individually, but the rack is long, exposed and usually the tallest thing on site after the tanks.
Wind is the governing load on an open rack: the pipes and the rack itself present a large area, and a rack that is empty during construction presents a very different wind case from a rack that is fully piped. Both cases have to be designed.
Thermal movement has to go somewhere
Hot lines expand. Long runs of pipe on a rack move several centimetres between cold and operating condition, and the rack has to allow that movement without transferring it into the tanks.
The usual arrangement is an anchor bay with expansion loops either side, and sliding supports elsewhere. Where that logic is not followed, the movement arrives at the tank nozzle, which is the one place it cannot be accommodated.
Fire separation is a layout decision
Tank spacing, bund spacing and the position of the access roads are all set by fire separation requirements. Those distances are usually larger than the process would like, and they are what gives the site its shape.
Getting them settled before the rack route is drawn saves a redesign. A rack routed through a separation distance is a rack that will be moved.
What I want before drawings
- The tank schedule with sizes, heights and contents.
- The bund arrangement and the required separation distances.
- The pipe routes, sizes and operating temperatures.
- Where the anchor points are and how expansion is accommodated.
- The access requirements at each level of the rack.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Tank farm steelwork is straightforward once the containment and separation are fixed. The difficulty is that those are decided by others, and the steel is expected to fit afterwards.
Written by Johnny Joe, who advises owners and project managers in Africa and South America on steel buildings. If this decision is live on a project, send the layout and the constraint that worries you and I will tell you what it changes.
Related: where the access goes on a rack · clear height set by the longest item · separating a fire load · a raised route across a site
