Choose storage from a time-based product balance. Nominal vessel capacity, usable inventory and interruption reserve are three different quantities.
Construct the inventory curve
For each time interval, add accepted liquid production and deliveries, then subtract consumption, dispatch and estimated losses. The resulting cumulative curve shows when inventory peaks and when it runs short. Use hours or individual dispatch events where a daily average would hide a shortage. Starting inventory must be stated.
The difference between the highest and lowest points gives the working inventory swing for that scenario. Reserve for a defined interruption is a separate requirement. Usable inventory excludes the portions outside the vessel’s approved operating range; a nominal water volume or nominal mass rating is not automatically the usable amount.
Example: regular production with one daily dispatch
| Event | Inventory change |
|---|---|
| Accepted production of 1 t/h for 24 h | +24 t/day |
| One tanker loading of 20 t | −20 t at the loading event |
| Local demand of 4 t/day | −4 t/day |
| Balance before losses | Zero daily net change, with an event-driven working swing |
Assume local demand is uniform and the tanker takes its 20 tonnes at the start of the day. The ideal inventory falls by 20 tonnes at loading, then recovers by 20 tonnes over the day. It needs a 20-tonne working swing before adding losses or reserve. Starting immediately before loading requires enough available inventory to make that dispatch.
Add an explicit outage scenario
If a 12-hour recovery interruption must be covered while the same uniform local demand continues, local use alone consumes 2 tonnes during that interval. If a 20-tonne tanker must also load during the interruption, the total withdrawal can reach 22 tonnes. Do not add a generic percentage without checking whether the outage coincides with the normal inventory minimum. Simulate the agreed combination and decide whether delayed dispatch or backup delivery is an acceptable alternative.
Translate usable mass into a vessel selection
Ask the vessel supplier to convert the required operating inventory into an approved size using the actual storage condition, permitted filling limit, minimum operating inventory and instrumentation. Liquid density varies with state. Heat ingress, pressure control, withdrawal rate and vaporization capacity require separate engineering checks. This article does not specify a filling fraction, relief setting or operating procedure.
Our storage discussion also covers tanker access, foundations, inspection responsibilities, isolation, prevention of backflow contamination and trained operating personnel. EIGA Doc 66 addresses refrigerated storage at users’ premises within its stated scope; destination requirements and the actual installation still govern the design.
Avoid the oversized-tank trap
A larger tank can bridge a defined time mismatch. It cannot correct a persistent annual production deficit or create a market for surplus product. Before increasing storage, compare the cost of additional recovery capacity, alternative delivery timing, reliable backup supply and a different operating schedule.
Sources and scope
We use these sources for the physical principles or guidance identified in this article. Our examples and decision tables are explanatory calculations, not measured plant results. Industry guidance does not replace the edition, customer specification and local requirements agreed for your project. Publication listings are cited for their public scope; we do not claim to reproduce their full standards.
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