A container put into storage for a season should come out serviceable, and frequently does not. The damage that happens in storage is slow and invisible – creep from being stacked under load, embrittlement from UV, deformation from heat – and it is discovered when the fleet is needed, which is the worst possible time. Storage is not a neutral state.
The stack load problem
Containers stacked for months carry a sustained load, and plastic creeps under sustained load. The bottom container in a stack that stands for six months is measurably different from the one at the top. Where containers are stored for long periods, either the stacks are lower than in normal service or the fleet is rotated – and neither happens by default. The mechanism is described in creep and permanent deformation.
Heat, and what it does
Creep accelerates with temperature, and a storage building in summer can reach temperatures where the effect is several times faster than at ambient. Where containers are stored stacked in an unventilated building or a container, the summer is where the damage happens. Ventilation and shade are cheap; replacing a deformed fleet is not.
UV, and outdoor storage
Polypropylene degrades under ultraviolet light, losing impact strength and becoming brittle. A container stored outdoors for a season loses a significant part of its remaining life, and the loss is invisible – the container looks fine and then cracks from an impact it would have survived. Where outdoor storage is unavoidable, covering the stack is the cheapest effective measure.
Nested versus stacked for storage
Nested or folded empties take far less space and, importantly, put far less load on the containers at the bottom. Where containers nest, storing them nested rather than stacked removes most of the creep problem for free. Where they fold, the same applies with a larger gain. The volume arithmetic is in folding empties and storage density.
Clean and dry before storing
A container put away wet grows mould, and one put away dirty comes out needing a wash it will not get before the peak. Where a fleet goes into storage, it should go in clean and dry, which is an argument for scheduling the wash before storage rather than after. Where containers are stored closed and wet, the smell is the least of the problem.
Where to store them
Under cover, off the ground, stacked no higher than necessary, and somewhere that will not be needed for something else during the season. That last point is the one that fails in practice: a storage area that is convenient gets requisitioned, and the containers end up outside.
Label the storage
Containers in storage are out of sight and out of the count. Marking the storage location with the quantity and the date stored means the fleet total can be reconciled without moving anything, and it prevents the storage area becoming an unrecorded part of the fleet.
What to check on retrieval
A sample from the bottom of a stack, checked for flatness and for brittleness, before the fleet goes back into service. Where the bottom containers have deformed, the whole stored population is suspect and sorting is required. That check takes minutes and it is the difference between a fleet that works in the peak and one that does not. The checks themselves are set out in what long storage does to a container.