A stored hose does not wear out the way a working hose does. What changes on the shelf is the material itself: plasticisers migrate, the surface is attacked by ozone and ultraviolet light, and the elastomer slowly cross-links or relaxes depending on what it is exposed to. None of that is visible from the outside until it is well advanced.
This is why a shelf life figure for silicone is a guideline rather than an expiry date. The clock is driven by storage conditions far more than by time alone. A hose kept cool, dark and relaxed in its original sleeve ages far more slowly than an identical hose left on a sunny rack or hung over a narrow peg.
Light, and ultraviolet light in particular, attacks the surface of elastomer. Ozone, which is produced around electric motors, welding equipment and some lighting, attacks the same surface and is the classic cause of fine surface crazing on stored rubber and silicone goods. Both work slowly and both are easy to avoid.
Compression and deformation are the third factor. A hose bent tightly or hung on a thin peg for months takes a set in that shape. When it is finally fitted, the bend is already there and the wall is already biased, which shortens the working life of the joint and makes tight routing harder to achieve.
Silicone is generally more resistant than natural rubber to heat ageing, ozone and ultraviolet light, so it survives storage better than many people expect. What it does not tolerate well is contact with oils, fuels and some solvents, which can be absorbed into the wall even in storage if a hose is left beside an open container or shares a shelf with oily parts.
It also picks up airborne contamination. Dust, workshop mist and metal particles settle on the surface and can be pushed into the joint at fitting, where they create a leak path. Bagging a hose rather than leaving it open on a shelf is a cheap way to keep both the material and the surface in good condition.
Keep hoses flat or in loose coils, off the floor, away from windows and away from heat sources such as ovens, compressors and welding sets. Coil them to a generous diameter rather than a tight one, and avoid stacking weight on top of a coil, since long-term compression is exactly what sets a bend into a part.
Original packaging is worth keeping. It identifies the part, keeps the surface clean and protects against light. Label coiled stock with the date it arrived so that older material is used first, and review the shelf periodically rather than assuming that anything left in stock is still suitable for a pressure application.
Look at it in daylight. Chalking, a whitish bloom, a tacky or sticky surface, or fine cracks that appear when the wall is flexed are all signs that the surface has aged. Compare a suspect hose with a fresh one of the same performance silicone hose construction if you have one on the shelf.
Then squeeze and twist it. A healthy hose returns to shape quickly and feels firm through the wall. One that feels mushy, or that stays flattened after being pinched, or that has stiffened at the ends where it sat against a fitting, has already changed. Small-bore silicone tubes are easiest to check this way, because the whole section can be felt by hand.
Discard any hose with visible cracking, a tacky surface, visible reinforcement, or a permanent bend that will not straighten by hand. Also discard hose that has been stored where fuel, oil or solvent could have splashed onto it, unless the material is known to suit that fluid, because the swelling may only become obvious after the joint is in service.
The economics are simple. A stored hose costs very little to replace, while a hose that fails under pressure in service can cost a session, a tow and possibly an engine. Where a joint is difficult to access or carries a critical duty, fit new material and keep the old part only as an emergency spare.
