There is not a set shelf life beyond which an electrolytic capacitor is guaranteed to fail. In one study, electrolytic capacitors were verified to perform adequately after 30 years of storage. Shelf Life is 16yrs with periodic reforming in accordance with manufacturers standards, otherwise 5yrs or manufacturers recommended shelf life. Can electrolytic capacitors, typically greater than 1 inch in length and diameter used in power supplies, should have a shelf life of about 20 years, based upon storage temperatures. High storage temps are to be avoided leads to greater dry out of electrolyte. Radial and axial lead electrolytic capacitors should have a shelf life greater than the can lytics.
Accelerated aging tests have shown that capacitors show a small decrease in capacitance but proportionately larger increases in ESR and DC leakage current. The increase in ESR was on the order of 65% and DC leakage a magnitude of over 400%. As ESR and DC leakage goes up, the resistive heating of the capacitor in service increases which may cause rupture of the seals and blow up. Improved vapor seals limit the evaporation of the electrolyte and as long as there was enough electrolyte left in the capacitor, the capacitor could reform itself.
In general, the reforming process consists of applying voltage to the capacitor without exceeding the specified leakage current. The voltage is increased up to the rated value using a Variac, or light bulb limiter. Panasonic recommends applying rated voltage across a 1Kohm resistor for 30 minutes.