A relays useful life depends upon its contacts. Once contacts burn out, the relays contacts or the entire relay has to be replaced. Mechanical Life is the number of operations (openings and closings) a contact can perform without electrical current.
A relays mechanical life is relatively long, offering up to 1,000,000 operations. A relays Electrical life is the number of operations (openings and closings) the contacts can perform with electrical current at a given current rating. A relays Contact electrical life ratings range from 100,000 to 500,000 cycles.