SRB (Solid Rocket Booster) - O-ring Failure Issues, Pg 2

This 17 December 1982 memo, discussing SRB (Solid Rocket Booster) Critical Items, reports on O-ring failures in a test mode: 

...O-ring can withstand a minimum of four pressurizations before damage to the ring can permit any leakage. 

It also states that after 540 joints were exposed to increased pressurizations, "no leakage experienced past the primary O-ring."

Credits

NASA memo online, courtesy NASA.