I never came across an expiration date for a validation. If an equipment was validated 30+ years ago and is still operational without any new changes to the fixture than the original validation is still valid. The only instances that I can see a need for a revalidation is if an engineer notices that the validation does not meet the company standards after the 30+ year timeframe. A medical device company is always updating the way they document and validate a process or equipment. So, if the company decides to update all validations to a new format then I can understand the need for revalidation. Other than that, if the fixture has not changed and is operational then there is no need for revalidation. The fixture is maintained per preventative maintenance and calibration dates.