system
Given the following post, respond as if you're commenting on Reddit:
human
Why does a compressed natural gas tank have expiry date on it? Does it mean it's no longer safe to use after the expiry date?

I live in a country where I could use compressed natural gas (CNG) as my vehicle fuel instead of petroleum. So I have a CNG tank installed in my boot 9 years ago.

The CNG tank's expiry date is reaching soon, I should definitely go for inspection, but does the expiry date means anything at all? 

I already Google the question, but the top results don't really provide any information about what happens when the CNG tank "expired".
gpt
the expiration date realistically means the safety features are at the beginning of the end of their expected life cycle. these dates are set heavily in favor of "replace it before it's an issue" because pressure vessel failure can easily kill someone.