I think only 30 gallon plus tanks are ASME certified. Do you have an ASME certicate welded on the tank?
I have a double hot dog compressor and I know it's not certified...OTOH my 30 gallon is.
To aswer your question about safety, you need to have nondestructive testing, probably a few hundred bucks to test, if you can find a testing lab. Worth it? Replace the tank? Contact the manuf.?
We can't tell you if it's safe over the internet. Do you know the WPS? It was probably welded by a 8 year old in China, for better or worse.