I bought this tank less than a year ago and on the bottom center where the t-valve seats it cracks the metal tank and now leaks badly. Would this be covered under warranty whereas I cannot find receipt.

Without a receipt.. how would it be covered under warranty? You are responsible for proving when you bought it to prove its within the warranty period.

Was it something that you registered a warrany with the manufacturer when you bought it?

Contact the place where you purchased the tank. They may have a record of the purchase. Even if they don't, they may be able to help you.

where the t-valve seats it cracks the metal tank
This crack, did the tank crack when you installed the valve? Was the tank crack before you install the valve? Can you give me more details about the crack? Back to you, Tom

Look for a model number and a serial number on a rating plate/ If you find the model number and the serial number and you contact the place of purchase and/or the manufacturer they can tell you when it was manufactured and whether you are under warranty!

Good luck!

Mark