Understood, meant no disrespect. I would offer more but they only have one more hydro left in their lifetime (30 yr limit on Al) and no guarantee they will pass. If you ever change your mind, I'm right down the road!
For USA application:
DOT-3AL certified tanks have no set life limit - 20, 30, 40, 50, + years and there is no reasonable expectation for them to fail simply because it has been a long time since they were extruded. Unlike cheese or guacamole or sushi, aluminum doesn't just "go bad".
The 5 year hydro interval is intended to detect compromised tanks by testing structural integrity (ability to hold test pressure, usually 167% of service pressure, within expansion limits) and elasticity (ability to return, within limits, to the non-pressurized volume after hydro pressurization is released (not becoming too brittle)) measuring the aluminum's ability to still "do its job". Visual inspections serve to detect other compromises such as physical damage, corrosion, and contamination. Hydros include a cursory visual (but I personally don't consider it to be a very comprehensive visual inspection - I've seen a lot of tanks straight out of hydro that I would not pass without further probing).
Within those constructs, there is no reason to have to take an aluminum bottle out of service.
This includes bottles made from the 6351 alloy that was susceptible to sustained load cracking - but the ongoing testing and certification requirements for those bottles are more extensive. For me, those make maintaining and using a 6351 bottle too much of a PITA.
There are certain life-limit restrictions on fiber-wrapped (hooped) aluminum bottles (15 years) and bottles made under a special permit are limited to the life of the permit and any subsequent DOT renewals.
I will concede that there are fill station operators that may spread falsehoods re: tank safety either intentionally through greed and the desire to sell new bottles or ignorance/superstition/voodoo that have not taken the time or expended the effort to learn actual fact (aka lazy-assed folk). After all, "IT'S FOR THE CHILDREN!" so it cannot be debated.
