DiveSite:As the photo in THIS LINK shows, 3AL is stamped from the factory on tanks that were made out of the 6351-T6 alloy, not just the 6061 alloy. There is no 6498 alloy (that i'm aware of). I believe the 6498 that you speak of is an Exemption or Special Permit number. The Visual Plus 3 tester WILL in fact test the 6061 alloy. BUT with that being said, it is very UNLIKELY that a 6061 alloy tank will have a neck crack.
Thank you for correcting me! I do not know nearly as much about tanks as I do about stage theatrical lighting fixtures Yes, the 6498 is one of several numbers used for a special exemption alloy, I cnnot remember it's number, but 6498=special alloy that was old and supposedly sfufers from radial cracks from stress. I think they stopped using the "6498" alloy in the 80's. The tank marked 6498 of the OP's is not too new
VP3 will test it, but were there other models that will not? I could swear that somewhere I heard someone say that older testing methods on new tanks (and using the VP stuff on steel tanks) will usually result in faulty tests if not read by someone who knows how to overlook many "problems" that the data shows which don't actually exist.