How old is "too" old for aluminum cylinders?

[Still Kicking]

My 1978 cylinders are indeed 6351 alloy, so Eddy current testing will show stress around the neck threads; Later 6061 alloy cylinders may give false positive results if Eddy current testing, indicating stress fractures where there are none.

I have had no problems getting 6351 tanks with Eddy current tests that pass hydro filled.

I have seen tanks pass eddy current test and crack during hydro. It's not worth risking the life of a fill station operator IMO.

1990 onwards in hydro -- no problem.

 

[landlockeddivingdoc]

Appreciate all the replies- they seem to confirm what I've read, and have given me more reassurance.

I'm going to have the LDS hydro/vip/fill/replace the valve--their upcharges are reasonable and they don't try to upsell me (more than once they've turned me to a used or alternative product they had instead of the shiny new toy in the catalog, when it suited my purposes better). The current valve looks ok, but I'm planning to swap out a pro valve instead of just rebuilding what's on there, and I'll let them do it to stay in their good graces and keep a business that I trust in business.

I doubt that they'll have an issue with the age of the tank itself since it's not a 6351, although I will say that's one aspect of this situation I'm still curious about--the alumininum tank lifespan opinions in the scuba community tend to be based on empirical observations and standard practice instead of hard data, even though there is an actual lifespan limitation due to pressurization/depressurization cycles causing metal fatigue, and oxidative corrosion. That shouldn't be a huge factor here (hasn't had a pressure cycle in 20 years), but I once read about (and for the life of me, I can't find the paper, but I'll post if I do) the opposite problem: sustained load cracks developing even in non-AL6351 cylinders due to prolonged high (>300psi) pressure storage, and an increased rate of oxidation due to the higher ppO2 at higher storage pressure.

I'll let you guys know if they find anything interesting.

 

[OMyMyOHellYes]

I have seen tanks pass eddy current test and crack during hydro. It's not worth risking the life of a fill station operator IMO.

1990 onwards in hydro -- no problem.

Statement for the most part may be true, but it may be better to say "6061 T6 -- no problem". Or as I see two manufacturer's bottles around now - Lux and Catalina - a better application would be "any Catalina bottle or Lux after 06/88 -- no problem".

Nothing magical about the number 1990. Older Catalina Al bottles were always 6061 and Luxfer had discontinued use the of 6351 by middle of 1988 in all bottle sizes (it was a phased changeover that occurred over several months so certain other size bottles the switch was earlier - I think the 40s were the last bottle converted - for 80s I think the cutover was January 1988).

Other minor players like WK - all WK aluminum bottles are suspect. Cliff Imapct also, I believe. Norris and Kaiser (I believe all made under special permit now expired - permits not renewed so no longer usable.

It's pretty widely referenced, but Luxfers cutover schedule can be found at:

Oops. Wrong cut and paste. Sorry.

Dates when Luxfer changed its aluminum alloy from 6351 to 6061 - Luxfer Gas Cylinders

Between 1987 and 1988, Luxfer Gas Cylinders discontinued use of 6351 aluminum alloy and began using a proprietary version of 6061 aluminum alloy for all its aluminum cylinder models manufactured in the United States. Listed below are the dates by model number when the transitions to the new...

www.luxfercylinders.com

 

[Still Kicking]

NM

 

[OMyMyOHellYes]

All Catalina, Luxfer mid-88 also = simple.

Also adds more than a year and a half of tanks to availability.