Help needed with this tanks markings

[tursiops]

All of the information above is accurate. No worries.
About the SP6498 number.... SP6498 is a U.S. PHMSA special permit number to manufacture and offer for sale a "special" pressure vessel. The SP6498 number can be referenced through the Pipeline Hazardous Material Safety Administration (PHMSA) web site. For this particular special number, see link: Hazardous Materials Special Permits Lists | PHMSA

Here you can find information about SP6498. The PHMSA web site will reference to a lot of literature about SP6498 to include an alloy composition of AA-6351. It also references a number of reports that speak to explosive ruptures of these cylinders; albeit, the rupture numbers are small quantities, ie. 13 tanks total.

The funny thing is everyone talks about 6351 as the bad alloy and everyone yammers on about "Sustained Load Cracking". I can't find any reference to SLC in the engineering databases of the American Society of Materials (formerly Metals) or the American Society of Mechanical Engineers (the design authority for pressure vessels). Funny thing, if you reference this document: https://www.luxfercylinders.com/img...uminium_scuba_cylinders_safety_alert_2217.pdf

front and center is a pretty clear picture of a ruptured AA-6351 tank. Look closely at that picture. That picture showcases a classic "brittle fracture" failure mode..... Hmmmm..... brittle fracture? Just my opinion, but that speaks to a bad heat treatment process on that particular tank. Is there a lot or two of 6351 tanks floating around with a bad heat treatment ?? Inquisitive minds wonder.

You'd be better off doing more homework on SLC and 6351 than inventing conspiracy theories.

 

[Scuba Lawyer]

Pulled an old Aluminum Pony out of the bin-o-dive-stuff-past. Hard to read the markings, may have to take off the coating to see how deep the pits are. Anyway, can anyone tell if this is good alloy or bad alloy? Born date 1992. Might try to resurect it if it doesn't need eddy testing. Thanks.

 

[Boarderguy]

3AL with no special permit markings. Born after 90 I'd say you're pretty well and safe. Take it to your lds and see what they say. Some have a stupid and baseless 20 year old rule for filing tanks.

 

[OMyMyOHellYes]

How can you determine the alloy from the markings? Do you have to look up the SP number in a database somewhere?

Shorthand without looking up the special permit >>> The little Snoopy doghouse/arrow in the middle of the 3^75 hydro date (born on date). That says "Luxfer" and Luxfer used 6351 on their aluminum tanks prior to a cutoff point in 1988 (cutoff dependent on tank size).

 

[OMyMyOHellYes]

Pulled an old Aluminum Pony out of the bin-o-dive-stuff-past. Hard to read the markings, may have to take off the coating to see how deep the pits are. Anyway, can anyone tell if this is good alloy or bad alloy? Born date 1992. Might try to resurect it if it doesn't need eddy testing. Thanks.

Given the '92 date, and the DOT-3AL cert, I'd wager it was 6061 alloy. I would carefully scrape/lift/remove all the bubbled paint to verify it is just lifted paint with some light, white fluffy AL oxide powder underneath and not pits eaten into it.

 

[rjack321]

Given the '92 date, and the DOT-3AL cert, I'd wager it was 6061 alloy. I would carefully scrape/lift/remove all the bubbled paint to verify it is just lifted paint with some light, white fluffy AL oxide powder underneath and not pits eaten into it.

It's a Catalina and they never used the 6351 alloy like the OP's tank.

That said the paint isn't original looking, there is a ton of bubbling paint, and it's 30 years old. It needs a VIP and hydro which it may fail. Some shops may balk at filling it. I'd probably strip the paint to see the underlying condition then make a call on scrap or proceed with a hydro (which are $35+ around here now so not something I just do lightly)

 

[Scuba Lawyer]

It's a Catalina and they never used the 6351 alloy like the OP's tank.

That said the paint isn't original looking, there is a ton of bubbling paint, and it's 30 years old. It needs a VIP and hydro which it may fail. Some shops may balk at filling it. I'd probably strip the paint to see the underlying condition then make a call on scrap or proceed with a hydro (which are $35+ around here now so not something I just do lightly)

All good advice. The paint is original as I was given the tank at the end of a DEMA show from the manufacturer. It has been sitting in a box of old dive stuff since last hydroed in 2007. I'll take it to a friend that has a shop and does on-site hydro testing. No big loss if it is FUBAR.

 

[OMyMyOHellYes]

It's a Catalina and they never used the 6351 alloy like the OP's tank.

Catalina never used 6351, correct, but I must have missed where it was rollmarked "Catalina" or "M4002". Reading through the crust, it looks like it's a Cliff Impact Div tank made under the Parker ownership (pre-Catalina purchase in '97). Did I miss something under some crustiness or were there other mfg markings?

 

[rjack321]

The

Catalina never used 6351, correct, but I must have missed where it was rollmarked "Catalina" or M4002". Did I miss it under some crustiness or were there other mfg markings?

They didnt/haven't marked "CATALINA" on the small ones like they do on the larger AL80s and such. But the "CL" is a tipoff, that is Catalina's "independent testing facility" / manufacturer's mark. It would normally be between the 7 and the 92 of the first hydro, why they put it after is a bit of a mystery.

 

[OMyMyOHellYes]

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