How many people "over fill" Steel 72's ?

[oxyhacker]

A 3A or 3AA steel scuba tank can be plus rated at anytime in its life, regardless of whether it has been plus rated in the past, as long as the proper test is done:

49 CFR section 173.302a:
(b) Special filling limits for DOT 3A, 3AX, 3AA, 3AAX, and 3T
cylinders. A DOT 3A, 3AX, 3AA, 3AAX, and 3T cylinder may be filled with
a compressed gas, other than a liquefied, dissolved, Division 2.1, or
Division 2.3 gas, to a pressure 10 percent in excess of its marked
service pressure, provided:
(1) The cylinder is equipped with a frangible disc pressure relief
device (without fusible metal backing) having a bursting pressure not
exceeding the minimum prescribed test pressure.
(2) The cylinder's elastic expansion was determined at the time of
the last test or retest by the water jacket method.
(3) Either the average wall stress or the maximum wall stress does
not exceed the wall stress limitation shown in the following table: (omitted for brevity)
(i)(A) The average wall stress must be computed from the elastic
expansion data using the following formula: (ommitted for brevity)
(4) An external and internal visual examination made at the time of
test or retest shows the cylinder to be free from excessive corrosion,
pitting, or dangerous defects.
(5) A plus sign (+) is added following the test date marking on the
cylinder to indicate compliance with paragraphs (b) (2), (b)(3), and
(b)(4) of this section.

I'm not too sure that this is entirely correct. Only those steel tanks bearing the plus rating at the initial manufacturers hydro can be retested to a plus rating. For example, I have a nice set of steel 38 doubles with a pressure rating of 1800 psi with no original plus rating. They cannot now be magically calc'd for a plus rating.
Yea or Nea?

 

[VaPadiDiver]

I also have a pile of 72's. I love them. Great smaller tanks for shallower dives, short dives. I use them alot when I teach becasue I never come close to using a whole 80 with students. However, on my real dives the 72's are used only as a deco or stage bottle. I like the negative factor about them and they are a great size for most deco plans.

One thing you must be careful with, especially with the old 72's, they are steel tanks. People who have their own compressors sometimes feel exempt from hydro or VIP test. With steel tanks, get a little moisture in them and your tank rusts from the inside out. Add a deco mix in them (high O2) and you are accelerating the oxidation Over time, unless you tumble and clean your tanks often (every 6 months to a year), your tank literally becomes a bomb.

If you want tanks you can pump up, the newer LP steel tanks are overfilled alot (cave fills). PST steel 95's and 104's. In fact, Pressed Steel redesigned and re-rated their LP series to the new E series because most cave and tech guys were swapping burst disks and overfilling anyway. (Not a safe practice though) Now the 104's are 130's. The tanks are a little different though.

Bottom line: 72's are cheap. Don't be a cheap skate and buy 72's when you need more gas. Buy tanks for the diving you are doing. 80's are the perfect size for almost any type of diving. Most people run out of bottom time before gas with them. Aluminum tanks are cheaper to maintain. Need more gas, double 'em up or use 100's. If your a tech diver ... you shouldn't even need to be reading this... you know better than to overfill 72's.

A side note, don't use HP (3500 psi) tanks with older regs. The HP seats in some older models do not do well with the pressure. The new Black Dive Rite regs will though. They are reated for 5000 psi. (Euro specs).

 

[duckbill]

Aluminum tanks are cheaper to maintain.

Nice write-up, VaPadiDiver, but aluminums are only cheaper to maintain if your LDS doesn't require the yearly additional fee for Vis-plus on your make and alloy of tank.
In addition, I have only known of older steel tanks requiring a light tumble every 10 years or so if filled with good, dry air and are properly maintained. Many hydro shops don't charge anything additional for a light tumble.

 

[oxyhacker]

Rust, unless caused by really imbecilic neglect, happens slowly and is easily detected long before it reaches bomb proportions. Typical light surface rust that can build between inspections isn't going to cause a tank to let go, it takes deep pitting. I've got steel 72 which are used constantly with nitrox, and usually stored full or near full, that after 5 years showed only light surface rust which was easily removed with a homemade whip. Now if you want to leave them with a quart or two of salt water inside, and store them on their sides, that's another matter...

Anyone with a bunch of steel tanks or running old steel 72s, self-filled especially, should just learn to do a basic visual inspection (which doesn't necessarily have to mean taking the PSI course), and inspect their tanks regularly. No big deal.

One thing you must be careful with, especially with the old 72's, they are steel tanks. People who have their own compressors sometimes feel exempt from hydro or VIP test. With steel tanks, get a little moisture in them and your tank rusts from the inside out. Add a deco mix in them (high O2) and you are accelerating the oxidation Over time, unless you tumble and clean your tanks often (every 6 months to a year), your tank literally becomes a bomb.

 

[rgbmatt]

Nice write-up, VaPadiDiver, but aluminums are only cheaper to maintain if your LDS doesn't require the yearly additional fee for Vis-plus on your make and alloy of tank.
In addition, I have only known of older steel tanks requiring a light tumble every 10 years or so if filled with good, dry air and are properly maintained. Many hydro shops don't charge anything additional for a light tumble.

Never mind that Al tanks will corrode plenty if you get water inside - they don't look as spectacular as steel tanks, but they get pits just the same. And there's the whole neck crack issue to worry about!

At my workplace, we've condemned 6 aluminum tanks in the past year - 5 for neck cracks, one for internal pits. In the same timeframe, only two steel tanks haven't passed - one had been crossthreaded and the other was a non-galvanized tank with serious rust issues on the outside.

I'm not convinced that either sort of tank is much better than the other as far as maintenance goes.

 

[kidspot]

Never mind that Al tanks will corrode plenty if you get water inside - they don't look as spectacular as steel tanks, but they get pits just the same. And there's the whole neck crack issue to worry about!

At my workplace, we've condemned 6 aluminum tanks in the past year - 5 for neck cracks, one for internal pits. In the same timeframe, only two steel tanks haven't passed - one had been crossthreaded and the other was a non-galvanized tank with serious rust issues on the outside.

I'm not convinced that either sort of tank is much better than the other as far as maintenance goes.

Do you see more aluminum or steel? Around here I'd say 80% are aluminum at my lds and the remainder are steel 72's (the older variety - mostly belonging to the shop iteself)

Most lds around Maui see nothing but aluminum 80's and 63's

Tim

 

[wedivebc]

My friend just hooked up her steel 72 that has been sitting the the garage for a couple of months and it had 3000+psi. It had just got back from hyrdo and vis so the LDS must have felt really good about the condition of the tank (or the tank monkey forgot to read the rating)

 

[Curt Bowen]

All my old 72's are converted to 100% Oxygen stages

no more than 1800 to 2000 normally, because the pressure is transfered from a bank O2 that normally has no more than 2400 to start

 

[Rick Murchison]

How many people over fill the older steel 72's?

I don't.
But it's not uncommon to have one come back from a fill station at 3000-3100 psi - even though I always tell the shop rat "these are steel 72's, 2475 max" when I turn 'em over for filling.
Rick

 

[Day]

Where's dmdalton???

Paging Dave Dalton!