Question Older steel 72 Pitt Depth

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Pitting and hydro are two different criteria for evaluating a tank's condition. Tanks that can be condemned for pitting can pass hydro (a test of the metal's elasticity) and vice versa. A hydro tester checks for pitting before/after hydro.

Fwiw i pass many ancient 72s but the ones that seem to fail are the "barn finds" that have been sitting with little to no pressure for years. Purely anecdotal and many "barn finds" pass hydro and go on to become productive members of the diving community.

I am no metalurgist but i would be interested to know what happens to the metal in tanks that are neglected for too long.

This is correct. A cylinder can actually be structurally capable of passing a hydro test, but still have a small diameter cavity deep enough to be a the verge of leaking through. It could also be very capable of passing a hydro test, but have enough corrosion to not make it to the next 5 year cycle.

For those reasons (and a few more) what we call a hydro test is not just a hydro test. It is really a “re-qualification procedure” that uses a hydro as part of the process.

Before the re-qualifying facility does the hydro they require by CFR (Code of Federal Regulations) to do a visual inspection and determine if the cylinder is fit to proceed to do a hydro. This is done by the DOT licensed facility and is not to be confused with the Scuba industry standard VIP.

A DOT facility can legally Reject or even Condemn a cylinder based on the visual inspection prior to the hydro.

The definition of both Reject and Condemn are specified in CFR. The short answer is that Reject means it can still be cleaned, tumbled, sand blasted, wire brush, etc. and re-inspected to determine if it is fit for hydro.

Condemn is normally final. The damage or imperfections are too severe to be re-qualified.

Again this is all supposed to be determined by a licensed DOT facility (and hopefully qualified).

Violations even for simple documentation errors can cost the facility some serious fines.

Note: by law no one is allowed to drill or damage the threads of a cylinder (unless you signed a relase in a dive shop, giving authorization) even if the cylinder in condemn. But a "licensed DOT re-qualifier" can cross out the DOT numbers by stamping XXX on it. The cylinder is personal property, but the numbers belong to the DOT. They better have good records showing why it was condemn. I have had 3 cylinders replaced by a hydro facility.



I am not a metallurgist either, but I have some working knowledge due to my structural engineering background, and I have dealt with a reasonable amount of steel (and aluminum). There is nothing particular to a barn or age that will affect the metallurgy of a pressure vessel, with a few exemptions.

The first is fire. Fire can and will totally ruin the heat treatment of both steel and aluminum cylinder. Aluminum is affected by relatively low temperatures, but a fire will also ruin a steel cylinder. The metallurgy is definitely affected by heat and in the case of aluminum the temperature can be low enough to leave no visible mark. Steel requires a hot fire that would normally leave some surface indications, but not always.

The only other thing that will typically ruin a pressure vessel is anything that will cause corrosion (inside or out). An empty cylinder in a barn can corrode inside or out.

Hay bales (as found in a barn) are actually very corrosive. Read story below.

Age alone doesn’t do anything to either metal, but it allows more time for corrosion… in a corrosive environment.



About hay bales and corrosion: This is my 32 year being a volunteer (mostly Sunday) ski patrol here in Maine. For over 10 years of patrolling we used to use hay bales as padding on front of the steel snow making water hydrants. The patrol used to deploy the hay bales from the summit using are toboggans. It was great recue toboggan training. Well that practice stopped when they started to find deep pits on the water pipes next to the hydrants. The pipes started leaking through pin holes.

Keep in mind our mountain elevation 1200 feet. The snow making water pressure required to make snow at the summit is over 520 psi.

It turns out that hay is fairly acidic. I though that was fairly interesting...
 
This is correct. A cylinder can actually be structurally capable of passing a hydro test, but still have a small diameter cavity deep enough to be a the verge of leaking through. It could also be very capable of passing a hydro test, but have enough corrosion to not make it to the next 5 year cycle.

For those reasons (and a few more) what we call a hydro test is not just a hydro test. It is really a “re-qualification procedure” that uses a hydro as part of the process.

Before the re-qualifying facility does the hydro they require by CFR (Code of Federal Regulations) to do a visual inspection and determine if the cylinder is fit to proceed to do a hydro. This is done by the DOT licensed facility and is not to be confused with the Scuba industry standard VIP.

A DOT facility can legally Reject or even Condemn a cylinder based on the visual inspection prior to the hydro.

The definition of both Reject and Condemn are specified in CFR. The short answer is that Reject means it can still be cleaned, tumbled, sand blasted, wire brush, etc. and re-inspected to determine if it is fit for hydro.

Condemn is normally final. The damage or imperfections are too severe to be re-qualified.

Again this is all supposed to be determined by a licensed DOT facility (and hopefully qualified).

Violations even for simple documentation errors can cost the facility some serious fines.

Note: by law no one is allowed to drill or damage the threads of a cylinder (unless you signed a relase in a dive shop, giving authorization) even if the cylinder in condemn. But a "licensed DOT re-qualifier" can cross out the DOT numbers by stamping XXX on it. The cylinder is personal property, but the numbers belong to the DOT. They better have good records showing why it was condemn. I have had 3 cylinders replaced by a hydro facility.



I am not a metallurgist either, but I have some working knowledge due to my structural engineering background, and I have dealt with a reasonable amount of steel (and aluminum). There is nothing particular to a barn or age that will affect the metallurgy of a pressure vessel, with a few exemptions.

The first is fire. Fire can and will totally ruin the heat treatment of both steel and aluminum cylinder. Aluminum is affected by relatively low temperatures, but a fire will also ruin a steel cylinder. The metallurgy is definitely affected by heat and in the case of aluminum the temperature can be low enough to leave no visible mark. Steel requires a hot fire that would normally leave some surface indications, but not always.

The only other thing that will typically ruin a pressure vessel is anything that will cause corrosion (inside or out). An empty cylinder in a barn can corrode inside or out.

Hay bales (as found in a barn) are actually very corrosive. Read story below.

Age alone doesn’t do anything to either metal, but it allows more time for corrosion… in a corrosive environment.



About hay bales and corrosion: This is my 32 year being a volunteer (mostly Sunday) ski patrol here in Maine. For over 10 years of patrolling we used to use hay bales as padding on front of the steel snow making water hydrants. The patrol used to deploy the hay bales from the summit using are toboggans. It was great recue toboggan training. Well that practice stopped when they started to find deep pits on the water pipes next to the hydrants. The pipes started leaking through pin holes.

Keep in mind our mountain elevation 1200 feet. The snow making water pressure required to make snow at the summit is over 520 psi.

It turns out that hay is fairly acidic. I though that was fairly interesting...
Interesting info on hay bales.

Fwiw i didnt necessarily mean tanks found in a barn but tanks that had been in long term storage. It's not always the case but when I see the water climbing way up the burrette, I check the previous hydro and, more often than not, it's decades old. The tank might be pristine inside and out.

I very rarely see this with 72s that have been in current use. Just an odd thing I noticed.
 
I really do need the extra air

full


So when I want to look 72

full


I strip the paint off 232bar-3364.88psi Faber 100s
 
I just bought a pair of LP72 tanks (along with a pair of eeeevil pre-1991 Aluminum tanks). I want to turn them into a pair of small doubles (because I won't pay retail for epoxy tanks and I can't find used LP50's for anything less than 80%+ of retail).

760F86AE-CEBF-4261-9FF3-553F16F2ADCC.jpeg

They're Healthways tanks from 1969 and they're painted. I don't know who actually made them. The original hydro date stamp has a triangular symbol between the month and the year. I have a couple of questions about such tanks:

1) Are they galvanized, or is the paint the only corrosion protection?

2) How hard is the paint to remove? And if you do, do you then coat them with something like ZRC, or is there something else to consider?

I really don't like painted tanks: I usually only buy hot-dipped galvanized. But the price was right on these, so I bought them. The paint should be fine: I'm only going to use these in freshwater, so corrosion is manageable. Honestly, I can't imagine I will want to go through the effort purely for cosmetic issues (and I kind of like the Healthways stickers!), but seeing as @happy-diver mentioned it, I thought I would ask.
 
Do you see any rust where the paint got cut by the hydro stamp? The hydro stamp can sometimes even cut some of the galvanizing, but if there is no galvanizing you should be able to tell from rust getting under the paint.

If you post close up pictures of the numbers around the neck it would help identify the manufacturer.

I think Healthways normally used Norris. But a triangular symbol is not what I expect. You sure it is not a diamond?
 
I’m sure of nothing! :) Pictures below.

Yeah, it seems that the other tank has a much clearer Hydro Mark: the tank I initially looked at looks like it was inperfectly made. I would buy an N inside of a diamond on that second one.

And I wouldn’t call the bare metal Hydro marks like the 1977 one at the bottom rusty. So I guess that means that the tanks have been galvanized. :) Cool: I still don’t like painted tanks, but I like painted tanks with galvanized below it slightly better. :)
 

Attachments

  • 9E7F8694-185F-43CC-95D8-89F6ED4981DA.jpeg
    9E7F8694-185F-43CC-95D8-89F6ED4981DA.jpeg
    48.5 KB · Views: 109
  • 11544FF6-8790-4B8E-BFF9-D1E4857D0B49.jpeg
    11544FF6-8790-4B8E-BFF9-D1E4857D0B49.jpeg
    43.4 KB · Views: 100
I’m sure of nothing! :) Pictures below.

Yeah, it seems that the other tank has a much clearer Hydro Mark: the tank I initially looked at looks like it was inperfectly made. I would buy an N inside of a diamond on that second one.

And I wouldn’t call the bare metal Hydro marks like the 1977 one at the bottom rusty. So I guess that means that the tanks have been galvanized. :) Cool: I still don’t like painted tanks, but I like painted tanks with galvanized below it slightly better. :)
Norris tanks as Luis said.
 
Yeah those are Norris for sure.

On the second tank you can see a chip of paint missing next to the number 7. You should be able to tell that it is galvanized. It looks like it is.


I like this comment on you post above...
Honestly, I can't imagine I will want to go through the effort purely for cosmetic issues (and I kind of like the Healthways stickers!)

Why put the effort to strip paint... I would just dive them. But that is just me.
 
I want to turn them into a pair of small double
They make beautiful doubles, I have 3 sets,
My oldest 1966, just prime them and paint with a decent paint, with some boots, in fresh water I have no problems
 
...
Note: by law no one is allowed to drill or damage the threads of a cylinder (unless you signed a relase in a dive shop, giving authorization) even if the cylinder in condemn. But a "licensed DOT re-qualifier" can cross out the DOT numbers by stamping XXX on it. The cylinder is personal property, but the numbers belong to the DOT. They better have good records showing why it was condemn. I have had 3 cylinders replaced by a hydro facility.

...
I had a scuba shop in Cape Cod Mass take a pair of steel 50s that I dropped off for hydro. He gave me back my valves & other hardware but kept my tanks, saying that it was illegal for him to return them to me. He said that they failed due to having NPT threads & they didn't even need to get pressure tested. He had failed them visually. I was very angry that he took my property & would not return it, but I was young at the time & didn't understand my legal options. I never shopped there again. I doubt that he is still in business. It was a long time ago.
 
https://www.shearwater.com/products/swift/

Back
Top Bottom