Forum rules
Regulator specific information can also be found on the main page of the website in the Regulator Id Guide.
User avatar
luis
VDH Moderator
Posts: 1536
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Vintage tank hydros and "+" stamping

Sat May 08, 2010 2:02 pm

I spent the day yesterday doing hydros on seven of my tanks. My LDS has a hydro station that I use… I still pay for the hydros, but I do the work and control the duration of the pre-test, etc. I like doing my own hydros.

I also got wall thickness readings on 9 of my steel 72. A co-worker took the readings using a precision ultra-sound NDT equipment. I drew a pattern of dots on my tanks and took reading every 3 inches to get a precise average.

This procedure meets (and exceed) CGA C-5 in determining an average REE for this class of tanks. I own enough Norris and PST steel 72 tanks that I can calculate an average REE number for the type of tank (per the CGA procedures). Whether your local hydro station accept this REE number to plus “+” stamp your tanks or not, I don’t know. You are always welcome to bring them up to Maine I can recommend a nice dive shop that would gladly hydro them with the + stamp for you (assuming it meets the criteria, which probably does).

All but a few of my 3AA tanks are already + stamped. By the after the next hydro I expect all my tanks to be plus stamped, including my 45s and 40s double tank sets.


Below is some of the data on my tanks. There is still a lot of empty blanks, but I should have at least one data set for all of my tanks by the end of the year or early next year.

In the first two tables each row is for the data associated to a tank. The third table is in columns; with each column has the calculations for the tank identified on the top. On the far right of table three shows the equations used in each column.

Tank dimensions and wall thickness:

Image


Tank hydro data and volume data:

Image


Tank REE and hydro calculations:

Image



more later
Luis

Buceador con escafandra autónoma clásica.

jviss

Re: Vintage tank hydros and "+" stamping

Sun Aug 22, 2010 2:11 pm

Wow, that's an impressive piece of engineering work, well done! I may take you up on that - I'm in Massachusetts - and I'd love my U.S. DIvers twin 53's to have the plus stamp.

jv

User avatar
luis
VDH Moderator
Posts: 1536
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: Vintage tank hydros and "+" stamping

Wed Nov 24, 2010 10:54 pm

I have 14 steel 72 tanks that I have been taking some precise measurements.

Wall thickness measurements were taken using a precision ultrasound measuring device. The ultrasound probe was calibrated before each set of readings using a cut off (condemned) steel 72 tank. The cut off tank wall thickness could be confirm with a caliper and provided a sample of the exact same material to calibrate the ultra sound equipment. Measurements are good to about 2/1000 of an inch.

I measured the actual internal volume by using water at room temperature and precisely measuring the weight of the water. I took into account the reduced volume from the valve threads.

I am only showing some of the data below to save space. The “Tank #” is only the number I assign and painted on all my tanks to keep track of them. I have full records (in a spread sheet) with all the tank information, including serial number and all the tank markings (including all the hydro test markings).

I also have records of all the hydro test data, etc.

I am only including seven of my tanks at this point (plus a friends Walter Kidde tank). I still need to take precise volume data on the other tanks. I do have wall thickness for all of them. I need wall thickness and volume data to calculate REE numbers for that specific tank.

At this point I have complete data for four Norris tanks, three PST tanks, and a friends Walter Kidde tank (I don’t own any Walter Kidde).

The data is shown as follows:
Tank# / manufacturer >> average wall thickness / tank empty weight (with boot and valve) / tank actual volume at 2475 psi / actual REE nunber

1 / Norris >> 0.177 inches / 30.26 Lbs / 72.2 cu ft of air (@ STP) / REE = 61.3
2 / PST >>>> 0.171 inches / 28.88 Lbs / 70.5 cu ft of air (@ STP) / REE = 58.6
4 / PST >>>> 0.181 inches / 30.11 Lbs / 70.8 cu ft of air (@ STP) / REE = 61.5
5 / Norris >> 0.179 inches / 29.73 Lbs / 71.4 cu ft of air (@ STP) / REE = 60.7
6 / PST >>>> 0.173 inches / 30.43 Lbs / 70.9 cu ft of air (@ STP) / REE = 58.7
7 / Norris >> 0.178 inches / 31.01 Lbs / 70.3 cu ft of air (@ STP) / REE = 58.4
8 / Norris >> 0.175 inches / 29.73 Lbs / 71.4 cu ft of air (@ STP) / REE = 61.2
No# / WK >> 0.183 inches / 29.63 Lbs / 71.0 cu ft of air (@ STP) / REE = 63.6


The variation in volumes is not very much considering the manufacturing process used for these tanks. As a mater of fact I consider the variation in wall thickness to be fairly impressive. The wall thickness standard deviation for the data collected for each tank is also relatively small.


Tanks with a + stamp (DOT 3AA code) are always advertised as having the capacity with the extra 10 % overfill.

An interesting side note. I also measured two PST HP 80s. They are supposed to have 80 cu ft of air at 3442 psi… they actually have 85.3 cu ft and 85.0 cu ft.

Note: as expected, the actual REE numbers are all higher (or equal) to the published number by PST. As a mater of fact I believe the REE number on tank 7 came out low due to lack of precision on the hydro test data. I believe I had a tiny leak during hydro, but not bad enough to do it over. I will confirm the data in 5 years.
Luis

Buceador con escafandra autónoma clásica.

User avatar
usddude
Master Diver
Posts: 317
Joined: Wed Jan 30, 2008 2:17 am
Location: Tennessee

Re: Vintage tank hydros and "+" stamping

Thu Dec 16, 2010 6:20 pm

Thank you Luis for all this work. Invaluable information to say the least.
You the man!!

usd

User avatar
SurfLung
Master Diver
Posts: 1275
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Vintage tank hydros and "+" stamping

Fri Feb 04, 2011 4:07 pm

I have some questions and I'd sure appreciate some comments or suggestions...

Question #1 I have a couple of small tanks with tapered thread valves on them. I'm wondering if I can bring them for hydro testing with the valves loose and get them back that way? I'm trying to avoid somebody buggering them up any more than they are.

Question #2 It has always rubbed me the wrong way that a DOT 5 year hydro test is good enough for every other industry but every year I have to subject my tanks to getting the valves wrenched off and on and then another ugly sticker pasted on them. Is the VIP program really necessary or just another profit string for the dive shop?

Question #3 (related to #2) I read about the Luxfer 6351 tanks and how there have been 12 ruptures since the early 70's attributed to SLC. That's 12 out of an awful lot of tanks over many years and several of those 12 were considered abused... Over filled, out-of-hydro, etc. I wonder what the rupture stats are for tanks used in other industries in comparison to the Scuba industry with their VIP. In other words, has VIP actually accomplished anything that hydro testing wasn't already doing?

Comment: I like my tanks to look nice and I resent the VIP messing them up. :wink:
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
antique diver
Master Diver
Posts: 1679
Joined: Sun Dec 10, 2006 12:50 pm
First Name: Bill
Location: North-Central Texas

Re: Vintage tank hydros and "+" stamping

Fri Feb 04, 2011 5:23 pm

SurfLung wrote:I have some questions and I'd sure appreciate some comments or suggestions...

Question #1 I have a couple of small tanks with tapered thread valves on them. I'm wondering if I can bring them for hydro testing with the valves loose and get them back that way? I'm trying to avoid somebody buggering them up any more than they are.

Answer #1: I have the same concerns, so I take my cylinders for testing with the opening covered with a plastic plug or tape so there will be no problems like you mention. You are right, don't give them a chance to screw up your valves!

Question #2 It has always rubbed me the wrong way that a DOT 5 year hydro test is good enough for every other industry but every year I have to subject my tanks to getting the valves wrenched off and on and then another ugly sticker pasted on them. Is the VIP program really necessary or just another profit string for the dive shop?

Answer #2: My reasoning for thinking that Scuba tanks need inspections more often is that they are used in and around the water and sometimes even filled in the water. Most non-Scuba high pressure cylinders don't have the plethora of opportunities for getting water into them. I have also seen instances where the fill operator carelessly dunked the valve or even dropped the fill hose end in the water before filling, giving an opportunity for small amounts of water to be introduced when the valve was opened and air flowed in. It doesn't take a whole lot to cause some corrosion. I service compressors for fire departments, dive shops and other breathing air uses, and it is not uncommon to find air filters that have not been changed often enough, with the result that moisture has entered their storage cylinders and/or breathing air tanks.

In another example of cylinders being around and in the water, I recently bought a nice 1955 Scott Hydropac with a 2 year old hydro date on the cylinder. Every component including the cylinder and valve looked almost perfect. Being very particular about the internal condition of my tanks, I pulled the valve. There was about 8 ounces of water inside, so I had to clean it up and dry it. Had I waited too long it probably would have corroded to an unsafe condition. I looked into a lot of cylinders during 31 years in the diving business, and the great majority of them were fine, but there were occasions that we found moisture that had already caused significant damage, and occasions where it was discovered early enough to save the cylinder


Question #3 (related to #2) I read about the Luxfer 6351 tanks and how there have been 12 ruptures since the early 70's attributed to SLC. That's 12 out of an awful lot of tanks over many years and several of those 12 were considered abused... Over filled, out-of-hydro, etc. I wonder what the rupture stats are for tanks used in other industries in comparison to the Scuba industry with their VIP. In other words, has VIP actually accomplished anything that hydro testing wasn't already doing?

Answer #3: Surflung, I hope you don't think that I am arguing with you or that I don't respect your views on the subject. I do want all of us to be as safe as possible. I base many of my thoughts about this on the experience of 31 years owning a dive shop, and the past 10 years still involved in the compressor and high pressure cylinder business. I'm not saying that I am an expert... there are many more knowledgeable on this subject than I... I just believe in doing this thing safely, because the consequences of a cylinder failure are so severe. I can't help but wonder how I would feel if I owned one of those 12 cylinders that failed... somebody did. I absolutely believe in carefully inspecting all aluminum cylinders thoroughly for neck cracks annually. Luxfer says their 6351's must be checked twice a year. Steels should be checked annually, or sooner if there is reason to believe moisture has had a chance to enter.

Comment: I like my tanks to look nice and I resent the VIP messing them up. :wink:
Comment about your "Comment": I AGREE WITH YOU ABOUT THE VIP STICKERS! Get to know your local air provider and ask if they would go for placing their VIP sticker in your logbook with a notation of the cylinder's serial number. They might be willing to accept that in lieu of one on the cylinder... I would. I am lucky enough to have my own compressors, but a quarry dive site that I frequent accepts my VIP records in my log instead of on my cylinders.
"I get plenty of excercise just pushing my luck!"

User avatar
luis
VDH Moderator
Posts: 1536
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: Vintage tank hydros and "+" stamping

Fri Feb 04, 2011 8:45 pm

Basically I agree with the answers given by “antique diver”.


Question 1:
I would take the tank directly to a hydro station without the valve (not to a dive shop that then sends it out). My local dive shop has their own hydro facility (actually two different LDS have hydro facilities locally). They allow me to do my own hydro’s at my LDS (I started doing hydro’s almost 40 years ago).


Question 2:
I have seen very few steel cylinders fail hydro, but have seen plenty fail due to excessive rust and pits.

I have had to tumble three tanks that were less than a week old due to a wet fill on a dive shop in a marina in PR that used salt water for cooling water. I saw them filling them while I was unloading other tanks from the boat. I am glad I did a VIP when I returned back to the LDS were I worked (this was in the early 70's).

I do my own VIP (have been doing them for 40 years, plus I got certified about three years ago). I don’t pay anyone and every dive shop I deal with accepts my “PSI” stickers. I VIP most of my tanks every year (I don’t VIP as often tanks that I am not using, but I am certain they had a good dry fill before I store them).

To me the information I get from a VIP is basically more important that the information I am going to get from a hydro. With the records I keep, I have a fairly good idea what the hydro results should be.

All stickers should be removed every year to inspect the outer surface. Only the last sticker should be on a tank and it can be placed anywhere you want. As mentioned, a good record could be kept without a sticker, but you may have trouble at some dive shops.

Question 3:
Only a hand full of aluminum 6351 cylinders have had catastrophic failures, but many… many more are been pulled out of service every year with cracks due to SLC. My guess (just a guess by observation) is that the numbers could be in the thousands that are being retired every year. I have personally witness and caught several cracked necks (and I don’t actually work at the LDS… I only help when I am visiting).

Stories of aluminum tanks leaking from a crack during the filling process are not uncommon. Some I have heard first hand from people that were present. Having to stop a fill mid-track, close valves, disconnect a fill whip, and empty a tank leaking from a crack is an experience that would probably a life changing experience… It is an experience I totally want to avoid.

My LDS still services and fills 6351 aluminum tanks… again when I am there, I help them fill tanks, etc., but I avoid filling the old aluminum tanks.

A good high magnification visual inspection of the neck should catch any crack (the eddy current testing should also catch it), but I just don’t feel the need to take a risk on this old tanks. I personally retired my only old aluminum tanks and there are no signs of cracks on it.

BTW, an aluminum tank with a crack can pass a hydro test without any issues unless the crack is all the way through causing a leak. A hydro test will not normally detect a crack unless it is leaking.

It is very possible that many old 6351 aluminum tanks have been abused (by overfilling), but that does not explain the large number of tanks failing. The “Sustained Load Cracking” (SLC) phenomenon is a unique failure mode that I am not aware of it happening to other metals (or even most aluminum alloys)… definitely not steel.


I hope this helps. Good luck with your tanks.
Luis

Buceador con escafandra autónoma clásica.

User avatar
captain
Plank Owner
Posts: 1322
Joined: Mon Jul 04, 2005 11:32 am
Location: LaPlace, LA

Re: Vintage tank hydros and "+" stamping

Sat Feb 05, 2011 12:12 pm

To quote Luis,"Stories of aluminum tanks leaking from a crack during the filling process are not uncommon. Some I have heard first hand from people that were present. Having to stop a fill mid-track, close valves, disconnect a fill whip, and empty a tank leaking from a crack is an experience that would probably a life changing experience… It is an experience I totally want to avoid."

I also don't want to become a one man bomb disposal squad technician.
Captain

User avatar
Bryan
Plank Owner
Posts: 5206
Joined: Fri Jun 24, 2005 11:40 am
First Name: Bryan
Location: Wesley Chapel Florida
Contact: Website

Re: Vintage tank hydros and "+" stamping

Sat Feb 05, 2011 2:46 pm

captain wrote:To quote Luis,"Stories of aluminum tanks leaking from a crack during the filling process are not uncommon. Some I have heard first hand from people that were present. Having to stop a fill mid-track, close valves, disconnect a fill whip, and empty a tank leaking from a crack is an experience that would probably a life changing experience… It is an experience I totally want to avoid."

I also don't want to become a one man bomb disposal squad technician.
Pucker factor is off the charts in the above scenario :shock:
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

User avatar
Gilldiver
Master Diver
Posts: 273
Joined: Thu Feb 22, 2007 1:29 pm

Re: Vintage tank hydros and "+" stamping

Sat Feb 05, 2011 10:15 pm

In the helicopter world we call it “Flaw Tolerance” or how long this thing will last in the air with a crack in that part of size “X.”

I have flushed all of the old alloy tanks out of the garage. A good friend of mine who runs a LDS and Hydro shop said, tanks should be considered to be like tires, at some amount of mileage or age, you just need to replace them. Luckily for us the Steel 72’s are like to solid rubber tires on the old MACK trucks of the early 1900’s, they just don’t ware out unless you abuse them.
Double Hose Regulators, It not just a Hobby, it’s a Disease

User avatar
SurfLung
Master Diver
Posts: 1275
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Vintage tank hydros and "+" stamping

Sun Feb 06, 2011 12:23 pm

Hey, Thank you all for taking the time to explain that. I think I may have had a chip on my shoulder from having my DH regulator insulted by few Dive Shops back in the early '80's... Sort of like, "Oh yeah? Well I don't respect their opinion" and it tainted everything else they said they're experts about.
I have two US Divers Aluminum 50s that I bought in '71-'72. They're at the hydro tester so I can't check the markings but I bet they're the bad ones. My diving got kind of infrequent after high school and these tanks were barely used... probably less than 10 fills each. It's a shame to waste them but I see your point.
Antique Diver, thank you for your courtesy as well as your knowledge... I am not offended in the least. Louis, Captain, Bryan, and Gill Diver... Thank you all. I am slowly embracing the realities of modern sport diving... :)
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
antique diver
Master Diver
Posts: 1679
Joined: Sun Dec 10, 2006 12:50 pm
First Name: Bill
Location: North-Central Texas

Re: Vintage tank hydros and "+" stamping

Sun Feb 06, 2011 8:59 pm

Surflung,
All of us have benefited greatly from all the forum members' contributions on many subjects, and I am indebted to all of you for that! I'd try to list specifically all the folks that have helped me out, but I am afraid (with my "antique diver" memory)that I would miss someone. I hope no one will be offended if I just give this blanket statement of appreciation.

Also, I feel compelled to put in another two tanks-full of hot air about aluminum cylinders, but you don't have to read it 8) :

I have thirteen 6351 alloy cylinders that I will not use, but intend to sell for scrap aluminum. That ought to tell you how I feel about them. I found at least two dozen cracked cylinders while doing inspections on this type of cylinder during my years in the diving business, maybe more... it's hard to say for sure, so that's a conservative estimate... not exagerated.

The first crack that I found was before I had even heard about the Sustained Load Cracking problem (SLC), and believe me, I tried to stay up on everthing going on the business. I was filling a cylinder that I had sold some years previous to this incident, and as the filling progressed, air began to leak from the neck of the cylinder. At first I just suspected an oring failure at the neck, but when I saw air leaking along a lengthwise line just under an inch long, I didn't know whether to run like hell or stay and shut off the valve! I was already there, so shut off the valve (only open a turn), then left the room for a while to let the pressure bleed down some.

I contacted US Divers, but all they would say about it was something to the effect that I should just return the cylinder for them to inspect, and if there was "really a problem" with it they would replace it.

I really believe that the low number of catastrophic failures (that have been reported) has been due to the diligence of many inspectors carefully doing their job, finding tiny beginnings of cracks, and condemning those cylinders early enough to prevent explosions. What scares me is the fact that not everyone inspecting cylinders knows how to properly do that job. Ugh... I just won't fill 6351's. To prevent pissing off friends, I just loan them a newer cylinder instead.

If you will allow me one more comment, I have seen one 6061 (newer alloy) cylinder that appeared to have a small crack beginning inside the neck. It was in an SCBA firefighting cylinder manufactured by Luxfer, but the same alloy as used for SCUBA cylinders. A PSI inspector instructor trainer that I know said that he had heard of other 6061's that had cracked, but could give me no specific facts or numbers. I'd like to hear more about that if any of you has information.

So, don't get lax in inspecting the newer cylinders either. They should be a great improvement over the old ones, but only time will tell. Y'all be careful.
"I get plenty of excercise just pushing my luck!"

User avatar
SurfLung
Master Diver
Posts: 1275
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: Vintage tank hydros and "+" stamping

Mon Feb 07, 2011 2:32 pm

That's pretty eye-opening :shock: news. Especially regarding even the newer aluminum alloy. I was already discouraged from considering another aluminum tank and that seals it. But I'm looking at the bright side: Its an excuse to get new tanks! I've been looking at the XS High Pressure 3400+ psi steel tanks with the idea of running them at 2600-3000 psi and keeping a big margin of safety.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

User avatar
Bryan
Plank Owner
Posts: 5206
Joined: Fri Jun 24, 2005 11:40 am
First Name: Bryan
Location: Wesley Chapel Florida
Contact: Website

Re: Vintage tank hydros and "+" stamping

Mon Feb 07, 2011 3:10 pm

Eva likes the high pressure steel cylinders because they are compact and she needs less weight on the belt. I pump them to 3500psi and she dives them with a Royal, Phoenix or even a new AquaLung Mistral which she likes. They sometimes freeflow slightly till they get to 3300 or lower.

Anyone can take the PSI visual inspection course. Contact them and they will put you in touch with someone who teaches it in your area. Next buy one of these and you can kiss the dive shop goodbye...

http://www.airetex.com/a45.html
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

User avatar
Bryan
Plank Owner
Posts: 5206
Joined: Fri Jun 24, 2005 11:40 am
First Name: Bryan
Location: Wesley Chapel Florida
Contact: Website

Re: Vintage tank hydros and "+" stamping

Mon Feb 07, 2011 3:11 pm

Eva likes the high pressure steel cylinders because they are compact and she needs less weight on the belt. I pump them to 3500psi and she dives them with a Royal, Phoenix or even a new AquaLung Mistral which she likes. They sometimes freeflow slightly till they get to 3300 or lower.

Anyone can take the PSI visual inspection course. Contact them and they will put you in touch with someone who teaches it in your area. Next buy one of these and you can kiss the dive shop goodbye...

http://www.airetex.com/a45.html
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

Return to “Technical Information / Diver Training Information”

Who is online

Users browsing this forum: No registered users and 1 guest