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Post by Captain on Feb 13, 2006 9:53:58 GMT -8
I offer the following for anyone interested. hazmat.dot.gov/regs/rules.htmA search of this site showed only one regulation pretaining to a private automobile. CFR49 §176.90 [hit count: 1] A private automobile which is carrying any Class 1 (explosive) material (except permitted fireworks or small arms ammunition) may not be transported on a passenger-carrying ferry vessel unless the Class 1 (explosive) material is in compliance with packaging, labeling, marking, and certification requirements of this subchapter. Permitted fireworks and small arms ammunition may be carried without the required packaging, labeling, marking, or certification if they are in tight containers.... In every other instance the regulation referres to " offered in commerce"
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Post by mossback on Feb 13, 2006 10:53:43 GMT -8
thanks.......don't know if this will put this to bed but it helps ..........
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Post by luis on Feb 13, 2006 12:35:01 GMT -8
Tom is correct in that the only things that will affect the structural integrity of a steel tank are corrosion/ rust, fire / extreme heat, and abuse either mechanical or from over pressurizing them. The age of a steel tank is totally irrelevant to its structural integrity.
Please notice that I am not referring about aluminum. Some aluminum alloys are susceptible to sustain load cracking (SLC: cracks developed from the material being stressed for extended periods of time). Steel is not subject to SCL or any other behavior caused by the application of constant stress over any time period.
The only reason age of a steel take comes into play is that an older tank has had more chances to been exposed to corrosion, fire or abuse. At that point you are just playing probability of exposure games.
If I know the history of a tank since the last hydro, I am wiling to bet if a tank will pass hydro again or not. I do recommend hydro testing tanks, especially if they were not in your possession since new. I believe a paint coat can hide if a tank has been in a fire or not. A well performed hydro test is cheap insurance and I am not referring about the legal aspects of it. Regular VIP’s performed by a qualified individual are actually more important.
Last summer I had three tanks condemned by a certified DOT hydro test facility (not the LDS) because the technician decided to be conservative since this were old SCUBA tanks. To make a long story short. After I insisted on seen the test data and pointed to the facilities manager that their own data showed residual expansions below 10% they had to replace my tanks. I don’t even believe some of their test data.
Not all certified technicians are necessarily qualified. Most of them probably are, but you have to be careful who you deal with. Hydro testing is subject to regulations (CFR49) and it should not be subject to the operator’s personal judgment. A VIP obviously involves the judgment of the inspector. Condemning a tank (by drilling or stamping XXXXX over the numbers) just because of age (with no other prove of failure) is in essence destroying personal property, and therefore illegal.
We had a hydro test facility in the first dive shop that I worked. I personally performed many hydro tests in the mid 70’s. That was before I got my engineering degrees. In my professional life, as a mechanical / structural engineer I have spent a number of years involved in the design, performing calculations, manufacturing, and testing of pressure vessels (tanks). Some of these pressure vessels were under ASME codes. I haven’t designed tanks under CFR 49, but I am familiar with these regulations and from a technical stand point they are very simple. The legal wording is bit more subject to interpretation.
In all the years I have been involved in engineering, I have only heard the term “metal fatigue” in relation to cyclic loading (as in vibration loads or loads that are applied and removed or reversed on a regular basis), not a steady load. The following portion of the statement is incorrect: “A full tank that has sat in a dry place for 20 years still undergoes pressure fatigue from stress...”. A steel 72 (minimum wall thickness 0.164”) at a working pressure of 2250 psi will have a tangential hoop stress of 45,082 psi. This is well below the maximum allowed of 70,000 psi (per CFR49. 178.37 for 3AA tank material). The test pressure (3,750 psi) on a healthy tank would take the stress to 67187 psi, which is still below the allowed and the yield strength (if the material properties has not been ruined by fire or abused, or the structural wall thickness has not been compromised by corrosion).
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Post by luis on Feb 13, 2006 12:36:14 GMT -8
In reference to buoyancy: The weight of “standard” air is 0.075 Lbs per cu ft. Therefore:
80 cu ft = 6 Lbs 72 cu ft = 5.4 Lbs 65 cu ft = 4.9 Lbs
This will give you the difference in weight (and buoyancy change) from an empty tank to a full tank. It is independent of the tank material or the maximum operating pressure.
Therefore, there must be a typo in the following statement: “Nemrod........I believe a US manfactured steel 72 is about 6.8 lbs negative when full and around -3.6 or something close to that when empty......”
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Post by mossback on Feb 13, 2006 14:41:01 GMT -8
Luis
You could be right, however, I think the issue of bouyancy/displacement and the additiion of tank weight contribute to the negative bouyancy equation, I don't know the math that figures this up, was going from 30 year plus memorys......I could be way off as I stated " I believed" and stated "or something close"....
faber has a chart that shows their tank bouyancys, They still sell a 71.2 cuft tank (again I think).....I look it up tonight and post it here.
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Post by mossback on Feb 13, 2006 14:53:36 GMT -8
Well I was off a bit..... Faber's spec's are as follows: PSI, BAR, Capacity, Dia, Length, Weight empty, bouyancy empty.. type desig. FABER 3300 230 72 6.75(171.3) 23.5(596.6)* 30.2* -5.2 MP72
Doesn't show bouyancy full......higher pressure but approx. same size as on 71.2 so walls must be a bit thicker..weight is higher than what I remember of the US made steel 72, I thought they were 27 lbs empty w/o valve ......note: neg. bouyancy is 5.2 lbs......that's empty......a bit higher than my memory but this is a foreign made tank from Italy.......
Y'all make the math assumptions.....my mind is tired........
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Post by RMannix on Feb 13, 2006 15:36:29 GMT -8
All specs and science aside, I personally floated an old 72 in fresh water (Lake Travis, Austin TX) with a Scubapro k valve and 500 PSI in it. Not very bouyant, but definitely floated without touching the bottom.
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Post by Ron Hearn on Feb 13, 2006 18:32:58 GMT -8
I don't about evey one else but I'm starting to loose the point of this thread. LOL
Ron
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Post by luis on Feb 13, 2006 19:19:53 GMT -8
I scanned this data from the book Inspecting Cylinders, from PSI. I believe that there are a few mistakes and the character recognition (OCR) program might have made some errors during the scan. I only checked it briefly so there may be errors. At least the numbers for the steel 72 looks somewhat reasonable.
Specifications for Selected SCUBA Cylinders ALLOY VOLUME SERVICE LENGTH DIAMETER EMPTY WT. BUOYANCY (advertised) pressure (in.) (in.) (Lbs.) empty full steel 15 3,000 13.8 4.0 7.5 -1.3 -2.5 steel 42 1,800 19.1 .8 20.1 1.4 -1.9 steel 52 2,250 19.4 6.9 22.0 0.0 -4.2 steel 53 2,250 19.1 6.8 20.5 1.4 -2.8 steel 65 2,460 21.4 7.2 28.5 -3.3 -8.2 steel 65 3,500 16.8 7.0 2.40 -1.5 -6.4 steel 71 2,250 25.0 6.8 29.5 3.5 -2.0 steel 71 3,000 20.5 6.8 28.6 -4.6 -10.3 steel 80 2,460 24.0 7.3 31.9 -2.0 -8.0 steel 80 3,500 19.8 7.0 27.0 -1.0 -7.0 steel 94 3,000 25.0 7.0 39.0 -6.0 -13.3 steel 95 2,400 23.8 8.0 37.2 1.5 -6.2 steel 95 2,460 23.8 8.0 38.8 -3.0 -10.1 steel 100 3,500 23.9 7.0 33.0 0.0 -7.4 steel 104 2,400 26.5 7.8 44.0 0.0 -8.2 steel 108 2,400 26.8 8.0 41.0 0.0 -7.0 steel 120 3,500 27.9 7.0 38.0 1.0 -8.0 steel 121 2,400 29.3 8.0 45.0 0.0 -8.0
alum. 13 3,000 12.9 4.4 5.8 1.7 -0.7 alum. 14 2,015 16.5 4.4 5.4 1.4 0.4 alum. 50 3,000 19.0 6.9 21.2 4.4 0.7 alum. 53 3,000 19.6 7.2 28.2 -1.6 -5.6 alum. 60 3,300 19.1 7.2 27.8 -1.6 -6.1 alum. 63 3,000 21.8 7.2 26.6 1.7 -3.0 alum. 67 3,000 23.0 7.2 30.5 0.4 -4.6 alum. 70 3,300 23.0 7.2 32.8 -0.3 -4.9 alum. 71 2,475 28.8 6.9 30.6 10.6 5.2 alum. 72 3,000 26.0 6.9 28.4 2.8 -2.4 alum. 80 3,000 26.1 7.2 33.0 2.2 -3.8 alum. 80 3,000 26.1 7.2 31.5 3.8 -2.1 alum. 80 3,300 24.5 7.2 34.5 0.6 -5.4 alum. 100 3,000 26.6 8.0 40.9 2.5 -5.0
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Post by Linda on Feb 13, 2006 19:59:08 GMT -8
I don't about evey one else but I'm starting to loose the point of this thread. LOL Ron Luis is still on track... James (Nemrod) deleted his original (and subsequent) posts in this thread so it has lost a bit of its cohesion.... The thread evolved into several related discussions, but I think he was originally asking about steel 72's and bouyancy.
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Post by Captain on Feb 13, 2006 20:22:59 GMT -8
I don't know about the rest of you but I am a skinny old guy at 5'10' 150#'s and with just a 71 and regulator. no BC or wet suit I am slightly negative with 2500 psi and about neutral at 500 psi in salt water. Like RMannix said a 71 with regulator at 500 psi will barely float in fresh water.
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Post by Captain on Feb 14, 2006 6:34:36 GMT -8
I don't want to start anything again but my view is that since the old 72 is so close to ideal for most rec and vintage diving we shoud do what we can to prevent them from being destroyed out of ingnorance or the dive shop's greed to sell new tank.
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Post by Broxton Carol on Feb 14, 2006 6:44:17 GMT -8
Back up the line someone offered that if a tank is marked DOT it is covered under DOT regulations. My tanks were made in the 1950's and are NOT covered by the DOT or anybody else. I use them for my personal use, and fill and maintain them myself. I remember taking in tanks that were 45 and 50 years old for hydros up in Ohio. The man there said "Look here" he dropped his inspection light into those tanks, and they were a light brownish patina, and he said that was normal for a steel tank. He said as long as it had no visual rust scale, it was most likely to pass hydro. In fact I never had one out of say 15 fail!! These were all steel tanks. I bought a couple sets of doubles, steel ones. I took them in there , and one set had the old air tanks from the early 40's which were 38's, made into a pair of doubles,and the other was a set of 1961 twin 38 doubles. Marked USD with original hydro in 1961. He passed these with plus marks on them!!!!!!!! Said they were good as new! They were still bright on the inside! I sold the tanks with the hydros, , and asked about steel tanks from the hydro shop. The manager said "see those tanks over there? They were made in the early 1900's and they all pass hydro, steel is the way to go" Now I walked over and there were dates from 1909, 1912, through the 1920's on these air cylinders. I was amazed. He said if you just take care of em and keep air in them, you likely wont have trouble. I believe him, and check all my personal equiptment myself.
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Post by mossback on Feb 14, 2006 7:32:57 GMT -8
Looks like this dog won't die........
Everyone who as commented is correct to a degree given most info today is regulated to tanks made in the last few years...... but no one has provided Nemrod the hard documents he asked for...I can't, don't have anything but memory and apparently it's fading fast into inaccuracy.........
I mentioned it once earlier and Tom today, we should be more concerned with preservation from the ignorant of these tanks.......they will out last our lifetimes but they won't out last ignorant LDS/Hydro shops......
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Post by mossback on Feb 14, 2006 7:45:06 GMT -8
{Now if this were scubaboard I would be right in the middle of it but I think here it would be nice to BE NICE.} Rereading your comment Nemrod, I think the ego battles on this forum and over on Bryan's are nothing more than a bad case of CABIN FEVER!!!.........cureable by some much needed diving............ I don't think there are many followers here, but in fact I think they are mostly leaders in their own right or out and out rebels........even that Canadian guy....... Friction will develop, it's just natural.......... Just my thoughts........
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