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Post by red on Oct 2, 2015 11:26:09 GMT -8
I have a steel tank, in excellent condition, that was originally plus rated. For years scuba and hydro shops lied about "That can only be done once when it is made" and last year I found the DOT letter online, dated 2003, that says pretty simply that if the tank was originally plus rated, it can be plus rated again and again "forever" as long as it still is hydro tested by the water-jacket method and the tank expansion numbers remain within the original certification requirements.
Pretty simple, right?
Well...maybe. I spoke to the hydro shop that seems to know their stuff--including ongoing plus ratings--and they say there should be some kind of "REE" stamp on the cylinder neck as well. Which DOT never mentioned, and I can't see at all.
Anyone know anything about additional secret stamps needed for plus ratings on steel tanks?
Or should I just buy a case of the "Canned Air" spray at Office Depot and dive with that instead?(G) |
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Post by luis on Oct 2, 2015 15:36:00 GMT -8
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Post by red on Oct 2, 2015 20:26:19 GMT -8
Thanks, but those links seem constrained to LP72 tanks. I've got one of the hens' teeth: A PST "steel 96" rate for 3000PIS +.
I did find the CFR sections cited by the DOT's public letter, and there is only one ambiguity. IF the tank was originally stamped plus, they say it can be retested and restamped + forever.
They also mention that the correct expansion number for the tank can be found IF there is a REE stamp (which PST apparently didn't bother with) OR in conformance with the CGA booklet formulas. My shop might be ornery enough to do the calculations.(G)
But presumably, since the DOT did accept the original + rating, the tank should have an expansion % at 3300# which is very similar to the expansion % at 3300 PSI. Especially since they are tested to, what, 5/3 of the original pressure? That's approved for use at 5000 psi for 10,000 cycles in order to pass the DOT test in the first place. So without ignoring safety...if the tank was found safe for 10,000 cycles at 3000PSI, I'd be rather surprised to hear it could take 200 cycles at 3300 psi, a mere 2% of the number of higher pressure cycles that the DOT tested it to. So I'm hoping the shop will find a happy solution, but in the meantime, I did write to the DOT to see if the REE number might have originally been filled with them, on still be on file.
Now, if I could find any other PST '96 owners who could actually report SEEING a REE number....
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Post by luis on Oct 3, 2015 4:29:15 GMT -8
I own two of those cylinders. I got them after I wrote those posts, but I have recently measured all their critical dimension (including wall thickness), performed hydro test on them and calculated their specific REE number.
The REE numbers for these two cylinders are 56.0 and 54.8.
The REE numbers were not typically stamped on cylinder back when these tanks were manufactured. One is dated 12/77+ and the other 5/78+.
The document you are reading that requires the REE number to be stamped on the cylinder is probably a more recent document and would not cover all the requirements from the past. The older cylinders are still grandfathered and to obtain the REE you have to either go to the manufacturer, find another record, or calculate it based on actual physical dimensions.
Note: I have email Faber, in Italy, for the REE numbers on several cylinders and they have always responded with the information requested (very quickly I may add).
IIRC, the CGA C-5 pamphlet requires to take the calculated REE average of at least 3 cylinders of a type/class, to be able to use that average REE number for other cylinders of the same type.
I only have two of those cylinders, therefore it is not considered statistically sufficient number of data points, but I will be glad to share all the data and calculation sheets I have on those two cylinders.
BTW, I shared all my calculations with the local/ regional DOT inspector and even offer to stamp them with my Professional Engineer license number, but she felt that the calculations were very clear and actually exceeded the requirements.
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Post by red on Oct 3, 2015 8:19:11 GMT -8
Thanks, Luis!
I will bring those numbers along at hydro time. Maybe we can find someone who has actually seen or touched one more tank, as I've already corresponded with PST and as far as they were concerned, I could have been a fashion designer asking if the remembered who knitted King Tut's socks.(G)
IF the DOT has anything on file, I figure I'll hear from them in a week or two. After all, they have to pull historical records from the last century, you know, back before there were computers and things.(G)
Silly question but since I've never needed to know these things before...What exactly is a REE? Residual Expansion Somethingorother? I would have expected a number like a percent, i.e. .55% or 100.5%, to indicate the tank was returning to near-normal. But...large whole numbers? What's that all about anyway?
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Post by luis on Oct 3, 2015 10:00:44 GMT -8
The REE is the Rejection Elastic Expansion. It is measure in cc (cubic centimeters).
Typical hydro test on 3AA cylinders takes the cylinder to 5/3 of its stamped pressure.
In the case of the 3000 psi cylinder the test pressure is 5000 psi.
The cylinder is full of water and it is inside a water jacket container attached to a calibrated burette used to very accurately measure the cylinder volumetric expansion.
The test number of my two cylinders is as follow:
All volumes are measure in cc’s.
Maximum expansion; residual expansion; elastic expansion; percentage residual expansion.
56.0; 1.0; 55; 1.8%
53.2; 1.2; 52; 2.3%
Maximum expansion: is the volume measured at test pressure.
Residual expansion (or permanent expansion): is permanent deformation due to the hydro pressure. A perfectly elastic cylinder should return to 0.0, but the hydro pressure exposes the cylinder to the lower limit of plastic/ permanent deformation.
Elastic expansion: is the “Maximum expansion” minus the “Residual expansion”. This is the expansion that returned when the pressure was removed.
Percentage residual expansion: is the “Residual expansion” divided by the “Maximum expansion”. This number cannot exceed 10% to pass the basic hydro test.
To get the plus stamp the only extra requirement is that the “Elastic expansion” has to be less than the REE. It is that simple if you have the REE number.
You may notice that my first cylinder, the "Elastic expansion" (55) was fairly close to the REE number of 56. As long as it is below, it is OK. I suspect there was a slight error due to thermal expansion of the water. We have confirm that at that time of the day the water thermal expansion can make the numbers look a bit worst than they actually are.
On a related subject. Make sure that your hydro test facility does the pretest hydro expansion procedure as required for all galvanized cylinders and specified by PST. This extremely important to make sure your tank doesn’t fail the hydro.
Let me know if you have trouble finding the letter from PST requiring the pre-hydro procedure.
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Post by time2dive on Oct 3, 2015 10:49:44 GMT -8
Some Hydro facilities do not stamp a "+" on any cylinder, they don't know any better. I do stamp a "+" on any 3AA cylinder that DOES have a REE number. I am aware that I could stamp REE on cylinders if I calculated the wall thickness by measured it with ultrasound equipment, however if I spent the money to purchase the ultrasound equipment I would have to charge a whole lot more for hydro testing the cylinders....it is not economically feasible to do so. Some HP steel cylinders and aluminum composit SCBAs have a REE number but they are not eligible for the "+" stamp.....only 3AA cylinders.
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Post by red on Oct 3, 2015 11:08:10 GMT -8
Thanks guys. I could use that "pretest" instruction, just to keep on file to make sure.
in the Northeast, it isn't that the shops would have to charge more, or the REE numbers are or aren't accessible or stamped. They just all (ALL) like to lie, dive shops and hydro facilities alike. They all say "No, that's impossible, that's only for the first five years, it's ILLEGAL" one and all.
The sane way that the dive shops all require a hydro, plus a VIP at the shop. They conveniently forget to mention that the DOT requires a VIP before the hydro is begun, and the guy doing THAT VIP is federally certified as competent to do it. The shops all say "Well, but they might not do it right" in which case, why would I trust their hydro either? Hmmmm....
It turns out a die set is $125 and up, includes A-Z and 0-9, and if you want a "PLUS SIGN" that's a custom die stamp which will cost another $120. And then, you have to offer customers two choices, charge two rates, count on more than your fingers....
No insult to any honest guys out there, but the in the Northeast? The industry is full of FUD. They could do a spin-off of The X-Files about the search for a simply honest dive business. (sigh)
Sounds like those REE numbers in the mid-fifties are actually bracketing a 2% expansion figure for the steel 96, maybe that's the goal they were designed for, and the slight differences are simply manufacturing variance.h
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Post by luis on Oct 3, 2015 11:30:19 GMT -8
In general, industrial gas places have no interest on the plus stamp. Industrial gases are sold by the pound, not by the tank full. If you need more welding oxygen, you just get another cylinder. There is very little to no advantage to fill a cylinder to the maximum possible. It is not like they are carrying it on their back. If you know the history of the + stamp was to carry more gas with less containers during the war effort (WW-II) when there was shortage of many raw materials. We do not have a shortage of pressure vessels at the moment. So there is very little incentive to + stamp cylinders for other applications outside of Scuba. SCBA (for fire fighting, etc.) are also going to different type of cylinders. Sounds like those REE numbers in the mid-fifties are actually bracketing a 2% expansion figure for the steel 96, maybe that's the goal they were designed for, and the slight differences are simply manufacturing variance.h It is a bit more involved than that. Where in the Northeast are you? I am in Maine. |
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Post by luis on Oct 3, 2015 11:35:27 GMT -8
Some Hydro facilities do not stamp a "+" on any cylinder, they don't know any better. I do stamp a "+" on any 3AA cylinder that DOES have a REE number. I am aware that I could stamp REE on cylinders if I calculated the wall thickness by measured it with ultrasound equipment, however if I spent the money to purchase the ultrasound equipment I would have to charge a whole lot more for hydro testing the cylinders....it is not economically feasible to do so. Some HP steel cylinders and aluminum composit SCBAs have a REE number but they are not eligible for the "+" stamp.....only 3AA cylinders. If you want some REE numbers for steel 72, I will be glad to share. Including the calculations. I have enough Norris and PST cylinders to take an average for each. Maybe I need to hand carry the data in person.  |
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Post by time2dive on Oct 3, 2015 12:25:38 GMT -8
I would do that, however if the DOT people ever come and inspect my shop I would have to be able to prove those figures....I don't think that DOT would accept "I got them from Luis"  |
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Post by luis on Oct 3, 2015 12:53:22 GMT -8
I am totally OK with that. I am not very concern about any liability in this case, but this actually limits my exposure even further. In any case, you probably didn't see my post above that said that the calculation sheets spoke for themselves. I even offer to stamped them with my PE license stamp when I talked to the local DOT inspector and she said that it was not necessary. I was more than OK with that, since a PE license stamp is legally traceable and it would open my potential exposure (even if there is extremely little chance of an issue). If you change your mind, I can send you pdf files (or even Excel calculation sheets), but no, they will not be stamped. |
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Post by luis on Oct 3, 2015 12:55:55 GMT -8
Wow, I have not posted this much in years... I need a break. |
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Post by red on Oct 3, 2015 17:12:56 GMT -8
Luis-
Native New Yorker, temporarily sojourning on the mainland. Well, near the mainland.
I'd certainly appreciate the excel or pdf files.
I DO appreciate time2's point that a shop can't earn nay brownie points by telling the DOT "Well, I got these numbers from some guy..." I'd just like to have them on hand when I see him, and see what he has in mind.
And again, from the wording in the CFR, once and if a tank was plus stamped originally--there ARE options to do it again. That's the big point. I'll leave it to the shop to figure out which options they can explore, and I don't ask them to cheat. But stop into any dive shop in the metro NY area, and they'll all tell you "Oh no, that can never get another plus stamp after the first five years have gone by."
They say it SO convincingly, you'd immediately realize you'd never want to play poker with these guys. Except, with a loaded deck. They'd deserve that. :-)
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Post by duckbill on Oct 3, 2015 21:17:05 GMT -8
...and if you want a "PLUS SIGN" that's a custom die stamp which will cost another $120. Nay. Not a valid excuse. Most "+" stamps I have seen were made using a simple chisel. Only the intitial, factory stamps were routinely done with an actual "+" stamp. |
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