Plus ratings and hydros'

[rstofer]

Darrell,

I am pretty sure I missed the answer to the most important question when I read Paragraph 6 which starts:

Now let's talk about overfilling cylinders.

The important question, to me, is how can old LP 72 cylinders which lack a REE number stamped on the head be tested to and receive a '+' rating?

I don't care HOW as much as I care about IF. I have a LP 72 that just received the '+' rating although a) it has no REE number stamped on the cylinder and b) the previous several hydro's did not have a '+' stamp although the original factor hydro did have a '+'. Again, if there is a method that the hydro facility could have used, fine. I don't necessarily need the details. If, OTOH, it is more likely a mistake, I need to know about it so I don't overfill the cylinder.

Unlike many, I do NOT want to overfill my cylinders. But if the '+' is correct, I wouldn't mind moving from 2250 to 2475 psi because that is the only way to actually get 72 cf in the tank.

Richard

 

[ctcdg]

Hallmac,

You got it.

And... you GOT it!! You DON'T have to do the maximums!! Just pick up the REE from the table in C-5 and you're good to go.

BTW... you might notice some cylinders with the REE marked on them appear higher than the REE listed in C-5. That's because the numbers in C-5 are conservative numbers from the worst case designs submitted by mfg's with a built in safety factor to account for strays from nominal. So, you can always use the REE stamped on the cylinder by the mfg. That REE on the cylinder represents the actual value calculated for that cylinder, and it will always be slightly higher than what you find in C-5.

Take care, and I hope to see you at seminar some day!

DG

 

[halocline]

Richard, why don't you just call the hydro facility and ask them if they know the REE number. If you send me their number via PM, I"ll be glad to call them and simply ask them if they have the REE number for my tanks. I won't even bring up your tanks.

You have raised the pertinent question, though. Which is, can we get the plus rating stamped on our LP72s if we don't know the REE number? Or, more directly, is a hydro tester breaking regulations if he stamps the plus based only on the permanent expansion? It sounds like there is a published table (CG-5, whatever that is) that allows the hydro tester to calculate REE. Why couldn't I simply tell the hydro tester in my area to use this table to calculate REE for my tank and give the plus rating.

A couple more quick questions for Darrell. One, have you ever seen a 3AA scuba tank that passed hydro fail a plus rating? Two, the hydro guy in my area stamped the words "no plus" on my tank because he could not find the REE number. This annoyed me because I feel he should have simply stamped the date on his ID, and had no right to add his commentary about my tank due to his inability to administer the plus rating. My tank did not fail this test, it was simply omitted. However, as I'm sure you know, scuba fill stations are often manned by employees with very little knowledge about compressed air cylinders, and I'm worried that I won't even get a normal fill on these tanks, or that some stations will refuse to full them assuming they failed a plus test. So I guess my question is, did the guy break any rules by stamping these words on my tank?

Thanks!

 

[rstofer]

Richard, why don't you just call the hydro facility and ask them if they know the REE number.

Two reasons: First, I have no idea who did the hydro. The LDS sends them out and everything happens by magic. Sure, I can ask the LDS about the hydro facility but I'm trying to keep a low profile on the '+' rating.

Second, if it is an error, I don't want to create a dust-up. It will simply get resolved at the next hydro.

But, apparently the REE number should be in the CGA C-5 document. If I were interested, I could buy a copy but I'm just not. I am assuming that the hyrdo facility is competent, that they have the documents they are required to have and that they know how to test cylinders.

I have every reason to believe that the '+' is correct and no reason to believe it is not.

Richard

 

[SparticleBrane]

So, when you put it all together, one of the primary criteria for putting the plus mark on the cylinder it that the elastic expansion does not exceed the REE. It's all about the wall thickness, and if the elastic expansion exceeds the REE, it means we have lost wall thickness.

So it sounds like I was partially right. Cool.

The guys filling to 3600 and think its OK might want to buy some earplugs. You are approaching the pressure at which cycle fatigue occurs, and one day you might experience that BANG! I mentioned earlier.

On the other hand, this kind of overfilling has been going on for decades in certain parts of the country, and I can't honestly say I know of any case of an exploding cylinder due to overfilling in cave country (doesn't mean there haven't been -- just saying I haven't heard of any). If there have been, they are few and far between -- LP (2400+) cylinders are regularly filled to 3600+ day after day, week after week, but they aren't exploding in some kind of tank epidemic. Many of these cylinders are well into multiple hydro cycles. Just saying...

Ironically enough, I have heard of PST HP (3500psi) and exemption (3442psi) cylinders having issues passing hydro, but their LP cylinders that are consistently overfilled don't seem to have issues with passing.



On a slightly different note -- the life of a cylinder just sitting around at service pressure shouldn't have it's life reduced since this is lower than the fatigue range, correct? I have two 119s, a set of double 72s, and an Al80 just sitting around all at service pressure. I would much rather have them like this and be ready to dive, than have to run to the shop and get fills on short notice...


Darrell, thanks for the comments. Always nice to have more information thrown into the discussion, even if I am proved to be incorrect...

 

[Scared Silly]

Just pick up the REE from the table in C-5 and you're good to go.

BTW... you might notice some cylinders with the REE marked on them appear higher than the REE listed in C-5. That's because the numbers in C-5 are conservative numbers from the worst case designs submitted by mfg's with a built in safety factor to account for strays from nominal. So, you can always use the REE stamped on the cylinder by the mfg. That REE on the cylinder represents the actual value calculated for that cylinder, and it will always be slightly higher than what you find in C-5.

Great info THANKS.

As for finding the REE in C-5. I was in my hydro facility last week. While waiting I took look through the REE table. I did not find LP72 listed!!

 

[SparticleBrane]

As for finding the REE in C-5. I was in my hydro facility last week. While waiting I took look through the REE table. I did not find LP72 listed!!

The REE number for steel 72s is going to be the bane of our existence. I always have my ears perked, captain is always asking if anyone knows it...I know a few others want to know as well...


Why couldn't cylinder manufacturers just put relevant information on the crown of the cylinder?! Faber and PST didn't put anything about cylinder size for the longest time, and PST didn't put size or REE numbers on their 72s. The markings on a lot of cylinders were practically illegible for quite awhile too, until Worthington came along -- their marking are large, easy to read, and have all the information.

</rant>

 

[captain]

I try my best to dispel false information and learn as much as I can about tanks particularly steel 72's as they are all I use. I still use the first one I bought new in 1957 and it still passes hydro. I have 10 and they all stay full 95% of the time. I fill them myself and have always filled them to 2500 psi plus or no plus. If an extra 250 psi is going to blow me away it was my time to go.

I keep looking for the REE more out of curosity than anything else but it bugs me to a certain extent that the hydro testers don't put much effort into trying to do it. I can see if someone doesn't ask for it but if you do ask they should at least try and I wouldn't mind even if I have to pay extra.

 

[SparticleBrane]

captain, got any photos of your tank fleet? I'd love to see them.

 

[halocline]

If an extra 250 psi is going to blow me away it was my time to go.

Now that's the spirit!

BTW, thanks for the ZRC galvilite recommendation. I used it on my galvanized doubles and it worked great. I just used the spray cans. It's funny, those tanks were originally painted over galvanizing, but the galvanizing did not seem to be very tough. I wonder if PST just sprayed on galvanized primer or if they were hot dipped. The original dates on the tanks are 74 and 75, I think.