Hydro data- steel 72 pressures and REE

[duckbill]

For the purposes of a hydro, what is considered the "service pressure" of a steel 72? Is it the marked 2250psi, or the pressure at 72CF, being 2475psi?

In other words, would the test pressure be 3750psi (2250 X 5/3), or 4125psi (2475 x 5/3)?

I have a 72 where a hydro guy used a test pressure of 4166, based on a service pressure of 2500 (?!).

Also, he used an REE of 70. My 72s so far have qualified for the 10% overfill "+" rating, since the elastic expansions have fallen within a range of 60-62. Somewhere here, I read one poster who gave the REE for a steel 72 as being 58.4, in which case none of my 72s would qualify for the "+" rating, which would seem odd. Does anyone know where the 58.4 REE figure came from, or what the correct REE for the old steel 72s is?

 

[halocline]

The 58.4 REE came from a PST document that was posted here as a pdf. In terms of legality, it would apply only to the PST tanks covered by that document.

The test pressure is 3750. If the guy used 4166 he made a mistake. Who ever would have thought that a hydro shop would be less-than-perfect? (dripping with sarcasm...)

I would not surprise me that your LP72 would exceed the REE if the guy used the wrong test pressure. Maybe you could bring it back to him and kindly suggest that he try again, with the correct pressure? Or, just go someplace else.

 

[Luis H]

The test pressure for a 2250 psi tank is 3750 psi.

The REE came from a PST document. You can find a copy here:
http://ctcseminars.com/Files/PST REE values.pdf

You should take a look at this thread:
http://www.scubaboard.com/forums/tanks-valves-bands/277461-plus-ratings-hydros-2.html

In particular take a look at posts #69, #75, etc.


Your hydro tester doesn’t seem to know what he is doing.


Added:
Don’t be surprised if that tank fails hydro in the near future. By pressurizing it above the test pressure he is getting more permanent expansion than it is designed for (going into the low end of the yield strength) and therefore he has worked hardened the tank some. It may not have any consequence, but it may.

 

[Scared Silly]

To answer your first question - the service pressure is what is marked on the cylinder.

At this point I would not be talking to the tester but the owner. The actual pressure must be with in +1% of the required test pressure of 3750psi. In other words I would be asking for a new cylinder.

 

[Leadking]

To answer your first question - the service pressure is what is marked on the cylinder.

At this point I would not be talking to the tester but the owner. The actual pressure must be with in +1% of the required test pressure of 3750psi. In other words I would be asking for a new cylinder.

Exactly!!!! The test pressure was exceeded by almost 400psi. This may have damaged the cylinder. a replacement cylinder is called for.

 

[duckbill]

Thanks to all for the help on this. Well, at those pressures it's no wonder the elastic expansions are what they are. I will not be using this guy again, and may even confront him as to why he lists the service and test pressures so high (well above the allowed +1%). However, doing so will probably result in my being alienated by a couple of local dive shops who use him.

Thanks, Luis, for those links. Too bad about the typo of "3AA250" for "3AA2250". I suspect some hydro facilities might be leary of trusting the document because of that typo due to liability concerns. I read through that linked thread and it was very informative. I hope I can find a local hydro-tester who will bear with my being certain they know what they are doing, and that they perform the proper tests on my cylinders.

Here's another question regarding the rounding out procedure. Is it necessary for the data to be recorded during the rounding out, or is it just necessary to do the preliminary pressurization? Also, I saw that the rounding out test pressure has to be less than 90% of the hydro test pressure. Is 80% of hydro test pressure the normal rounding out pressure? I think I remember reading that, but all the saved pages on that are on my other computer that is currently disconnected and in "quarantine".

 

[Luis H]

There is no data collection during the round out procedure since that is not actually part of the test.

The 90% is the maximum allowed pressure by CFR49 without it being considered a miss-test. A miss-test (I am sure I am not using the correct term, but it is something like that) is a test where there was an equipment malfunction or similar occurrence. A miss-test can be repeated (as opposed to a fail test), but the test pressure is increased by 100 psi (or 1% of test pressure, whichever is the smaller, in this case 100 psi).

You can do a round out to 80%, but the higher the pressure, the more physically effective the procedure is. Therefore I insist on doing it to 90% on all steel tanks. At 90% it follows the codes and it is most beneficial.

A couple of weeks ago, I hydroed two steel 72 that were given to me and after a proper round out procedure they had a perfect test score. There was basically no readable permanent expansion. I held them at 3350 psi (90% of 3750 is 3375) for almost a minute before dropping the pressure back to zero and setting the burette back to zero to start the test.

 

[Scared Silly]

Thanks to all for the help on this. Well, at those pressures it's no wonder the elastic expansions are what they are. I will not be using this guy again, and may even confront him as to why he lists the service and test pressures so high (well above the allowed +1%). However, doing so will probably result in my being alienated by a couple of local dive shops who use him.

Honestly I would not worry about that. If nothing else report the tests to DOT and request an inspector visit. DOT will go over all of their hydros and more ...

 

[captain]

There is no data collection during the round out procedure since that is not actually part of the test.

The 90% is the maximum allowed pressure by CFR49 without it being considered a miss-test. A miss-test (I am sure I am not using the correct term, but it is something like that) is a test where there was an equipment malfunction or similar occurrence. A miss-test can be repeated (as opposed to a fail test), but the test pressure is increased by 100 psi (or 1% of test pressure, whichever is the smaller, in this case 100 psi).

You can do a round out to 80%, but the higher the pressure, the more physically effective the procedure is. Therefore I insist on doing it to 90% on all steel tanks. At 90% it follows the codes and it is most beneficial.

A couple of weeks ago, I hydroed two steel 72 that were given to me and after a proper round out procedure they had a perfect test score. There was basically no readable permanent expansion. I held them at 3350 psi (90% of 3750 is 3375) for almost a minute before dropping the pressure back to zero and setting the burette back to zero to start the test.

Luis, how much expansion did you see during the round out.

 

[duckbill]

Honestly I would not worry about that. If nothing else report the tests to DOT and request an inspector visit. DOT will go over all of their hydros and more ...

...if I can remain anonymous I may do that, though I really, really hate to "snitch". However, this isn't a one-time occurence. Every data sheet I have gotten from him shows he has over pressurized all my tanks. He liststed my 1800 PST tanks as having service pressures of 1960, and pressurized to test pressures of 3633. According to my calculations, he should have pressuized to 3000, or 3300 maximum (assuming the 5/3 rule is correct for these tanks).

Nobody likes to be told how to do their job, so I make it a rule to try to refrain from getting too involved with preliminary questions and requests when dealing with "professionals" in any field since it always strains the relationship from the beginning. But, situations like this prove that vigilance is necessary. Once the damage is done, it is done.

Are hydo-testers required by law to provide the accurate data to the owner of the cylinders upon request, or is it just a courtesy for them if they do? When the data sheet shows 4166 as being the test pressure, does that mean that it was the actual test pressure (within the tolerances of the equipment used- seems "4166" is to the nearest 1 psi to me!)?