Gotta love the 72

[jbrians]

I dropped my 1971 Healthways branded tank for a hydro on Tuesday.
Picked it up today and the LDS employee (about 19 yr/old) was just filling it with air before handing it over to me. Apologised for not being able to bring it right up to max because they only had a 4000lb air bank.
She said my tank passed with only 58ml of displacement and 1ml permanent stretch. I wonder what she tested it at???
So now I have a 72 that had just shy of 4000psi in it. I expect it's OK but I don't really know. I bleed about 1500psi out. The shop says they will replace it, basically tank for tank if there is a problem with it.
So my next question is...what is tha max pressure a stock RAM will operate at?

I think an AL tank would have been all over the room with that kind of percentage over pressure.

 

[Luis H]

The first stage of the RAM is the same as the Conshelf, the Titan, and similar to many other diaphragm regulators. It can and will operate at the same pressures.

The only limiting factor is the yoke. The long yoke in most RAM will easily handle 3000 and it should not have any problems with 3500 psi.

The good thing with a yoke is that its failure mode would be slight elastic stretching with the consequences that the O-ring will let go before there is any permanent damage.

To reduce the chances of an O-ring blow out, just make sure to tighten the yoke screw…just don’t use a wrench.

If you have a RAM with the heavy yoke (a late model 1973) then 4000 psi or higher is no issue.

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

 

[jbrians]

Yeah...I thought the hydro pressure was below 4000 psi. Needless to say I was surprised to pick it up with 4000 psi of air in it and standing in the corner ready to go for me.
Would you recommend condemning this tank for future use given it had 4000 psi in it for half an hour or so? I think it should be fine but I'm no expert.

 

[DA Aquamaster]

a steel 72 with 4000 psi in it is a 115(!)

I don't think having 4000psi in it for an hour or so would be an issue.

 

[Gilldiver]

I am more surprised that the blow out plugs didn't let go, I bet they are a bit weak now. If I was you I would request new blow out assemblies be instaled at the next fill.

As for the tanks, you should still be in the elastic range of the tank at Hydro pressure. But if you have any questions, have the shop re-Hydro the tanks and then you will know that they are good or bad.

Pete

 

[Luis H]

I am more surprised that the blow out plugs didn't let go, I bet they are a bit weak now. If I was you I would request new blow out assemblies be instaled at the next fill.

As for the tanks, you should still be in the elastic range of the tank at Hydro pressure. But if you have any questions, have the shop re-Hydro the tanks and then you will know that they are good or bad.

Pete

That is exactly what I was going to suggest.

Have the shop re-hydro it.

The tank was taken above it hydro pressure, which is kind of the low end of its yield strength. Since it was over stressed it is possible (but not likely) that there was some work hardening which could affect the material's ductility.

The ductility/ elasticity is what the hydro test is measuring. You want pressure vessels to be elastic, not brittle.

As I mentioned it is unlikely that the material was affected since the over stress was minimal, but a hydro test can tell if it is OK.

The amount of time that it was over stressed is actually basically irrelevant. Steel is not time dependent under static loads.


BTW, also have them change the burst disk and ask them to use the correct burst disc for that pressure cylinder. It sound like they put a burst disk for a 3000 psi tank in it. The burst disc for a 2250 psi tank should have let go at 3750 psi max (the same as the hydro pressure).

Good luck

 

[Nemrod]

I use a permanent marker and write in bold letters at the base of the valve on the tank the fill pressure. Even at that the fill monkeys have routinely filled my 72s to 3,000 psi. Now I don't mind them doing that to my steel 85cf LP Fabers but I really wish they would stop doing that to my 72s.

Look, this is sexist, sorry, it is simply my experience, never turn your tanks over to a woman for a fill without watching her do it. Why did she put 4,000 psi in it for a fill? I don't understand, what are we missing here?

I am with the others, have the blow out plugs replaced, have the tank re-hydroed by a competent facility at the shops expense, if it fails they owe you a new tank. Since LP steel 72s don't grow on trees how is that going to happen?

N

 

[duckbill]

She said my tank passed with only 58ml of displacement and 1ml permanent stretch. I wonder what she tested it at???

Did she hydro-test it? I doubt it. Most shops send the tanks out to a separate hydrotesting facility.
It's nice she told you the figures. Now, if you have it retested you can point to the numbers indicating any damage they caused with their overfill- if any. You're probably O.K.

Ditto the others.

 

[jbrians]

The shop has their own test equipment to hydro tanks and SHE did the testing.
I'm going to ask to see the log to determine what pressures were used. She was very surprised when I pointed out to her that it was a LP tank and not a fancy new HP one. I've just discovered one thing. If your equipment looks too good, it's given the respect vintage stuff deserves...
Good advice about the blow out disc. I forgot all about that.

 

[Luis H]

Something here just doesn’t sound right. A hydro test technician making this kind of error is very bad. We are talking about some serious human error.

The hydro test technician is supposed to record the serial number, tank pressure and type of tank that he / she is testing. Most hydro test facilities (even dive shops) do many different types of tanks with many different pressures in order to stay in business.

It is not uncommon for a small hydro test facility (like in a dive shop) to be doing paint ball tanks and other odd small cylinders.


If she hydro tested that cylinder like if it was a higher pressure cylinder, she should have had a lot more permanent deformation (material yielding) than she reported. On the other hand the elastic expansion that you reported seems kind of high for that cylinder, but still with in spec. Actually, IMO with that elastic deformation that can still be “+” stamped, but just barely.


I recommend that you ask her to show you and explain the whole hydro test process. You may learn something and she hopefully will review the procedures and be more careful.

Part of the procedure should include the pre-test procedure per PST bulletin D-100, but at this point it is kind of academic since the cylinder has probably being well rounded out.