The Final Word on + Ratings?

[Chocula]

Last winter I took some old PST LP72 in for hydro. The shop did not have REE but I did thanks to Certified Training Company - Hazmat Training Seminars. A month later they looked up the test numbers did the calcs and viola a shinny +.

Do they have to test the tank at a higher pressure to qualify for the + stamp, or is the test the same, but the amount it expands determines if it fails, passes, or passes with + rating?

-Chocula

 

[Scared Silly]

Do they have to test the tank at a higher pressure to qualify for the + stamp, or is the test the same, but the amount it expands determines if it fails, passes, or passes with + rating?

-Chocula

No the plus rating is based on the 5/3 test and the measured expansion that is used for the "+".

 

[Nwcid]

This is what I was looking for, you're the man!

Do you think it's a big problem if I go into a shop somewhere and a kid that doesn't know an old 72 from an AL80 gives me a 3000 fill?
Not all the time, but once in a while?
Would you keep your mouth shut or would you say something?

I've never heard of a 72 that has a current hydro and is in good shape blowing up from a 3000 fill, but I have heard of AL 80's blowing up.

Well the hydro test of 5/3 would be 3750 psi. Hydro pressure is NOT burst pressure. I have 2 sets of these tanks as doubles. I generally fill to 2500 psi which gives me 80cf/tank.

You might want to do some more reading on "tanks blowing up". Obviously if ANY tank blows up it is NOT in good shape even if it has a current hydro, which can be almost 5 years previous. This is a whole different subject with TONS of threads on it.

 

[underH2Oman]

Look at the second row. If they don't say "TC" (Transport Canada) they are not legal for use in Canada. All TC stamped tanks are now dual rated in metric.

There are some exceptions as indicated on Transport Canada's website.
Repealed Section 7.32 - Transport Canada

Looks like as long as it was in use in Canada pre 1993 it is good to go..

(ii) CFR 49, or an exemption in respect of packaging and handling issued pursuant to Subpart B of Part 107 of CFR 49, and the cylinder or tube has displayed on it the letters «ICC» or «DOT» and was in use in Canada before January 1, 1993.

 

[Chocula]

No the plus rating is based on the 5/3 test and the measured expansion that is used for the "+".

So to clarify, a steel 72, that originally had a working pressure of 2250 and a + rating would be be tested at 3750 (5/3 of 2250) if no + rating is requested, and 4125 (5/3 of 2475) if one is requested?
The question then becomes, is it worth the increased risk of failure for the additional capacity.

 

[Dr. Lecter]

So to clarify, a steel 72, that originally had a working pressure of 2250 and a + rating would be be tested at 3750 (5/3 of 2250) if no + rating is requested, and 4125 (5/3 of 2475) if one is request.
The question then becomes, is it worth the increased risk of failure for the additional capacity.

No. The tank is tested to 5/3 of working pressure (2250) and passed/failed depending on REE being within spec. If that REE figure is also within the more stringent spec for a + rating, one may be applied.

One hydro test pressure. One expansion number resulting from said test. Two different ranges within which the test result may (or may not) fall.

 

[Chocula]

No. The tank is tested to 5/3 of working pressure (2250) and passed/failed depending on REE being within spec. If that REE figure is also within the more stringent spec for a + rating, one may be applied.

One hydro test pressure. One expansion number resulting from said test. Two different ranges within which the test result may (or may not) fall.

Ok, that is what I was attempting to ask the first time. I think I then misinterpreted the response from Scared Silly. Thank you for the clarification.

 

[halocline]

No. The tank is tested to 5/3 of working pressure (2250) and passed/failed depending on REE being within spec. If that REE figure is also within the more stringent spec for a + rating, one may be applied.

One hydro test pressure. One expansion number resulting from said test. Two different ranges within which the test result may (or may not) fall.

Sort of. The tank is placed in a column of water and filled with water, there's no air in the tank. The displacement of the tank is carefully recorded, by measuring the water level in the column. The tank is then pressurized to test pressure (in this case 3750) and the tank expands. This expansion is measured by the change in water level in the column. (there's a system of tubing, I believe, to facilitate this) The total expansion is recorded in CCs. Then the tank is depressurized and the final water level is recorded. So you have three numbers; pre test displacement, total expansion, post test displacement. If the difference between pre test and post test displacement is less than 10% of the total expansion, the tank passes hydro. It's a measure of elasticity, basically measuring if the tank returns to near-enough it's original volume.

The plus rating is simply, does the total expansion not exceed a number of CCs assigned to the particular tank by the manufacturer, called the REE number, often stamped right on the tank. This is why it's SO STUPID that many hydro shops have trouble dealing with it.

 

[Nwcid]

Hydrostatic testing of scuba cylinders - divecellar.com - YouTube

Here is another showing the tanks actually being made, then hydro, Making Worthing Steel Scuba Cylinders - YouTube

 

[Luis H]

Here are some instructional videos from Hydro-Test Products. I am familiar with their hydro test machine.

This is very good detail information of how to do a water jacket hydro test (the typical hydro test).


Hydro-Test Instructional Video for Cylinder Testing
The procedure for cylinder testing to DOT requirements

Hydro-Test Instructional Video for Cylinder Testing - YouTube


Hydro-Test Calibrated Cylinder Verification Procedure
An Instructional video for cylinder re-qualifiers showing the proper procedure for test system verification to DOT requirements. For cylinder testing equipment visit hydro-test.com

Hydro-Test Calibrated Cylinder Verification Procedure - YouTube



Hydro-Test Water Jacket Cylinder Test System Setup.wmv
Instructional video on setting up of a new cylinder test system

Hydro-Test Water Jacket Cylinder Test System Setup.wmv - YouTube



For 3AA cylinder the test pressure is always 5/3 of the stamped pressure.
For a steel 72, stamped at 2250 the test pressure is 3750.

The basic pas/ fail criteria is residual (permanent) expansion has to be less than 10% of the total expansion.

In addition to passing the basic criteria, to get the + stamping, the elastic expansion has to be less than the REE (Rejection Elastic Expansion) number.

The elastic expansion is the total expansion minus the residual (or permanent) expansion.