Plus ratings and hydros'

[phillybob]

I've done a search of this and I think I found an answer, but I'll ask anyway. Does a lp 2400 with a plus rating (2640) automatically loose that plus rating after it's first hydro ?
There needs to be some type of structural defect found for that to happen, correct ? I defer to the experts... Thanks.

 

[fdog]

Testing for the "plus rating" (elastic expansion) is a different test from the one used for the general 5 year hydrotest (permanent expansion). Not all hydrotest facilities will test for the 10% overfill, as it is extra work; it is worth asking for to make sure you can get the plus if possible.

It will lose the + rating if:

• The test facility does not perform the additional test for the rating, or
• The cylinder does not pass the additional test

Once a cylinder no longer is marked with the plus (for example, the shop didn't do the test), it isn't gone forever. If the cylinder is tested for the plus at the next hydrotest, and passes, it may again carry the 10% overfill.

173.302(b)

(b) Filling limits. (See Ž§173.301(e).)

(c) Special filling limits for Specifications 3A, 3AX, 3AA, 3AAX, and 3T cylinders. Specifications 3A, 3AX, 3AA, 3AAX, and 3T (Ž§Ž§178.36, 178.37, 178.45 of this subchapter) cylinders may be charged with compressed gases, other than liquefied, dissolved, poisonous, or flammable gases to a pressure 10 percent in excess of their marked service pressure, provided:

(1) That such cylinders are equipped with frangible disc safety relief devices (without fusible metal backing) having a bursting pressure not exceeding the minimum prescribed test pressure.

(2) That the elastic expansion shall have been determined at the time of the last test or retest by the water jacket method.

(3) That either the average wall stress or the maximum wall stress does not exceed the wall stress limitation shown in the following table (see Notes 1, 2 and 3):

Steels of analysis and heat - treatment specified in spec. 3AA
Average wall stress limitation 67,000
Maximum wall stress limitation 73,000

(4) That an external and internal visual examination made at the time of test or retest shows the cylinder to be free from excessive corrosion, pitting, or dangerous defects.

(5) That a plus sign (+) be added following the test date marking on the cylinder to indicate compliance with paragraphs (c) (2), (3), and (4) of this section.

All the best, James

 

[NorthWoodsDiver]

I had several tanks (LP72's) that I took in last year for hydro and they all were in great shape yet I didn't get the plus stamp. The place told me they didn't check for i cause I didn't ask but they would recheck for an additional charge.

Being who I am I figured I would just stick with filling them to 3000psi instead of 3400psi (cave fill).

Its only an issue if someone else fills your tanks, in which case go to harbor freight or other cheapo store and buy a set of punches and put the hydro stamp on yourself.... I didn't just say that.

 

[luckydays]

I thought LP72's were only rated for 2400 psi without the plus. Your place fills them to 3000. How sweet is that.

 

[phillybob]

... in which case go to harbor freight or other cheapo store and buy a set of punches and put the hydro stamp on yourself.... I didn't just say that.

That thought crossed my mind...

 

[NorthWoodsDiver]

Yes LP 72's are rated to something like 2400psi. We fill our own tanks and do what we want at our own risk. People have forever filled LP steel tanks (2400psi ish) to 3500psi!!! for technical diving, its coined a cave fill and not something any dive shop is likely to do.

I wouldn't try this with tanks that appear to be lacking (IE the pipe thread ones or tanks with excessive internal or external rust) and its probably not a good idea to ask your dive shop to fill them to 3000 unless you have a really good relationship with them. It comes down to liability and common sense, just like most things these days.

People have varied opinions on what pressures of overfill are acceptable and what are not and also for how long to leave them pressurized. my sidemount lp72's were filled last fall to about 3100psi and have sat all winter that way...

 

[tc]

I had several tanks (LP72's) that I took in last year for hydro and they all were in great shape yet I didn't get the plus stamp. The place told me they didn't check for i cause I didn't ask but they would recheck for an additional charge.

Being who I am I figured I would just stick with filling them to 3000psi instead of 3400psi (cave fill).

Its only an issue if someone else fills your tanks, in which case go to harbor freight or other cheapo store and buy a set of punches and put the hydro stamp on yourself.... I didn't just say that.

If you want to overfill your tanks yourself, then your just putting yourself at risk, therefore your problem.

Advocating alteration of hydro marks isn't needed for that- it's only needed to get someone else to fill it to a higher pressure, and creating greater risk for them. Sorry, but in my opinion that is incredibly irresponsible to suggest that.

 

[SparticleBrane]

Testing for the "plus rating" (elastic expansion) is a different test from the one used for the general 5 year hydrotest (permanent expansion). Not all hydrotest facilities will test for the 10% overfill, as it is extra work; it is worth asking for to make sure you can get the plus if possible.

fdog, you usually post great stuff but I have to disagree with you on this one. "Testing for the plus" is literally comparing one number to another to see if one is smaller than the other. One of these numbers is a result of a standard hydro test, the other is the REE number stamped into the cylinder.


NorthWoodsDiver, the reason you didn't get the + on LP72s is because no one seems to know the REE number that is required to test for the +.


Testing for the + is NOT a huge amount of extra work. Here's how a standard hydro test is performed:

• The cylinder is pressurized to hydro pressure, and the displacement in mL is recorded. This is the Total Expansion.
• The pressure is released, and the amount of expansion left over is Permanent Expansion.
• Total Expansion - Permanent Expansion = Elastic Expansion (how much the tank expanded and contracted during the test).
• Was the permanent expansion 10% or less than total expansion? If so, then the cylinder passes hydro.
• Here is the "extra work:" -- Is Elastic Expansion < Rejection Elastic Expansion (REE)? If yes, then +. If no, then no + rating.

For a numeric example -- this is information from a hydro test on a PST LP80 I had awhile back:
Since this is an LP cylinder, the service pressure is 2400psi. 5/3 of 2400 = 4000. Thus, the hydro pressure is 4000psi.

• REE is 66.3mL as stamped into the side of the cylinder.
• Total expansion was 56.3mL.
• Elastic expansion was 56.0mL.
• Permanent expansion was 0.3mL.

First, did the cylinder pass hydro?
10% of 56.3mL = 5.63mL. Is 0.3mL < 5.63mL? Yes. Thus the cylinder passed hydro.

Does the cylinder get a + rating?
REE = 66.3mL
EE = 56.0mL
Is 56.0 < 66.3? Yes, thus the cylinder qualifies for the + rating.


Why some hydro shops don't "test for the plus" (effectively performing some 1st grade math) is completely beyond me. It literally takes 2 seconds to see if one number is less than another number, especially when most testers don't have to look far for these two numbers: one is usually stamped into the cylinder, and the other is a result of the hydro test.

 

[fdog]

Sparticle, you always post excellent information, and it is a pleasure to see you on the boards.

It's entirely possible I'm incorrect. The source of my information is a hydrotest tech here in town; he passed on to me that they have two different methods to test expansion, a water jacketed method and a direct expansion method.

The water jacket is permissible to test for the 10% + rating, and the direct expansion method is not. At least that's what he said. If you want to requalify for the + rating, you should ask for it, otherwise they use the faster direct expansion test.

As always, a pleasure to see you on the board!


All the best, James

 

[SparticleBrane]

James, thanks for the information. I will have to see what I can dig up on this matter -- it is entirely possible (with my luck, "probable" might be a better description ) that I am way off base.

I will investigate and return...


--Charles
PS: I thought your recent batch of information about scooter thrust was particularly interesting. Keep up the good work, we are all ears!