That's not really a "defect" it's a trait of the stronger but thinner walls and heat treating giving the walls a "set" that is slightly out of round. It doesn't' effect strength but the volume slightly increases when the tank is pressurized not only from elastic expansion but also from the tank "rounding out". It's like a flat fire hose becomes round as it fills. The proper procedure for those tanks is to do a slightly lower pressure hydro to "round out" the cylinder before the hydro test.
Plus ratings and hydros'
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That's not really a "defect" it's a trait of the stronger but thinner walls and heat treating giving the walls a "set" that is slightly out of round. It doesn't' effect strength but the volume slightly increases when the tank is pressurized not only from elastic expansion but also from the tank "rounding out". It's like a flat fire hose becomes round as it fills. The proper procedure for those tanks is to do a slightly lower pressure hydro to "round out" the cylinder before the hydro test.
SparticleBrane
Contributor
Right, I am familiar with the pre-test (talked with Luis about it at length awhile back
). I am saying that cylinders are failing even with that. Then again, many aren't. So who knows?My fiancee and I have a set of PST LP72s from the 70s -- I believe 74 and 78, although the dates are starting to get a bit difficult to read. They are hot-dipped (or at least look like it) and don't have any rust at all. Prettiest 72s I've seen yet.
Tamas
Contributor
WOW Nelly! LOT of info at once to digest
Looking for Coles notes
captain
Contributor
captain
Contributor
captain, got any photos of your tank fleet? I'd love to see them.
The tank farm
Attachments
rstofer
Contributor
Captain,
I'm more interested in the compressor! What are you using?
Richard
I'm more interested in the compressor! What are you using?
Richard
captain
Contributor
They were made by Luchard of France in the 60's and 70's and sold by US Divers as the Cyclone. I have two of them. The one in the picture I bought in 1968. It has been updated with a better filtration system and aluminum frame. It is rated at 3.5 cfm @ 2800 psi. It is an all cast iron, low RPM unit.
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ctcdg
Registered
OK Guys, I was afraid of this!!! I will try to answer questions, but I just don't have a whole lot of time to go through individual questions when MUCH of this is what I cover in my training courses (I just got back from one, and have to leave Saturday for another!).
Richard,
Ahhhh... reason and logic, I love it! You are absolutely correct in your thinking.
The "+" marking for 110% fill is valid. So, the question is how did the retester do it? 49 CFR 180.215(b)(2) specifies that the test report must include the method by which the average or maximum wall stress was computed. Ask your retester to provide that information. He better have it, since it is a federal requirement. You say later that you don't know who it was. There is a RIN number stamped between the month and year of the requal. It goes in a clockwise fashion, so for A123, "A1" would be over "32" (notice the "23" is reversed). You can look it up on the DOT website or you can email me and I'll tell you who it was.
Mattboy,
That is correct, he is not following the reg's if he doesn't check the wall stress, and record how he did it.
CGA pamphlet C-5 does give REE numbers for common industrial gas and medical gas cyl's. REE's for SCUBAS are not listed. However, the calculations are there in an easier format than the CFR - there is even an example of how to do the calc's. (Keep reading, I'm going to get you guys the REE's.)
Yes, failing hydro means you exceeded 10% permanent expansion, which means the cylinder yielded (like bending the paperclip). Exceeding the REE means you have lost some wall thickness, which does not mean the cylinder will fail hydro. So, you would no longer get the plus rating, but the cyl could remain in service so long as it did not exceed 10% permanent expansion.
You are absolutely correct. That is unauthorized marking (see 180.213), he had no business putting that on the cyl.
You're welcome, but your previous comments (post #13, second half) SCARE ME!!! Your suspicions are wrong!! All cylinders are built to a specific wall thickness (called Tmin) based on their specification and service pressure. While it is true that mfg's overshoot the minimum to make sure any deviations keep within tolerance, you cannot simply say that it's OK to fill to higher pressures. You have convinced your LDS to violate federal regulations. Yes, that cylinder would pass a test at 4000, but if you are still "comfortable" filling to 3000 all day long, you need to go back and read my previous post.
SparticleBrane... you REALLY scare me!!
Each year we have incidents on fill lines. Every year or two a fill operator is killed or maimed, or both. The statement is generally, "Gee, THAT never happened before!" It only takes one to ruin your whole day (spelled L-I-F-E). Apparently you weren't listening, or didn't understand what I was saying about cycle life and fatigue failure. Most incidents can be tracked back to not following the regulations.
As I mentioned before, hydro isn't likely to pick up a fatigue issue. Fatigue failure is sudden and catastrophic. Just ask someone who has experienced it... Oh, I guess you can't, most of them are dead. WD8CDH nailed this one. If you have a cylinder that was put through the 90% "pre-test" and it still failed hydro, it is either a BAD cylinder, or a leak (generally at the test connection). [Scared Silly: I will address your post in a separate reply.]
*** EVERYBODY READ THIS!!! ***
You are correct. In fact 180.205(c) even states that a cylinder may remain in service until empty. When properly filled and stored at atm below 130Ž°F (Hmmm, can't get the degree symbol to come out right, that's 130 degrees F) there is no issue with fatigue. BTW it is ALWAYS best to store cyl's at service pressure or empty (5-10 psi will keep moisture out, and is safe). However, storing cyl's with the 500psi reserve air is DANGEROUS. If there is a fire and the cylinder is stored at service pressure, as the heat rises the pressure increases until the safety will blow and vent down in a safe manner (P=T/V). However, at 500psi, as the heat of the fire increases, the pressure increases, but not enough to blow the safety. Then the cylinder will reach the temperature at which it loses its heat treat strength properties, and the cylinder will explode with far more than 500psi (due to the heating of the gas) without ever blowing the safety. 350 F for aluminum and 650 F for steel are where cylinders are damaged. Fires begin at 450 F and can quickly reach 1000 F to 2000 F.
*******
This is correct. This phenomenon is especially true for the HOT DIPPED galvanized cylinders.
That TC stuff was for you, buddy!
Yep, PST hot dipped.
OK, now for you die-hards who have made it through all this.
I will post the REE values for PST SCUBAS on my website. You can refer your retester to my website, ctcseminars.com, for the values. Give me a week to get them on the webpage.
(Now for the shameless sales plug...) More importantly, if the guy testing your cylinder hasn't been to a CTC training course, I WOULDN'T TRUST HIM WITH YOUR LIFE!!! Seriously, you guys aren't alone. NOBODY seems to really understand this stuff. The average incoming score on the test at one of my classes is about 25 out of 100 questions (and that's for people who have been testing cyl's for 5-10 years!!). Some of you sound like retesters... Get to a class! Getting a rubber stamped piece of paper for your Hazmat Training requirement from someone who doesn't know what they're doing is like going diving with some
who never got certified. If you are testing cylinders and didn't know the answers to these questions, I must assume you haven't had proper training.
Take care, keep safe, DON'T OVERFILL CYLINDERS!!!
Darrell
Richard,
Ahhhh... reason and logic, I love it! You are absolutely correct in your thinking.
The "+" marking for 110% fill is valid. So, the question is how did the retester do it? 49 CFR 180.215(b)(2) specifies that the test report must include the method by which the average or maximum wall stress was computed. Ask your retester to provide that information. He better have it, since it is a federal requirement. You say later that you don't know who it was. There is a RIN number stamped between the month and year of the requal. It goes in a clockwise fashion, so for A123, "A1" would be over "32" (notice the "23" is reversed). You can look it up on the DOT website or you can email me and I'll tell you who it was.
Mattboy,
That is correct, he is not following the reg's if he doesn't check the wall stress, and record how he did it.
CGA pamphlet C-5 does give REE numbers for common industrial gas and medical gas cyl's. REE's for SCUBAS are not listed. However, the calculations are there in an easier format than the CFR - there is even an example of how to do the calc's. (Keep reading, I'm going to get you guys the REE's.)
Yes, failing hydro means you exceeded 10% permanent expansion, which means the cylinder yielded (like bending the paperclip). Exceeding the REE means you have lost some wall thickness, which does not mean the cylinder will fail hydro. So, you would no longer get the plus rating, but the cyl could remain in service so long as it did not exceed 10% permanent expansion.
You are absolutely correct. That is unauthorized marking (see 180.213), he had no business putting that on the cyl.
You're welcome, but your previous comments (post #13, second half) SCARE ME!!! Your suspicions are wrong!! All cylinders are built to a specific wall thickness (called Tmin) based on their specification and service pressure. While it is true that mfg's overshoot the minimum to make sure any deviations keep within tolerance, you cannot simply say that it's OK to fill to higher pressures. You have convinced your LDS to violate federal regulations. Yes, that cylinder would pass a test at 4000, but if you are still "comfortable" filling to 3000 all day long, you need to go back and read my previous post.
SparticleBrane... you REALLY scare me!!
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...
Each year we have incidents on fill lines. Every year or two a fill operator is killed or maimed, or both. The statement is generally, "Gee, THAT never happened before!" It only takes one to ruin your whole day (spelled L-I-F-E). Apparently you weren't listening, or didn't understand what I was saying about cycle life and fatigue failure. Most incidents can be tracked back to not following the regulations.
As I mentioned before, hydro isn't likely to pick up a fatigue issue. Fatigue failure is sudden and catastrophic. Just ask someone who has experienced it... Oh, I guess you can't, most of them are dead. WD8CDH nailed this one. If you have a cylinder that was put through the 90% "pre-test" and it still failed hydro, it is either a BAD cylinder, or a leak (generally at the test connection). [Scared Silly: I will address your post in a separate reply.]
*** EVERYBODY READ THIS!!! ***
You are correct. In fact 180.205(c) even states that a cylinder may remain in service until empty. When properly filled and stored at atm below 130Ž°F (Hmmm, can't get the degree symbol to come out right, that's 130 degrees F) there is no issue with fatigue. BTW it is ALWAYS best to store cyl's at service pressure or empty (5-10 psi will keep moisture out, and is safe). However, storing cyl's with the 500psi reserve air is DANGEROUS. If there is a fire and the cylinder is stored at service pressure, as the heat rises the pressure increases until the safety will blow and vent down in a safe manner (P=T/V). However, at 500psi, as the heat of the fire increases, the pressure increases, but not enough to blow the safety. Then the cylinder will reach the temperature at which it loses its heat treat strength properties, and the cylinder will explode with far more than 500psi (due to the heating of the gas) without ever blowing the safety. 350 F for aluminum and 650 F for steel are where cylinders are damaged. Fires begin at 450 F and can quickly reach 1000 F to 2000 F.
*******
This is correct. This phenomenon is especially true for the HOT DIPPED galvanized cylinders.
WOW Nelly! LOT of info at once to digest
That TC stuff was for you, buddy!
Yep, PST hot dipped.
OK, now for you die-hards who have made it through all this.
I will post the REE values for PST SCUBAS on my website. You can refer your retester to my website, ctcseminars.com, for the values. Give me a week to get them on the webpage.
(Now for the shameless sales plug...) More importantly, if the guy testing your cylinder hasn't been to a CTC training course, I WOULDN'T TRUST HIM WITH YOUR LIFE!!! Seriously, you guys aren't alone. NOBODY seems to really understand this stuff. The average incoming score on the test at one of my classes is about 25 out of 100 questions (and that's for people who have been testing cyl's for 5-10 years!!). Some of you sound like retesters... Get to a class! Getting a rubber stamped piece of paper for your Hazmat Training requirement from someone who doesn't know what they're doing is like going diving with some
who never got certified. If you are testing cylinders and didn't know the answers to these questions, I must assume you haven't had proper training.Take care, keep safe, DON'T OVERFILL CYLINDERS!!!
Darrell
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ctcdg
Registered
Scared Silly,
I would have a couple of concerns. The first being that the other cylinder had 7% perm. As you said if they were sistered together, they both should have experienced the same conditions. 7% is actually a somewhat high permanent expansion - but, as Mason said to Dixon, "You gotta draw the line somewhere!". So, that cylinder passed, but with high perm.
So, what happened? Well, either the one cylinder was bad, or there was a leak. Your analysis was right on. If the other cylinders tested before these and after these were OK, then the system must have been OK. However, we do see situations where there is a leak at the test connection that only affects a couple of cylinders. Depending on the type of spud or adapter that was being used, we can see leaks that occur at lower pressures, but then seal up and stop leaking at higher pressures (an o-ring will sometimes do this). In that case, there is water leaking out of the connection at lower pressures (adding to the expansion), but once there is enough pressure, the leak seals up and stops. So, when the cylinder reaches test pressure it holds, and doesn't look like a leak. But when we bleed back down, all that water that was leaking out of the test connection is now permanent expansion, and the cylinder fails the test. The only way to find this problem is to repeatedly pressurize to low pressures (200 - 500 psi) and see if there is a leak and/or permanent expansion occurring. I'm assuming that wasn't done by the retester, so the cylinder was rightfully condemned. This looks like a failed cylinder, and he did what he was supposed to do. This can be really tricky, because what you described is EXACTLY what a cylinder will do when it fails. You get high perm, and the higher the pressure you go to, the higher the permanent expansion goes. If you look at a stress-rupture curve with expansion plotted over pressure, cylinders expand in a linear fashion until they reach the yield point - then the curve goes logarithmic. Just a little more pressure induces a lot more expansion (the cylinder is yielding, it's deforming and it just keeps getting worse).
So, I am NOT going to question your retester. He did what he was supposed to do. But, you asked what could have happened, and there are some tricky issues that occur that don't always get caught until they repeat themselves.
Generally, the proper procedure is to do another "pre-test" below 90% of test pressure if you fail the first one (so long as you stay below 90% of test pressure, you're OK). The fact that you failed the pre-test means either something went wrong, or the cylinder is REALLY bad. So, if you do another pre-test, and the cylinder still comes back with high perm, something is wrong. Once the cylinder has been to a specific pressure, it has been stretched out, and will not experience much more permanent expansion at that pressure. So, the second pre-test should come back very close to zero. You really shouldn't go up to full test pressure until you get a successful pre-test. (You might suggest that to your retester.)
Hope that helps.
Darrell
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