Steel tank overfill damage?

[SparticleBrane]

4500 is nothing. I'd start worrying around 6000.

 

[CompuDude]

Wow, sorry to hear that.
But then what was it being overfilled to? Surely not something crazy like 4500psi???

Which brings me to my question a couple pages ago in this thread.. most overfills I hear about are filling LP tanks to HP-like pressures. Grossly overfilling HP tanks seem as common as overfilling AL tanks. (Read: pretty rare.)

So do people actually overfill(more than the usual hotfill 10% or less) HP tanks too?

No idea how much/often it was overfilled, again, I bought it used. I'd sure like to have words with the original owner, if I ever found them.

LP tanks, specifically the 3AA series, are the ones that are "safest" to overfill.

Or so they say.

HP and aluminum are not overfilled nearly as often. It's a lot harder to do (and requires really expensive compressors and/or boosters to get there), for one thing, of dubious safety (don't get me started) for the filler and the tank, and in the case of aluminum, considerably more fraught with peril ... for the filler moreso than the user.

 

[SparticleBrane]

LP tanks, specifically the 3AA series, are the ones that are "safest" to overfill.

Or so they say.

HP and aluminum are not overfilled nearly as often. It's a lot harder to do (and requires really expensive compressors and/or boosters to get there), for one thing, of dubious safety (don't get me started) for the filler and the tank, and in the case of aluminum, considerably more fraught with peril ... for the filler moreso than the user.

Did you read my post? The newer exemption tanks are much stronger than the old 3AA LP tanks...I'd have to say that that makes them safer to overfill.

Still--show me any incident of a tank exploding from a 3600psi cave fill (not involving oxygen tanks, that's another story by itself). I'd love to read one.
Your term of "fraught with peril" is a bit of exaggeration, wouldn't you say? They overfill hundreds of tanks to 3600 (or more) in north florida every day, day after day, with no issue.

 

[CompuDude]

Did you read my post? The newer exemption tanks are much stronger than the old 3AA LP tanks...I'd have to say that that makes them safer to overfill.

Still--show me any incident of a tank exploding from a 3600psi cave fill (not involving oxygen tanks, that's another story by itself). I'd love to read one.
Your term of "fraught with peril" is a bit of exaggeration, wouldn't you say? They overfill hundreds of tanks to 3600 (or more) in north florida every day, day after day, with no issue.

I did read your post, but I don't see any more proof of what you claim in your post than mine (referring to alloy strength). If you want to chase down links and posts, have at... I've said my piece.

The fraught with peril comment, if you read carefully, was specifically referring to aluminum tanks, which have been shown to fail rather spectacularly, as opposed the steel tanks simply failing hydro.

IMO, anything that causes a tank to fail hydro is nearly as bad as something that causes it to explode (nearly). A LOT of people in Fl. sell those drastically overfilled tanks as used just before needing hydro, and let the buyer beware. No thanks.

Fool me once...

 

[SparticleBrane]

I did read your post, but I don't see any more proof of what you claim in your post than mine (referring to alloy strength). If you want to chase down links and posts, have at... I've said my piece.

Enjoy:

As my name is mentioned, I will reply;

U.S.tensile strength (105,000-125,000 psi for 3AA cylinders) is not the same as European tensile strength (135,000-155,000 psi as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi for their 3AA cylinders (as required by DOT)

As an example, all of the E cylinders, Exempt or soon to be SP, Special Permit cylinders are made from a harder steel and cannot exceed 159,000 psi yield which exceeds 3AA tensile yield by as much as 50%. As you can see the E/SP cylinders being produced more closely follow the European metallurgy which allows for higher pressures.

view all the posts at
http://www.scubaboard.com/showthread.php?t=119180&page=2&highlight=tensile

I spoke with our engineers today and found that DOT 3AA cylinders have a typical tensile strength of 105,000-120,000 psi and Worthington's tensile strength on our X-Series (E-14157) is 135,000-155,000 psi with nominal at 145,000 psi which they tell me they hit "pretty well on the money" every time.

This demonstrates that a high pressure E cylinders is at least 30% higher tensile than 3AA cylinders.

 

[lamont]

Wow, sorry to hear that.
But then what was it being overfilled to? Surely not something crazy like 4500psi???

Which brings me to my question a couple pages ago in this thread.. most overfills I hear about are filling LP tanks to HP-like pressures. Grossly overfilling HP tanks seem as common as overfilling AL tanks. (Read: pretty rare.)

So do people actually overfill(more than the usual hotfill 10% or less) HP tanks too?

booster at the shop only goes to 3800 psi. if i'm not in a hurry i'll let the tanks cool and then run the booster until it shuts off, but thats still a rounding-error overfill...

 

[in_cavediver]

While I respect your experience (and number of dives), I think it is verging on gross negligence to encourage someone to overfill a tank. Just my take on the matter.

That said: 10% overfill is no big deal, on nearly any tank, but especially no big deal on hot fills, which cool to the correct fill.

And no offense, but if you have only been been cave filling PSTs for 5 years, that means you have NO IDEA if your tanks will fail hydro or not, since they only need hydro every 5 years.

I'm not saying any of your tanks will fail... in fact the odds are probably in your favor. But gambling with your tanks, and advising someone else to do the same with their tanks are two different things.

Sorry, I'm a little touchy on the subject since I bought a used PST tank that failed it's first hydro, 9 months after I bought it.

Thanks for the respect - don't know if its justified or not but thanks anyway

On the overfill issue. While I admit to doing it and feel the risks are manageable, I do not want to be known to encourage it. I may not have phrased my response very well to the individual who was concerned about 250-500psi over fills. Those 500psi or less overfills are nothing to worry about, especially if hot.

Personally, I am willing to trade tank life for gas capacity for some dives. I do not always overfill my tanks, only when the dive calls for or is better with more gas. Most of the time, I give them a hot 3000 which cools to 2500-2800. (still 210cft of gas vs the 275 or so at 3600). When its time to get new/additional tanks, I'll get 130's so its not an issue.

Oh on the old HP100's. A friend had a late 2001 vintage tank that during O2 cleaning in 2003 showed what can only be described as internal cracking. We sent the tank to PST after describing it and they sent a brand new one back. No questions asked. I wonder if your's failed for a similar reason.

 

[oxyhacker]

Yield strength is just one measure of how strong a tank is. Most steel alloys can be heat treated to various yield strengths. High numbers are impressive, but aim too high and the steel can become more brittle and less resistant to fatigue. So it is possible for a tank to be "stronger" in terms of ultimate tensile strength when new but still have a shorter service life or be less able to withstand abuse. The engineers, in designing a tank, aim for a good balance between strength and toughness, but it may be years before the tank had developed an extensive enough track record to know how well they succeeded. The record at this point (though admittedly mostly anecdotal) suggests that the HP exemption tanks, PSTs at least, fail hydro at a higher rate than the LP 3AAs, even though HP tanks are rarely overfilled, and LP tanks often.

It is also interesting to note that while aluminum tanks and steel exemption tanks are required to be cycled-tested, there is no such test requirement that I've been able to find for 3AAs.

Please note that this is not intended as an argument for overfilling LPs, but rather, as an argument for NOT overfilling HPs.

Did you read my post? The newer exemption tanks are much stronger than the old 3AA LP tanks...I'd have to say that that makes them safer to overfill.

 

[duckbill]

I may not have phrased my response very well to the individual who was concerned about 250-500psi over fills. Those 500psi or less overfills are nothing to worry about, especially if hot.

Yea, I didn't mean to start the whole cave diver overfill debate all over again. In fact, my original question was aimed toward the opposite end of the spectrum- that of being conservative to maximize the life of the tank. I really just was interested to find out how much the life of the tank could be shortened by an occasional and accidental 40% overfill, and if increased time at overfill would increase the damage. To me, permanent expansion is DAMAGE, since I'm aiming at keeping my tanks going for life.

I think I've gotten my answers, though, so just go on with the discussion.

As an addendum, the LDS owner realized what he had done when I asked him about his "40% overfill burst disc test". He forgot that the 50s were lower pressure than the 72s. That's O.K.

 

[DepthCharge]

While I respect your experience (and number of dives), I think it is verging on gross negligence to encourage someone to overfill a tank. Just my take on the matter.

That said: 10% overfill is no big deal, on nearly any tank, but especially no big deal on hot fills, which cool to the correct fill.

And no offense, but if you have only been been cave filling PSTs for 5 years, that means you have NO IDEA if your tanks will fail hydro or not, since they only need hydro every 5 years.

I'm not saying any of your tanks will fail... in fact the odds are probably in your favor. But gambling with your tanks, and advising someone else to do the same with their tanks are two different things.

Sorry, I'm a little touchy on the subject since I bought a used PST tank that failed it's first hydro, 9 months after I bought it.

I've "Cave Filled" when I dove OC, went thru 2 hydro's with plus ratings. Still over fill on RB tanks......3500 in 2640's just been hydroed with "+" rating