pony bottle question

[windapp]

There is, but its not the same type of fatigue. While any metal fatigue is bad, holding pressure keeps it at the same level of fatigue. Where as filling it allows it to contract, expand, and do all kinds of weird stuff.

Actually, this is not correct. Fatigue, by definition, is caused by cyclic loading. Metal does not fatigue under constant load (pressure in the case of a tank). Scuba tanks are designed for over 100,000 cycles, and will therefore never fail from fatigue over the life of the tank. When tanks fail hydro, it is not because they have fatigued from filling; it is because they have been damaged during handling and transportation.

 

[g1138]

Actually, this is not correct. Fatigue, by definition, is caused by cyclic loading. Metal does not fatigue under constant load (pressure in the case of a tank). Scuba tanks are designed for over 100,000 cycles, and will therefore never fail from fatigue over the life of the tank. When tanks fail hydro, it is not because they have fatigued from filling; it is because they have been damaged during handling and transportation.

Unless you're talking about Aluminum 6351 tanks that suffer from sustained load cracking at the threads. I wouldn't knock metal fatigue under constant pressure. Keep in mind there is 3000psi pounding back and forth on the walls of a tank; its gotta do something. Air molecules aren't completely static.

 

[Superlyte27]

You're a divemaster asking this question? Yikes....
Um, you VIP it once a year. You hydro it once every 5 years.

The DOT regs and the industry standards don't say, "you must inspect.... unless you don't use it, or breathe off of it, or neglect to fill it". LOL.

 

[Dr. Lecter]

You're a divemaster asking this question? Yikes....
Um, you VIP it once a year. You hydro it once every 5 years.

The DOT regs and the industry standards don't say, "you must inspect.... unless you don't use it, or breathe off of it, or neglect to fill it". LOL.

So how often would you have to get it hydroed if it was almost never used and there wasn't a 5 year (US/Can.) rule?

Actually reading the OP before making smart-ass remarks: too hard for some.

 

[dumpsterDiver]

Actually, this is not correct. Fatigue, by definition, is caused by cyclic loading. Metal does not fatigue under constant load (pressure in the case of a tank). Scuba tanks are designed for over 100,000 cycles, and will therefore never fail from fatigue over the life of the tank. When tanks fail hydro, it is not because they have fatigued from filling; it is because they have been damaged during handling and transportation.

I do not agree that only mishandled tanks fail. I saw one fail, less than 1 yr old tank.. just opened up a crack arounfd the threads when we completed filling it... leaking loud and fast... We ran inside the boat and stayed away from it and when we came back the tank was just barely fizzing, the 3/4" crack had closed up and the pressure was down to 1000 psi.. A Catalina tank... scared the crap out of me...

 

[mikeawags]

I work at a dive shop and I take care of tank visuals and sending them out for hydro. The tanks that I usually fail hydro are the ones that have been stored without pressure in them, and pony tanks that are just left at full pressure all the time. I'm sure someone will have something to say about that, but in my experience that's what I've seen. Tanks are designed to be filled and emptied, and not fail.

Sent during my 10' deco stop

 

[redacted]

You're a divemaster asking this question? Yikes....
Um, you VIP it once a year. You hydro it once every 5 years.

The DOT regs and the industry standards don't say, "you must inspect.... unless you don't use it, or breathe off of it, or neglect to fill it". LOL.

I believe that is exactly what the DOT regs say about hydro. A tank with expired hydro must be requalified before it can be filled but there is no prohibition against continuing to use the tank until a refill is required. For example, just because your emergency O2 tank has an expired hydro, there is no requirement to immediately drain and inspect the tank. It can continue in service until it is used and requires a refill.

"(ii) No cylinder required to be retested by paragraph (e)(1)(i) of this section may be
charged or filled with a hazardous material and transported in commerce unless that cylinder has been inspected and retested in accordance with this section and the retester has marked the cylinder by stamping the date of retest, the cylinder retester identification number unless excepted under this section, and any other marking required by this section. No person may mark a test date or a retester identification number on a DOT specification or exemption cylinder unless all applicable requirements of this section have been met. "

So what was it you found to be so funny?

 

[Superlyte27]

Actually reading the OP before making smart-ass remarks: too hard for some.

Oh, well let me correctly answer that....
You don't HAVE to do anything you don't want to do. But I thought we were working with common sense here. I'm sorry. Sometimes I expect too much of people.

These rules/guidelines aren't arbitrarily made. They are made to protect people's lives. I'll get out of the way now, proceed forward with your upcoming darwin award.

---------- Post added March 7th, 2013 at 07:29 PM ----------

I believe that is exactly what the DOT regs say about hydro. A tank with expired hydro must be requalified before it can be filled but there is no prohibition against continuing to use the tank until a refill is required. For example, just because your emergency O2 tank has an expired hydro, there is no requirement to immediately drain and inspect the tank. It can continue in service until it is used and requires a refill.

"(ii) No cylinder required to be retested by paragraph (e)(1)(i) of this section may be
charged or filled with a hazardous material and transported in commerce unless that cylinder has been inspected and retested in accordance with this section and the retester has marked the cylinder by stamping the date of retest, the cylinder retester identification number unless excepted under this section, and any other marking required by this section. No person may mark a test date or a retester identification number on a DOT specification or exemption cylinder unless all applicable requirements of this section have been met. "

So what was it you found to be so funny?

I think you are overlooking the purpose of the law. It's not about filling, it's about blowing up. I used to run a hydro facility. I've seen tanks that had just a cup of water in them for that made the inside of a steel tank look like a volcanic eruption of molten rust. So, if that tank with a cup of salt water was sitting for say 8 years, are the walls of that tank getting thinner and thinner every day with 3000psi of air in it? Yup, you betcha.

This law was written because there was no way for the DOT to govern 100,000 scuba divers, but they were able to govern the several thousands businesses that fill tanks. But regardless of that, their goal was to keep people from blowing up. Try not to miss that.

 

[Dr. Lecter]

Oh, well let me correctly answer that....
You don't HAVE to do anything you don't want to do. But I thought we were working with common sense here. I'm sorry. Sometimes I expect too much of people.

These rules/guidelines aren't arbitrarily made. They are made to protect people's lives. I'll get out of the way now, proceed forward with your upcoming darwin award.

Uh huh. They were precisely calibrated by wise and knowledgeable USG personnel and the final lines drawn involved no compromises with economics or feasibility. You probably think setting the drinking age at 21 was a scientifically optimal choice, too.

Which is not to say the 1 year vip/5 year hydro test rules aren’t actually a good approach even for a pony bottle that’s filled to 3000psi and then sees little to no change in pressure for several years of use—but your ‘THERE ARE LAWS FOR THIS AND OMFG HOW COULD YOU EVER SUGGEST THEY MIGHT NOT ENTIRELY COVER THIS SITUATION?!?!111’ isn’t much helping anyone see why it still might fit the circumstances described.

The OP’s question was a hypothetical inviting discussion, not a ‘gee, I bet I could get away with less safety!’ comment. If a mark of the educated mind is an ability to entertain and discuss an idea without embracing it, I guess we have an indicator as to where you fall in the scheme of things.

 

[redacted]

I think you are overlooking the purpose of the law. It's not about filling, it's about blowing up. I used to run a hydro facility. I've seen tanks that had just a cup of water in them for that made the inside of a steel tank look like a volcanic eruption of molten rust. So, if that tank with a cup of salt water was sitting for say 8 years, are the walls of that tank getting thinner and thinner every day with 3000psi of air in it? Yup, you betcha.

This law was written because there was no way for the DOT to govern 100,000 scuba divers, but they were able to govern the several thousands businesses that fill tanks. But regardless of that, their goal was to keep people from blowing up. Try not to miss that.

If your interpretation were correct, why do you think they chose to write "no cylinder ... may be charged or filled...." rather than the much clearer, "no cylinder may be used...." ? It would have been so much simpler.

Are you suggesting that it is OK for a tank to sit for 5 years or lwess with a cup of water inside; but not 8 years? BTW, that cup of water has little effect on the metal of my aluminum tanks.