Point being, I knew that before an engineer told me, as did everyone else in this file
So "data" that comes from the real world can be just as valid and be used just as well as data from scientists and engineers.
Roak
Overpressurizing / Overfilling steel tanks
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So "data" that comes from the real world can be just as valid and be used just as well as data from scientists and engineers.
Roak
Question joewr...
If an [in the know] Faber engineer came up and told you "We design our cylinders to take 10k cycles of 4.5k psi without failure" would you then agree that overfilling is Ok?
or, also from Faber:
The same LP cylinders in the US are rated for use at 4.5k psi in Europe?
Roak
If an [in the know] Faber engineer came up and told you "We design our cylinders to take 10k cycles of 4.5k psi without failure" would you then agree that overfilling is Ok?
or, also from Faber:
The same LP cylinders in the US are rated for use at 4.5k psi in Europe?
Roak
Roaky,
But like the Greek philosopher, I will answer it with another question: if a Ford engineer told you it was safe to corner an Explorer at 70 mph even though the company recommendation was 35 mph, would you do it?
I guess I did not make my point clear enough. What I was saying was that there is data about failure rates at the various pressures discussed. And that the lower pressures recommended by the mfg will have lower failure rates--perhaps, even "0". As you exceed the recommendations, you will have higher failure rates. What I have not seen is the data that tells one what those rates are. I would hazard a guess that one could get that info from the companies in question, but I do not know. With the data in hand, then one can truly evaluate the risk. Otherwise, one is relying on "real world experience" which may not have had sufficient "experience" to be statistically significant.
Data, Roak, was what we used to design reactors and systems that make scuba tanks look like tinker toys. But, we also used data to design systems that were not much more elegant than a scuba system.
And, one more thing...when one is only dealing with one's own health, safety and life, that is one thing. But when one starts recommending things to others, that is a very different situation.
So, I come back to my original point, get the data. I would be more "believing" if you had written that you had the failure data for the tanks and that at 3000 psi, under proper conditions, there were no failures for, say, 10,000 cycles of pressurization/depressurization. Whereas, at, say 4500 psig, the failure rate was 2 in 10,000 cycles. But I have never heard anyone cite data; I have only heard anecdotes...
Let's get back to the engineer...I spent most of my life with engineers and, I found, that like all humans, they come in many varieties. Some were more risk taking than others. Thus, in technical organizations, "final" technical decisions are not usually made by a single engineer, scientist, or manager. They have to pass the muster of several responsible souls. So, no, I would not just hang on the advice of one engineer. And neither do you when you strap on that gear that we all love so much! Believe me, even that simple little dive mask has a lot of data that went into the design...you probably do not want the lens to crack on one of your cave dives in a silty environment...or the lens to be pushed out of its mounting... Data collected by design engineers is what makes that avoidance possible...
Sorry for the long answer...
Joewr...oh yes, am I allowed to agree with you about something? Doubling of lights...good idea...I think Barbara and I will do that on our next night dive...
But like the Greek philosopher, I will answer it with another question: if a Ford engineer told you it was safe to corner an Explorer at 70 mph even though the company recommendation was 35 mph, would you do it?
I guess I did not make my point clear enough. What I was saying was that there is data about failure rates at the various pressures discussed. And that the lower pressures recommended by the mfg will have lower failure rates--perhaps, even "0". As you exceed the recommendations, you will have higher failure rates. What I have not seen is the data that tells one what those rates are. I would hazard a guess that one could get that info from the companies in question, but I do not know. With the data in hand, then one can truly evaluate the risk. Otherwise, one is relying on "real world experience" which may not have had sufficient "experience" to be statistically significant.
Data, Roak, was what we used to design reactors and systems that make scuba tanks look like tinker toys. But, we also used data to design systems that were not much more elegant than a scuba system.
And, one more thing...when one is only dealing with one's own health, safety and life, that is one thing. But when one starts recommending things to others, that is a very different situation.
So, I come back to my original point, get the data. I would be more "believing" if you had written that you had the failure data for the tanks and that at 3000 psi, under proper conditions, there were no failures for, say, 10,000 cycles of pressurization/depressurization. Whereas, at, say 4500 psig, the failure rate was 2 in 10,000 cycles. But I have never heard anyone cite data; I have only heard anecdotes...
Let's get back to the engineer...I spent most of my life with engineers and, I found, that like all humans, they come in many varieties. Some were more risk taking than others. Thus, in technical organizations, "final" technical decisions are not usually made by a single engineer, scientist, or manager. They have to pass the muster of several responsible souls. So, no, I would not just hang on the advice of one engineer. And neither do you when you strap on that gear that we all love so much! Believe me, even that simple little dive mask has a lot of data that went into the design...you probably do not want the lens to crack on one of your cave dives in a silty environment...or the lens to be pushed out of its mounting... Data collected by design engineers is what makes that avoidance possible...
Sorry for the long answer...
Joewr...oh yes, am I allowed to agree with you about something? Doubling of lights...good idea...I think Barbara and I will do that on our next night dive...
Since I'm not a Greek philosopher, but an engineer whos used to answering questions when asked, Ill answer the question.
If a Ford engineer told me it was safe to corner an Explorer at 70 mph and I felt it was safe to corner a Ford Explorer at 70 mph and a whole bunch of Florida cave divers told me that they've been cornering their Explorers at 70 mph for years without any problems, you bet I would.
In fact, even if NO Ford engineer told me it was safe to corner my Explorer at 70 mph and I felt it was safe to corner a Ford Explorer at 70 mph and a whole bunch of Florida cave divers told me that they've been cornering their Explorers at 70 mph for years without any problems, I'd corner it at 70 mph.
Once again we're at that impasse where you think engineers and scientists have some monopoly on good, usable data. Aint so. Just like the data *I* collected over the years let me know that letting go of a weight belt above my foot is a bad idea, even before joew the engineer told me so. Ya know, I just realized that no engineer or scientist has told me that joew is really an engineer, so his statement is now suspect
In addition, by picking something that is unsafe (cornering an Explorer at 70 mph) for your analogy, you've used your conclusion (overfilling is unsafe) to support your argument. As an engineer you should realize that that is a flawed argument.
Despite the flawed analogy, I gave you an answer to your question (readers digest version: yes, with stated conditions), how about you me give an answer to my question?
Roak
Ps. In case I wasn't clear, the 4.5k psi for 10,000 cycles resulted in zero failures. My question is if this is a design parameter for the cylinder, would you fill it to 3.5k even if it was stamped 2400+?
First off Roak, I believe that JoeWR did answer your question.
Secondly, I agree with Joe, that if some rogue engineer decides to disagree with his company that does not make him a credible source. In fact, that someone would jeopardize his company only makes his motivations suspect.
Thirdly, define abuse. Could it be that fast or overfilling of tanks would be defined as abuse? It would to me. Could it also include holding pressure for sustained periods? Hey, I fill my tanks to 3500 (yes, they ARE 3500 tanks) and then let them sit until I dive... I fill them up the next day. All of my tanks stay at their max rated load 24/365. Thats a lot of time containing a lot of pressure. Now, lets factor in weak spots from manufacturing, and scratches and dents that occur while under pressure. How about normal thermal shock from filling, hot trunks, and submersion into colder waters? A perfectly round steel object (a sphere) has the greatest strength, both in compression as well as tension. Tanks are cylinders, though and not spheres, and their shapes are often modified by dents, scratches and what not. Even a small alteration to the shape of a cylinder has dramatic effects on the actual strength of the vessel. Could it be that we are introducing some work hardening here? Are we overlooking factors that should be considered? Is there stress being introduced that is not so obvious? All of these factors are cumulative, some even acting as multipliers as to how they affect the final strength of the vessel.
As for the failures of the various metals, they differ significantly. Steel has a far greater elastic AND plastic range (how it deforms) than aluminum. If you pull a steel bar to failure, you will notice very little deformation until the end. Immediatly prior to fracture, the steel necks down (the narrow part will be less than half of the nominal diameter of the specimen) into an hourglass shape until it fractures at a 45 degree angle. Al on the other hand necks down very little and the resulting fracture is far more oblique (@ 75 degrees if memory serves me right). While various cracks may be evident on the aluminum specimen, there will be none on the steel specimen. Heating or cooling either specimen has a resounding effect on these properties. This is why steel splits and aluminum shatters.
Unlike some, I have yet to see a tank fail. I have, however buried a co-worker who had a sidewall blow out on a tire while he was inflating it that was only 35 psi, and still deadly. Many tires are speed rated, and many people ignore the rating when buying tires But, I dont drive that fast is a common excuse. No, but you sometimes brake that fast and sometimes corner that hard. You need all of the strength of that speed rated tire. I do not pretend to understand all of the factors that are in effect on my cylinders. I have been guilty of letting shops overfill my LP tanks. I do believe that there is more there than either side has covered. Consequently, I think I will err on the side of caution. If I need more air; Ill simply dive with duals or carry some stage bottles. Right now, I am fine with my HP 120 s for the foreseeable future.
Finally, I would never attempt a 70mph turn on an Exploder even with Goodyear Eagles on them. I also refrain from pissing in the wind, filling up Pintos and arguing with JoeWR. Go figure
:tease:
Secondly, I agree with Joe, that if some rogue engineer decides to disagree with his company that does not make him a credible source. In fact, that someone would jeopardize his company only makes his motivations suspect.
Thirdly, define abuse. Could it be that fast or overfilling of tanks would be defined as abuse? It would to me. Could it also include holding pressure for sustained periods? Hey, I fill my tanks to 3500 (yes, they ARE 3500 tanks) and then let them sit until I dive... I fill them up the next day. All of my tanks stay at their max rated load 24/365. Thats a lot of time containing a lot of pressure. Now, lets factor in weak spots from manufacturing, and scratches and dents that occur while under pressure. How about normal thermal shock from filling, hot trunks, and submersion into colder waters? A perfectly round steel object (a sphere) has the greatest strength, both in compression as well as tension. Tanks are cylinders, though and not spheres, and their shapes are often modified by dents, scratches and what not. Even a small alteration to the shape of a cylinder has dramatic effects on the actual strength of the vessel. Could it be that we are introducing some work hardening here? Are we overlooking factors that should be considered? Is there stress being introduced that is not so obvious? All of these factors are cumulative, some even acting as multipliers as to how they affect the final strength of the vessel.
As for the failures of the various metals, they differ significantly. Steel has a far greater elastic AND plastic range (how it deforms) than aluminum. If you pull a steel bar to failure, you will notice very little deformation until the end. Immediatly prior to fracture, the steel necks down (the narrow part will be less than half of the nominal diameter of the specimen) into an hourglass shape until it fractures at a 45 degree angle. Al on the other hand necks down very little and the resulting fracture is far more oblique (@ 75 degrees if memory serves me right). While various cracks may be evident on the aluminum specimen, there will be none on the steel specimen. Heating or cooling either specimen has a resounding effect on these properties. This is why steel splits and aluminum shatters.
Unlike some, I have yet to see a tank fail. I have, however buried a co-worker who had a sidewall blow out on a tire while he was inflating it that was only 35 psi, and still deadly. Many tires are speed rated, and many people ignore the rating when buying tires But, I dont drive that fast is a common excuse. No, but you sometimes brake that fast and sometimes corner that hard. You need all of the strength of that speed rated tire. I do not pretend to understand all of the factors that are in effect on my cylinders. I have been guilty of letting shops overfill my LP tanks. I do believe that there is more there than either side has covered. Consequently, I think I will err on the side of caution. If I need more air; Ill simply dive with duals or carry some stage bottles. Right now, I am fine with my HP 120 s for the foreseeable future.
Finally, I would never attempt a 70mph turn on an Exploder even with Goodyear Eagles on them. I also refrain from pissing in the wind, filling up Pintos and arguing with JoeWR. Go figure
:tease:
Sorry if I did not make myself clear (and going back over my posts, this was my fault).
Faber's (the company as a whole) design specification for their LP cylinders is zero failures for 10k fills at 4.5k psi. This is not a "rogue" engineer's statement. This is what their cylinders are designed to handle and a specification that they are tested against.
However, because of DOT rules and regulations, they can only be used up to 2400 (plus the + rating).
So, joewr, for the moment let's assume that someone handed you a Faber company document that stated that 10k cycles at 4.5k psi with zero failures is a true COMPANY design and testing specification for their product. Would you overfill?
Roak
Ps.
Of course neither would I, because my real-world experience says it's unsafe. I just didn't want to deal with some "Well if you wouldn't corner at 70 mph then why would you overfill?" statement, like the two had anything to do with each other
and no one could see my point...
The 10,000 fills were probably in an ideal environment under ideal circumstances (wasn't there, can't know for sure, but it's a basic inference). The fill rate, discharge rate, and condition of the tanks were optimum. Once in the real world, those "optimum" conditions evaporate and are replaced by lazy/tired fill techs and tanks banging around in the back of the truck. There are valves taking a hit here and there and all sorts of non-ideal, non-optimum real world happenings that will introduce stress and fatigue into the pressure vessel. Add to that equation manufacturer induced issues, such as the tank being built or inspected at 4:30 on a Friday afternoon before a Labor Day weekend, and I can see why Faber, PST or any manufacturer would want to keep their fudge factor high. Are they even on record asking DOT to increase the rating on their tanks?
Murphy's law is as real and present today as it ever was. Constants aren't and variables won't is the corollary that comes to mind. I should know... it was Murray's law before that typo at the printers. Don't mess with Murphy or Murray, cause we're still haggling over who should get the credit! If I have learned anything about manufacturers, its that they will ALWAYS present their products in the best light consider the Firestone/Explorer debacle. If you listen to either manufacturer, their products were designed by the engineering Gods and are perfect. Together they can be lethal (not my opinion, just read the paper) even WITHOUT trying to turn at 70 mph. No, I refuse to own either an Exploder OR a Firestone tire. You don't have to drop that weight belt on these toes... I get the picture. If I need more air, I will just have to carry more tanks. That, or get into a better shape... this soft round one doesn't work too well and uses waaayyyy to much air.
:tease:
Tire tip #238... never cross an Exploder with a Hotrock... it will ignite!
The 10,000 fills were probably in an ideal environment under ideal circumstances (wasn't there, can't know for sure, but it's a basic inference). The fill rate, discharge rate, and condition of the tanks were optimum. Once in the real world, those "optimum" conditions evaporate and are replaced by lazy/tired fill techs and tanks banging around in the back of the truck. There are valves taking a hit here and there and all sorts of non-ideal, non-optimum real world happenings that will introduce stress and fatigue into the pressure vessel. Add to that equation manufacturer induced issues, such as the tank being built or inspected at 4:30 on a Friday afternoon before a Labor Day weekend, and I can see why Faber, PST or any manufacturer would want to keep their fudge factor high. Are they even on record asking DOT to increase the rating on their tanks?
Murphy's law is as real and present today as it ever was. Constants aren't and variables won't is the corollary that comes to mind. I should know... it was Murray's law before that typo at the printers. Don't mess with Murphy or Murray, cause we're still haggling over who should get the credit! If I have learned anything about manufacturers, its that they will ALWAYS present their products in the best light consider the Firestone/Explorer debacle. If you listen to either manufacturer, their products were designed by the engineering Gods and are perfect. Together they can be lethal (not my opinion, just read the paper) even WITHOUT trying to turn at 70 mph. No, I refuse to own either an Exploder OR a Firestone tire. You don't have to drop that weight belt on these toes... I get the picture. If I need more air, I will just have to carry more tanks. That, or get into a better shape... this soft round one doesn't work too well and uses waaayyyy to much air.
:tease:
Tire tip #238... never cross an Exploder with a Hotrock... it will ignite!
Bob3
Contributor
Hey, I wonder what you were dreaming about last night, eh? or did ya even get any Z-time in?
I have a set of 4400psi doubles, and it's not only a pain in da butt finding a place to fill them, the hydro pressure is over 12kpsi, meaning that the $8 hydros don't apply to those bad boys.
Even tho they're by a "European" company (Interspiro) the guys not only have a US DOT rating, the suckers were made in West Allis (Milwaukee).
I do suspect that the way US companies do business (cover their butts) plays a role in tank ratings, because the US obviously has the wherewithall to crank out HP tanks with a US DOT rating, & that started over 30 years ago.
BTW, Officer Chuck actually had an aluminum tank 'till I introduced him to the evils of "Satan's metal".
He was a worthy pupil.
I have a set of 4400psi doubles, and it's not only a pain in da butt finding a place to fill them, the hydro pressure is over 12kpsi, meaning that the $8 hydros don't apply to those bad boys.
Even tho they're by a "European" company (Interspiro) the guys not only have a US DOT rating, the suckers were made in West Allis (Milwaukee).
I do suspect that the way US companies do business (cover their butts) plays a role in tank ratings, because the US obviously has the wherewithall to crank out HP tanks with a US DOT rating, & that started over 30 years ago.
BTW, Officer Chuck actually had an aluminum tank 'till I introduced him to the evils of "Satan's metal".
He was a worthy pupil.
Ok, I have two people reaching the same conclusion but joewr argues that you can only believe the manufacturers information and that real world data doesn't count and NetDoc says that you cant always believe the manufacturers information and that real world data counts.
I can't debate against two positions that totally contradict each other, so... Uncle
Time to stop flogging the deseased equine.
However, still when in Rome I'll do as the romans do...
Roak
You have misquoted/misinterpreted what I said...
Testing pressure... 10k cycles at 4500... This is done under ideal conditions. Lets show them just how STRONG and BUFF our product is. Sure we eliminated most of the variables of the real world, but our tanks hold a lot of air. Heck, even Microsoft products work under lab conditions.
Service pressure... whatever is on the tanks... These are for LESS than ideal conditions. Lets give them something safe to work with that won't have a chance of popping in their face when the tanks roll around in the back of their pickup. Exceed these parameters at your own peril. Unfortunately, Microsoft has yet to make allowances for field conditions. Thank goodness, they don't design/label tanks.
However, I agree with you about the deceased equine... Some people will almost always err on the side of caution, some merely live to throw it to the wind. Most are somewhere in between... You can not debate ones propensity for risk taking.
:tease:
As for mimicking the Romans; I refuse to wrestle another man in the nude...
Testing pressure... 10k cycles at 4500... This is done under ideal conditions. Lets show them just how STRONG and BUFF our product is. Sure we eliminated most of the variables of the real world, but our tanks hold a lot of air. Heck, even Microsoft products work under lab conditions.
Service pressure... whatever is on the tanks... These are for LESS than ideal conditions. Lets give them something safe to work with that won't have a chance of popping in their face when the tanks roll around in the back of their pickup. Exceed these parameters at your own peril. Unfortunately, Microsoft has yet to make allowances for field conditions. Thank goodness, they don't design/label tanks.
However, I agree with you about the deceased equine... Some people will almost always err on the side of caution, some merely live to throw it to the wind. Most are somewhere in between... You can not debate ones propensity for risk taking.
:tease:
As for mimicking the Romans; I refuse to wrestle another man in the nude...
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