Tanks Rated Pressure ???

[ermaclob]

So ive been wanting to know, why is it that the Department of Transportation (DOT) rate LP tanks to 2400 /2640. Its my understanding, as a and example Faber, rates there steel tanks to work at much higher pressures, with service pressure ~4000 and catastrophic failure happening at close to 6000 Psi more or less.

more over, if you look up "faber steel tanks uk" on google you find that all the tanks for sale are rated to no less then 232 Bar = 3364 psi and some rated to 300 Bar = 4351 psi

maybe im miss informed, but after reading some threads it seems a tank can be made at the company and sent to the U.S. and get a Lp stamp but another identical one get sent to the U.K. and get a HP stamp..... whats up with that?

 

[Luis H]

The Department of Transportation (DOT) does not rate any tanks. The manufacturer designs, builds, and rates their tanks based on their design. They do have to comply with the DOT Code of Federal Regulations (CFR) requirements during the design, but so does Faber or any other manufacturer that sells tanks in the US.

FABER tanks built and stamped under DOT rules meet all the same requirements.

If it is a DOT 3AA code it has to meet the same design stress criteria. And that is why 3AA cylinders at higher pressure are often so heavy and negative.

There are three basic variables in pressure cylinder design (other variables are much less critical): Cylinder diameter, wall thickens, and allowable material stress. The designer can adjust the first two in other to meet the design requirements, but the allowable material stress may require new materials and special permits.

There are plenty of cylinders built under DOT regulations (for US market) designed to higher pressures (both in 3AA code and Special permit materials). It is just determine by what pressure the manufacturer designed them to.

 

[ermaclob]

The Department of Transportation (DOT) does not rate any tanks. The manufacturer designs, builds, and rates their tanks based on their design. They do have to comply with the DOT Code of Federal Regulations (CFR) requirements during the design, but so does Faber or any other manufacturer that sells tanks in the US.

FABER tanks built and stamped under DOT rules meet all the same requirements.

If it is a DOT 3AA code it has to meet the same design stress criteria. And that is why 3AA cylinders at higher pressure are often so heavy and negative.

There are three basic variables in pressure cylinder design (other variables are much less critical): Cylinder diameter, wall thickens, and allowable material stress. The designer can adjust the first two in other to meet the design requirements, but the allowable material stress may require new materials and special permits.

There are plenty of cylinders built under DOT regulations (for US market) designed to higher pressures (both in 3AA code and Special permit materials). It is just determine by what pressure the manufacturer designed them to.

Does not really answer my question, Im asking why 2 identical tanks can get different ratings depending on the country, the U.S. Being more strict about it then over seas.

 

[Scared Silly]

maybe im miss informed, but after reading some threads it seems a tank can be made at the company and sent to the U.S. and get a Lp stamp but another identical one get sent to the U.K. and get a HP stamp..... whats up with that?

You are misinformed and have been reading about a myth that has been debunked ad nauseum. The cylinders have the same external form factor but they are made from different alloys. Different alloys have different strengths. Also IIRC there is also a difference in wall thickness. Thus they are not identical.

 

[Luis H]

How do you know they are identical?
Do you have fabrication drawings and matetial specifications?
A small diffetence in wall thicness or different steel and they are totaly different tanks.
It is very likely that they are different matetal. The alloys specified under 3AA have being around since before WWII.

 

[ermaclob]

How do you know they are identical?
Do you have fabrication drawings and matetial specifications?
A small diffetence in wall thicness or different steel and they are totaly different tanks.
It is very likely that they are different matetal. The alloys specified under 3AA have being around since before WWII.

Same question apples to you my friend, do you have fabrication drawings and material specifications? im in the search of proof, with out it i can only assume whats what through reasoning and what information others provide.

so if this has been debunked already can you provide the proof for it

the way i see it is, if i was faber or whatever company, and i had a tank i wanted to make/sell. Why would i conform to anyones standards other then my own when designing the tank, especially when i know that i can make a tank that super exceeds the Pressure rating of who ever regulates fill pressure. In other words why would i lower production standard to a lower grade when i can just give them what i know works and have the legal entity regulate it however they want. Also how cost effective would it be to have production lines for a every specific government agency...

I have a very strong feeling that this whole thing is just the DOT being over cautious with there rating on tanks. as i am aware there no tanks in the U.S. that the DOT rates at 300 bar... but those tanks defiantly do exist over seas. adding to all this is the subject of "cave fills" which make me wonder even more if tanks in the U.S. are just underrated.

 

[halocline]

Same question apples to you my friend, do you have fabrication drawings and material specifications?

Luis is an engineer and does have a lot of knowledge of the structural properties of scuba tanks. I don't know if he has the materials on hand that will satisfy you, but in general he's very accurate with his statements about scuba equipment.

The only thing that I am aware of that's different in the U.S. is the plus rating system; my understanding is that tanks that are 2400 PSI (+ 10% to 2640) in the U.S. are simply 2640 in some other countries. But I don't know the details.

There are other differences between DOT rules and those of other countries, for example hydro test is more frequent in some other countries than in the U.S. AFAIK.

 

[Scared Silly]

Same question apples to you my friend, do you have fabrication drawings and material specifications? im in the search of proof, with out it i can only assume whats what through reasoning and what information others provide.

so if this has been debunked already can you provide the proof for it

As my 5th grade teacher would say - the answer is left as an exercise for the student.

Hint: you bring up Faber so why don't you contract them directly instead of challenging those of us who you obviously do not believe and whom have already done their research.

As for your business sense (or really lack there of) in making a cylinder that would "

super exceed" the ratings regardless of requirements. Why would a company piss away money on what is not required?​

 

[ermaclob]

As my 5th grade teacher would say - the answer is left as an exercise for the student.

Hint: you bring up Faber so why don't you contract them directly instead of challenging those of us who you obviously do not believe and whom have already done their research.

As for your business sense (or really lack there of) in making a cylinder that would "

super exceed" the ratings regardless of requirements. Why would a company piss away money on what is not required?
​

Im not challenge in anyone, all im saying is that there is a lot of talk about this subject on these forums as well as other places you may seek out this info. Though no one ever backs up there claims with sources etc. So the creditability of everyones claim is lacking. That's why i come asking here. As im defiantly not the first to ask around about this.

You again ask me "Why would a company piss away money on what is not required?" its is the same exact thing i was saying in my last post. Why drop the cash on designing and mass producing 8 different tank, when you can design 4 that will that will still meat requirements in both market places. how much do you think it cost to prototype, test, and keep quality control on more and more tank models. This argument is kinda irrelevant, what really matters is that someone can confirm the difference in tank martial, wall thickness, other relevant specs between similar tanks from the same manufacturer in different locations. Which you might just be right, i may only be able to get this info from the manufacturer.

 

[Scared Silly]

No there is not much talk about on this particular subject. Do a search on this board and you find this same discussion with the same results. It is all a myth that has been debunked.

Read this thread (note the date of the thread and the date of the original post some 6 years ago):

http://www.scubaboard.com/forums/tanks-valves-bands/410067-overfilling-life-expectancy-lp-tanks.html

http://www.scubaboard.com/forums/ta...g-life-expectancy-lp-tanks-3.html#post6217847

My sources are Faber and their USA importer Blue Steel as well a few others such as Lee (aka Lead King) whom I have had direct communications. As said if you want real confirmation seek them out with your questions.

As for the mfg design, production, and QA again talk to the mfg. However, I can give you a good example. I just took a part a light module for a car. It comes in one outer case with the same electronics board but it gets configured 16 different ways just to save the cost on resistors and led modules that probably cost pennies. (i.e. the board is same but components on the board are different). Might seem silly but they certainly went through the cost analysis and I know cylinder mfg do the same.