Is a 2 ply cylinder as strong as a 1 ply twice the thickness?

[Stormer]

If you want to make a cylinder of for example 4 mm thick steel but you just have 2 mm sheet available to roll into a cylinder and weld it. If you then roll 2 cylinders with 2 mm wall thickness and make sure one is the right size for a interference fit over the other and then heat the larger one to shrink fit it over the smaller one will the resulting cylinder then be as strong in tension and against buckling from external pressure as a solid 4 mm wall cylinder would be?

And would there be any point in spot welding the 2 cylinders together after shrink fitting them? Or is the friction from the interference fit so strong that the spot welds make no difference?

 

[Lnewqban]

You will not be able to achieve anything close to interference fit working with two rolled pieces of sheet metal.

 

[DaveC426913]

Not sure if this is relevant but I bought two sono tubes the same size and discovered inadvertently that they naturally nest. How? A very slight taper.

If two "identical" steel cylinders were made that had a slight taper, could you hammer them together for a tight fit?

 

[Baluncore]

Big gun barrels are made by shrinking tubes onto the barrel. The outer hoop tension causes compression of the inner, that is then better placed to withstand positive internal pressure before yielding, because zero on the stress-strain diagram has been moved.

Spot welding is unnecessary, and would be bad because it causes local stresses, and prevents full plastic settlement of the shrunk assembly.

 

[Stormer]

You will not be able to achieve anything close to interference fit working with two rolled pieces of sheet metal.

Why? What if you used some turned mandrel to put inside and outside of the rolled and welded sheets to make sure they where round?

 

[Lnewqban]

That is just the way it is, in my experience working with sheet metal.
The edges can't be bent by the rollers as round as the middle area, and any welding introduces deformations to the edges and increase of wall thickness.

But assuming that miraculously you achieve two tight 2 mm cylinders, their combined resistance to pure traction and compression will be similar to a single 4 mm cylinder, but their resistance against buckling due to bending or compression, will be reduced.

Why do you believe that "buckling from external pressure" will occur?
It should not, if that pressure is equally distributed all around the external cylinder.

 

[Baluncore]

I believe that resistance to buckling is proportional to t³.
A 4 mm sheet will have t³ = 64.
A 2 mm sheet will have t³ = 8.
Two x 2 mm sheets will have 2 x t³ = 16.

 

[Stormer]

I believe that resistance to buckling is proportional to t³.
A 4 mm sheet will have t³ = 64.
A 2 mm sheet will have t³ = 8.
Two x 2 mm sheets will have 2 x t³ = 16.

But does that account for the fact that the 2 sheets are interference fit together so they can not move relative to each other?

 

[Stormer]

Why do you believe that "buckling from external pressure" will occur?
It should not, if that pressure is equally distributed all around the external cylinder.

Well any imperfection from a perfect cylinder can cause buckling i guess. Because large tanks that is emptied without opening a vent in the top of the tank and where the tank does not have internal reinforcing rings will boucle and collapse.

 

[Lnewqban]

@Stormer , how big your cylinder needs to be?
What material?
What fluid and temperature-pressure will it contain?

 

[Baluncore]

But does that account for the fact that the 2 sheets are interference fit together so they can not move relative to each other?

Once constructed, with hoop tension in the outer layer and compression of the inner layer, a slight impact that deforms the combined layers will result in local delamination, followed by an explosive buckling of the inner layer, as the stored energy is released.

An interference fit will be insufficient for a thin sheets. The materials must be bonded with a solder or with a secure adhesive, to make a single laminated material that is resistant to delamination and will prevent the gradual entry of air or fluid between the two sheets.

 

[sophiecentaur]

And would there be any point in spot welding the 2 cylinders together after shrink fitting them? Or is the friction from the interference fit so strong that the spot welds make no difference?

As a confirmed bodger, I would be tempted to bond the inner and outer cylinders with resin or even with soft (lead based) solder, which would melt at a low temperature and not cause distortion (careful heating, of course, with hot air or a large flame).

 

[Stormer]

@Stormer , how big your cylinder needs to be?
What material?
What fluid and temperature-pressure will it contain?

I have not come so far yet. Just toying with a energy storage idea that involves a vacuum tank and a pressurized tank, but i don't have access to cheap steel plates of more than 2 mm thickness, and i don't think i have the capacity to roll much thicker sheets than that either. And i feel that will be to thin for walls of for example a vacuum tank of any significant size beyond a few tens of centimeters in diameter.
I could use ready made propane tanks or sandblasting, or CO2 tanks (better with sandblasting or CO2 tanks so i don't have to fill it up with water first to cut it so it won't explode like i have to with a propane tank...), but then i don't get to make it exactly the size i want and i want to nest one tank inside the other so it can not be two tanks of the same size.

 

[cjl]

For energy storage, it's likely not worth it to use the vacuum at all. It's much more difficult structurally due to the buckling concerns, and it honestly just doesn't store much energy per unit volume because you can only get a 15psi differential pressure. Since you can achieve hundreds or thousands of psi in a pressure vessel pretty easily, it's much more space and cost efficient to store energy using pressure only (though it's still not that space or cost efficient - the energy stored in even a fairly large amount of compressed gas is still pretty small compared to other energy storage methods, and it's pretty inefficient too).

 

[sophiecentaur]

FGS don’t contemplate trying to build yourself a pressure vessel for energy storage. Compressed gases can store A LOT of energy which can be released in a very short time if it splits. Described by a scuba instructor as “a bomb”, a diving bottle destroyed the boot (trunk) of his car during a collision.

Short term storage can be adiabatic but vessels get hot and a lot of the energy can leak away and reduce efficiency.

 

[cjl]

Yeah, the safety is absolutely a concern with something like this, and compressed gas energy storage falls into the unfortunate category of not really storing enough energy to be worthwhile as an energy storage mechanism while still storing more than enough to be potentially dangerous or harmful.

(The heat losses you mentioned are a problem too, unless you're either talking very slow, effectively isothermal use or if you use it fast enough for the temperature to not bleed down to ambient between filling and use)

 

[jrmichler]

Just toying with a energy storage idea

As long as your are toying with your idea, you are on solid ground. If you actually want to build something, be very careful. All pressure vessels that can be pressurized to more than 15 PSI are required to meet the standards of the ASME Boiler and Pressure Vessel Code: https://www.asme.org/codes-standard...n-pressure-vessels-division-1/2021/print-book. This code was originally created because steamboat boiler explosions, with accompanying loss of life, were a common occurrence in the mid-1800's. This website is by a law firm, and unusually for a law firm, understates what can go wrong and why: https://www.explosionaccidentattorn...conducted,installation of the pressure vessel. Good search terms to learn about what happens when things go wrong include scuba tank explosion and water heater explosion.

If you want a tank 3 or 4 inches diameter, you can buy a piece of Schedule 40 pipe and screw on a pair of end caps. That pipe is heavy enough to handle vacuum also.

If you are working with pressures on the order of 100 PSI, you can use standard air compressors and air motors. Just be aware of the efficiency losses - it takes a 20 hp air compressor to run a 5 hp air motor. That's because air is compressed adiabatically, then cooled, then expanded adiabatically. Those are the largest losses. There are also various flow losses and mechanical friction.

The practical realities, especially the laws of physics, make compressed air energy storage a minor niche application.

 

[Stormer]

For energy storage, it's likely not worth it to use the vacuum at all. It's much more difficult structurally due to the buckling concerns, and it honestly just doesn't store much energy per unit volume because you can only get a 15psi differential pressure. Since you can achieve hundreds or thousands of psi in a pressure vessel pretty easily, it's much more space and cost efficient to store energy using pressure only (though it's still not that space or cost efficient - the energy stored in even a fairly large amount of compressed gas is still pretty small compared to other energy storage methods, and it's pretty inefficient too).

The vacuum tank is for thermal insulation. And that is also why i need the tanks to be different sizes to be able for one to be nested inside the other.

 

[Stormer]

As long as your are toying with your idea, you are on solid ground. If you actually want to build something, be very careful. All pressure vessels that can be pressurized to more than 15 PSI are required to meet the standards of the ASME Boiler and Pressure Vessel Code

If you want a tank 3 or 4 inches diameter, you can buy a piece of Schedule 40 pipe and screw on a pair of end caps.

I don't live in the US. So US laws does not apply for me.

Where i live pretty much all metal suppliers only serve professional customers with a registered company. And you usually can only buy full length 6 meter pipes also. I would love to live in a country where there was a good metal supply in cut lengths for private persons. Where i am now i would have to go to some metal fabrications shops and ask for some cutoffs and hope they have some in the right size...

 

[sophiecentaur]

for one to be nested inside the other.

For insulation, why would the inner one need to be 'strong'? Virtually no pressure difference.

 

[cjl]

For insulation, why would the inner one need to be 'strong'? Virtually no pressure difference.

Presumably, the inner one would be holding high pressure for the actual storage, and the insulation is to get around the issue of losing a bunch of energy when the compressed gas cools down after compression.

 

[DaveE]

I don't live in the US. So US laws does not apply for me.

OK, but if you lived in Germany, China, Japan, Australia, or Chile, you would probably have similar regulatory requirements. Granted regulations can be burdensome and sometimes not make sense for unusual applications, but they are there for good reason. Just because you can do something doesn't mean you should. Just because your country doesn't have regulations to support safe product design doesn't mean they shouldn't. Some regulations are in place to protect you and others from the consequences of avarice or ignorance. Professionals seek out these safety standards to answer questions just like yours. There is a wealth of historical experience and safety testing embodied in the best standards. There is also some legal protective value in compliance if things go really wrong.

 

[sophiecentaur]

Presumably, the inner one would be holding high pressure for the actual storage, and the insulation is to get around the issue of losing a bunch of energy when the compressed gas cools down after compression.

I may have missed something about the design idea but, if you just need an insulated high pressure cylinder, why does it need a vacuum? But even if a dewar container is worth it, you'd only be dealing with 1Bar pressure difference between the inner (energy store?) and the surroundings. I feel that the conversation is moving ground and not getting to a viable solution.

 

[jrmichler]

Post #1:

If you then roll 2 cylinders with 2 mm wall thickness and make sure one is the right size for a interference fit over the other and then heat the larger one to shrink fit it over the smaller one will the resulting cylinder then be as strong in tension and against buckling from external pressure as a solid 4 mm wall cylinder would be?

Post #13:

Just toying with a energy storage idea that involves a vacuum tank and a pressurized tank,

Post #18:

The vacuum tank is for thermal insulation. And that is also why i need the tanks to be different sizes to be able for one to be nested inside the other.

This whole thread is wandering in various directions because it is unclear what the OP wants to do. In Post #1, you want to build a pressure cylinder. In Post #13, you say it's two tanks, one for pressure, the other for vacuum. In Post #18, you want to put a pressure tank inside a vacuum tank, and imply that you want to build a Dewar flask for a gas under pressure.

You are describing three different problems. We want to help you, but only you know what you are trying to do. You need to CLEARLY communicate this to us in order for us to help you. If you choose to post again, describe in detail what you want to do, and why.

If it involves improving the efficiency of compressed gas energy storage by storing the heat of compression, just tell us and we will show you how to do the calculations. Hint: If you do the calculations, you will then know exactly how good an idea it is. And it will be a good learning experience.

 

[Stormer]

Post #1:

Post #13:

Post #18:

This whole thread is wandering in various directions because it is unclear what the OP wants to do. In Post #1, you want to build a pressure cylinder. In Post #13, you say it's two tanks, one for pressure, the other for vacuum. In Post #18, you want to put a pressure tank inside a vacuum tank, and imply that you want to build a Dewar flask for a gas under pressure.

You are describing three different problems. We want to help you, but only you know what you are trying to do. You need to CLEARLY communicate this to us in order for us to help you. If you choose to post again, describe in detail what you want to do, and why.

If it involves improving the efficiency of compressed gas energy storage by storing the heat of compression, just tell us and we will show you how to do the calculations. Hint: If you do the calculations, you will then know exactly how good an idea it is. And it will be a good learning experience.

The idea should be pretty simple to understand. I want 2 tanks, one inside the other with the inner one pressurized and the outer one having a vacuum for thermal isolation. And I'm asking how i can construct this with limited access to cheap sheet metal material thicknesses, and limited slip roller capacity.

When the energy storage idea in it self is novel i can obviously not describe how the whole system works on a public forum, and that is not required to answer my question either.

 

[Lnewqban]

The idea should be pretty simple to understand. I want 2 tanks, one inside the other with the inner one pressurized and the outer one having a vacuum for thermal isolation. And I'm asking how i can construct this with limited access to cheap sheet metal material thicknesses, and limited slip roller capacity.

When the energy storage idea in it self is novel i can obviously not describe how the whole system works on a public forum, and that is not required to answer my question either.

If I understand your situation correctly, your original question is directed only to the external cylinder, manufactured from the scarce available sheet metal and limited roller you have access to.
We will not give you any advice about how to build a pressurized tank yourself, which future use would be very dangerous.

As you have stated that you may use carbon dioxide tanks for the pressurized part, I believe that your vacuum chamber to enclose such tank could be made out of the available sheetmetal.

Rather than rolling two cylinders of interferring diameters, which difficulties we have discussed above, I would roll and weld capped cylinders of different diameters (they will not be pretty or perfectly round), and would inject some expanding foam (the type used in construction, if available) inside their common cavity.

That composite structure will have a greater cross-section area moment of inertia, which will increase the resistance to buckling of the vacuum enclosure.

 

[Stormer]

Rather than rolling two cylinders of interferring diameters, which difficulties we have discussed above, I would roll and weld capped cylinders of different diameters (they will not be pretty or perfectly round), and would inject some expanding foam (the type used in construction, if available) inside their common cavity.

That composite structure will have a greater cross-section area moment of inertia, which will increase the resistance to buckling of the vacuum enclosure.

That is a really good idea. Thank you. And i guess the foam would give some extra insulation from the radiative heat that can cross the vacuum space between the two tanks as a bonus. But expanding foam *expands* and create a lot of force in an enclosed space from what i have heard. Don't i run the risk of buckling the inner tube when the foam expands? Would maybe epoxy granite be a better choice of filler material because it has minimal expansion when it is hardening and has really high compressive strength when hardened?

 

[Lnewqban]

Yes, that may be a concern, but leaving at least one vent per cap should be sufficient, as long as you have availability of low-expanding foam (closed cells would be more rigid after curing).
The cylinders should be stiff enough radially.

Please, see:
https://www.whysprayfoam.org/spray-foam/types-spray-foam/

 

[sophiecentaur]

When the energy storage idea in it self is novel i can obviously not describe how the whole system works on a public forum, and that is not required to answer my question either.

It may be "novel" but it would still be subject to efficiency constraints of thermodynamics. I seriously think that you could store more energy in a coil spring of the same diameter as your cylinder. Springs of all shapes and sizes are available at reasonable prices. Also, gravity storage works well. A heavy mass (as big as you can handle) lifted by a motor will return useful energy at a constant rate. Both those methods would be safer and more predictable than a dodgy home made pressure vessel. That really scares me.

 

[jrmichler]

a dodgy home made pressure vessel

You need to tell us exactly what maximum pressure you are designing for, and how you will do it safely. Keep in mind that 15 PSI is not the same as 150 PSI, and 150 PSI is totally different from 1500 PSI. Also tell us what maximum temperature you are anticipating, what maximum temperature you are designing for, and how you arrived at those numbers. Compressed gases can be dangerous to the point of killing people, and you will satisfy us that you are approaching this problem properly, or the thread will be closed.

 

[sophiecentaur]

what maximum pressure you are designing for,

Yes; the details are very important. Springs and gravity stores have been used for hundreds of years for a good reasons.

I can only think of one example of compressed gas energy storage and that's in air guns. Apparently, a 12g CO2 cartridge can deliver up to 200 shots (maximum permitted is 10J a shot so a couple of kJ stored - that's one Watt for half an hour, minus the efficiency losses). I brought that up as a ball park figure for what can be done. Of course, that ignores the actual energy involved in filling up the cartridge which would be very relevant in terms of 'energy storage'. Also one would have to consider the health and safety considerations involved in the factory producing them and the very high spec needed for the canisters. [Edit: about 60Bar]

 

[DaveE]

I can only think of one example of compressed gas energy storage

I've been on dive boats that use a scuba tank to power the starter for their diesel engine, which seemed to work well. No dead battery issues. But it's telling that you only see this in a niche application where they had to have a bunch of high pressure cylinders onboard anyway.

 

[Baluncore]

But it's telling that you only see this in a niche application where they had to have a bunch of high pressure cylinders onboard anyway.

Many big diesel engines, in generators, HGV trucks, railway engines and ships, use compressed air to start.
https://en.wikipedia.org/wiki/Air-start_system

 

[sophiecentaur]

I've been on dive boats that use a scuba tank to power the starter for their diesel engine, which seemed to work well. No dead battery issues. But it's telling that you only see this in a niche application where they had to have a bunch of high pressure cylinders onboard anyway.

Now you’ve jogged my memory I remember starting aero engines with a blank cartridge.
Better than carrying a large battery. But I remember a light plane being forbidden to take off with its flat (lunch box size) battery. A jump start was’t allowed either.
No real excuse for a defunct dive boat battery though. Makes me wonder what else could have let them down in an emergency. But five bottles always(!) should have some air in them after a dive.
The numbers count in this project so other applications may not be relevant. Modelling does not always give valid conclusions in some engineering problems.