Gas tank – S/S or brass?

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Gas tank – S/S or brass?

This topic has 15 replies, 9 voices, and was last updated 24 September 2016 at 16:56 by John Rudd.

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23 September 2016 at 15:28 #29634
Rik Shaw
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@rikshaw
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23 September 2016 at 15:28 #257496
Rik Shaw
Participant
@rikshaw
On the model I have started the designer calls for the small butane gas tank to be made from 1.5mm thick stainless steel sheet. My inclination though is to make it from silver soldered seventy thou brass sheet simply because I have piles of it.

Maybe though, the designer knows something I do not regarding the unsuitability of brass for this purpose – do you?

Rik
23 September 2016 at 15:40 #257498
Pero
Participant
@pero
Rik

I have seen brass used for this purpose before (including on professionally made tanks). It could possibly have been for strength for a particular design but quite possibly that was what the designer had in stock. Since nearly all the commercially made fittings for butane and propane are made of brass there is no question of the general suitability of brass for this use.

Pero
23 September 2016 at 16:28 #257508
John Rudd
Participant
@johnrudd16576
Just make sure that the strength test is carried out before putting into service…..
23 September 2016 at 16:59 #257517
Rik Shaw
Participant
@rikshaw
"the strength test"

Which one is that John?

Rik
23 September 2016 at 18:20 #257522
JasonB
Moderator
@jasonb
Much like a boiler you are making a pressure vestle so if playing with it in public you will have to get it tested and certified. Not sure of the numbers but its quite high, more than a copper boiler and higher than a lot of steel ones too.

I'll have a look later as I know where there is a post that mentions the pressure.
23 September 2016 at 18:30 #257524
SillyOldDuffer
Moderator
@sillyoldduffer
Posted by Rik Shaw on 23/09/2016 16:59:59:

"the strength test"

Which one is that John?

Rik

At room temperature butane liquefies at about 2.6 atm. The pressure will be higher if the tank gets hot. So the tank has to be made strong enough to resist the worst case pressure, which may be why the designer suggested stainless steel rather than brass.

I don't know if there's a formal test needed for a butane tank as there is for steam boilers. As people wander around with butane lighters made of plastic in their pockets, it can't be too difficult at least for a small one.

Dave

Jason posted first: he's more likely to know than me.

Edited By SillyOldDuffer on 23/09/2016 18:31:59
24 September 2016 at 00:13 #257572
julian atkins
Participant
@julianatkins58923
I would make it out of thicker copper steam tube grade for the tube and all silver soldered up plus pressure tested on a boiler test rig. This is what I do on my lubricator displacement tanks for my hydrostatic sight feed lubricator systems on my locos. Quite a few of my locos had these tanks made out of high pressure bronze tubing ex RN. Sadly I've used up this supply but was lovely stuff.

Cheers,

Julian
24 September 2016 at 08:32 #257588
Pero
Participant
@pero
I can't disagree with Julian about the need to test your gas tank for leaks at operating temperatures, but you need to keep in mind that the vapour pressure of butane is very low compared to the working pressure of even a small boiler. Two important considerations are that the vapour pressure increases as the temperature rises and also that mixtures of butane and propane have higher vapour pressures than pure butane, increasing as the propane fraction increases.

One reference indicates that at 90 degrees Fahrenheit the vapour pressure of pure butane is 29 PSI (presumably above ambient pressure [14.7 PSI at sea level] but this is not stated. The addition of a small amount of propane will increase the pressure significantly e.g. approximately double with the addition of 20% propane.

Pero
24 September 2016 at 08:52 #257589
Keith Hale
Participant
@keithhale68713
As long as the joints are designed to operate in shear ie the components overlap and you get good penetration of the silver solder into the joint, you can expect a joint strength of 10 – 20,000 psi dependent on the joint gap.

The copper will fail before the joint!

It's one of the reasons you silver solder in the first place!

For more information go to http://www.cupalloys.co.uk/best-practice/

Keith

Edited By CuP Alloys 1 on 24/09/2016 08:54:35

Edited By CuP Alloys 1 on 24/09/2016 08:58:14

Edited By CuP Alloys 1 on 24/09/2016 09:00:37
24 September 2016 at 09:01 #257590
Keith Long
Participant
@keithlong89920
Rik the following pdf from the Model Power Boat Assoc'n will tell you what pressure testing you need to do on a gas tank for a model. Covers 100% butane and the butane propane mixes as well – the pressure test is higher than you'd think.

Keith
24 September 2016 at 10:08 #257597
JasonB
Moderator
@jasonb
Thanks Keith L. that saved me looking through a long thread to find the pressures.

Rik, this is the same thread and shows a copper gas tank being made which may be of interest, the actual talk of teh gas tank starts a page or two earlier but construction is part way down this page

Edited By JasonB on 24/09/2016 10:14:45
24 September 2016 at 11:53 #257618
Rik Shaw
Participant
@rikshaw
Thanks to you all for the advice / pdf's / links, all of which I will carefully note when making the gas tank. I think I have a lot to learn about the properties of butane which is what I intend using (as in aerosol lighter fuel I am imagining).>>

At this early stage in my learning curve I am still puzzled for instance by the required test pressure in Keith's PDF of 210.50 psig when any smoker can carry a plastic container of the stuff in his pocket to light his fag! I would not have thought that a disposable plastic lighter would have withstood anywhere near that sort of pressure. So I must be missing something here!>>

As a school boy I was hospitalized in a science lab explosion. Here in my dotage I have no intention of taking risks and repeating the experience. Rest assured I will proceed with due caution.>>

Rik>>
24 September 2016 at 13:21 #257628
John Rudd
Participant
@johnrudd16576
Rik,

The ciggy lighter thing and your gas tank build, the butane vp is goverened by a number of factors including liquid volume, temperature ambient and temperature max achievable….(external heat source e.g heat from your boiler)

There comes a point at which the vp cannot increase any further either by increasing the temperature or by lack of liquid volume allowing boil off…

Imagine a car engine, leave the rad cap off, the water will boil at 100C, replace the cap, increase the rad pressure, the boiling point goes up ( by how much? Take a look at steam tables )….

Edited By John Rudd on 24/09/2016 13:23:09
24 September 2016 at 16:31 #257670
duncan webster 1
Participant
@duncanwebster1
Posted by CuP Alloys 1 on 24/09/2016 08:52:20:

As long as the joints are designed to operate in shear ie the components overlap and you get good penetration of the silver solder into the joint, you can expect a joint strength of 10 – 20,000 psi dependent on the joint gap.

The copper will fail before the joint!

It's one of the reasons you silver solder in the first place!

For more information go to **LINK**

Keith

Edited By CuP Alloys 1 on 24/09/2016 08:54:35

Edited By CuP Alloys 1 on 24/09/2016 08:58:14

Edited By CuP Alloys 1 on 24/09/2016 09:00:37

This pdf is one of the best guides to silver solder I've seen. Should be compulsory reading for people making boilers!
24 September 2016 at 16:56 #257673
John Rudd
Participant
@johnrudd16576
Duncan,

Same applies to folk making gas tanks….

( myself included….)
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