G1 boiler

[littlechuffer]

hi guys
G1 boiler
what is the recommended wall thickness for copper tubing ?

i have a couple of lenghts 54mm O/D with a 1.2mm wall thickness
any good ?
thanx all
mick.

[ianmac]

I made mine from 2mm. 64mm dia though.

1.2 is pretty thin but im not expert.

Ian

[baggo]

Hi Mick,

Kaye, a gauge 1 LBSCR K class loco described in Model Engineer uses a 50mm dia. barrel of only 0.7mm thickness. I can't find mention of the working pressure but it's at least 60psi (test pressure is 150psi).

The 9F by Roger Thornber uses 1.6mm for 60psi working but his GWR 1400 uses 0.9mm. I would think that your 1.2mm tube will be fine.

John

[mackintosh]

Hello Mick
I agree with John 1.2 mm is fine. I have just started a boiler for a 16mm Tattoo Class Kerr Stuart and that uses 2" dia. 20 swg and that's 0.036" which is less than a mm.
Bob

[littlechuffer]

hey thanx guys
a scratch build is looming, probably something like a 2 40 t
to run alongside my other projects.

cheers, Mick.

[ianmac]

Well im safe then ;D


Whats the wall thickness for the end plates

[baggo]

I can't find any details for the Kaye boiler but the 9F and the 1400 use 1.6mm for the tube plates. It is interesting to see that none of these G1 boilers use flanged tube plates - all are plain butt joints. It is assumed that such joints are perfectly adequate for this size of boiler.

John

[bookworm]

The G1MRA Project and Dee loco boilers both use 20 gauge (0.9MM) for boiler tubes and 16 gauge for the end plates.

Both run at 60 lbs pressure.

[ianmac]

I do remember looking up what the 2mm tube was rated for and it was something stupid like 1680psi

Ian

[steam4ian]

G'day Mick

An Authority here would be the AMBSC Code Part 3 Sub-miniature boilers. For medium pressure boilers 200 kPa to 520 kPa, barrel minimum thicknesses are as follows:- Up to 60mm 0.9mm thick with 1.2mm thick for 60 - 77mm. In Oz stardard potable water pipe is thicker than these values.

Hope this helps

Regards,
Ian

[circlip]

Wish I had a penny for every time I offer this one, "Model Boilers and Boilermaking" K.N. Harris.
Enables you to size everything SAFELY without hearsay/herecy.
Regards Ian.

[brozier]

Good point Circlip,

I went through this process when re-designing my Spencer boiler from imperial to metric (1.6mm to 1.5mm) and using copper rivets rather than PhBr rod for stays.

The sums are not too difficult even for someone with a university education

I also looked at the Martin Evans Book "model locomotive boilers" which adds an extra safety factor for Temperature. (0.8)

I'm not sure whether the Martin Evans book is bit OTT adding this as there is already a safety factor of 6 - 10 added in.

For those thats don't have the book(s) the safety factor reduces the Ultimate Tensile Strength of Copper from 25000 psi to between 2500 psi and 4166psi.

The temperature factor would reduce it by another 20% or so!

Anyone else looked at Boiler design?

Cheers
Bryan

[brozier]

Actually I may as well do the sums :

P = D x F x WP / S x R x C x T x 2

P = plate thickness in inches
D = outside diameter barrel inches
F = safety factor
WP = working pressure psi
S = ultimate tensile strength material in psi
R = rivetting allowance
C = corrosion allowance
T = Temperature allowance

For this example

D = 2.125"
F = 10
WP = 60psi
S = 25000 (copper)
R = 0.8 (silver soldered)
C = 1 (not needed for copper)
T = 0.8 (between 60 - 100 psi WP)

P = 2 .125 x 10 x 60 / 25000 x .8 x 1 x 0.8 x 2
= 1275 / 32000
= 0.03984375 "
Multiply by 25.4 to get metric :
P = 1.012 mm

So for 60 psi you have a well over specced boiler barrel.

Or for P = 1.2mm (0.04724") you could say max pressure is

WP = 0.04724 * 32000 / 21.25 = 71 psi

That is with the highest safety factor too.

Cheers
Bryan

[GWRdriver]

I've built a number of larger scale boilers and I regularly consult Harris and Evans. But I've also built about a hundred Ga1 boilers and quickly learned that the most common copper tube available to us also exceeded the usual needs of Ga1. We are no longer blessed with the range of tube sizes and gauges as you are in the UK. Typically our 2" (nominal) copper water tube comes in three wall thicknesses, .058" (1.47mm) , 070" (1.77mm) and . 083" (2.1mm) any of which will serve so in a sense, pick one - you can't go wrong. My personal preference is for the .070" wall. I typically also use 1/16" material (1.58mm) for heads as it is likewise easiest to find and as above exceeds normal requirements.