Author Topic: Scotch Marine Boiler  (Read 65518 times)

Offline Maryak

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Scotch Marine Boiler
« on: July 22, 2012, 02:51:14 AM »
Hi Guys,

The boiler I am attempting may be familiar to some of you and below is where I am at.

Machining the shell.









In addition I have cut the 2 shell end plates and will be marking them off and machining them in the near future.
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline SandCam

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Re: Scotch Marine Boiler
« Reply #1 on: July 23, 2012, 06:12:28 PM »
Hi Bob,

Just been looking at your power station small boiler design and must say you have got it pretty well sussed out  8) 8) 8).

One or two small observations, if I may... On your calculations file (obtained from the other site... yes!! I have been keeping an eye) you show the furnace tube as being 3" OD with a wall thickness of 1/8" ( as against the 0.010" calculated thickness required).

This would make the ID 2 3/4".

On your drawings, however, you show it as being 3" OD with 2 1/2" ID... making the wall thickness 1/4" which one is correct?.

If the 1/8" figure is correct, then the dimensions shown for your GRATE and ARCH are incorrect.
If the 1/4" is correct, then I would suggest that you try and find some 1/8" wall tube as 1/4" is a bit on the thick side for heat transfer.

Moving on... Fire tubes and Grate...

As drawn... the area of your grate is 10.839 sq ins.

In your calcs. you show the wall thickness of your fire tubes as being 0.060" (just shy of 16swg @ 0.064") and the OD as 1/2"... This yields an internal tube cross section of 0.11045 sq ins.
you have 18 tubes making a total area for combustion gas flow of 1.9881 sq ins.

If you are planning on using natural draught for combustion then the tubes cross section total should really be approx. 1/4 of the grate area... as things stand you are somewhere between 1/5th and 1/6th... which may mean you will need to use forced draught (fan or some such).

If you could reduce the wall thickness of your fire tubes to say 0.036" (20swg) this would increase your cross section total to 2.5897 sq ins... which is much closer to the 1/4 grate mark.
The only other way would be to increase the number of tubes... and it should be possible to fit 8 more between the existing rows if you move them apart a little more... or above the top row.

I don't know how you are planning on fitting your fire tubes (but imagine you expanding them) in which case the thinner wall tube would again be a better option.

The above ratio's are based on your DRAWING dimensions... if your furnace has a larger ID ( as per the first observation) and you keep your Grate height as per your drawing... then the grate will have a larger area... making your tube/grate ratio even worse.

I hope this all makes sense and doesn't come to late to make any corrections to parts made... just thought I would point them out.

Other than the above, it looks like you are well on your way... well done.

Best regards to you and your good lady.

Sandy.




Offline Maryak

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Re: Scotch Marine Boiler
« Reply #2 on: July 23, 2012, 11:27:07 PM »
Sandy,

Thank you.

My drawings were done without reference to the materials I could scrounge and I must admit with no thought as to the grate/ flue ratios.

I have now scrounged a piece of boiler tube which is  high pressure. I have started to machine it and it should end up with a wall thickness around 1/8" and an OD around 2-5/8"

My reasoning is that the smaller I can get the OD the better will be the clearance between the bottom of the furnace and the shell. It should also allow more room for the welds shell to tubeplate and furnace to tube plate especially at the front where the furnace passes through the airspace.

Thanks once again for your very valuable input.
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline steamer

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Re: Scotch Marine Boiler
« Reply #3 on: July 24, 2012, 05:51:53 AM »
Whats the plan for the weld prep and ends on the boiler?
Looks like flat ends....what kind of stays?......just curious....

 :)
Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Maryak

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Re: Scotch Marine Boiler
« Reply #4 on: July 24, 2012, 07:35:02 AM »
Hi Dave,

Not to put too fine a point on it but my original PDF shows weld chamfers for the tube plate. Solid stays 5/16" dia.

Attached is a new PDF of the tube plates with 27 tubes. In addition I have done some checking as recommended by Sandy and here's the rub. My tube wall thickness is 0.028" so this gives me a X section of 0.1548 ins2. My grate area will be 10.98 ins2 so I should end up with a tube to grate ratio of around 3/8 which should satisfy the draught OK.
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline SandCam

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Re: Scotch Marine Boiler
« Reply #5 on: July 24, 2012, 11:22:53 AM »
 :ThumbsUp:

Hi Bob,

That looks like it should work just fine.  :bandrock:

Just thought it was worth checking before you got too far in to the build...  >:D

Been there... got the tee shirt and the video.

I think your dimensions on the latest PDF should get some of the metric guys thinking. He He... Nice one !!!!!

Keep happy.

Sandy.
« Last Edit: July 24, 2012, 11:27:43 AM by SandCam »

Offline steamer

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Re: Scotch Marine Boiler
« Reply #6 on: July 24, 2012, 06:16:24 PM »
Hi Bob,

Not a slight in the least friend.....I have visions of fig drawings from Section 1 dancing in my head from my boiler build.   I sized my ends on my watertube boiler to not need stays ( 5" steam drum)   .....was just curious to compare and contrast say Aussie techniques/code verses those stateside.....Again just curiosity.

Thanks!


Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Maryak

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Re: Scotch Marine Boiler
« Reply #7 on: July 27, 2012, 08:06:49 AM »
Hi Guys,

Geez am I glad I did not go for anything bigger. This really does not fit my lathe without removing things like the tailstock.

A couple of shots of machining the furnace tube. Why, because the piece I was given was 3000psi boiler tube and just a tad oversize for this boilers needs.

Outside



Then Inside.




Next comes the tube plates.  :insane:

Best Regards
Bob
« Last Edit: July 27, 2012, 08:13:20 AM by Maryak »
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline swilliams

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Re: Scotch Marine Boiler
« Reply #8 on: July 28, 2012, 11:17:04 AM »
I'm following Bob, trying to learn a little more about boilers; a subject I've got precious little experience (knowledge) with.

First question: what goes on with these model steel boilers after 10 years or such? Do you have to retest them regularly to make sure they haven't rusted to a point where they become dangerous?

Second dumb question: any idea what you want to drive with this beast?

:cheers:
Steve

Offline Maryak

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Re: Scotch Marine Boiler
« Reply #9 on: July 28, 2012, 02:37:29 PM »
First question: what goes on with these model steel boilers after 10 years or such? Do you have to retest them regularly to make sure they haven't rusted to a point where they become dangerous?

Hopefully if you either keep them totally full of water with a ph of 10.5 or alternately store them completely dry providing mild heat, ( a low watt incandescent light bulb), and allow for air circulation they should last around 30 years. A hydraulic test to working pressure every 12 months and a test to 1-1/2 times working pressure every 2 years followed by floating the safety valves and finally an accumulation test every 5 years to make sure the safety valves can clear the over pressure with the boiler at full power.

The fire side should also be regularly cleaned especially if using solid fuels as the combustion by products block tubes and also allow the formation of sulphuric acid dependent on things like the dew point and condensation during light up and after shut down.

Quote
Second dumb question: any idea what you want to drive with this beast?

This



Plus I'm messing about with a compound twin generator.

Thanks for asking. There's no such thing as a dumb question. :)

Best Regards
Bob

Если вы у Тетушки были яйца, она была бы Дядюшкой

chuck foster

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Re: Scotch Marine Boiler
« Reply #10 on: July 28, 2012, 02:51:51 PM »
thanks for the explanation on how to care for a boiler,i understand the testing of a boiler but i thought you just drained them and put them away when you are done.
but now that i think about it what you said makes sense as water has lots of minerals and stuff that can accumulate inside the boiler (scale i think it is called).
i never thought about cleaning the fireside of the boiler.

i have never had a boiler to work with i always run any little engine i had on compressed air.

thanks again bob

chuck



Offline Dan Rowe

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Re: Scotch Marine Boiler
« Reply #11 on: July 28, 2012, 03:42:52 PM »
Bob,
Nice progress on the boiler. The price of copper has me thinking about steel boilers again.

Dan
ShaylocoDan

Offline swilliams

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Re: Scotch Marine Boiler
« Reply #12 on: July 29, 2012, 01:07:18 AM »
Thanks for the clear explanation Bob. The whole setup will be very impressive when it's all finished

Steve

Offline Maryak

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Re: Scotch Marine Boiler
« Reply #13 on: July 29, 2012, 03:46:39 AM »
Chuck, Dave and Steve,

Thanks for the input and support.

I am having no luck uploading the revised drawings etc. I will try and upload them individually.
« Last Edit: July 29, 2012, 03:50:10 AM by Maryak »
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline steamer

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Re: Scotch Marine Boiler
« Reply #14 on: July 29, 2012, 04:01:24 PM »
I can see it just fine Bob!

.....and your welcome friend!


Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

 

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