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Steam & Excursion > Boiler tube thickness

Date: 03/01/21 12:59
Boiler tube thickness
Author: wcamp1472

this may be of interest, if you're into boiler tubes, thicknesses , etc.

From an advertisement, on line, for Elliot Tube-rollers manufacturing..

" When ordering tubes, it is very unlikely that each wall thickness will be exactly the same. Industry tolerances allow for ±10% thickness. That’s a total variation of up to 20% from the smallest to largest thickness, resulting in a wide range of sizes. For example, if you have .083” average wall tubes, the actual wall could be anywhere between .091” and .075”. If you were to buy a 14 BWG expander to fit .083, it would likely still work for either extreme due to the expansion range that the tool is capable of achieving.However, many times a heat exchanger manufacturer needs to achieve a very specific thermal transfer. In order to achieve this, they need to guarantee that the wall thickness of the tubes will be a minimum thickness. So for many applications, the manufacturer will request minimum wall (min wall) tubes.A min wall tube offers the same total variation in wall thickness that an average wall tube does, but the variation is applied differently. It allows for -0% and +20%. So the wall will never be less than the specified thickness. For example, a .083” min wall tube will range from .083” to .100” wall thickness. At the upper end of that range, a normally sized tube expander will not have enough clearance to enter the tube. If you have min wall tubing, it is recommended that you drop down one expander size. So instead of ordering a 14 BWG expander, you would drop down to a 13 BWG. This ensures that the expander will fit inside of the tubes and still achieve the proper range of expansion.If you are unsure whether or not you have min wall or average wall tubing, it is important that you measure the inside diameter (ID) of your tubes prior to ordering tooling. If you do not take an average measurement, you may end up having to order additional sizes or spend time re-rolling tube joints later on. Taking ID measurements are always recommended, even if you know what type of tubing you have. The more precision measurement you have, the more accurate you can be when
ordering your tooling.Overall, it is important to understand the difference between average and min wall tubing, and to know the type you are working with in order to achieve the best results.End of adv.

Wes CampShare This 



Edited 1 time(s). Last edit at 03/01/21 13:06 by wcamp1472.

Date: 03/01/21 14:13
Re: Boiler tube thickness
Author: Illbay

Wes, thank you for your technical insight.
Have a question. Did any loco manufacturers use copper boiler tubes?  Seems to me, thermal conduction would improve and maybe require many fewer tubes.   First cut, I'd guess copper cant handle 300 psi, but I see in engineering tables that "drawn" copper pipe up to 3-1/2" diameter can tolerate 600+ psi. Maybe that's not enough. Maybe metallurgy problems with the tube sheets too.  Any insight is welcome.

Edited 1 time(s). Last edit at 03/01/21 14:15 by Illbay.

Date: 03/01/21 14:58
Re: Boiler tube thickness
Author: DWDebs/2472

British railways often used copper (insted of steel) fireboxes. Each has its advantages and disadvantages. This is discussed in (British) Heritage Railway Association publication HGR-B9021-Is01 "Inner Firebox Repair and Renewal", section 7 Replacement Inner Fireboxes. Free download at: https://static1.squarespace.com/static/59f1c5ec51a58457c01eaed0/t/5a12c7d6419202823592d018/1511180251486/HGR-B9021-Is01-Inner+Firebox+Repair+and+Renewal.pdf

- Doug Debs

Date: 03/01/21 15:03
Re: Boiler tube thickness
Author: wcamp1472

I don't have any knowledge about copper tubes in boilers.
I think I remember about the Brits using copper for boiler tubes, in the 20th century..
Also, I think it's common in live-steam models of locomotives to use copper boiler tubes..
But that's just a supposition..

My guess is that the greater the conductivity, the more quickly ( shorter disatance)
those tubes transfer heat, I suspect  that the flame-fingers cool-down way-quicker 
and in a much shorter distance.... inside of copper tubes.  

Remember, that the surrounding boiler water is very 'frigid-cold' compared to the firebox 
combustion temperatures... Flame temps, under strong drafting, can reach 3000F,
and boiler water, even at elevated pressures, is typically 450-500F...

SO, boiler water at very cold temps ( compared to the firebox)  quickly sucks the
heat out of the flue gasses... so, I presume that copper would cool the gasses down more rapidly.

I also see that adding the tubes'   'seal-welds' at the firbox-end would be more difficult to apply
with soft copper.  The theory with the 'seal weld' is better heat transmission ( conductivity) between
the tube sheet and the individual tubes.  

The tubes at the firebox ends are flared with the flue roller during installation.
The flare is like the open end of a funnel.....  boilermakers use a medium size air impact
hammer and an appropriate shaping 'chisel', to complete the curling of the flared opening,
to curve the tube ends back onto the tube sheet. That curling of the steel tube back onto
the tube sheet is called 'beading' 

To get uniform heat transfer between the beaded tube-end and the flat tube sheet.
The tube sheets are typically 1/2" steel, tubes are much thinner, than the tube sheet.
That disparity in thickness leads to different rates of expansion between the sheet
and the tube steels.

Those expansion-rate differences lead leads to leaky joints at the sheet-tube interface.
Boilermakers applied a single-pass weld at both the beaded tube and the sheet,
That weld makes a thermally-unified conducting surface.... so that the seal-welded beads
become leak-proof, across the whole rear tube sheet.   

Water Temperatures at the bottom of the flue sheet are MUCH colder, than the temps at the 
crown sheet.   

I think copper boiler tubes have greater drawbacks, than they have advantages..




Edited 3 time(s). Last edit at 03/01/21 15:28 by wcamp1472.

Date: 03/01/21 15:28
Re: Boiler tube thickness
Author: LarryDoyle

Copper tubes, copper boilers, and copper fireboxes were abundant in the US 19th century, but fell out of favor before 1900.  Copper is a better heat transfer material and is easier to work at the builder and service facilities, but iron, then steel, won out for its better strength and service performance.

Early iron boiler sheets were forged, not rolled.  That is, they were made of iron blocks which were hammered and hammered and hammered into rods which were hammered, and hammered, and hammered by blacksmiths until they joined together into thin sheets, which were then hammered and hammered and hammered until they joined together into thicker sheets.  UFFDA!  Ever wonder why boiler failures (spell that e-x-p-l-o-s-i-o-n-s) were more common then?  (That, and lap-seam longitudinal joints).


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