Steel Shell, Copper Tubes?

[Fred_V]

Another factor is that the flues are annealed and thus soft enough to take it.

[LVRR2095]

This is analogous to the way welded rail on full-size RRs is prevented from expanding on hot days because the track is anchored solidly to the roadbed.

Welded rail does expand and sometimes dramatically! When I worked for Conrail on days when the temperature rose above 90° F they would send out track patrols continuously looking for sun kinks. Conversely in the winter they would send out the track patrols looking for pull aparts where the welded rails would literally rip apart as they contracted.
On exceedingly hot days, even with track patrols on the lookout, the train dispatchers would issue temporary speed restrictions as the sun kinks could develop at any time. I have seen rails kicked out ten feet or more out of alignment.
Keith

[Bill Shields]

yes, copper will expand more than steel, but not enough to worry about...

the biggest concern should be: how long will STEEL FLUES last in a steel boiler as compared to copper tubes in a steel boiler.

I will let you know when my oldest (30+ year old) copper flues in a steel boiler go bad...and yes, you can still see straight through them from the smoke box to the firebox...they are as straight as the day I installed them.

[Curtis_F]

Often, the tube ends are procerred (if spelled correctly), by a sort of flaring, rolling process on the outside of the boiler's end. I'm troubled by the fact that I see no constraint placed on the tube's insertion through the end (what are those ends called again?)

Primary Seal: When a Tube is Rolled the whole ID and OD of the Tube is expanded both inside and outside of the Fire Box Front Sheet and the Tube Sheet. Thus the Tube is flared on both sides of the steel sheets, though the portion outside of the sheet is flared far more so. Generally only the ends of the Tube protruding through Fire Box Front Sheet get Beaded Over to look a little like the edges of a mushroom top. This is to minimize how much of the Tubes extend into the Fire Box and does not significantly add to the sealing ability of the tube.

Secondary Seal: When heated the Copper does expand more than Steel, which forces the OD of the Copper Tube into the ID of the hole in the Steel sheet, thus giving it better sealing. In full-size practice the tubes are almost expected to "weep" when the boiler is cold then expand to a full seal at working temperature/pressure.

Tertiary Seal: As the pressure builds up in the boiler, and the metals become hotter and more elastic, the Front Tube Sheet and Fire Box Front Sheet will try to bulge outward. It's the flares on the ends of the tubes, outside of the pressure vessel, that hold the sheets from blowing out. The Tubes act like a bundle of Stay Rods. This bulging outward is more noticeable the larger the boiler and over time will permanently deform the sheets to the point that replacement Tubes must be cut to length individually to match each hole set.


Cheers,

Curtis F.

[Fender]

Keith,
I'm speaking of concepts here, not absolutes! To say that rails do kink occasionally is a distraction from the point that 99+% of the time, the rails are held in place by the track anchors, ties and roadbed. If this wasn't true, the railroads certainly wouldn't use welded rail, because they would be de-kinking the track almost every day in the summer. Similarly, copper flues are anchored in the steel boiler, and are restrained from expanding in length. If they weren't, we'd have to re-roll the flues after each steam-up!

[johnpenn74]

Ok, so why don't many live steamers roll steel tubes in boilers?

Not welded in, but rolled in. Prototype rolled for a long time. Why don't we?

JP

[Rich_Carlstedt]

If you were a body and fender man, you would be seeing the effect all the time.
That is that metal moves in 3 dimensions during thermo expansion/contraction and Yield point has a lot to do with it.
When the tube heats up, it expands both radially and axially .
If in expanding axially like in a boiler, it reaches a point where resistance to linear growth is greater than the yield of the material, which then at that point converts to radial expansion IN ADDITION to what already would occur .
In plain terms , because the tube cannot grow one way, it grows another . Now, when the boiler cools, the tube then goes into tension, because the tube contracts and again is restricted linearly . However the tube stays in tension mode at room temperature , so part of its future growth is not as great as when first fired ( as long as temps do not exceed former temp range)

Rich

[LVRR2095]

Keith,
I'm speaking of concepts here, not absolutes! To say that rails do kink occasionally is a distraction from the point that 99+% of the time, the rails are held in place by the track anchors, ties and roadbed. If this wasn't true, the railroads certainly wouldn't use welded rail, because they would be de-kinking the track almost every day in the summer. Similarly, copper flues are anchored in the steel boiler, and are restrained from expanding in length. If they weren't, we'd have to re-roll the flues after each steam-up!

Dan,
I spent my entire working life on the railroad and I can tell you that spikes and tie clips are there to hold the rails in gauge, but to allow them to slide longitudinally as the rails expand and contract. Steel rails slowly expand and contract as temperatures rise and fall. In fact, an 1800-foot length of rail will expand almost one foot with an 80-degree change in temperature! If you have ever seen a sun kink...the track remains in gauge. The way they repair the kink is to cut several feet of rail out and then re-weld with thermite.
And in very hot weather they are out there every day patrolling for thermal expansion.
Keith Taylor Retired Conrail Road Foreman of Engines

[Bill Shields]

giggle....

ever seen the new electrical welding units they have now...?

they push the rails together like two welding electrodes, hit it with a gazillion amps and voila...one piece of rail...

[elm53]

If you were to build a fire in an empty{no water} boiler,all kinds of damage happens. But the smart ones among us put Water in the boiler FIRST.When raising steam,wich should be a gradual process from cold,the water helps to stabilize any radical expansion of individual parts.By what some of you are saying, how could a locomotive with a copper firebox and rolled steel tubes work?It does and this was on a 3'gauge Irish tank engine! Personally,I feel blowing a boiler down to bone empty ....and hot at the end of tthe day is about as abusive to a boiler as you ca get.Rolled copper tubes ,soldered tubes steel and copper,welded all work when properly installed.

[Big Northern]

Keith,
I'm speaking of concepts here, not absolutes! To say that rails do kink occasionally is a distraction from the point that 99+% of the time, the rails are held in place by the track anchors, ties and roadbed. If this wasn't true, the railroads certainly wouldn't use welded rail, because they would be de-kinking the track almost every day in the summer. Similarly, copper flues are anchored in the steel boiler, and are restrained from expanding in length. If they weren't, we'd have to re-roll the flues after each steam-up!

Dan,
I spent my entire working life on the railroad and I can tell you that spikes and tie clips are there to hold the rails in gauge, but to allow them to slide longitudinally as the rails expand and contract. Steel rails slowly expand and contract as temperatures rise and fall. In fact, an 1800-foot length of rail will expand almost one foot with an 80-degree change in temperature! If you have ever seen a sun kink...the track remains in gauge. The way they repair the kink is to cut several feet of rail out and then re-weld with thermite.
And in very hot weather they are out there every day patrolling for thermal expansion.
Keith Taylor Retired Conrail Road Foreman of Engines

Glad we went from boiler expansion considerations to rail expansion! I can attest to your statements regarding serious problems from expansion. As a kid, I recall the Chicago Tribune Newspaper printed a picture taken somewhere in the vicinity, of CBQ railbed distorted to an unbelievable degree! The rails were actually deformed squiggly! It was very hot that summer.

FWIW, we learned in Physics and Mechanics of Materials that one of the unimaginably powerful natural forces is that of thermal expansion. To think that any kind of railbed support could be built strong enough to prevent rail expansion with temperature increase is sheer folly. BN

[cbrew]

i have on better, our local club, uses steel bar for rail, well some of the guys that it would be smart to weld it all up. well on most of the track, it will just push out on the curves.. no big deal right?? well the yard that was in at the time did not fair so well, with all the tracks empty, at the pick of the day all the rail was bowed up about 18 inches. being that one end of the rail was hard set against a concrete curb, it had no where to go..