Steam & Excursion > What is a safe-ended boiler tube?

Boiler tubes are some of the strongest parts of the boiler.
Because their wall-thicknessm compared to a tubes diameter, 
turns-out to be about 16:1.  Meaning that the tube walls are stout,
compared to tubes diameter.

A modern loco's boiler can typically be 100-inches in diameter, and have
a wall-thickness of 1-inch...  So, the weaker structure, tubes or boiler shell,
is the source of greatest attention.  Thus, defects in the boiler-shell can be
100-times more risky.   That's why there is the 1472-day boiler shell inspection 
and ultra sonic testing.

Boiler tubes:
Back In the day, RRs also used 4-years (& 12 mos. 'Out of service' credit.
For expediency, they used to typically remove and apply new  superheater 
units.  Also they would remove the 5" diameter superheater-flues, and all the smaller
 boiler tubes.

The flues and tubes are physically expanded and rolled into the front sheet of 
the firebox, and extding to the front flue sheet.  in the 1930s, a lots of testing 
was used to determine the optimum tube-length, for greatest thermal utilization.

The tests all concluded that 19-ft was about the gratest useful-length, extract 
the greatest amount of heat out of the flame-path.   Boiler water temperatures 
vary from "warm", at the lowest level wash-out plugs to the HOTTEST temperstures
at the roof of the furnace, commonly called: the "crown sheet".  The flame-tip 
temperstures, under the strongest draft conditions, can reach 3000 F !!,
while burning oil or coal, under strong loading and strong drafting velocities,

Both burn similarly in firebox, in that both have very short-duration journeys..
fractions of a second, before diving into the water-surrounded flues and tubes.
 At the hottest temperatures and greatest drafting speeds, the water in the boiler
is exposed to the greatest flame temperatures, reaching 3,000F.  

The hottest the water gets is over the crown sheet; and, boiling water, at 300psi
has steam and water temperatures right at 400F.  The only way to get hotter 
steam temps in the boiler, is to increase the pressure that the safety,
pressure-relief valves opening-pressure point.  Adding a hotter fire,
only boils the water at a faster rate, it's steam temperature is limited 
to the pressure relief point of the safeties...

So, to sum-up, the boiler tubes are proportionately much stronger than
the boiler shell.  If a tube fials, it instantly blows-out the fire.  The fire is 
backdrafted, just like when you blow out a candle, or blow down chimney
top of a kerosene table lamp.  Bang!  The fire is instantly put out!
the water in the boiler drains down to the level of the rub that had failed.

Now, pay no ettention to worries or concerns that a popped tube is a
dramatic risk.   It will stop any further progress, if it fails on a trip.
The loco will have to towed, from wherever it failed.

So, that's one reason why you need not have-to yank and replace all the 
flues and tubes in a boiler, to comply with the 1472-day inspection regs.
The biggest advantage to requiring the 1472-day boiler safety re-certification
is the expansion and development of boiler tube skills and methods.

Almost nobody has the skills or the strength to replace all the flues and tubes
in a boiler undergoing the 1472-day process.  But, the advantage is that new 
learners can practice and begin to build the muscles and experiences in 
a truly hands-on process.  

There is no better teacher than experience. You can't learn boiler tube skills from a book.  
The ONLY way to learn the skills is by doing the work.  
That's why I whole-heartedly cheer when locos become due for their re-crtification.
 A lot of the skills are learned at early stages of assistance to the boilermakers
thst are doing the work.   There's so much labor and grunt- work, it takes 
a small team, and coordination to successfully remove and replace a full-set of tubes.

Owners do have a choice over whether to yank all the flues and tubes, or 
remove sufficient tubes to gain access to the seams and rivets below the top
row tubes.  You want to encourage every opportunity to build muscle strength and 
"muscle memory" needed to precisely control the installation process.

The most common mistake made during tube installation, is overzealous operation 
of the tube rolling-in process.  The tool used to roll in the fkues and tubes is :
the flue-rolling tool.  It is a cylinder that contains several sets of small rollers ,
driven by a long papered 'steel pin',  The tube holes in the front and rear 
tube sheets are larger in diameter than the tube that is rolled into place.
The wall thickness is thin, compared to the 1/2" -thick front and rear tube sheets.

The internal rollers in the flue-rolling tool are mounted at a slight angle to the 
centerline of the cylindrical portion of the tool that is inserted into the tube-end,
at the start of the flue rolling-in process.   The sets of rollers are slightly angled 
from the true horizontal centerline of the rolling tool.  So, when torque is applied 
to the tapered pin, the rolling action draws the pin deeper, forcing the rollers 
to expand that end of the tube.

The there is nothing preventing the entire length of the tapered drive-pin
When to STOP rolling is the ART of the flue-rolling skills.
There is a precise, rolled tension,  where the expanded tube-wall is squeezed 
against the tube hole in the flue-sheet.  There is no 'automatic stop' to how
tightly the expanded tube is rolled into the sheet-hole.

If you don't get a tight-enough squeeze, you set-up the conditions for a
certain, future-leaky tube.  

If you advance the tube rolling drive-pin too deep
into the rolling tool, the rollers will expand the thin tube-wall into the flue-sheet,
so that the tube rolled-in to the flue-hole, is very thin, and will certainly break after 
several fire-up cycles.

The first several fire-ups and cool-down cycles will eventually break the over-rolled
and defective boiler tube.... and yes, it instantly puts-out the fire in the firebox .

The proper tension for each tube-end rolled-in, is different for each rolling-in
joint.   It is a combination of muscle-torque, sounds of the air-motor doing tye rolling..
The air motor spins-easily when the drive pin is first inserted, and the air-tool slows
slightly as the pin continues to spin, and gets drawn deeper into the tube-rolls.

If you continue to power the air motor, the tube sheet will make the tube end
as thin as tissue-paper!  Instant failure, under low pressure is the future risk.
Flue rolling is a true craftsman's ART.  Where are we gonna get future boiier 
makers, if we didn't have the 5-year rule?  There are near 400 to 500 tubes in
big loco boilers, and two tube-sheets to be properly rolled-in.  It is the art 
of the craft .... it's more brain and senses, than it is pure-brawn, strength.

A true ART, that takes many boilers to provide the opportunities for developing 
the skills, the muscles, and the senses to know when to STOP rolling,
and move to the next hole.   That's the BIG advantage to replacing ALL the 
tubes and flues --- to give your boiler-team the opportunities to build their
skills and crafts.  It's why I cheer whenever I read about a boiler that's 
about to under-go the recertification, 1472-day inspection

Now, let's explore the origin of safe-ended boiler tubes.
When rolled in-place, the tube ends permanently distorted,
tight into the flue sheets.  The firebox-end of the tubes is further 
secured by curling the small protruding ring of tube, back, on to 
the surface of the tube sheet.... a medium sized air-hammer and
it's chattering tool are moved over the flue extension, multiple passes,
each one gently curling the tube-end back and hard-against the flue sheet.

The chattering tool used in the air hammer, has a long downward-curving
'finger' and at its base has a curving up-right 'thumb'.  The curling action
smoothly bends the the tube's end where the "thump and finger'  meet,
forming a curled 'bead' at each tube.

Once all the tubes at the firebox-are rolled and beaded in place, a weldor 
makes a smooth, even pass of steel welding-wire.  The purpose of adding 
the weldment has to do with forming a one-piece, thermally joined seal.
the weldment eliminates the mechanical-only joint made by the rolling process.
The rolling process invariably leaves a mechanical-joint --- that has the two 
different-thickness steels that expand at differnt rates when subjected to 3,000
degree flames.

So, ekectic-welding is at very high temperatures, and thermally-fuses the thin
walled-tube into the thicker, 1/2" -steel of the tube sheet.  It is the thermal conductivity 
that is needed .... Remember that water on the outside of the tubes is at 400F, compared 
to the 3,000 F of the flames in the firebox .

Now, after 5 years of service, the boiler comes-in for its 1472-day boiler inspection.
of the riveted seams, below the water level.  It's time to remove the flues and tubs to 
gain access for the seams' inspection, and ultra-sound testing.

The RRs routinely removed tall the flues and tubes from the boilers,
by peeling away the 'seal-weld' of the tubes at the firebox end of the tubes,
and the smokebox tubes thst had been rolled-only, are collapsed and the old tubes 
passed out the smokebox, to be "recycled."

The ends of each flue are cut and bent and mangled during removal..
but, 98% of the tube's length is re-usable, once it's cleaned up, can 
be used, beck into a different boiler.  "New" ends are created, and short,
new sections of tubing are added at the individual tube's firebox-ends.

let's go to the 'flue shop',  as with 1522 as our Guide...😃







 



Edited 4 time(s). Last edit at 09/23/24 02:31 by wcamp1472.

Allow me to get this out of my system.  Its a boiler tube with a condom on one end.

Now, when all the stays of execution and flue extensions have run out, the fluestubes are removed.  Decent sized shops had what they called a flue rattler.  They all spent time in there until all the scale had been "rattled" off and they  were cleaned.  I would assume they were inspected at this time znd the ends, which had been cut out of the flue sheets with a torch were squared up znd faced off, one end wzs cut off a foot or two, i zssume the firebox end.
At that point, I would guess there were dedicated lathes with a set up to weld a new section to bring the flue/tube to a length long enough to equal the length of a new one.  I would think they were pressure sested to assure a good weld and then either installed back in the engine or put "in stock".
Shops were also able to swedge superheater flues, so could renew that end also.
That's as much as my feeble mind can picture at this time.

Was a rumor floating around about a gang that thought about safe ending staybolts or building up with weld the threaded end of new staybolts and recutting threads to fit bigger holes.  Wow, that  would be spectacular.

So, we're in tte flue-shop where the tubes will be reclaimed and made-whole,
and added to the 'new' tubes stock, in the Stores Dept

Please make sure to wear your hearing protection, your safety glasses, and 
work-quality foot wear.

In the Flue Shop, it's very noisy, and loud.  Out back, behind the 'Shop,
is a flue-roller.  The flue Roller is from an older loco that had been scrapped,
and its boiler reused as a  "flue-tumbler..".  One end of the tumbler is hinged
and about 100 "old tubes" are tumbled together for 3 or 4 days.  

The damaged ends of the flues have been cut-off, before tumbling.  
The tumbler's door is closed, and the roller slowly rotates, noisily tumbling
the tubes against eadch other.

Its very LOUD, so we go back into the Flue Shop... its a little more quiet, 
but, occasional crashing and banging in the shop, means keeping your 
hearing protection in-place.

We're going to watch the "friction-welder" in action!  
Keep your safety glasses on at all times in the flue shop.
The workers have just gone 5-years without a reportable injury
in the Flue-Shop.

In front of us is the friction-welder.....  short, new pieces of steel tubes are
welded to the firebox-end of the reclaimed flues.  
A tube that's to be recovered is clamped, in one end of the welder and does
NOT rotate.

In the fruction-welder machine, opposite the fixed tube, is a short tube-extension,
to be spun & attached to the re-used tube.

Superheater flues can be 5- inches in diameter,  but the rear tube sheet in
the boiler is about 20% smaller in area, yet has the same number of tubes
as the larger, Front Tube sheet.  Therefore, to fit all the superheater flues 
together at the firebox, the last 18" to 22" of the 5-inch flues are purchased,
new from the supplier, with the firebox-end of the flue, 'swedged' down to 
a much smaller diameter... like, maybe, 3" diameter.

The section of "new" tube ( 3-inch diameter) is attached to the smaller end
of the re-claimed 5" flue.  The reused tube looks like it's factory-new,
after being tumbled around the clock, for several days.

 If the tube has been reclaimed, several times, it's smaller diameter-end
will show 'rings' of earlier-applied "safe-ends"... A new safe-end is always
added to any prior addded safe-ends.

Common practice was to scrap any removed flues that have 5 'rattle-snake'
rings.  Each ring was added at 5-year intervals + the original tube 
was removed at it's first visit to the Flue Shop --- so, a tube with 5 "rings",
would be 30 years-old ( 1 new-tube 'life' + 5 safe-end rings = 25 years, 
30 years total service.). Any tubes with 5 rings were scrapped.

The subject tube in the welder has one ring, so today's addition 
gives us two rings.  

The short repair section, is set spinning and slowly brought into contact
with the, fixed,  full-tube, and soon the spinning 'safe-end' is brought into contact 
the clamped & fixed tube --- for a few seconds, and the two pieces are friction-welded,
at high- speed and mashed together for a few seconds, in a shower of sparks..

The safe end-ed flue is moved to the cooling rack, and another tube to be
reclaimed is chucked-up, and ready for a new, added extension.

When, cooled the safe-end flues are added to the 'new' stock in the 
Stores Department.  The next engine getting re-tubed, will get a mix of 'new' 
and 'safe-ended' tubes to form a set of new tubes to be applied to the next 
ready boiler.

With a RR having hundreds of engines, installing all new flues and tubes
was a very costly proposition.  So, safe-ending had been an effective use of labor,
to hold down the costs associated with the art of fleet-maintenance and upkeep,

Thank you for taking the tour,  Work and be Safe, at whatever is your 
daily activities.

​W.
 
( Recently, I've heard about superheater flues ( 5" size) being kept in-place, 
   During the 1472-day inspections, as I've said, the 1472-day inspection relates 
    only to the boiler-shell integrity.  Some folks elected to remove only sufficient 
   flues and tubes to allow physical access the the shell interior, especially the 
   riveted seams.   The subject of the undisturbed boiler flues. led to the need 
   to perform ultra-sound inspection of the boiler flues .... supposedly requested 
   FRA inspectors.

   Nowhere in the law are there any regulations regarding ultrasound testing of wall 
    thickness of flues & tubes, nor are there any specs listed as to what would be 
    boiler tube at-risk because of a thin-wall.

   But when an inspector makes a request, no matter how outlandish, or not even
    related to specific regulation, the operators are left to comply with the inspector's 
    requests, simply because he 'said-so'.   There is no regulation, except for original 
   construction, regarding suspicious wall-thickness, ultrasonic testing of boiler 
   flues and tubes.  

   When tubes, fail after several added safe-ends, such  failures can extinguish any
    fires in the firebox, by back-drafting the air flow..  its a true case of "failing to safe state"
   The steam cloud goes POOOF, and instantly blows out the fire, and boiler water
    floods the smokebox, and puts-out the fire in the firebox.).
   
 



Edited 4 time(s). Last edit at 09/23/24 15:33 by wcamp1472.

Many thanks for th3e great explaination Wes!

A fascinating tutorial, to be sure!

​Might anyone be able to post images of a friction welder, and also an old boiler in use as a flue roller? Thanks.

S_W

Friction welding is a process not a piece of equipment. Theoretically you could do this with a drill motor and some
small tubing if you spun one side and held the other. The process is the result of using friction to generate enough
heat to "weld" the two tube pieces together. It's a bit tricky in that the heat level is crucial and even observing the
glow color isn't always enough for a good weld. 
As for the boiler as a tube roller, picture anything large enough to hold a decent number of tubes spinning on the
long axis. It removes scale by the rotary rubbing action of one tube against another. It just that an old boiler section
is one of the few things large enough to hold a decent number of tubes. Since it's round it easy (well sort of) to
place it on a number of rollers and power it with a friction (rubber tire) or chain from underneath. 

Out 

https://youtu.be/ZY_QW5aOGOo

This is how Cass "rattles" the flues.

Very simple, and very effective. Thank for sharing!

S_W

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