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Date: 05/25/11 12:31
Flue Life Limits
Author: donstrack

I am helping to answer a question to the Union Pacific Historical Society:

The “3700 Class Challengers” article in the Spring 2011 Streamliner noted the accumulated flue miles and machinery miles for each loco in the class.

Question: Was there an upper limit on flue miles and machinery miles for the Challengers (and other locomotives) that dictated mandatory shopping (or retirement)? And if so, what were the limits?

Don Strack

Date: 05/25/11 12:55
Re: Flue Life Limits
Author: Frisco1522

I don't know about the UP practices, but the ICC rules mandated a 4 year life for flues/tubes, with a possibility of a one year extension.

Date: 05/25/11 13:44
Re: Flue Life Limits
Author: tomstp

And in some areas flu's would not even last 4 years because of the water, even with chemical treatment.

On excursion engines I think you can get extensions past one year but, only one year at a time and that would be after they were inspected. Don (Frisco 1522) can tell you more about that than I can.

Date: 05/25/11 14:13
Re: Flue Life Limits
Author: HotWater

Don (Frisco 1522) is correct. As far as "excursion engines" today, the newer FRA regulations require a complete boiler inspection, internal & external every 15 years or 1472 days of operation, which ever comes first. ABSOLUTELY NO EXTENSIONS are given anymore!

Date: 05/25/11 14:26
Re: Flue Life Limits
Author: wcamp1472

Flue Life Limits, commentary;

Thanks for the thoughtful question, here's one man's thoughts....

There are 3 accurate responses to the question:
A. The 'physical' useful remaining 'life' of flues, in years.
B. The individual RR's reclamation/safe-ending practices.
C. Flues removed for boiler shell interior inspections.

Flues are removed from the boiler shell to permit the close visual inspection of the boiler shell interior condition Particular attention is paid to the riveted circumferential and longitudinal seams (inspecting for rivet hole-to-rivet hole cracking, as well as other integrity inspections). The removal of the flues, for shell inspections, is typically mandated after 4 years of service in a fired-up boiler. (365.25 days/year X 4 years = 1461 days --- 1472 days: current maximum FRA specs).

When removed, the ends of the flues are collapsed and the flue withdrawn. The center portion, that portion not collapsed, is re-claimable by cutting off the ruined end portions and applying a replacement section of good flue to restore the original length: the process is called "safe-ending" of the flue. "Back in the day", railroads reclaimed thousands of removed flues in special facilities where the removed flues were cleaned , trimmed, friction welded and returned to stock for the next application to a similar class locomotive.
The safe end's weld rings were retained after after each successive removal --- they became similar to rattle snake 'rattles'. Each ring representing. typically, 5 years of prior use. Safe ended flues commonly included as many as 5 or 6 rings! Safe ending in today's world may not be economically feasible, or maybe there are shops than can do it at a cost savings over 'new'.

Railroads may have set their own limits on the practical useful life of flues (40 or 50 years?). It may be possible to find archives from varying roads as to their practices.

The physical life of the flues derives from the wall thickness ratio with the tube diameter (typically 36 to 1). Structurally, tubes are immensely strong and can last for many years. Comparatively, the ratio of a boiler's shell diameter to its wall thickness can be in the vicinity of 100 to 1 (yielding a much 'thinner' wall with respect to the boiler pressures). The removal of flues is not required for flue integrity, but for boiler shell integrity and thorough inspection. Typically the jacket and insulation (lagging) is removed at the same time to make a complete boiler inspection report.

In today's practice, the ultra sound (NDT) readings of the boiler shells are a crucial tool for documenting the shell's presumed suitability for continued service, yet a competent, interior and exterior VISUAL inspection is vital for everyone's protection and safety. This includes staybolts, boiler stays and firebox sheet inspections, etc.

Wes Camp1472

Date: 05/25/11 15:31
Re: Flue Life Limits
Author: Lurch

Flue life depends upon service and care of the boiler as well as the type of water in the area(s) the boiler operates. Some railroads have to re-flue locomotives before FRA time limits expire (the same would go for boilers in daily service under the old ICC rules).


Date: 05/25/11 15:38
Re: Flue Life Limits
Author: johnacraft

wcamp1472 Wrote:
> The removal of flues is not required for flue
> integrity, but for boiler shell integrity and
> thorough inspection.

Below is a scan of the original (1911?) Boiler Law language on flue removal. The language in the 1978 and 1999 rules are similar. Basically, as Wes said, you can reuse a tube / flue as long as the metal is good.

Date: 05/25/11 16:22
Re: Flue Life Limits
Author: RJRimmasch


We should focus on UP Super Power here. The Super Power rules on the UP were different than the short haul, lower tonnage locomotives on the UP, for very specific reasons. First the 3700/3900 Jabelmann Challenger design. First off, in the Challengers, unlike the 800 and the 4000 (Big Boys) had type E super-heater units as opposed to type A's. Type E's had a smaller tube and therefore, the number of tubes was increased. A type E super heater element is difficult to work with to say the least. The pipe configuration can actually span over two tubes, where-as a Type A makes all four of it's passes in one tube. None of this is key to the question, except that a Challenger has a smaller Super Heater Tube than the same tubes found in an FEF (the 4-8-4's) and the Big Boys.

It is true that railroads including the UP would remove tubes from larger locomotives and install them in smaller locomotives. This was done primarily on locomotives that all used a common 2 inch tube. However, the UP super Power did not use standard 2 inch tubes. In fact, they used 2.250 inch small tubes and then super heater tubes to match the units that were installed (A's or E's). So, for the UP super power, using tubes in smaller locomotives was not always the option. The super power normally got new tubes as needed and as required.

On the UP between 1941 and the end of steam, it was not uncommon to see super power get new tubes annually or even every six months. This was due in large to a number of conditions. A.) The water in Utah and Wyoming was hard enough that the flue bundle would clog up and tubes would burn quickly. B.) The UP Super Power was high pressure steam, which means we had a lot more heat. 800's, 300 psi, Big Boy's 300 psi and Challengers 280 psi. C.) The length of the tubes in the 800's, 3900's and 4000 was nearly the maximum allowable tube length for any locomotive (respectively 20-22 feet long). It was found that when tube lengths near or surpass 18 feet long, they had more of a tendency to bounce and tear apart. The stretching effect on these long tubes precluded many of them from being re-used.

In the case of the UP, when you combine all three symptoms above, you end up having to change tubes more often. Usually the tubes had failed, or were about to fail and rather than loose a locomotive on tube failure, the UP (and other lines) found it cheaper and better to simply change them more frequently. On the UP it is reported that Ogden and Cheyenne could tube a Big Boy in three shifts. First shift removes front end, fire brick and cuts and removes tubes. Second shift cleans tube sheets, makes tube sheet repairs and repairs to front end items as needed, cleans interior of boiler. Third shift installs new tubes, rolls and beads new tubes and Hydro Inspection of boiler and assembles front end. Fourth shift, fires locomotive, steam test, placed in Round house for inspection and called to service. A Big Boy could get new tubes in less than 36 hours. A failure of the same locomotive would or could cost days! One or more days to get the locomotive to Cheyenne or Ogden, then change tubes and then re-assemble rods and motion if removed to get locomotive to the roundhouse.

When you read the old UP roundhouse records, it was common to see the 7000 class, (Mountains) go months on bad tube reports. However, when you look at service records of the 800's 3900's and the 4000's, when a bad tube or tubes were reported, often, the report went no more than a month before the tube or tubes were replaced. Interesting fact also, the 3900's and the 4000's had periods in Cheyenne, Green River and Ogden where the boilers were washed EVERY TRIP. One shift boiler washes were common for some time as a measure to extend tube life on the UP.

The simple answer, there was no set rule on the UP, but, Super Power got new tubes as needed and as required.

References: Kratville Might 800, Challengers and Big Boys

Kindly yours,

John E. Rimmasch
Wasatch Railroad Contractors


Edited 1 time(s). Last edit at 05/25/11 16:24 by jrimmasch.

Date: 05/25/11 17:38
Re: Flue Life Limits
Author: Harlock

Very informative John.

I always think it's sad that we've lost the ability to re-tube a steam locomotive in 36 hours. Boiler overhauls now take months with a very small crew and little money available in a lot of cases.

Locomotive overhauls that took a week and a half at Baldwin or Lima's shops now take years or decades without specialized tools, facilities and workforce and of course, a large business behind it paying for lots of tasks in parallel, because the time value was such that it was losing money for the railroad every day it was in the shop.

just the economies of scale...


P.S. thanks for the gloves at Hillcrest. They have fired many a live steamer already. :)

Mike Massee
Tehachapi, CA
Photography, Railroading and more..

Edited 1 time(s). Last edit at 05/25/11 17:39 by Harlock.

Date: 05/25/11 18:47
Re: Flue Life Limits
Author: Daylight4449fan

jrimmasch Wrote:
First off, in the
> Challengers, unlike the 800 and the 4000 (Big
> Boys) had type E super-heater units as opposed to
> type A's. Type E's had a smaller tube and
> therefore, the number of tubes was increased. A
> type E super heater element is difficult to work
> with to say the least. The pipe configuration
> can actually span over two tubes, where-as a Type
> A makes all four of it's passes in one tube.

So would it be safe to say that UP went with the Elesco A superheater
on the FEFs for ease of maintenance?

Date: 05/25/11 19:40
Re: Flue Life Limits
Author: RJRimmasch

An Interesting fact is that the First few Big Boy's were delivered with type E super heaters with the rest of the batch delivered as type A's. I have never seen the actual records as to why this was done, but I can tell you this about type E's and Type A's.

In a boiler, any boiler, the ultimate goal is heating surface area. The larger the tube, the lower the heating surface area. For example, a boiler that has 12 tubes usually has less heating surface area than a boiler with 24 tubes. The goal during the days of steam was to create as much heating surface area as possible. To do this, some locomotives were fit with type E super heaters which in turn increased the heating surface area, which in turn increases the Pounds Per Hour that the boiler is capable of making.

For example the big Challengers (3900-3999) had a total of 2162 sq ft of TUBE (super heater) area. The Big Boy had 2734 sq ft of TUBE area. Meaning, the two locomotives only had a difference of about 600 sq ft of heating surface area. Simple math tells me that the 600 feet was found in the fact that the Challengers tubes were 2 feet shorter than the Big Boy's tubes. BUT, the only way they (ALCO) could get the 2162 sq ft out of the Challenger was to install a smaller tube and have more of them. The Challenger has 177 TUBES, with a total of 45 Flues (small tubes) while the Big Boy has 73 total TUBES (Super heaters)and a total of 212 flues (small tubes)

By the way, a TUBE has something that normally goes INSIDE of it, where a FLUE normally has nothing but gas pass through it. So, Super Power locomotives or any locomotive with TUBES and FLUES normally has Super heaters and small tubes that only allow gas to pass through them. Thus the wording TUBES and FLUES

At any rate, if you took the Challenger and converted it to type A units, you would be installing a larger tube and there-by you would be reducing the square feet of heating surface and in effect, you have lowered the pounds per hour the boiler is capable of making.

Now, look at this fact: The Bore and stroke of the Challenger is 21 inches by 32 inch stroke. The Big Boy is a 23 3/4 inch bore by a 32 inch stroke. I assume that the Big Boy originally had type E's with an increased heating surface area as ALCO was unsure if they had produced enough heating surface area to support the bore and stroke (multiplied by 4) and, after delivery quickly found that they had enough steaming capacity that the locomotive did not require type E's and was therefore reduced to type A's. The Challenger on the other had (as I have fired one) is hard on steam capacity and I doubt highly that by reducing the sq feet of heating surface as much as would be required to install type A units that the boiler would produce enough steam to sustain the engines at 100% for an extended period of time.

Keep in mind, boilers were designed to compensate for worn out mechanical items, clogged up boilers, plugged tubes and leaking smoke boxes. However, if you put all of these items right, you could assume that you could decrease the steam capacity of the boiler between 5 and 15%, however, you begin to risk things when you do this.

So the question was: Why did UP use type A's on the 800's. I doubt it was strictly maintenance related, I think it had to do with the fact that the boiler had enough sq ft of heating surface with type A's to sustain the bore and stroke at 100% capacity for extended periods of time, even with a clogged boiler, leaking smoke box, plugged tubes and or other mechanical issues that simply put, type A's were an advantage. A's are much easier to deal with than E's! FEF-3 had 2204 sq ft of super heater surface area. They made and had plenty of steam for two 25x32 cylinders!

Hey, don't forget to check out or You Tube Channel. We have just put out another video on Injectors. You can see it by coming to our web page or looking up Wasatch Railroad Contractors on You Tube. Or, you can see it here in our news section: http://projects.wrrc.us/?p=661

Thanks for watching:

John E. Rimmasch
Wasatch Railroad Contractors


Date: 05/26/11 07:43
Re: Flue Life Limits
Author: johnacraft

donstrack Wrote:
> Question: Was there an upper limit on flue miles
> and machinery miles for the Challengers (and other
> locomotives) that dictated mandatory shopping (or
> retirement)? And if so, what were the limits?

It looks like the "machinery" portion of your question got lost in the flue discussion, but yes, many railroads had regular preventive maintenance cycles for at least some of their locomotives (the ones producing the most revenue) based on mileage. The N&W's program is covered pretty well in Lewis Jeffries' book, and if I recall correctly John Rehor's 1962 article on the NKP Berks mentions 100,000 miles as the interval between running gear overhauls.


Date: 05/26/11 08:27
Re: Flue Life Limits
Author: filmteknik

I always had thought the opposite regarding tube vs. flue but perhaps the terminology varies among regions or railroads.


Date: 05/26/11 09:23
Re: Flue Life Limits
Author: Frisco1522

I have also used the flue terminology as being the large flue which holds the superheater units and tubes as the smaller units.

Date: 05/26/11 09:47
Re: Flue Life Limits
Author: filmteknik

Turning to the three Kratville books:

UP is not consistent on this. Or maybe I should say UP and ALCO. Looking at diagram cards for Challengers, they list both sizes under "Tubes" but when you go over to see Evaporative Surface, the one for 3900-3914 gives the larger square footage for tubes, the smaller figure for flues (the larger number goes with the smaller diameter ones as they are far greater in number). So that agrees with my thinking. But when you look at the card for 3950-3969 it's the opposite. ALCO's promotional card with photo on the front and details on the back again lists the lengths and diameters just under the collective "tubes" but once again has the greater evaporative surface area under tubes.

Looking at a large fold-out diagram of an 800 class, it describes 201 2 1/4" tubes and 58 5 1/2" Flues.

I think Kratville himself preferred flue for the larger diameter but in the Big Boy book he refers to them having 144 flues.

Date: 05/26/11 10:03
Re: Flue Life Limits
Author: HotWater

I was always taught that "flues" had super heater units in them, and "tubes" had nothing in them.

Date: 05/26/11 15:31
Re: Flue Life Limits
Author: rehunn

The flue/mileage thing was only given as a measure of how far the locomotive had run since the
last flue changeout and would have accrued only if the locomotive had enough life left for the next
Class level repairs. Note they range anywhere from low twenties to nearly one hundred thousand.

Date: 05/26/11 18:59
Re: Flue Life Limits
Author: aztrainmaster

Grand Canyon Railway received a waiver for the 1472 this year for 4960.
Ervin H White
GCR - Trainmaster

Date: 05/27/11 13:57
Re: Flue Life Limits
Author: wcamp1472

To Ervin!

Congratulations, Ervin, on your success in the application for extension of time on the removal of flues of the 4960. I am presuming that your RR's record-keeping practices are impeccable. The accurate record and your relationship with the local FRA professionals must be of a high level. You and your team should be proud of your accomplishment, and deservedly so. Your operation is of an admirably high standard; the rest of the steam operators should emulate your maintenance procedures.

It was a gutsy move to decide to make the application to the FRA and the result proved economically rewarding for your operation (the WORST outcome from your request
would have simply been a 'No' --- your decision was a correct choice).

BTW, does the Grand Canyon use a water treatment, and monitoring program, and what role do you feel that the program played in your boiler maintenance success and the extension application process?

You are a credit to the preservation industry.

Thank you!

Wes Camp1472.

Date: 05/28/11 17:29
Re: Flue Life Limits
Author: dick_harley

Regarding the 'flue' and 'tube' debate, I'm sure many folks have their own preferences, and some folks are not consistent. I hate to provide the obvious, but here is what the 1941 Locomotive Cyclopedia Dictionary of Locomotive Terms has to say:

FLUE - The fire tubes of locomotive boilers are often designated as flues, but since the introduction of the superheater, the ordinary small fire tubes are called Tubes, and the larger ones containing the superheater units, Flues. The small tubes making up the superheater units are called superheater pipes.

TUBE - One of the small pipes that convey the products of combustion from the firebox to the smokebox and stack, and which does not contain a superheater pipe. Tubes are fitted in holes in the tube sheets ...

That was the word in 1941. Don't know if things are the same today, or not.

Dick Harley
Laguna Beach, CA

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