Tek Tube is a leading manufacturer of welded boiler and heat exchanger tubes located in Tulsa Oklahoma. I recently did some design consulting on a stationary boiler project where XID tubes were specified. I did a little research on these and wonder if they might not make a good replacement for locomotive boiler tubes. Technical data is available here. It seems to me these might make a real improvement in fuel economy especially for engines operating for long periods at somewhat constant loads. Of course, there might be an increase in tube cleaning and maintenance due to the finned surface, but for locomotives that burn light fuel oil, that might not be a problem.

Very curious what some of the other boiler folks think.

All the products I see are externally finned and made for water tube type boilers.

I just checked the link and it works fine for me. Fin Tube LLC owns Tek Tube. The Ken Tube line has externally finned tubes. If you go to www.tektube.com you'll be directed to the Fin Tube web site. Click on the Tek Tube Products tab on the bottom left of the page, then click on the Tek Products tab on the left, then on X-ID Boiler Tubing in the list.

An interesting product indeed, I'm not aware of their use in a firetube boiler, but... In the "modern steam" community there had been talk of using externally finned tubes for superheater units. In David Wardale's book "The Red Devil" he mentions them as a part of his plan for the upgrades of Chinese QJ locomotives. Test superheater units were built and installed and gave something like 17% greater heat transfer. I know that finned superheaters were a part of Phil Girdlestones plan for the next stage of improvements on the NG-G16A Garratts in South Africa, but I don't believe any were ever actually tried there.

Pat.

The Tek Tube tubes look like a real pain to clean if you're burning coal, due to the circumferential ribs. Would have to brush to loosen and hope that an air brush could clear the loose stuff. Probably not that bad if you're burning oil. Spiral ribbed tubes look like they'd be easier to clean and less likely to start blockage in the first place. I once wondered if you could get away with using aluFer tubes from Cleaver Brooks if you were burning 'clean' lite oil. They are the full-finned sections in bottom of the photo here - http://www.cleaverbrooks.com/products-a ... index.aspx. When they were being tested it was claimed they had 5 times the heat transfer rate of plain tubes and that was in a horizontal return path boiler. CB's smaller package boilers are down-fired and are now rated around 85% efficient. One concern I have for heavy finned tubes is flexibility (or lack thereof) and impact stresses in a locomotive that you don't see in stationary. Would be a great experiment if you've got the $$$.

Cleaning would be a bear esp if used for larger diameter tubes with super heater units. The draft created by a working locomotive is pretty violent compared to a stationary boiler, and I imagine on a coal fired loco the fins would take a beating.

It looks like from the literature that these are designed for multi pass fire tube boilers where locos are basically one pass designs. Because I don't design, build, or service boilers, I am interested to know if applied to a loco boiler would similar efficiencies be achieved.

Side bar: Where multi-pass boiler designs ever tried on a steam loco?

I seem to vaguely recall the Italians had some "return flue" locomotives... one of them males an appearance in one of the B&W WWII movies, The Train, maybe? The stacks appeared to be mounted in the middle of the boiler.

This is getting OT, but those were Franco Crosti boilers: https://en.wikipedia.org/wiki/Franco-Crosti_boiler. The cylinders on either side of the boiler also contain firetubes and serve as pre-heaters for the feedwater before it enters the main boiler.

"The Train" was set in France. You're thinking of "Von Ryan's Express" starring Frank Sinatra. A bunch of POW's escape an Italian POW camp near the end of the war and wind up in an Italian train trying to make it to the Swiss border. The Germans find out and give chase in another train with an engine featuring a Franco Crosti boiler, something like this:

Hmmmm.... If that's a separate heating chamber for feedwater, then it's not really a return flue boiler. My mistake.

The direct link to the TekTube products page is

http://www.fintubellc.com/TEK/TEKproducts.aspx

from which the X-ID brochure is downloaded as a PDF file.

The 'basic' idea here appears to resemble shallow fins roughly at 'right angles' to those in historic Serve tubes. If I understand the rationale, the small fins act the same way as 'riblets' in marine hydrodynamics, with the same effect of inducing microturbulence close to the surface that gives reduced laminar drag to the adjacent flow in the tube. I do think that this microturbulence would also aid convective heat transfer to the larger effective surface area in the bore, so I see no overt reason to reject the figures given -- ASSuming the convective transfer on the other side of the pipe allows proportionate heat transfer to match the additional uptake.

But ... has ERW tubing been fully approved for locomotive boiler service? Because that's what this is, and of course you couldn't draw tube with these characteristics. If there is an actual perceived advantage here, the ESC might take this up as a specific agenda item at one of the upcoming meetings, and determine exactly what kinds of testing (probably including linear x-ray and other NDT of the full weld region) might suit it for use. (The brochure mentions use in up to "2200HP" boilers, but doesn't go into pressure or cycle characteristics, and I suspect this is formula horsepower only). I would also be somewhat neurotic about the repeated sharp changes in tube cross-section causing circumferential stress raising that would be highly difficult (and probably not at all cost-effective) to detect.

Since the tubes are helical and not circumferential, the maintenance issue is not as bad as you might think. You would arrange a power drive on a cleaning head that would revolve it at a corresponding rate to 'feed speed' to sweep out the grooves, then follow with compressed air as the head advances through the tube. It would be difficult at best to apply this to flues unless the elements were withdrawn. You could probably NOT use a mop or 'tennis ball' kind of draw-through cleaner as the "rifling" is far too shallow in pitch to cause the cleaning device to track the grooves as it is pushed or pulled through, even with a ball bearing on the rod or carrier to let the head revolve freely.

It might be interesting to see if the 'riblet' action would work on tubing that had a more 'rifled' set of microribs, set up as multiple parallel threads with the pitch dependent on the physical dimensions of the ribs. At some point that would become 'cleanable' with a non-powered rotating head, and if an adequate measure of turbulation were still present, this might be workable.

As an aside: using X-ID with Besler tubes might be an interesting experiment, although the 're-radiant' uptake from the Besler tube itself is nearly the same for one of these as for a plain tube, and there is of course the extra metal radially.

Dennis: Franco-Crosti is not a "return flue" per se; the return path is intended as a gas economizer, and my admittedly restricted knowledge is that experiments with steaming economizers on locomotives were almost uniformly unhappy. That's not to say there aren't interesting theoretical advantages to return-pass boilers; the old TurboFire XL being a particularly interesting one to adapt to locomotive practice. Their use in historic preservation, though, is incredibly slight.

Not as much a mistake as you might be thinking.

The point of the fairly extensive Franco-Crosti experimentation was to utilize more of the heat in the exhaust gas than could effectively be used in the convection section of what is essentially a once-through firetube boiler with Schmidt superheaters in flues. The required gas speed (dictated by firing rate and front-end conditions) and tube length govern how effective the heat transfer in the 'last few feet' is; you may be familiar with the calculations for the Porta 'sectional boiler' which puts a leaky partition wall on the last couple of feet of tube before the front tubeplate so that convection patterns on the 'hotter' part of the tube remain undisturbed but there is some recovery of gas heat to where the feedwater (from whatever sort of feedwater-heater train) is injected.

What the Franco-Crosti devices do is to route the exhaust steam through a fairly typical economizer arrangement, where the flow resistance to the gas is minimized (using a bundle of some kind of firetubes) and there is further heat transfer to the Rankine cycle. In practice, there is a hard limit to the amount of heat you can recover, and it is dictated by the effective dew point of sulfuric acid/sulfur trioxide from "combustion" of the sulfur content of coal or oil fuel. If this condenses on ordinary carbon steel sheeting or components you get greatly accelerated corrosion (and back in the days of the Italian and British experiments with these things, using noncorroding materials in this service would be cost-prohibitive net of any possible gain in thermodynamic efficiency!)

Now, I believe the typical exhaust temperature in steady-state operation when it gets to the nozzle area in a conventional front end is supposed to be somewhere around 580 degrees F, so there is plenty of heat to be extracted from the gas mass between those limits. This is clearly hot enough to do some 'steam generation' at reduced pressure, and in marine practice you commonly find 'steaming economizers' which actually do produce some additional steam (in my opinion best developed at reduced pressure and hence temperature, for auxiliaries) -- in some case, these only 'steam' at one end and you make your circulation, heat expansion, and piping connections accordingly. I do not believe any Franco-Crosti installations were intended to develop pressure, and of course in the modern regulatory framework one that did would have to be considered a 'separately fired pressure vessel' and that is a design direction you probably don't want to go considering cost-effectiveness (including the smaller physical plant for a given mass of steam per hour) involved.

There appears to be surprisingly little added restriction on locomotive performance from installing one of these things, even routing the exhaust "aft" from the typical cylinder location to the effective 'front end' nozzling that is now at the back end of the boiler, sometimes wrapped around the barrel with a surprisingly long vertical dimension giving good mixing and ejection kinetics.

Well, now that I've totally hijacked this discussion, I might point out that this is essentially the same as the Santa Fe "hinged boiler" articulated did in a more conventional layout (except for the hinge), with the "boiler" shell ahead of the metallic diaphragm being nothing more than a large feedwater heater.

Back to the finned tubes, aside from complicating installation issues (you certainly can't roll them without additional preparation) I suspect that at locomotive firing rates and the temperature generated at the rear tube sheet, the fins wouldn't be long for this world anyway.

Here is the famed Catskill Archives version of the Baldwin Locomotive Works discussion of Mallet locomotives circa 1912. This has a section on the separable boiler with phantom-view drawing of the arrangement.

http://www.catskillarchive.com/rrextra/blwmal00.Html

Not sure (technically) why you couldn't roll them -- all the fins are on the inside where they wouldn't affect a prossering seal. You might have to make a set of rolls that have a 'matching' helical thread, and allow for some longitudinal motion of the device while it is rolling around the inside circumference to expand the tube metal. I also don't see much difficulty with seal-welding them.

I suspect there is a wealth of technical material on how these tubes are treated in package firetube boilers, and I suspect that a polite request to Teresa or Mary at FinTube would result in some useful information.

http://www.fintubellc.com/TEK/TEKcontact.aspx

Meanwhile, the Cleaver Brooks "aluFer" tubes appear to me to be very ill-suited to large locomotive design -- they have an aluminum (!) insert filling a fairly large percentage of the tube lumen with comparatively long, thin fins that divide the gas stream -- see the lower pictures in the link that was provided. I see these clogging with soot comparatively easily, eroding and corroding in hot and ashy conditions, and sagging dramatically quickly at high firing rates, perhaps quickly to the point that effective gas speed and mass transfer through the affected tube drops ... and cleaning becomes essentially impossible. There also appears to be no effective way to re-form deflicted fins, or to fix warpage other than drill out the insert substantially and insert a new one.

There is a resource library at Cleaver Brooks

http://www.cleaverbrooks.com/reference-center/resource-library/index.aspx

which contains many forms of useful reference, white papers, and drawings.

Personally, if you want to see results from Cleaver-Brooks internally-ribbed tubes, I'd look into the product visible at the lower right of the linked picture.

At least one, but it isn't exactly modern steam.



Roger

Here is a page that shows the Franco-Crosti versions of the British class 9F, the world's fastest 2-10-0s:

https://www.youtube.com/watch?v=G5hcECDRQ7k

I notice that Douglas Self has increased his coverage of Franco-Crosti locomotives to include the important types. (If you do not know this site, you may have some fascinating hours ahead of you...)

http://www.douglas-self.com/MUSEUM/LOCO ... crosti.htm

There is further coverage of CIE 356 (mislabeled by Self) in Rowle's book on Bulleid's Turf Burner CC1. Shades of Golden Rock! a bus engine running some of the esoteric plumbing. The CC1 boiler, as I recall, was a bit like the opposite of a reflex boiler: it had two convection sections off a common firebox that uses gas-producer techniques to produce a relatively large amount of relatively low-temperature combustion gas at required low emitted CO, so there was no need to implement an orthodox economizing pass on that locomotive.