There was a discussion about boiler tubes a month or so ago. Kelly Anderson posted a great ATSF procedure on safe ending boiler tubes. Included in that same procedure were lengths of supeherater units for safe ending as well. As we are currently building new boilers for former G&Q Railway locomotives in Ecuador, we are also in the process of building new superheater units for one locomotive. Included in this thread is a photo of the suphereater units that we removed. The front end of the units are all on the same plane. In other words, they are all even at the neck end. You will notice that the units are all different lengths.


The longer units shown in the photo have more damage. The return bends are cracked, the piping is damaged and the units are no longer straight. However, the shorter units are in much better condition. Some of these units have been safe ended and shortened. In the other thread mentioned above, comments were made by Mr. Day about shorter superheater units. I have to agree with Mr. Day that there is something to be said about shorter units. The past thread failed to discuss in depth the fact that RR's had procedures for plugging failed units between regular washings and repair. As such, if a locomotive had, say 18 units, but two failed after 22 days of operation, rather than removing the locomotive from service, the railroad may have simply plugged a few units until the next 31 day washing. As such, a locomotive clearly can operate with a certain percentage of units plugged, broken, or damaged. Well, if the designers and the railroads knew that they could run without a certain percentage of units, why then is it that Mr. Day would be incorrect in saying that shorter units may be more effective?

Personally, I dropped out of the last discussion as it had degraded to the point of "my dad knows more than your dad and my dad can kick your dad's ____..." well, you get the point. This discussion is to remain civil and grounded in first-hand experience. Mr. Day is to be credited for his first-hand experience in the matter! For the record, I feel that shorter units are better and would, and do, last longer with no compromise to the total locomotive.

Kindly,

interesting to find different lengths. probably one reason the longer ones experienced the more damage is it is closer to the firebox. That distance could be just enough to produce a higher temperature difference, the longer the tube the hotter the end would be.
But you would sure get a hotter steam from it, but the tube would wear sooner over time. It would also experience more heat differences per inch and you know how rail buckles in hot weather this is mini-sized in the boiler on the tubes on the molecular level. The longer tubes probably need a better sealing with a thicker tube.

You have to note the boiler and tubes have to transfer heat around.

I hadn't heard of plugging off failed superheaters, but now I know how 765 is done, that might be possible without removing them at the time until repairs are possible.

In reading the posts below by Dave i agree, parts cobbled together to keep the engine going. I would venture a guess that the units are so old that the metal is just far gone from any reasonable service life without thought for length or function.

From an old low budget shortline guy: you cut out the worst bits and weld the better stuff together and cross your fingers that it lasts for a bit longer. Hence, we have many different lengths, even taking the multiple rows into consideration. No mystery. No big deal.

Expansion is readily dealt with by the freedom of the elements to move inside the flue. Don't sweat that, on the "molecular level" or even on a practical mechanical level that we might actually want to think about.

There's a bunch of variables involved with superheater element design, steam flow speed and volume at different cutoffs and pressures, heat transfer or lack thereof, surface area for greater or lesser transfer surface.....needing to have enough "cool" steam flow to haul off enough heat to prevent burning the elements themselves........the lag factor during which the superheater element itself needs to warm up to a higher teperature than the interface of the internal steam flow enough to add heat in any meaningful way. Now, when this isn't all that tough to figure out based on a constant flow and pressure, when locomotives don't tend to run at a constant flow and pressure.......you have to solve for all variable conditions within the envelope.

Or, you just make a superheater element that will do a pretty good job and be mostly robust under the most likely conditions of use. That's about state of the art for adequately budgeted applications.

I know John and his crew will build something that is going to be light years better than status quo. I'd welcome further updates outlining the process.

dave

In response to BobK,

Bob, what we have actually found is that materials are a bigger issue. They do not have an abundance of what would be considered acceptable materials for these units. Rather than cobbeling things together.....they cut things down to keep them in service for lack of quality material.

Notice the return bends. In the photo alone, there are three different styles of return bends (at least). Most of which I believe to be German brands and makes. I have been told that the Germans were the last group of "steam professionals" to work on these boilers and that they brought most of their own material. I can tell you first hand that I question a great amount of the material that has been used.

Dave,

They have asked us to build the boilers to the most advanced technology/procedures and process available. These are not ASME Code stamped boilers, but are being built to the standards of TWO "Nationally Accepted Standards" and one of which is not a US standard. Indeed, Dave, I feel that we will provide an end product that is light years ahead of what they have now. Already we have added many more feet of heating surface area to each boiler in the way we have designed and cut the tube sheets, as well as with the number of tubes we have been able to add.

Thanks for the comments, guys.

JohnE.

What are you guys using for return bends these days? 30 years ago, I watched the Fort Wayne guys replacing superheater return bends on elements for 765 with off-the-shelf butt weld steel pipe fittings (90 degree elbows). They'd gas-weld 2 elbows together to make a 180, weld that to the element, and then build up material on the firebox side of the bend to serve as protection against cinder erosion. That seemed to work pretty well.

Are actual forged superheater return bends still available from China or someplace else, or are you using something like this?

The Strasburg return ends work well for me. Personally I would not consider making them up out of fittings or the like. The Strasburg product is spec material, dimensionally accurate, and welds beautifully.

Best,

Stathi

We just bought out all that Strasburg had in return bends and they are making more. So, Hugh, contact Strasburg if you need them......

You would almost think that in an industry as small as ours we would be fierce competitors. The guys at Strasuburg are great and they help us often. In fact, so many of our industry contractors work well together and I am proud that I can call so many of them friends.

Kindly,

JohnE.

At one time, the SLSTA (1522) had a mold with a local foundry and had investment cast type A bends made, which worked great. We had one for Type E units that the NS used, but unfortunately it appears there are more than on size for Type E units. We didn't find this out until we had cast an order for a restoration and they wouldn't work with their units. I still feel bad about that.
When we ceased operation, we sold the tooling. I think Strasburg has the same arrangement of investment cast bends.
I don't know of any forgings still available in this country, but never looked into it.
With the service that most engines see in today's world, I would think that putting shorter units in would be an advantage, particularly in oil burners.

I think those two are different questions.

Can an engine run without a certain percentage of the units? Certainly. Does that mean it's running more effectively? I don't think we have any reason to believe so.

Let's look at the diesel electric world. Can you run with a traction motor cut out? Does that mean it's more efficient?

Shorter units may well be more effective, I'm not disputing that. But I don't think you can prove it using the fact that some engines operated with plugged superheaters.

I hope my posting here is in keeping with the subject and includes my veiws on super heaters. The previous thread was not the correct place to put them. I certainly do belive that there is a place for a more practical veiw of technology than a debate on mathmatics and academical concepts. Most of what I discribe (and is proven) is freely avalable with more mathmatical forms if the reader wishes to go deeply in to the maths which I do not ever intend to do here. I give Mr Rimmasch fullest of respect for everything he dose and has said to keep this forum in a productive state.


For the basic proportions of tubes there is a ratio for heat transfer as included in Frys book. This in many ways appies for super heater flues with the super heater eliments as one and fire tubes.
The A/S raito where A is the cross sectional area of the flue for gas flow (in a super heater is where the eliments are) and S is the surface area of the tube (and eliment).
In model locos this figure can be 1/100 and small locos say up to 20 to 30 ft sq of grate 1/350 and the largest locos over 1/500. This can then be worked agenst many other factors of combustion. In an aproximate count I go past 20 items for an oil burner which would afect things. Some where mathmatical terms would be totaly useless. In the end maths will only give you a ball park figure.
For oil if you have a good A figure relative to the serface you will get a high super heat temprature, and need to shorten the eliment (which is to reduce the total heating area) to get it out of the hotest areas. Such changes and fuel canges efect the smoke box gas temprature and with oil having a higher combustion temprature the whole balance is efected and then the overal eficentcy of the locomotive.
When you proportion a super heater and flue you have to take into acount not only the A/S ratio but also the proportion of the heating surface for the super heater and the flue.

The upper limit of super heating is basicaly down to lubrication and that as one exsample I give is R711. I was not directly involved so do not have the figures. I now work with guys who where involved in it. It first ran with full length eliments and it burnt up every last drop of oil it was given. The best of oils will only work up to the 450 degree C range 500 the max. ( I see a drum of oil every day that is shipped half way round the world to get the proper oil and even when I was at snowdon the super heated loco used somthing very special for high temps.) So much as I would like to use super heat well above 500 degrees C then its not viable unless some one has some super oil? Cutting the story short R711 had its eliment changed for shorter ones. The loco's lubrication worked for the correct temprature of steam which was at the same as with coal. Maybe it had alot to do with the overal A/S figure for that particular flue?

So far in this thread and the previous no related thread little has been talked about the overal requirements of the elements in other areas. The traditional eliment has many passes down the boiler. This is not ideal for two reasons. Firstly the more length and bends the higher the pressure drop and resitance is to steam flow. Idealy you need a straiter large cross sectional area and short length. Velocities then become low and heat transfer more greter for the given length. Secondly once an eliment has made more than a down and back pass it is likly to be heating the steam on the way to the firebox and cooling it on the return. Repeating this as you get lower in the boiler where its cooler dose not nesicarily mean that you are gaining the best heating. So to sumerise the best super heaters have more shorter there and back eliments with a combined larger cross sectional area.

I do not quote eliments that are smaller (for oil firing) as being more efective, just in proportion to what is required. With the whole of a locomotive the total balance must be maintained and if one item is changed there can be a knock on efect and somthing else has to be ajusted to maintain the balance. Any eliment which is damaged or the flue is blocked will not help the situation and should be rectified. Its true that keeping the length down that the temprature and damage to the return bends would be less but then you have to re calculated the rest of the eliments area to achive the corect level of superheating.

I will still repeat that heat resisting stainless steel is best. I have used L316 as fire box super heaters for atomising steam and they last up to a year if not directly in the flame path. I also repeat that both fitting stainless ends is is a viable option in the right conditions even if they are not 'old ' practice, and that compered to some situations its not overly expencive in the long term. As to the coment about stainless as not being conductive well look in your ketlle.

I look forward to seeing John's new boilers. I am sure they will be of the best standard posible as all his work is.

I agree the distance and curves realize resistance to the steam flow but the purpose is to dry the steam more and give it even more "pop". Cutting off some from use will cut down effectiveness and efficiency, but you still get steam flow to keep you going.
We aren't running heavy mainline steam, its excursions pretty much for the enjoyment, doing what your doing in this thread is more about some frugality.

With the steam spread over all those superheaters in parallel I think you overcome the resistance but the real goal when it enters the cylinders you get the hottest possible dry steam at the peakest pressure possible. Giving the steam more heat means more pressure, probably why keeping the throttle slighly cocked even coasting keeps the forward pressures correct or it all backs back into the boiler.
I think the throttle valve tho is before the superheaters so that concept of backing back into the boiler is minimal.

You might have say 250-300psi in the boiler but them superheaters should bring that up, but you never have a meter on them to know.

oh, about the traction motor relation to this, lets say both the North Shore and South Shore ran trailer cars in their trains, no this doesnt help your accelleration but when running non-express trains its moot.

But I just learned the North Shore had some cars like diners having 2 motors than four, my guess to make the car do its own "helping" than rely on the powered cars.
Its like putting boosters on a tender.

In the case of superheater units, turbulence is actually a good thing. While it will lead to a greater pressure drop than laminar flow,it gives better heat transfer. At the end of the day, the efficiency of the locomotive is based on the temperature change between the admission and exhaust steam. Pressure is essentially a proxy for steam temperature. The increased temperature of the steam due to turbulent flow more than made up for the slightly reduced pressure. Part of the reason behind the shape of the Elesco forged return bends was to create turbulent flow in the units.
-Stu

Or was the turbulence simply an accident of the design which, because it empirically worked better, made it to the marketplace? Was there that much attention to that kind of thing "back in the day" before computers? I suspect that the designers had an idea of what was going on but could not prove it or have much control except by trial and error.