RE:

Boiler tube wall thickness, of 2" OD tubes, original spec is #12 gage. I seem to recall a recommendation that wall thickness of #10 gage gives longer tube life, but presents greater difficulty in rolling in the tubes to the tube sheet.

With some of the earlier commentary here about excessive pitting (and thus shortened tube life), is the use of the thicker tube material a good idea?

Or simply use good US-origin SA-178 material, #12 gage, and coat with Apexior? I know the Apexoir is the way to go regardless of tube thickness.

I'm interested in hearing the thoughts of the steam gurus on this subject.

Howard P.

Hi Howard:
If by "longer tube life" you mean having the ability to cascade or safe end the tubes to obtain more terms of service for the tubes, then a thicker wall might help a bit.
Unless you are planning to roll the tubes by hand, thickness isn't much of an issue as your tube rolling motor (air or electric) is doing the work, all you have to do is hang on.
Concerns about pitting, stress corrosion and the like are best addressed via an effective water treatment program.
I would suggest asking Dampney Corp. about the use of Apexior on fire tubes.
It is a wonderful product for the inside of a boiler, I have used it for many years with excellent results.
I recall discussing using it on tubes with them in the 70s'. They were concerned about the Apexior coating withstanding the heat at the firebox end. Also, I would ask about any reduction in heat transfer.
Which of your locomotives are you retubing?
Good luck!
J.David

JDC,

The concerns about pitting were based on memory of prior discussion here on RyPN about short life of tubes on the steam Thomas at Strasburg. I recall an "80-service-day" number (no, I did not go back and search it yet, but will). And I cannot imagine that SRC would operate any boiler without a good and effective water treatment program.

A water treatment program would certainly be a given for successful operation of a locomotive boiler, and would be a part of any operation that might be undertaken.

Nothing planned right now, just some mid-summer musing.....

Thanks,

Howard

I've hand-rolled ("expanded" in UK parlance) 10g tubes several times, it's easier if you anneal the ends first but I've also done it without. There seems to be great variation in steel quality. The first lot I did were from British Steel and lasted 11yrs without treatment but the next batch only lasted 7 and deep pitting was evident from about the 2nd year - I suspect they Far Eastern. Now there has to be "traceability" for everything so it is easy to see where the tubes are manufactured but it is worth paying for quality IMHO. One of my buddies used 2 types of Apexior, the bitumen type on the outside of the boiler and the matt finish one inside the boiler and on the tubes. I don't know if the Apexior really extended the life of the tubes but I'm converted to using water treatment these days. Ray.

heating the tube end (red hot) (annealing) softens the metal for spreading, perhaps prevents any cracking. Depending on the diameter closeness, probably not that super of an issue since its getting welded. Probably makes it easier to spread. For a thicker gauge certainly would make it easier if you Anneal. There may be certain reasons the railroads would pick X gauge for predictability of use, familiarty and cost. But fer them us preservators, longer life and reliability the bonus. But I guess doesnt change the Boiler rules. Thats right, watch your metal source.

The act of deforming steel by mechanical means introduces changes in the micro and macro structures of the steel. While some of the changes in the structure can be are removed by heat the entire effects of the mechanical deformation will not be completely counteracted. These areas of higher localized stress are typically the first to corrode.

It should be noted that in most historic railroad practice the tubes from boilers with longer lengths were reused in ones with progressively shorter lengths. By cutting the ends and reusing the centers tubes could be used in several locomotives before disposal of the tube.

An issue with thickening the tube wall is you can change the stress patterns within the firebox and put additional strain on the knuckle and increase the possibility of cracking the knuckle. These would be some of the considerations about increasing tube thickness.

Robby Peartree

I have come to dislike thicker tubes as they increase the stresses in the tube plate. Additionally with tubes which are seal welded the tendency is to weld them in a way where there is a sharp corner left. This is exposed to heat but further away from the water increasing the distance the heat has to be conducted. The result is a build up of heat and a fracture will start and extend into the tube plate. This condition is increased by making tubes thicker.

When you make the tubes thicker you also affect the gas flow area through the boiler. This I have found in one case to reduce the flow from the standard of 14% to 12% not a small amount so steaming is also effected.

In general making any plate thicker to off set corrosion is a bad thing. The boiler is a flexible structure. If you make it to stiff you will cause stress failures at week points. The solution is proper water treatment.

From Kelly Anderson, 2011:


"It seems that certified tube material (SA-178 A is probably the most commonly used standard) doesn’t do much to protect you these days. At the recent Engineering Standards Committee meeting, a large portion of the first day was spent in a metallurgy clinic of questions and answers to two retired metallurgists who spent their careers in the local steel industry, and it seems like we have a number of details working against us these days.

1. The accepted standard tube material (SA-178 A) has had the percentage ranges of alloying elements in the official recipe considerably widened over the years to the point that any given heat of SA-178 A tubes can be quite corrosion resistant, or can be “rusting out on the show room floor” garbage, and still meet the SA-178 A spec. This leads to a “luck of the draw” situation where our #90 is closing in on 1,300 service days with tubes that still look new, while our steam Thomas just had her tubes replaced after 300 service days due to having lost over ½ of their thickness. The metallurgists noted that you can tighten the specs of the alloying elements of your particular tube order to stay in the more corrosion resistant range, but that you will need to order a mill run of tubes to get your custom mix. Ka-ching.

2. Single orders of tubes under one set of mill test reports may or may not be from the same heat, regardless of what the paperwork may say. As long as they are all SA-178 A tubes, left overs from different heats can be consolidated by the steel company under one MTR to dispose of them. Not too ethical, but they said it is done. This can explain having one tube in a boiler looking pristine, while the tube next to it is shot, even though both are under the same MTR and were installed at the same time.

3. As the steel industry has modernized, the newer techniques (electric furnaces and the like) have resulted in a much cleaner product than what was available in the “steam era”. Ironically, the dirtier the steel, the more corrosion resistant it is. I asked one of the metallurgists where we could go to get some good old dirty open hearth or Bessemer steel, and he thought Russia or China, but advised me “not to go there”."

Are certain tube suppliers less likely to do what is described in #2?

Howard P.

Hi Howard:
Consolidations of different heats of tubes would occure at the steel mill, the supplier might/probably not even know.
One interesting issue mentioned at the ESC Meeting in 2010 in reference to modern vs. old fashioned steel manufacturing processes is that in the bad old days, silica was used to "kill" the molten steel in the ladle. Now, aluminium is used to "kill" the steel. Old "dirty" steel with traces of silica, copper, etc. seems to be more corrosion restistant than modern clean steel.
Nigel's points are well taken. I recall doing a tube job on a boiler which the owners proudly had installed 10 gage 2" tubes many years before. The tubes were a bit pitted but decent as were the tube sheets. But by the time I had removed all the tubes the tube sheets looked like pieces of bacon! It took us days with torches and strong backs to get them reasonably straight again. I didn't tumble to it at the time, but those sheets must have been under a great deal of stress to buckle like that.
When Wayne, et al removed the tubes & flues from what was to become our No.3025 no straightening was needed on either sheet. The Chinese use tubes & flues at the low end of the thickness needed for a "Factor of Safety" of 4 (four). Also, they use electric rolling motors which have adjustable torque settings. At Tangshan, the tubes and flues were rolled, then the boiler was hydro tested. Any "weepers" were dealt with on an individual basis by hand.
I would note that we inspected the tubes and flues removed from No.3025 (15 years +/- service) and decided to safe end them (after sandblasting, a further inspection and trimming). There was very little pitting on any of them. We hydroed them after safe ending and reinstalled them.
Be well,
J.David