Allow me to offer an alternative approach. I realize it may be viewed as not only radical but quite possibly heretical. Listen to the first hand experience of some who have successfully accomplished the assigned task.
I know this could be viewed as completely un-scientific and could be seen to fly in the face of all academia but it is a time-proven method. I would remind the gentle reader of the "P" in RYPN - Preservation. Preservation of method is, I believe, as important as preservation of machinery. The method of learning directly from success comes from a time where engineers began by sweeping the floor and worked up from there and quite possibly before.
Study & note what works. Imitate what fits your application & modify to make improvement from there.

As to the above mentioned corrosion of the steam line, looking at the pipe would tell you the story of whether the attack was internal or external. I have seen both. As a matter of fact one of the coaches at North Freedom pinholed a vapor pipe inside the car. Since the failure was along the baseboard inside the carbody the corrosion was from the steam side. We will have a bit of work to do on that car before next fall........mld

Not to be a besservisser -- One thing about 'time-proven methods" is that it's important to learn and understand why they work. Here, we have a "time-proven" approach to building heat with boilers running 15-30psi, often with substantial pipe runs, but we also have a "time-proven" rule of thumb of ~10psi per car. It is important (to me) to see the characteristics of a typical multipass 'package boiler' (of the size and construction that will fit properly into operating railroad cars) and see -- for example -- whether high available mass flow at lower pressure would allow adequate car heating, as opposed to a tapered-monotube or similar 'flash' steam generator with lower mass flow at much higher pressure, that benefits from 'being operated flat out' at design pressure to avoid problems that experience might not predict if operated at lower pressure.

That of course is not to say 'every new install should turn into a science project'. (Or, in my opinion, that preserved equipment shouldn't be operated, as far as possible, in contemporary ways as part of the historic preservation.

It seems to me that it would be relatively easy to 'borescope' an existing steam line to detect pitting, thinning, etc. and then clean and passivate the inside surface and pass an inflatable 'pig' or swab down the pipe to spread a good epoxy sealant on the inside walls. That does not alter the historic appearance of the equipment in any meaningful way... in my NASP opinion, anyway... and it precludes further invisible pipe damage going forward. One of the points of using high pressure in the trainline is that you have many of the potential dangers of high-saturation-pressure steam distributed down the first few cars of the train, should the sort of problems with poor trainline quality suddenly manifest themselves. Inherently restricting available mass flow, as the monotube generators would, might be a safety feature more than a 'bug'.

1951 Vapor Steam Heat manual and parts list from erixrailcar.com https://www.erixrailcar.com/techpubs/Vapor_Steam_Heat.pdf

Enjoy,
Mike Tillger

Perhaps you meant besserwisser? https://en.wiktionary.org/wiki/besserwisser

...............mld

The W is likely pronounced as a V, which is probably why he spelled it that way.

I perpetually pronounce German-looking names that start with W as V, as in Max Weber, as Vay-bear. I once pronounced a university professor colleague's name, Weiss, as Vice (as in weissbier, wheat beer, or hefeweizen, yeast wheat beer) and she came unglued, even though she had Max Weber's books on her shelf in her office and should have known what I was doing and why.

It's a sardonic expression; the original German is indeed 'Besserwisser' (with the appropriate capital for a noun) but I first came across it in the New York theatre community, so it might well have passed through Yiddish on the way. I don't remember how it's typically spelled in Chicagoland, where I think it's much more connomly used than on the East Coast. In New Jersey we generally used just the blunt 'wiseass' which doesn't have quite the bite, or 'weisenheimer' (sometimes seen without the initian 'e') which is that guy in the Polar Express movie who notes to nobody listening that the locomotive is a Baldwin.

And I not only say 'Veber', I pronounce his first name like 'Mahks'...

On page 138 of the Vapor tech info, it implies that the trainline pressure should be 75 to 225 psi.

But note the repeated references to intermediate reduction to ~50psi and then 8-12psi at the regulator, with the implication that near-atmospheric pressure with full condensation 'pulling a partial vacuum' to aid steam mass flow is being used in the actual radiators or elements.

Note in particular the mention that heat conduction through condensate between inner and outer pipes in the radiant heating is a major factor in even heating.

This is fascinating! I've never stopped to consider how steam heating in cars actually works. We just throw in the knife switches and let Ohm's law do the work!

In stationary building applications of steam heat, it is a closed system. Single pipe systems rely on gravity to return the condensed steam down the same pipe where the fresh steam is rising. Double pipe systems have a supply and return line.

WIth the train application, it seems that the system is a single pipe. But there is no gravity return. So am I understanding correctly that the system works by venting steam/condensate at the end of the train? If so, what regulates the rate at which the steam is vented?

I will only speak to the single pipe system used in the Lackawanna coaches, 1914 vintage, Pullman built, used at North Freedom. The coach is broken up into 4 heating zones or loops. Each zone has a valve to cut the "vapor pressure" steam to the heating loop in or out. Each of the valves has a steam trap to drain the condensate either from the valve alone (when shut) or that heating loop (when open). This way, even if a valve is shut the tiny amount of steam through the pilot opening of the valve can drain. The pilot opening is there to keep the valve thawed even if off.

The traps in this system open wide to only drain off the condensate. Otherwise they close to just a tiny pilot opening to keep enough steam flowing to keep them thawed out. In normal operation at Mid-Continent you can see when doors are held open & such by observing the train line steam pressure. When traps open up they take a large gulp of steam.

At each end of the train line we have a steam trap threaded into a Vapor connector and hung on the train line. This keeps the "metallic steam conduits" drained so they don't freeze up.

In this system there is no steam that is vented simply to keep steam flowing. The steam flows into each individual heating loop only when enough condensate collects at that particular trap to cool off the internal bellows in the trap enough to open the trap & drain onto the ballast. When the trap is "empty" and only steam is draining the bellows warms enough to force the drain shut, collect condensate and repeat the cycle............mld

Hopefully this diagram helps answers some questions.

Thank You for sharing that, Andy! I have an ICS book somewhere in my collection but have been unable as yet to dig it out.
Happy Holidays to All!!!..........mld