Steam & Excursion > Maximum successfully implemented boiler pressure?

In general, it seems in my causal reading that the maximum designed operating boiler pressure for any US railroad steam engine was around 300 psi.  I've seen some reference to slightly more than that in some cases, but in in general, it seems like 300 was typically the maximum that was successfully run, with the majority of mainline steam appearing to be more in the 225-275psi range.  I'm sure there were controlled experiments at higher pressures, but were there examples that I'm missing where they regularly ran significantly higher than 300psi? 

Obviously boiler material choices and availability were probably the limiting factor - I can't imagine trying to design a pressure vessel like a locomotive boiler to operate safely at even 200 psi, so I have a huge amount of respect for those that designed (and risked their lives operating) these high pressure boilers at 80-100 mph regularly. 

milwrdfan Wrote:
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> In general, it seems in my causal reading that the
> maximum designed operating boiler pressure for any
> US railroad steam engine was around 300 psi. 
> I've seen some reference to slightly more than
> that in some cases, but in in general, it seems
> like 300 was typically the maximum that was
> successfully run, with the majority of mainline
> steam appearing to be more in the 225-275psi
> range.  I'm sure there were controlled
> experiments at higher pressures, but were there
> examples that I'm missing where they regularly ran
> significantly higher than 300psi? 
>
> Obviously boiler material choices and availability
> were probably the limiting factor - I can't
> imagine trying to design a pressure vessel like a
> locomotive boiler to operate safely at even 200
> psi, so I have a huge amount of respect for those
> that designed (and risked their lives operating)
> these high pressure boilers at 80-100 mph
> regularly. 

D&H had some massive 2-8-0s and at least 1 4-8-0 that
had watertube boilers and operated at something like
1,200 or 1,300 psi.  However, those were oddballs.

There were some locos designed and built to operate
at 310 psi.  Notably Santa Fe.
 

Many successful fast locomotives operated in the 200s.   PRR K4s Pacific  205 PSI     NYC Hudson original 225 PSI. 

Flash steam boilers or monotube boilers (water tube boilers) have operate at much higher pressures. A very small volume with high pressure, used mostly for steam automobiles.

For locomotives, you are right the 300 PSI range is generally tops. Available fire making ability, sizing, boiler materials and power needed all contribute to an ideal pressure. And too much power vs. weight leads to wheel slip.

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

I thought the D&H engines (three 2-8-0's and a 4-8-0) used about 500 psi.



Edited 1 time(s). Last edit at 11/18/15 12:00 by CPR_4000.

I've read that as well, CPR_4000.

I think you will find that fire-tube boilers, fitted with 'stayed' fire boxes, that the limiting factor for maximum pressure was the practical spacing of the stays, the maximum stay diameter and the thickness of the firebox sheets.

3/8" -- thick, firebox sheets were determined to be the maximum thickness steels that could be used for fireboxes. However, our forefathers were wise in considering the typical mud/scale build-up, over time, of the contaminants baking onto the sheets.  
That layer of mud and accumulated calcium-derivatives is a very good insulator---- meaning  that a very thin layer of mud ( on the sheets) reduces the convected heat pass-through rate to the water by better than 60%.  A thicker accumulation, reduces the heating capacity even more severely.  Sheets thicker than 3/8" were subject to a greater degree of fire-side melting and erosion.
Reduced heating capacity, conversely, means a vastly reduced cooling capacity of the water ---- to protect the sheets.

The design of the firebox relies heavily on the rapid heat conduction through the sheets to the colder water on the steels comprising the furnace.  HOWEVER, if the steel cannot be sufficiently cooled, for long durations, some of the steel exposed to the 3,000 deg. fire, will begin to melt away and even suffer the effects of loss of the carbon elements in the steels. The melted-away steels cause the sheets to be thinner, with the resultant loss of effective number of threads holding the sheets from stripping off the staybolts and possibly producing a catastrophic firebox failure.

SO over time,  it was determined that the closest practical spacing of the stays (nominally 3-inches, on-center) the largest
diameter stays
( meaning that a big bolt's center will melt-away if the whole bolt is heated to red hot) AND the practical consideration of the strength ( sheet-holding ability) of the 12TPI threads ---- considering that there are less than 4.5 threads [ in a 3/8" sheet] "holding" in each stay bolthole----) together with a reasonable amount of baked-on, insulating scale the practical limit of conventionally stayed fireboxes seems to have been 310 PSI..

ALSO, remember that the "safety factor of 4" still applies to the firebox calculations.  A 250 PSI-rated boiler must be designed with a firebox to withstand a theoretical pressure of 1,000 PSI.

"Watertube fireboxes" have no-such flat-steel construction configuration, and so, can be designed with much higher design pressures.

For those in the EAST, the Ben Franklin Museum in Philly, houses the BALDWIN demonstrator loco number 60,000.  It is a low-drivered, 3-cylinder, compound drive 4-10-2*.
Remarkable because NO railroads bought a single copy--- even after a nationwide sales tour. ( compare to the numbers of Lima A-1, 2-8-4, copies that were sold following a similar Nation-wide sales tour).

So there's plenty of math that underlies the practical limit--- along with the heat-transfer capacity of the steels used in the construction of the firebox------ also, the accumulation of mud on the heating surfaces combines to make the practical limit of conventionally-stayed fireboxes to be 310 PSI.

Lastly, I'll leave you with another scary fact of steels:  at a heated state of 1,000 deg. F., steel glows a dull red --- barely perceptible in a darkened room.  It's strength, compared to conventional ambient temperatures, is reduced by 8-times it's strength at the cooler temperatures!  Meaning it is 8 times weaker than cold steel, or steel that is submerged in water.
How does that compare to the FRA's so-called "Safety Factor of Four"?

NOW, go back and revisit the recent discussion of how much water is left in a boiler after the BLEVEY !!!
And does that really matter?


Wes Camp

*. Addendum...
Wikipedia lists BLW 60000 has BP of 350, PSI.......
W.



Edited 1 time(s). Last edit at 11/18/15 17:17 by wcamp1472.

Supposedly a D&H 4-6-2 (number 653, maybe)
had 325 psi in its stayed-firebox boiler. Don't
know of any other US engine with more
than 310 psi on a stayed firebox-- maybe
none in the world?



Edited 1 time(s). Last edit at 11/18/15 15:31 by timz.

CPR_4000 Wrote:
-------------------------------------------------------
> I thought the D&H engines (three 2-8-0's and a
> 4-8-0) used about 500 psi.

You are closer than I was. at least one of the
2-8-0s ran at 400 psi, while the 4-8-0 had 500
psi.

It was a 4-cylinder, triple compound, with a tender
booster.
 

I read somewhere that a N&W A class was modified at one point with bp raised from 300 psi to 315 and some weight added to the frame. I would have to assume that the design of the boiler had enough leeway in it to allow this increase, if this even really happened. It may have been just one of those tales. 

I seem to remember that the KCS 2-10-4 locomotives were also designed and delivered at 310 psi. However as a result of some running gear machinery "issues", the working boiler pressure was subsequently lowered to 300 psi.

> I read somewhere that a N&W A class was modified
> at one point with bp raised from 300 psi to 315

That was Le Massena's surmise. Don't think
anyone else believed it.

To put this in perspective, I was in what I would think is a moderate size coal fired power plant.  They had two sides to the plant, each side was putting out a bit more then 750 megawatts of electricity.  That translates to over a million horsepower per boiler, without ineffciencies figured in.  Each boiler was fed with 8 pulverizers, each one driven by a 5000 horsepower motor.  The boiler pressure was in the 3000 PSI range, but I seem to recall they were licensed to run up to 4000 PSI.  And the generator itself, the windings are cooled by pure gaseous hydrogen!

"Cooling with hydrogen?"

I've seen transmission lines pressurized with liquid Nitrogen.
Do you published materials stating that these plants, in fact, DO use gaseous hydrogen?

Wes C

No offense, but I don't exactly feel compelled to dig up 'proof' on fun facts.  I'm sure you can research it as well as I can.  I found out when I was in the control room, one of the meters indicates the % concentration of hydrogen inside the generator casing. Asked what it was about. Obviously they have to keep the % concentration as close to 100% as possible to prevent an explosive mixture.  Reason given is that hydrogen apparently has a excellent capacity to remove heat, much better then air or other common gasses.

I seem to recall reading that getting access to sufficient quantities of the very best quality steels was problematic in the 1940's due to wartime allocations?  Perhaps the best steels would be more properly used to prevent failures in 16" Gun barrels, or fighter-plane engine connecting rods, than to build a steam locomotive with the utmost possible efficiency, for example?

wcamp1472 Wrote:
-------------------------------------------------------
> "Cooling with hydrogen?"
>
> I've seen transmission lines pressurized with
> liquid Nitrogen.
> Do you published materials stating that these
> plants, in fact, DO use gaseous hydrogen?
>
> Wes C
https://en.wikipedia.org/wiki/Hydrogen-cooled_turbo_generator

Kimball Wrote:
-------------------------------------------------------
> I seem to recall reading that getting access to
> sufficient quantities of the very best quality
> steels was problematic in the 1940's due to
> wartime allocations?  Perhaps the best steels
> would be more properly used to prevent failures in
> 16" Gun barrels, or fighter-plane engine
> connecting rods, than to build a steam locomotive
> with the utmost possible efficiency, for example?

I believe the restrictions were more related to running gear components, such as high strength light weight rods. That sort of material was pretty much used exclusively for war materials, thus the Santa Fe had to use "heavy" rods without roller bearings, as one example, and after the war they up-graded to the high strength light weight rods with roller bearings. The "heavy" boiler plate used in steam locomotives didn't seem to conflict with war production requirements.

wcamp1472 Wrote:
-------------------------------------------------------
> "Cooling with hydrogen?"
>
> I've seen transmission lines pressurized with liquid Nitrogen. Do you published materials stating that these plants, in fact, DO use gaseous hydrogen?

> Wes C

Come on Wes,  I heard that the turbos on 614 had to be cooled with Hydrogen when they put in all that train control elctronics.  ;)

Hydrogen??

Sounds plausible, now.
Maybe I learned something, today.

W.