Hi All

I think what we need to remember here is how the joint is designed. The free-body diagram showing the hoop stress (torque condition) in this type of construction which is causing the bending. Because the two sections of the sheet are not in the same circle they try to create the condition of a single radius. This action tries to balance or minimize the forces acting upon the sheets. In latter boilers a completely different design is used which places to two section of the boiler into the same circle by design instead of the boiler trying to achieve this on its own. It would be interesting to see just how many people know what a lap seam is.

Respectfully
Robby Peartree

http://www.texasescapes.com/TexasRailro ... losion.htm

not a failed boiler but example of explosion and why it happenned and where it failed.

Oh, I recall visiting the museum in Philadelphia engine 10000 I think, it has a watertube boiler, it has a normal steam pressure is about 600 pounds, the story was when it was first run, the engineer went into the cab and saw the steam pressure...and got off....

"The ONLY reason riviting was supplanted by welding was simply economics...only one guy is needed to weave a bead, but it can take a gang to flange and rivit a boiler together."

That is not the only reason riveting was supplanted by welding. On the boiler courses, the weak link is the riveted joints because of the need to put a bunch of holes in a line. Welding eliminated that problem and allows you to have a thinner piece of plate for a given pressure.

Rick

Welding does allow for a lighter plate, but if it was cheaper to rivit a boiler together, that would be the preferred method. Boiler manufacturers would glue a vessel together with Elmers if it were cheaper and safe. Believe it or not there is a Code for composite vessels made of very non tradtional material, and don't be surprised if someday there is some sort of "plastic" boiler made out of some carbon fiber and man made goop. Shops build boilers to make a profit, today and in the past. Most boilers made today are throw away units in any case, especially in the smaller process type.

Along these lines there was a boiler explosion on the Katy at Smithville on an old Mogul. If memory serves, they were setting the pops after a general shopping, and over pressured the boiler due to a faulty steam guage, and, I suspect, there was a significant contribution from John Barley Corn.

While the rivit seams are weaker than the parent metal, a well designed and executed joint is more than enough for the service intended if serviceable.

“not a failed boiler but example of explosion and why it happened and where it failed.” The link you refer to is a great example of a boiler failure due to what is considered to be one of the most common problems with boiler accidents, and that is operator error. This example has nothing to do with the subject of lap seam boilers other than the fact it was a lap boiler. Whenever a boiler explodes it is a failure regardless of what has caused it to fail. We take this business of boiler safety very seriously and this thread does not need to be derailed by comments or links to pictures that really do not have anything to do with the subject at hand. Bruce Babcock, Mark Jordan, Jim Templin and Robby Peartree have all addressed this subject in an effective and open manner. This subject has been a hot topic of traction engine owners and I know that the above named men have done an exhaustive amount of research regarding the issue of lap seam boilers and respect their opinions, thoughts and feelings about this issue.

Boiler Safety regardless of what kind of boiler is the biggest safety concern for all of us whether we are dealing with a locomotive or a traction engine. It does not matter if it’s a lap seam, butt strap or welded boiler, if it has not been maintained, inspected and operated within the parameters of its design then it will be unsafe. What it boils down to is human error whether it’s due to low water, failure of the shop to inspect the steam gage, improper inspection of the pressure vessel or something else. The purpose of this thread is to illuminate and discuss the issue at hand which is lap seam boilers and the cracking that may or may not occur in and around the lap seam. We who own and operate steam boilers are always interested in gaining more knowledge about this issue and how it affects the operation and safety of this type of boiler. The major issue here that still has not been answered is where did this sample of a crack come from, ie what kind of boiler was it, was it in service, who found the crack and how. These all need to be answered before we can go further with this thread.
John Deck

M Austin will have to converse with his other hemisphere friend to zero down on the hence mentioned boiler in question.

I illustrate the boiler explosion to show where it fails because of excessive pressure which is at the lap seam, which is the same effect shown in the graphic. The crack in the metal of the original boiler is not explained, I tend to believe there might be a manufacturing fault. There is a reason to cutting up a boiler like mentioned, and only when when cut like this the crack found, otherwise it would not have been found.

Should there had been cracks on that boiler explosion I mentioned, it could have done the same thing at normal boiler pressures.

cheers.

Ok, Kiddos, a little boiler 101...a circumferential lap seam is different than a longitudanal lap seam, and is figured much differently than a long seam. The discussion here, as it has always been, is on the long seam. None of the "cracking "models described apply to a circumferential seam.

Just so you know, every steam locomotive I have ever seen has circumferential lap seams.
The Smithville explosion was not due to the either the circumferential seam letting go, nor the longitudanal lap letting go...this engine was overpressured to the point that the crown sheet was pulled off the crown stays. The engine was a series of Baldwin built moguls constructed either side of 1890, so this old hog had been in service for at least 20 plus years. Since the engine was in switching service, it was likely pretty low on the totum pole as far as getting money spent...at this time locomotives of this same age and class were being sold off to both shortlines and scrappers...I doubt that the "thorough overhaul" mentioned was the complete remanufacturing that we would envision. What we don't know is if there were any patches, reenforcements, ect. applied to areas of the firebox to compensate for wasting. Rivited reenforcement plates were common practice when thinning was found...just rivit a patch over the affected area, drill a weep hole to let you know its leaking, and go to town. Sometime these weep holes didn't get drilled, and the patches became a time bomb. On a socio-historic level, there was much alcohol abuse on the railroads than anyone would care to admit, but booze was a huge contributor to many accidents at that time. The term "asleep at the switch" could very more often have been "piss drunk at the switch." Prohibition came not because there was a grand design at moral reform, but the general abuse of alcohol was rampant. Remember, there was no Prozac, ect., and everything a man did to make a living was physically exhausting and usually hurt. Sorry to go OT.

The Smithville accident was a direct contributor to the ICC requirement that when setting SRV's a certified or weight tested guage must be used.

I have made my living on boilers, of all kinds, and have made their study a major part of my life...I think anyone putting forth armchair expertise is ill advised.

BTW thanks for the good words, Brer. John

Bzzzzzz......Bzzzzzzzzz......Bzzzzzzzzzzz

Kelly? Rick?

(flash.....)

Thanks Jim. I'd not have been as patient with the irrelevant peanut gallery commentary as you were. Very different and not at all applicable to the topic, which is complex and needs qualified opinions from people like you, Matt, Robby, etc. I've learned a lot about lap seam issues that I had thought were adequately addressed by the current code, and now which makes me wonder if we have actually done more than pretend to address at all.....

dave

Now ya gots my curiosity way up, Matt, although I cannot see how the internal pressure (applied evenly outward) would have caused this. May this vessel have been injured in some way, ie dropping through a bridge, ect.? The destending of the outer sheet just doesn't compute in my feeble mind. I am also still curious to see the outside...it will tell us more, methinks.

I can build a mental construct of the stresses deforming the plate invisibly from within, not free to actually visibly deform it as shown until the section was cut free. I've had old metal and wood do things I hadn't expected more than once in the past when disconnected.

Besides, it's Australia. Gravity would have naturally pulled it up and away........

dave

A steam tractor (steam traction engine as we call it) likely works a rougher turf than your average steam engine, running on dirt and rocks and clunking around.
So being under pressure and roughing it and any metal faults adds to the fatigue.

Glad to see the problem found and perhaps news a new boiler was in order.

its all backwards down there...8-P

Hi Mr. Templim

The issue here is the force diagram for the plate. Newton’s third Law of motion states “For every action there is an equal and opposite reaction”. The joint has to satisfy this law but the forces do not act on the same radius in the joint as they do in the rest of the plate. The force on the plate can be drawn as a resultant on the center line of each plate. In the plate they are equal and opposite but in the joint they are not as illustrated by the Free body Diagram by Matt’s posts on page 2 of this thread. This unequal forces invokes Newton’s first law “Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.” The plate has unequal forces but the bending of the material around the joint “solves this problem” at least for the laws of motion. I hope this helps.

Robby