Folks,

Yes, the plate is bent to expose the crack.
There are multiple cracks in the making.
Yes, there are saw marks.
No, the boiler didn't fail to cause the bent plate....i.e. not an explosion.

No, the crack was not caused by bending the plate.

I spent nearly 20+ years thinking I knew what a lap seam crack is, and how it is formed, only about three years ago to realize I had no idea. Without really studying it, most people......including "veteran steam people" don't really know what happens.

I am going on record to say that I believe that this is a lap seam crack, most likely due to work hardening around punched rivet holes, aggravated by concentration of potentially alkaline water per Sir Conte's post. I'll have to drag out some of the material that has taught me, but the text of same can be somewhat overwhelming, and way too much to post here and now. In many ways, I'm still learning a lot!!

Once again, more information is needed. Lap seam problems plagued the boiler industry at one time, but were mitigated before the general conversion to butt strap production. However, if the workmanship is improper, the joint can be dangerous as noted in an English explosion in the 1950s......yes, and new lap seam in the 1950s....not the 1850s.

It ALL has to do with the details. This situation is somewhat akin to being scared by Grizzly Bears. Yes, you should be scared of a Grizzly Bear.........but only if you're in the woods full of bears. If we're surrounded by antique boilers built in the 'crack' era, then there's a problem. If the surviving boilers are "post crack" era, then we don't need to run from bears that aren't there.....

Was the adoption of a welt strip on to the lap seam the mitigation to which you refer? Can we then assume this problem won't occur in welted lap seams?

dave

That last diagram is a great illustration as to what is happening when the joint is under stress. Thanks!

IMHO a lap joint with a welt plate (poor man's butt strap) introduces many more problems than it purports to fix. The mitigation that Mark refers to isn't the application of a welt plate, but to a general improvement in boilermaking techniques. IE using rivit holes that have been drilled or reamed after punching to remove work hardened material around the hole, and a revision of caulking procedures to eliminate structural damage from this source.

Rivited boiler making was and is an art and a craft, and just punching a bunch of holes, rolling plate, and driving rivits resulted in a dangerous vessel, whether lap seam, butt strap, or bubble gum. There was, and is, a proper technique for rivit hole prep and edge caulking that is as important as the material used.

I still want to see the other side of the joint, and I would like to know the make and age of the unit.

Jim Templin:
You are correct that boilermaking methodology and practice is what I'm referring to.

M Austin:
Referring to the Australian method of detecting lap seam cracks, I have seen at least one traction engine shown at Rushville, Indiana this past summer that has these exact notches, along with "V" notches in it's seam. Apparently it has been this way since the inspectors created the notches in the 1950's-1960's without incident. However, I do not subscribe to the standard "Effect of Load on Lap Joint" as a purely physical phenomena resulting from overstressing "surface fibers". This effect is only part of the equation, with microscopic stress CORROSION cracking as the primary culprit. To be "nit-picky", I'll also say that the diagram is flawed in it's location of the crack. The crack cannot occur as shown, but rather just adjacent to the rivets or at the caulking edge area.....the reason is that there is no point of leverage for a bending moment to occurr as shown. The bending moment occurs under the rivet head, or in a weakend caulking seam. However, as I post this, I will admit that I have never seen an example of a crack outside of the seam area as shown in the (Australian) diagram. It seems to me that a crack as shown here does not have anything to do with a lap seam, butt strap, modified lap seam (welt), nor welded construction.

Please tell us more!!

To Kelly Anderson:

Yes, M Austin has shaken the jar, but we're not flies, we're FIREFLIES!! We want to shed light on the subject.........!!

Thanks Matt and Mark - I've seen a few welt straps that made me unhappy too, and I'm pleased to know that wasn't Mark's meaning. Fortunately, there aren't too many locomotives with lap seam boilers in service these days, welted or otherwise.....but probably many with punched and riveted holes of butt strap construction, maybe with a modicum of reaming but not much other treatment if the old stories I heard from steam era boilermakers are an accurate reflection of common standards.

What I don't like about riveted construction is the tear-along-the-dotted-line perforation thing......what I do like is the resulting loss of seam efficiency increases the necessary thickness of the plate itself, and adds all that nice margin that keeps them alive so much longer. Perhaps the best approach is a new replacement welded boiler with 100% efficient seams made of steel of identical thickness as the original - presuming you can find good 55K tensile steel and a source for 6018 rod. In our industry, lightweight strength isn't always of benefit when heavier durability was endemic to the technology from its maturity through its decline. Boiler design might have been different if it had developed with high tensile strength welded construction instead, maybe a lot more like modern power plants. Interesting to think about.

So, the loaded question in this thread seems to be whether there is any way to assure old order lap seam boilers are continually safe, and by what demonstrable margin - which begs the question of whether old lap seam boilers ought to be continued in service at all, and if so how?

dave

This has been, is, and will be the $69 question.

I don't recall steam traction engines running at pressures steam locomotives run at, like up to 100-120 psi vs 200-300 steam locos do.

Especially with that one graphic if you continued to raise pressure any lap joint is going to buckle and fail. But note boilers are made on a curvature which helps on the sealing. But I wouldn't trust a boiler based on just a riveted seam without some welding at the seam joints.

Joe Karol who helped with 765 restoration was taking a hammer and banging all kinds of parts inside the boiler, making noises and sounds and I recall him saying "thats in friggin good shape!", Joe if you didnt know was a real NKP boilerworker. I believe he knew the sounds the metals would make, if they ring well its pretty good, but if it went "THUD" wooops. problem....

I think we have today better metallurgical analyzing than just metal ringtones. I would not want to cut chips out of a boiler to see whats wrong, what to me will nullify a boiler right away just doing a test cut, but you could weld it back secure.

This has been a good discussion.

Factory traction was ~120psi to 190psi roughly. They run at 200+ across the pond.

Then you don't need to be around the 765 or 99.999% of the steam locomotives operating today. Now, I don't want to hurt your feelings, but mankind had been riviting boilers together for at least 150 years before anyone struck the first arc on boiler plate, and the average boiler maker in 1900 knew more about building boilers of many different and varied designs than just about any commercial manufacturer today. I know, I look at them every day.

I like to remind folks that think that riviting is a poor second to welding, and therefore have some idea that riviting is somehow patently unsafe, they better never, ever set foot on an airplane, because the whole structure, inner and outer, is rivited.

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. However, riviting requires a different level of skill than welding, and fine control isn't as critical. In other words riviting done at 8 am, and riviting done at 5 pm can and will have the same quality, but the weld an old boy does at 5 pm ain't gonna be quite the same as the one he did that morning.


Bruce Babcock, as well as Brother Jordan, have really done yoemens work on the phantom lap seam crack, and, with all due respect, I believe it to be an article of faith to believe that these seams behave in the way described, although that is the "company line". Most failures of longs seams were/are due to deterioration (grooving, ect) that should have been detectable by a competant, thorough inspection.