An excellent demonstration of why cracks in lap seam boilers will not show on a visual inspection and why many inspectors tend to seriously derate lap seam boilers (where allowed to operate).

Interesting crack propagation. Any details on the boiler? Railroad, traction, or stationary service? Also curious why the inside sheet is gapped as it is, this seems more than would occur with the rolling of the sheet over itself (it looks like something hit on the seam). I presume this defect was found with an ultrasound. How long did the crack appear in the UT? Details please!

It may not be fair to generalize the condition of all lap seam boilers based on the the findings of this failure, that's why the circumstances surrounding the failure of this boiler are important for all operators to know.

Michael Seitz
Missoula MT

http://www.smokstak.com/forum/printthread.php?t=29022
Some great information on the Lap Seam

Or, it looks like the specimen was placed in a press to deform it and open the crack. The crack may well have been pre-existing, detectable by X-ray, but not readily visible because in the normal non pressurized state it would be tightly closed.

what is this off of? what is its diameter, age, and composition of the steel? Under what circumstances was this discovered? Who was the manufacturer? Posting a photo like that with no additional information could be easily construed as inflammatory by some, and I assume the reaction saught was one of abject horror at the very thought of riveted boilers in general, and lap seams in particular. Obviously it was found by some means, which would prove the value and importance of vigilent inspection procedures, but the photo is worthless without any other information.

Agreed!

I am always pleased to see pictures like this. They are very instructive.
I wonder however what initiated the crack beyond an applied stress. Could this be hot shortness due to a high sulfur content in the steel? Could this be a stress corrosion crack? Is this even from a fired pressure vessel? If so which side was the fire on?
Anyone got more information?

I just spent an enjoyable lunch hour reading through the Mark Jordan thread at the link above. Always like to learn more about things.

It seems to me I read some discussion on lap seam boilers a couple years ago, might have been on this forum. Following the links at that time, I recall coming across a photograph of a lap seam joint that had cracked, and the crack had propagated far enough through the sheet that it had perforated the sheet, and was evidenced by a line of mineral deposits where water had been weeping out. Anyone remember this? The photo was being used to illustrate the "lap seam flexure cracking" problem, but reading Mark's recent work, which seems to be gathering evidence that this problem doesn't actually exist, it also may have been a crack caused by improper caulking of the inner edge of the lap; the crack appeared to be offset about the right distance from the rivets. I'm wondering if Mark ever ran into this photo, and would be curious to know the full story behind it.

I wish we could see the other side of the rivit seam...what little we can see of the rivit head on the side away from the camera seems to show a wasted or hammered down rivit. It appears that the factory finished head is on the inside of the shell...most boiler manufacturers put the finished head on the outside on commercial boilers for both appearance sake and for ease in driving on smaller diameter vessels. I wonder if this wasn't on a fairly large diameter externallyfired boiler of a type once popular in large commercial laundries? Lap seam cracks of this type of propogation have been not really been detected in smaller (under 42" diameter) internally fired boilers since work hardening of punched holes and impoper caulking were addressed over a hundred years back.

This type of crack away from the rivit holes does seem appear where many lap seam critics say it sould be. I would like to know much more before this is offered as damning evidence. For all we can tell from this picture, some one may have welded around the rivits on the other side and introduced localized stresses.

Look at the grain in the saw-cuts. They are straight in the picture. If it were bent open post-cut, I would expect the grain to have a dog-leg.

I agree...the more I look at this, the more I see a flattening deformation of the radius, and I would venture that itmay have been mechanical shock rather than thermal stress.

And another thing...if this crack occurred in service, why does there appear to be a lack of corrosion, grooving, scale, or any other evidence of water having contacted the defect?

My name has now been posted to this thread, so I guess I gotta post sumthin'?

1) Matt, we just had a telephone conversation not too long ago, and based on your credentials, I'd say that you are obligated to post specifics in this photo, as the lack of same can be offending to some folks. Please elaborate......."Lap Riveted Boiler Seam - BAD!" just ain't enough for some of us hillbillies...
2) Yes, I believe this is a standard 'lap seam crack'. They did exist, and they do exist, and anyone that sticks their head in the sand is an idiot.
3) Referencing #2 above, I am of the opinion that the cause of lap seam cracks was identified and mitigated by the turn of the century, prior to the general change to butt strap construction. I also am smart enough to say that although generally mitigated, that doesn't mean that one can exist. Thus....THUS, the need for more information from Mr. Austin before anything can be said nor conclusions made.
4) Also based on what I think I know......these types of cracks usually originated from punched/work hardened rivet holes or near caulking seams due to improper caulking. In either case, the crack and "grooving" are not related. Grooving can be seen adjacent to an internal seam, while a crack is UNDER the plate and not visible to the naked eye. This example may have originated from the adjacent rivet (hole) and run parallel to the seam. If so, I'd also suspect that there are other cracks from other rivet holes, that are trying to "connect the dots/holes". This is NOT due to an improper caulking procedure.
5) Corrosion / Crevice Corrosion may well be evident, but is a form that doesn't show as normal rust/scale due to the type of oxygen reaction......I'll have to read some before I try to explain (I'm not a chemist!).


I await more information please.

I'm sorry, Mark, the "this photo" I was referring to in my post is the photo of a perforated crack parallel to the rivet lines that I remember seeing in the past, not the photo M. Austin posted. At the time I viewed the photo of the perforated crack, I was wondering why the boiler should crack that far away from the rivet holes... reading the thread on the smokestack forum, the mention of improper caulking causing cracking made it all click. And no, I don't believe the photo I can't now find was of a power boiler; it was in an article discussion stationary boiler explosions, and the fact that it ran in service cracked entirely through the shell long enough to acquire mineral deposits along the crack would seem to indicate that it was in very low pressure service, such as a heating boiler.

I agree that from the location of the crack in the photo M. Austin posted, it appears to be propagating between the rivet holes.

I think people are making way too much of the direction of the saw cuts across the crack. I'm thinking this is a portion of a scrapped boiler, where someone was specifically looking for a sample to illustrate the potential for cracking at a lap seam. As such, it's likely the seam was torch cut out, then cut into short samples, again with a torch, the samples deformed in a press until a likely specimen was found, which was then saw cut to better show the crack. So yes, the sample was deformed before it was saw cut, but not while it was still in service.

This is, however, jst a guess, and it would be nice to know the real story behind this example of lap seam cracking.

You are all way off base on the saw marks. The REAL saw marks are the grooves you see at either end of the sample, at about a 45 degree angle. This sample was extracted by a chopsaw or perhaps by someone with a sawzall and a lot of time on their hands. After the crack was discovered and/or created, the sample was put on a belt sander and the surface smoothed up to show off the crack better.

I agree that without a backstory, this picture by itself is worthless. For all we know this is out of some engineering text with the caption "this artifically created lap seam crack clearly shows the danger....."

As for finding these in real boilers, why wouldn't magnaflux work?

Robert

I agree we need a stronger backstory on the picture.I am not seeing a lapjoint failure. I could be seeing either an already failed boiler for some other reason, or the sample was bent.

If the sample was bent you could produce such a crack. If there was a pre-existing crack it should have been visible before seaming it up. Judging by the visible radius it seems like a small boiler. And not a new boiler, most seams I see on locomotives wrap all the way around the boiler curvature so a crack failure explosion does not seem possible.

I would tend to think the boiler was made from a very old boilermaker and perhaps not mainstream capable for big large boilers. Hence the seaming done.

The boiler may be fine for low pressure use like heating, which was far more common in old homes, my grandfather had a coal fired furnace, the house has still the coal chute for the coal bin.

We still have here a coal fired water heater, a little tiny thing about the size of a large stepstool.