"Believe it!" does not sound very scientific.

Are not most all aircraft, excepting those of wood/canvas, not of composite material construction made of rivited lap seams, and wouldn't a passenger aircraft in the upper atmosphere act like a pressure vessel?

Jim,
You are absolutely correct. Modern aluminum airplanes do use lap joints. They also fail. The best known example of failed lap joint in airplane is Aloha Fight 243.



The NTSB accident report stated that:

“The National Transportation Safety Board determines that the probable cause of this accident was the failure of the Aloha Airlines maintenance program to detect the presence of significant disbonding and fatigue damage which ultimately led to failure of the lap joint a S-10L and the separation of the fuselage upper lobe. “

I am unable to compare the inspection and repair requirements that were in use for commercial aircraft at that time versus what are currently applied to boilers today. I can state categorically that the aircraft industry took the lesson to heart and the design, manufacturing, inspection and repair practices were significantly changed.
I think that Matt is concerned that the art and science of engineering is missing from many of these discussions. You here the experts making statements on the safety and reliability of boilers on the basis of their feelings or experience far more often than on the basis of scientific principles and sound engineering design. You even hear out right scorn for the subject from gentleman like the one from Wyoming.

I think that Matt is trying to do is to put a challenge before you, the experts in the field, and trying to generate a discussion and knowledge sharing. From what I am reading it’s a timely topic – from the comments made it’s clear that there is not universal knowledge of potential failure modes, such as the one presented here. You have been given an example of a real life problem and opportunity to discuss it and learn from it.

Kudos to Matt and the rest of you , I have certainly learned a lot from this discussion.

There are hard ways and easy ways to learn. Aloha 243 was the hard way.
Brockton was the hard way.

BarryD,

Matt knows about Aloha 243 in ways that take pages and pages......

Mark

Mark,

I guess Matt knows Lap Seams then!

Thanks

My question is why would any person start a thread if they were not the person that inspected the boiler, removed the item of concern with permission from the boiler owner and then tested/researched the item? At this point, there are six pages of discussion and the originator of the post is not even the person that has found the issue being discussed if I read all six pages correctly. To me, this thread or “debate” has no relevance yet with its supporting documentation of the original photo and is “hearsay”.

On another note about lap seams, it is my understanding after speaking to a friend that just had his traction engine inspected again, that a boiler inspection in Virginia requires a three dimensional non-destructive test on the lap seam that can determine if there is cracking in the joint.

I just cut apart a lap seam boiler (that was bad at the mud ring) so that I could make a display on how a boiler functions; one of the sections that I cut out was the lap seam specifically so that I could inspect it for my own curiosity (prior to finding this thread) and also to mail a piece to Mr. Jordon someday because I know that he is requesting pieces of lap seam boilers for research. It will be interesting once I glass bead off many decades, almost a century of paint and inside rust to see if the surface shows any of the same flaws that are shown in the piece in the photograph of the first post. I might cut it into three pieces and leave one “as is”, glass bead the second piece and then place the third peace in my electrolysis tank because that might remove more scale in the actual joint for better inspection. I do know that I will have been the person that owned the boiler and also cut the piece out so I will be able to provide documentation as to where the piece is from because I still have the boiler if anyone wants to question the piece that I eventually provide to Mr. Jordon for his research.

I would like to see a post from the person that took the photo and performed the research on the piece.

Jeff

Hooray for Steamenginesmitty!!

I agree with all that he has said.

I, too, have assisted with information concerning Virginia's inspection via shear wave UT of lap seams, and encourage all folks that have scrapped boilers to cut apart their lap seams and post what they find, including photos!

Mark

In my post above I forgot to add that I am not against boiler safety; in fact, I have been called a “fanatic” about boiler safety and proper procedures for operating, inspecting, repairing, etc. antique boilers.

Thank you,

Jeff

It is obvious that I don’t understand riveted joints as well as many of you. Maybe you can help me answer a few questions.

The traditional sketch shows a lap seam twisted to where the center lines of the two plates are aligned. With the ends in alignment, it appears to me that there would be zero bending moment available to twist the joint. If this is true, how can the joint be twisted the maximum conceivable amount if there is no force available to twist it? Is the illustration just a caricature and not an accurate representation of what really happens?

How is it possible to calk a lap seam if the joint bends and breaks the seal on the calked edge?

If a boiler fails at a pressure above its MAWP, and evidence of a crack is later found, did the crack cause the explosion?

In August of 1954, The American Society of Civil Engineers published a paper, Fatigue in Riveted and Bolted Lap Joints. (Volume 89, Separate No. 469, by J. W. Carter, K. H. Lenzen, Associate Members, ASCE, and L. Wyly, M. ASCE) This report contains 36 pages of documentation that includes a hypothesis, sources of information, photographs, charts, photoelastic studies, drawings, tables of data, results of tests, conclusions, etc. The presenting symptoms sound familiar, “Some special circumstances or combination of circumstances must cause the failures since only about one of six railroads report these failures, and only a few hangers develop failures in a given railroad.” Where can I find the research like this that is the basis of the restrictions that are being imposed by ASME and the various jurisdictions?

At the top center of Page 25 of the ASCE report there is a detailed drawing that shows how a triple riveted lap joint might fail. In this illustration, and throughout the report, there is no mention of twisting of the joint. How can it be that the heavy loading and severe vibration on a railroad bridge don’t cause lap seams to react in a way that is at least similar to how they are believed to react when they are used on a boiler?

The civil engineers identified a problem, researched the issues that were involved, and arrived at a solution that did not involve a major change in the design of the joint. Basically, they found that failures only occurred in joints where the rivets did not exert sufficient clamping force (workmanship?). Once again, Where can I find the studies that support the current restrictions on lap joints? Are the restrictions based solely on anecdotal reports?

To me, the lap joint that was pictured on this thread appears to be double-riveted with countersunk rivets. The mode of failure appears to be an example of what the civil engineers were addressing. How common is the use of countersunk rivets on longitudinal seams on pressure vessels? Wouldn’t the use of countersunk rivets reduce the efficiency of the joint and therefore require the use of thicker plates?

Thanks in advance for your assistance. Wherever possible, please cite the source of your answers.


Bruce E. Babcock

Dear Barry:

The conclusions of the NTSB in this investigation are a perfect example of 20-20 hindsight.

The original design of the 737 in the mid 60's was based upon a certain ground - air - ground cycle (g-a-g cycle). IIRC this was approximately a 30 minute take off and climb to altitude, a 1.5 hour cruise at 35K feet and a 30 minute descent and landing. From this flight spectrum, the fatigue damage was estimated for one g-a-g cycle. From this g-a-g cycle, a conversion was then made to flight hours for certain inspections.

From a basis of flight hours the Aloha A/C was well within the Boeing inspection requirements. However, IIRC the Aloha A/C had in excess of some 95k to 100k g-a-g cycles, while based upon flight hours, it should have had only about 45k g-a-g cycles.

IIRC, the Aloha flight spectrum was a 20 minute takeoff and climb, a 20 minute cruise at about 20k ft and a 20 minute descent and landing.

It did not come as a surprise in the investigation that the fuselage failed in the investigation. What was the surprise was that the A/C did land with only 1 fatality and that was a flight attendant that was sucked out of the A/C.

The difference between A/C fuselages and locomotive type boilers are that A/C fuselages are designed on a life limited basis and boilers are designed for a life unlimited basis with respect to fatigue. Thermal considerations and other degradation mechanisms are a completely different matter.

Boeing has a test facility where an entire fuselage is submerged underwater and the fuselage is fatigue tested to failure.

I disagree with some of Mr. Austin's statements. From what I can discern from this board is that he is in some sort of regulatory position of authority. From my career experience, people such as this are capable of issuing fiats when it comes to regulatory compliance. He does not have to justify his demands to the party that is under his jurisdiction other than on procedural basis and a citation of the appropriate regulation. The party under his jurisdiction does have to demonstrate compliance with his demands based upon his regulatory authority. This is not a slight in any manner to Mr. Austin, just an observation of my experience dealing with regulatory authorities.

For example, I had an assignment to verify the MAWP and integrity of a traction engine boiler. When talking with that state's chief boiler inspector his response was that he did not want the boiler to fail. To which I said that that was impossible to do. All that I could do would be to evaluate the current condition of the boiler and determine an MAWP in accordance with that state's requirements. The future safe operation of the boiler was highly dependent upon the care given and operation methods of the owner. He understood that and he was satisfied with the work I did that the safe operation of the boiler could be done.

With the determination of the MAWP of a locomotive style boiler, I have had people wave a 50th generation photocopy of some Baldwin sales spec sheet and claim that that was sufficient to verify the MAWP of a boiler.

My attitude towards locomotive style boilers to determine an MAWP is: 1) Obtain or make an as-built or as-found dimensional drawings of the boiler; 2) Determine an MAWP in accordance with the design codes and standards in effect at the original time of manufacture; 3) Determine an MAWP in accordance with the current requirements of the ASME B&PV; and, 4) Determine an MAWP in accordance with the requirements of 49 CFR Part 230.

Item 3) is needed so that the repair shop can apply the R stamp and that the underwriter will accept the risk on the boiler.

Item 4) is needed so that the Form 4 can be completed and that the FRA will then approve the operation of the boiler.

With respect to the title of this thread and the other thread, the following statements are just as valid:

6 dead in car accident --- CARS BAD!!!!
153 killed in airplane crash --- AIRPLANES BAD!!!!!
Refinery explodes --- REFINERIES BAD!!!!!
Building collapses ---- BUILDINGS BAD!!!!!
Ship sinks at sea --- SHIPS BAD!!!!!
Person dies in hospital ---- HOSPITALS BAD!!!!!

The question is to what extent will engineering and science improve our lives and what is the risk associated with that and is that risk acceptable.

As a reminder, Ammonia was once used as a refrigerant in household refrigerators, which is why the Freon refrigerants were developed, which led to a problem with stratospheric ozone depletion, which led to new types of refrigerants. So does this lead to the following statement:

Stratospheric Ozone Depletion ---- FREON BAD!!!!!

Ammonia does not cause stratospheric ozone depletion, so do we go back to that as a refrigerant?

Hope this helps

Sincerely

PKurilecz

Its not true. There is indeed a bending moment. Any cylindrical structure that is subject to an internal pressure will be put into tension. For the purposes of this discussion, the tension can be modelled as being concentrated on the centerline of the plate's thickness. Where the plate overlaps itself, you will have two opposite tensions separated by the thickness of the plate. Force times distance is by definition a moment.



Maybe.


Who, as a general rule, don't concern themselves with boiler design.



Jeter, S. F. "Riveted Boiler Joints." New York. McGraw-Hill. 1917. p8.
"The double riveted lap joint was the one used for practically all longitudinal boiler seams up to 25 years ago, and it is largely used for this purpose today, but it is being rapidly superseded by the various types of butt joints on account of the tendency of the lap joint to crack after considerable use. Such cracks are so located that their formation may not be readily detected; they often result in the explosion of the boiler."
Mr. Jeter was a member of the Boiler Code Committee of the ASME, as well as Chief Engineer of the Hartford Steam Boiler Inspection and Insurance Co.

Kuss, Robert H. "Steam Boilers." Chicago. American Technical Society. 1919. pp21-22.
"It is well to remember that the efficiency figures [for a longitudinal lap seam] are calculated without reference to the creation of an eccentric load on the sheets and rivets. The true efficiency figures are appreciably less than those calculated, for it is impossible when using lap joints to avoid the tendency of the sheet to pull into a curved line of a radius equal to that of the cylinder of which it forms a part."


No, they are based on a freshman level understanding of mechanics.