Greetings. Steam student here.

Found this historic retrofit of a lap seam on Virginia & Truckee #22 ("Inyo") interesting. Would it be advisable for a modern-day, professional steam shop to make this kind of modification today to an old boiler? Would there be any point in doing that? Open to hearing any thoughts.

Source & Credit:
Nevada State RR Museum Facebook Page, post and graphic by T. McReady, April 4, 2014
http://tinyurl.com/kuyrso8

Wouldn't the little pocket in the middle accumulate moisture and then rust?

Does anybody operate lap seam boilers?

This is a "Welted Lap Seam" and no, the pocket doesn't unless the seam is badly made and open to leakage. I'm sure there are still lap seam boilers in service...a lot of traction engines use them, for example.

dave

D&RGW 315 has a reinforced lap seam boiler, if that counts.

To answer the question as posed, NO.

The reason is modern welding technique. Boiler design, including joint design, evolved. The evolution went from 1) lap seam, 2) reinforced lap seam, 3) butt strap, 4) welded.

The original lap seam construction had a low joint efficiency (how much load the joint could withstand as a percentage of solid plate) and the retrofit/reinforcement was a means to improve the joint design. This was done before modern welding was standard.

Now, a boiler shop would remove the original joint and replace it with a welded retrofit. In other words, there would be a small portion of the cylinder that would be new material, the full length of the cylinder/barrel, with welds running the full length of the barrel on both sides of the new material, making two new longitudinal joints. These welded joints if done per code would be 100% efficient.

Clear as mud?

Thanks. Actually your answer is very clear. Yes, I knew the answer would be that modern welding beats anything riveted. My question was not well thought through and was badly phrased. What I should have asked was, could a preservation-minded steam shop that wanted to use historic methods, use this method to make a fix to an old boiler?

I imagine the answer is that it would be a better use of money just to build a new, welded boiler rather than reinforce an old one. In any case, the reinforcement would alter the original fabric of the boiler, so the work might not be considered "preservation".

Now, changing the subject off the topic of seams, I have noticed that some preservationist groups take on very major boiler rebuild projects. This video made at Midcontinent of Western Coal & Coke #1 sticks in my memory.

http://www.youtube.com/watch?v=Vne4usp9joM

Thanks.

for an educational standpoint, you would get a new boiler and put the old on display demonstrating the construction design and why the switch, that preserves the fabric but lets you get an operating engine.

Your double seam fix is an old technology answer to improve a seams stability, but obviously today we have better methods.

Yes, of course they could. Replicating old ways of construction is a great way to keep the knowledge of that technology alive. There are standards for inspection of boilers built with lap seams so providing you want to maintain them in service, it is your choice as to how to build them. There are valid engineering and economic reasons why they are not as popular as welded boilers today, but sometimes those interests take a second priority to historic authenticity.

I would point out that given the much lower seam efficiency of lap seam construction, they are built with much heavier material than what would be found in a welded construction capable of the same pressure at the same factor of safety. This additional margin could lead to longer life........which could also be done by simply using heavier than necessary material in welded boilers.

dave

Although Taylor assessment of the #22 is interesting it isn’t all that factual. I am not sure what code he is speaking of however there isn’t a prohibition against lap seams in Nevada or in 49CFR Part 230, the FRA rules. In fact as per § 230.30 there is a specific provision for lap seams although it makes operation a little tedious. It says “Every boiler having lap-joint longitudinal seams without reinforcing plates shall have sufficient lagging, jacketing, flues, and tubes removed at every annual inspection so that an inspection of the entire joint, inside and out, can be made, taking special care to detect grooving or cracks at the edges of the seams.” There isn’t clarification of what to do if there is a reinforcing strap present.

That said, the Inyo has the interior re-enforcing strap referred to. In 1983 when the boiler was put into service after years of non-operation the inspector of record de-rated the boiler from 130psi (not 135 psi) to 75 psi. The reasoning was that the interior of the lap seam couldn’t be inspected and so the condition was unknown. Why 75psi? We don’t know. There isn’t any record of calculations showing that 75 psi is justified. So it would appear that the number was capricious. It could have as easily been 100 psi or 50 psi at the whim of the inspector. Memory suggest that the statement was made that if the strap were removed and the interior inspected a greater pressure could be allowed. Of course there would be a lot of holes to fill if that were done.

It is interesting to note that if the locomotive were inspected under part 230 then the pressure could be higher if the calculations proved it was warranted.

This is a sample of a longitudinal seam from a locomotive boiler. This is the water side showing the strap. It is the worst of the worst. It is a single riveted lap with and inside reinforcing strap. This is one net section. I removed it, welded tabs to it and ran it through my Tinius Olsen testing machine and broke it. (Yes, I know that a straight pull isn't the same as a round vessel pressurized to failure).
I would like to call your attention to the crappy material used in the strap. Looks like the pages of a phone book.


Sample removed from an 1888 Cooke Locomotive, first course. The barrel is steel, the strap wrought iron, rivets are steel.

For reference to previous posting, here is a cross section of the same joint.

Couldn't ask for more interesting replies. Thanks CCDW and M Austin. Very revealing photos.