I am curious, Mr Austin...did a lap seam boiler regularly beat you up everyday when you were going to grade school? What do cheaply built HRT lap seam mill boilers have to do with railway preservation anyhow?
The only locomotive I can think of in service lately with a lap seam boiler is the Espee 2248...and it has a Sacramento built lap seam boiler with a welt plate (imho which is the worst of both worlds).
Here's a couple of interesting notes I made on this incident, from this article.
Firstly, the watchman and fireman noted that the usual practice when putting the boiler on standby for the end of work was to close the bottom guage glass valve "in case the glass broke only steam could escape, and not water". That seems like an open invitation for human error, to me.
Secondly, this account states that there was tearing in the parent material...if the lap was wholly at fault, wouldn't it have just 'unzipped' at the seam?
Mark Jordan, Bruce Babcock and others have devoted considerable resources and effort to finding the dastardly "lap seam crack", and I have too. Lots of failured due to grooving, broken stays, fiddled with srv's, but no lap seam cracks in anything under 40".
To put long story in short form, no one has been able to find an instance of a boiler failure due to a lap steam crack on any internally fired boilers in the last 120-130 years of records. You will also note that these HRT mill boilers were all invariably of the cheapest quality made, most with plain punched holes, with no reaming involved in finishing rivit holes. Plain punching the hole work hardens the metal around it, and leads to the cracking-not the design of the seam. I myself have examined several scrapped longitudenal lap seams on scrapped boilers, not a one had a crack.
The lap seam witch hunt of the turn of the last century was means to cover up poor practices and drive the marginal boilermakers out of business. Since there was no way to visibly verify if an assembled rivited joint had been reamed or drilled to remove work damaged material that would propigate a crack, the simple solution, from the inspection/insurance/engineering point of view was to go to a butt strap joint from the point the supposed problem was discovered. Bluntly, you knew good and well there wasn't a lap seam crack if the thing had a butt strap joint. Most all lap seam failure occured in boilers that had been in service 5-10 years, and any boiler that was going to get one and fail already did a hundred years ago. Just as in Britain before, after plainpunching of rivit holes was discontinued as a practice, so did the cracks due to it.
BTW you can still legally build and use a lap seam boiler in Britain...is the Scepter'd Isle just an amalgam of hot water bombs waiting to go off?
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