Editor's Note

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We are aware that many of our readers don't want us to print stories about boiler explosions, as they feel they emphasize the dangerous aspects of the hobby.

Nonetheless, we decided to print this story since it was submitted by John Bow ditch of the Henry Ford Museum, with the intent that it would serve an educational purpose. It is interesting as a piece of history and it dwells on the causes rather than the effects. Editor.

To the Editor:

In my work as Curator of Industry here, I often come across articles in early publications that might interest most of your readers. However, I rarely find one that most should read and think about very carefully. The attached piece entitled 'A Terrible Boiler Explosion and Its Lesson,' taken from the December 16, 1897 issue of American Machinist (reprinted below) is such an article. Readers may not like what it has to say, however their reading of it followed by the taking of appropriate action could save their lives and ultimately the hobby. One serious boiler explosion resulting in loss of life could cause most states to ban the operation of historical boilers, period.

While there are many causes of boiler explosions, lap seam cracks such as those discussed in the article are by far the most scary. They are not detectable by visual means. They do not show up in most hydro tests and in fact can be made worse by these tests if they are done incorrectly. The same is true of hammer tests. They are not prevented by the most careful of operation or maintenance. The only reliable ways to find them are seam notching and x-ray testing. Neither of these tests should be done by the hobbyist himself, and both are somewhat expensive.

Most hobbyists might say, 'I only run the thing a few times a year, and it's been around since 1902, so it must be safe.' That sort of thinking is very risky; periodic firing makes the condition worse because it causes the boiler to expand from cold to full temperature more often than continuous firing does. As to the boiler being safe because it is 91 years old, lap seam cracks develop slowly over a very long period of time. They are true stress cracks. This slow-to-develop characteristic is the reason why the ASME Boiler and Pressure Vessel Code prohibits the use of lap seam boilers over 20 years old in high pressure service.

All of this suggests that the prudent operator of a lap seam boiler that is old should either replace that boiler or get it carefully tested; specifically the lap seam should be x-rayed. It is also a good idea to check plate thickness with ultrasound equipment; you'd be surprised how thin things can get over the years. Above all (and this advice is not repeated enough), never hydro test any boiler to more than 1.5 times its intended working pressure! I hope readers enjoy the article and learn from it. It's a wonderful hobby, I hope we all can enjoy it safely and without witnessing a historically accurate boiler explosion.

John Bowditch, CURATOR OF INDUSTRY, HENRY FORD MUSEUM AND GREENFIELD VILLAGE