Explosion hazards

[Malcolm McLeod]

Anyone have such an inspection done on a small tank? ...

In meeting this morning, and just learned that local Fire Marshall may be able to perform air receiver inspections. Just in case someone is interested.

[Andy D Jones]

Think about this, steam engines ran boiler pressure between 250 and 300 PSI. This was in a boiler that was mounted to a frame that was running down the rails at as much as 100 MPH. No welded ribbon rail, just bolted, which meant there was a joint about every 39 feet on either rail. Some of the boilers were close to 100 feet long. As boiler was brought up to pressure and temperature, it grew both in length and diameter. I have no clue as to why they actually worked as good as they did. Remember when a boiler blew, the pressure on the water was instantly reduced, allowing the remaining water to boil even more rapidly.

Boiler explosions are deadly! At 300 PSI, the boiling water (and the steam) is over 400F.

Early locomotive boiler explosions (if not caused by collision or derailment) were often caused when the stay bolts suspending the firebox in the rear of the boiler failed due to corrosion, sending the firebox, followed by steam, back into the cab with fatal results for the crew. When the pressure is suddenly released from the boiler, the water is far above the boiling point at atmospheric pressure, and flashes to steam, and lots of it.

It turns out that many stay bolts would fail before the boiler failed, but there was not warning to indicate the stay bolts had failed. To make them safer, stay bolts were later designed with a hollow center open to the outer bolt head, so if the stay bolt cracked (and the weakest part was the hollow section), a tell-tale weep/steam leak would be visible and/or audible during periodic inspections at pressure. When a certain percentage of the stay bolts were damaged, the boiler had to be rebuilt. After each rebuild, the rated maximum boiler pressure was usually reduced for safety, eventually below 200 psi before they were scrapped.

Boiler explosions due to engine derailments and collisions at speed were often fatal to the engine crew (fireman and engineer). When the collision ruptures the boiler, all the boiler water flashes to a whole lot of steam.

-- Andy - Arlington TX