8/17/2019 History Boiler Safety Iron

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DuctilityFor most purposes, ductility is a more important measure of the quality of wrought iron than tensile strength. In tensile testing, the best irons are able to undergo considerable elongation before failure. Higher tensile wrought iron is brittle.

Because of the large number of boiler explosions on steamboats, the U.S. Congress passed legislation in 1830 which approved funds for correcting the problem. The treasury awarded a $1500 contract to the Franklin Institute to conduct a study. As part of the study, Walter R. Johnson and Benjamin Reeves conducted strength tests on various boiler iron using a tester they had built in 1832 based on the design of one by Lagerhjelm in Sweden. Unfortunately, because of the misunderstanding of tensile strength and ductility, their work did little to reduce failures.[59]

The importance of ductility was recognized by some very early in the development of tube boilers, such as Thurston's comment:

If made of such good iron as the makers claimed to have put into them "which worked like lead," they would, as also claimed, when ruptured, open by tearing, and discharge their contents without producing the usual disastrous consequences of a boiler explosion.[60]

Various 19th-century investigations of boiler explosions, especially those by in

surance companies, found causes to be most commonly the result of operating boilers above the safe pressure range, either to get more power or due to defectiveboiler pressure relief valves and difficulties of obtaining reliable indicationof pressure and water level. Poor fabrication was also a common problem.[61] Also, the thickness of the iron in steam drums was low by modern standards.

By the late 19th century, when metallurgists were able to better understand what properties and processes made good iron, it was being displaced by steel. Also, the old cylindrical boilers with fire tubes were displaced by water tube boilers, which are inherently safer.[61]