Cobra Effect · Engineering failures
Cheap steel and a costly mistake
How cheap steel failed for everyone except its inventor, and why.
7 cards, read aloud in 2:44, with a test and sources.
Before the 1850s, steel was strong and useful, but expensive to make.
Crucible steel had been made in Britain since about 1740, but only in small amounts. Rails and bridges were mostly made of wrought iron or cast iron instead.
In August 1856, Henry Bessemer described a new way to make steel in large amounts.
At a meeting of the British Association in Cheltenham, he explained that air blown through molten iron would burn out carbon and other impurities. Surprisingly, that burning made so much heat that the metal stayed molten without extra fuel. A whole batch could be converted in well under half an hour.
Ironmasters bought licences to use the process, and then their steel failed.
The metal they made was brittle, and would not forge or roll. Bessemer’s own trials had worked, but theirs did not. Bessemer ended up paying back licence fees.
There were two hidden problems.
Too much oxygen was left behind in the metal, which made it brittle. And most British iron ores contained phosphorus, which the process could not remove. By luck, Bessemer had tried his process on iron that was low in phosphorus.
Other people found the fixes.
Robert Mushet showed that adding an iron rich in manganese, after the blow, removed the extra oxygen and let the carbon be controlled. In Sweden, Goran Goransson made good steel by the process in 1858, using purer iron. That same year, Bessemer opened his own steelworks in Sheffield.
The phosphorus problem took more than twenty years to solve.
Around 1875, a young amateur chemist named Sidney Gilchrist Thomas worked out an answer. With his cousin Percy Gilchrist, a chemist at an ironworks, he lined the vessel with limestone or dolomite and added lime. The phosphorus was trapped in the slag. By 1879, the method was working at Middlesbrough.
So when a method works for its inventor but fails for others, ask what was different.
Bessemer’s process was real, but his success had depended on something he did not know he had. The method became reliable only after others found the hidden conditions. Steel then became many times cheaper, and railways, bridges and ships were built from it.
Sources
- The Rise of Steel, Part II, Construction Physics. How Bessemer steel actually took off, including its failures.
- Bessemer Process, Grace’s Guide to British Industrial History. The process, its licensees and its prices.
- Sidney Gilchrist Thomas, Science Museum Group. The man who solved the phosphorus problem.
Nearby ideas
- The ships that cracked in the cold. How welded wartime ships cracked in the cold, and the scientist who worked out why.
- The cracks nobody could see. How investigators found the hidden cracks that brought down the first jet airliner.
- The bridge that twisted itself apart. How a steady wind twisted a brand new bridge until it fell.
- Two rods instead of one. How a small change to a design doubled the load on a hotel walkway.
- The rubber that could not spring back. How engineers warned that cold would stop Challenger's seals working, and were overruled.