Cobra Effect · Engineering failures
The ships that cracked in the cold
How welded wartime ships cracked in the cold, and the scientist who worked out why.
7 cards, read aloud in 2:54, with a test and sources.
During the Second World War, American shipyards built thousands of Liberty ships.
In all, about two thousand seven hundred were built. To build them fast, the yards welded the steel plates together instead of riveting them. Welding was quicker, and it turned shipbuilding into something close to mass production. Tankers and other wartime ships were built the same welded way.
In January 1943, a brand new tanker lay moored at its dock in Portland, Oregon.
It was called Schenectady, and it had just finished its sea trials. The weather was calm. Suddenly, with a noise reportedly heard a mile away, its hull cracked almost in two. Schenectady was not a Liberty ship, but it had been built the same welded way.
Across the fleet, hundreds of welded ships developed serious cracks.
Most were cracks the ships survived, but a small number broke completely in two. Almost all of the brittle fractures happened in cold weather. In 1943, the US Navy set up a board to investigate welded merchant ships.
At Cambridge University, the metallurgist Constance Tipper studied the steel itself.
She showed that below a certain temperature, this kind of steel stopped bending and broke in a brittle way instead. The main problem, she argued, was not the welding itself, but steel that turned brittle in the cold. The Tipper test became a standard way of measuring this brittleness, though recognition for her came late.
Small details decided where the cracks began.
Sharp square corners, such as at hatch openings, concentrated the stress. Flaws in welds, and stresses locked into the steel, gave cracks a place to start. And in a welded hull, a running crack could cross from plate to plate, where riveted joints might have stopped it.
The fixes came from understanding the problem, not from giving up on welding.
Hatch corners were changed and strengthened, and straps were added to hulls to stop running cracks. After the war, tougher steels were specified for ship hulls. Welding went on to become the normal way to build ships.
So when a material seems strong, ask whether it stays strong in every condition it will face.
The steel behaved well in ordinary conditions, and the danger showed up in the cold. A weakness that depends on temperature can hide from anyone who only tests in the warm. Knowing where a material changes its behaviour matters as much as knowing its strength.
Sources
- The T2 tanker, the other Liberty ship, Institute of Marine Engineering, Science and Technology. The wartime tankers, including Schenectady.
- Constance Tipper, Cambridge University Engineering Department. A profile of the scientist who explained the brittle fractures.
- Constance Tipper, Imperial College London. A longer account of her life and work.
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