Titanic

This month marks the centenary of RMS Titanic, the ill-fated ocean liner that hit an iceberg near 41.44N-50.24W and sank, killing over 1,500 of her passengers in the process.

Aside from operational issues — poor sighting, late warning, incorrect instructions to change course upon sighting iceberg and inadequate time to “hard-a-port” around, the subject of my curiosity has long been on the causation — metallurgical changes that led to the loss of hull integrity upon collision with an iceberg in the North Atlantic.

In 2008, The New York Times ran a story, “In weak rivets, a possible key to Titanic’s doom”. While this may have been one of the problems, my suspicion — that it wasn’t all of it, and that the key to hull failure was inherently ingrained in mechanical properties of unqualified steel — turned out to be true. Typically, these properties are considered at standard temperature and pressures. Under high temperatures, the molecular grain distribution becomes denser, and vice a versa in cold. In a rectangular plate at low external temperatures, e.g., molecular grain distribution becomes denser at plate’s re-entrant corners, while significantly thinning out at its centre — like in magnetism. At a cruising speed of 22knots, her bow plates — brittle due to low temperatures, gave away.

In an article published by the ASME in its Mechanical Engineering magazine this April, titled, Testing The Titanic’s Steel, there’s a note by Henry Baumgartner, which suggests it more clearly than ever:

When the Titanic samples were also examined with a scanning electron microscope, the grain structure of the steel was found to be very large; the coarse structure made it easier for cracks to propagate. Rivet holes were cold punched, a method no longer allowed (they must now be drilled), nor were they reamed to remove micro-cracks.

The grain size; the oxygen, sulfur, and phosphorous content of the steel; and the cold punched, unreamed rivet holes were found to have contributed to the breakup of the Titanic, along with the steel’s relatively low ductility at the freezing point of water.

Update (Sep 16): Walter Sperko, chairman of the ASME Boiler and Pressure Vessel Section IX Committee on Welding and Brazing, responded in a June edition of letters to the editor in Mechanincal Engineering magazine with the following:

While the side-column about the toughness of the steel plates presents some of the research on the root cause of failure conducted in 1996, in the 2008 publication New Forensic Discoveries — What Really Sank the Titanic, Jennifer Hooper McCarthy and Tim Foecke contend that it was not the lack of toughness in the plates that was the root cause of the failure.

Several rivets that were still attached to the Titanic’s hull plates but were missing heads were metallographically examined, and large slag stringers were found in those rivets.

When the bar is cut, and the head is forged, the slag lines that are oriented down the axis of the bar rotate to parallel the rivet head. That, combined with the geometric notch at the root of the head, creates a plane of weakness in the rivet. When the Titanic hit the iceberg, the hull plates bent, loading the rivets in tension causing some rivet heads pop off. When one head popped off, its load was transferred to the remaining rivets — and the rest is history.