Titanic Facts
Cold
Water Sinks TITANIC
Iceberg Gets Bum Rap in TITANIC Sinking
Note
from Ed: Could not find a name attached to this artical but I like the way he
writes:
Cold
water sunk the Titanic: This should have been the headlines at the conclusion
of the Official Inquiry, except that the technical expertise and technology for
molecular analysis necessary to exonerate the Iceberg from direct responsibility
for the TITANIC sinking did not exist until decades after the fatal maritime disaster.
Cold
water temperatures, about 35 degrees Fahrenheit, caused the steel to crack in
a brittle manner, like glass, when it hit the Iceberg, instead of the ductile,
twisting, tearing manner, we are all accustomed. During the first half 20th century,
the temperature above which typical high grade ship steel changed to ductile,
tearing failure mode from the brittle mode was 50 degrees Fahrenheit. Not until
1963, over 50 years after the TITANIC sank in cold arctic water, was the first
authoritative documentation published by two researchers from the U. S. Naval
Research Laboratory providing a comprehensive, quantitative analysis describing
the phenomenon of ductile to brittle crack propagation in steel.
How
widespread and pervasive was this lack of knowledge, that fingers should be pointed
at the engineers that designed and built the TITANIC and should be held responsible
for the disaster? In all probability, cracks in steel hull plates of ships was
common place. Except that due to the riveted construction techniques of the era,
a crack in a single plate was not catastrophic and would be attributed to an occasional
single bad steel plate from the steel mill or faulty fit-up in manufacture. A
brittle fracture, would only run to the next riveted joint, typically not more
than 20 feet in length, with noticeable but not catastrophic leakage which could
be contained until the next reasonable scheduled repair.
Symptoms of the low temperature brittle fracture of steel were
showing, but the engineering community in the 1940s, like engineers (and doctors)
in 2007 are prone to treat the symptoms and not look into the true cause of the
failure (disease) and find a true and final solution (cure).
Sounds Familer:
The
engineering community was so clueless as to the low temperature brittle fracture
of steel problem that over 5000 Liberty ships were mass produced during World
War II without accounting for this phenomenon. Thirty years after the TITANIC
sank only because the water was about 15 degrees too cold, the US Government built
over 5000 Warships with the same fundamental flaw. Of these 5000 Warships,
1000 suffered significant failures between 1942-1946 because of low temperatures,
while 200 suffered serious fractures between 1942-1952. No one may ever know exactly
how many ships "just disappeared" in the North Atlantic and were falsely
chalked up as lost to German U-Boat torpedo attacks due to low temperature brittle
fractures. Some torpedoed ships may have even survived an attack, albeit damaged,
without the hull shattering due to the low temperature brittle crack phenomenon.
The Government knew something was wrong, because the failure rate of the welded
Liberty ships was statistically astronomical in the North Atlantic, while literally
NON-EXISTENT in the warm waters of the South Pacific.
Not
until 1947, that a ship literally broke into two pieces while tied to a dock in
the cold water of Boston Harbor, that there was enough evidence, left accessible
and dramatic enough, that the problem was taken seriously. This parallels
uncannily with the Aloha Flight 243 aircraft accident, which landed at the Maui
Airport after an 18 ft. section of the upper fuselage disintegrated inflight at
an altitude of 24,000 feet above the Hawaiian skies. The Aloha Flight 243 accident
initiated the "aging aircraft program" that changed the course of aviation
engineering history with the same magnitude as the breaking into two pieces of
the USS Ponaganset changed naval engineering history.
USS
Ponaganset cracks into two pieces from brittle fracture starting from welders
arc strike on deck of ship.
The
USS Ponaganset (AO-86) was a T-2 tanker, a Escambia class Fleet Oiler, built at
Marinship in Sausalito, California and commissioned on May 15, 1944. Only 3 years
old, on a cold day at dockside in Boston, Mass., at a temperature of 35 degrees
Fahrenheit, the stresses at a stray welding arc strike on the deck of the ship
exceeded the yield strength of the steel. Yield strength of steel is the stress
level when the steel starts to permanently deform. Typically, the yield strength
is only about one-half of the ultimate tensile strength, the stress where steel
actually breaks into separate pieces. Much deformation occurs in a piece of steel
between when the steel starts to yield and finally fails at ultimate tensile,
usually the steel will stretch between 20% to 40% of its original length before
it breaks, if it acts in a "ductile" manner.
"NIL
DUCTILITY TRANSITION" Temperature
The
"BIG OOPS" in the TITANIC and Liberty shipbuilding disasters is what
was defined by two researchers at the U. S. Naval Research Laboratory, W. S. Pellini
and P. P. Puzak, the "Nil Ductility Transition" temperature phenomenon.
On March 15, 1963, Pellini and Puzak published their findings after a 15 year
study, defining and also devising a method of quantifying the temperature at which
steel changes from DUCTILE to BRITTLE fracture modes. Above the Nil Ductility
Transition temperature, a certain piece of steel can be loaded to its ultimate
tensile strength, stretching 20% to 40% before it breaks. Below the Nil Ductility
Transition temperature, when a piece of steel is loaded to only the yield strength
(approximately 1/2 of the ultimate strength) the piece of steel will crack in
a brittle manner, like glass. Once the crack starts to run (at the speed of sound),
it will only stop when it runs out of steel, the load is released or the crack
is arrested by running into a piece of ductile acting steel.
In
the case of the USS PONAGANSET, the stresses reached the yield strength at a location
where a tiny crack existed on the deck of the ship in 35 degree Fahrenheit weather.
The NDT of the steel used to build the Ponaganset was determined after the failure
to be 50 degrees Fahrenheit. Consequently, the crack propagated in a brittle manner
and literally ran around the ship, near instantaneously, and the ship broke in
two.
The US War
Machine, and not unjustifiably, was priding itself that it could build a shipyard
that could deliver mammoth ships at a rate of one every 13 days. Marinship set
a record of building one ship, the S.S. HUNTINGTON HILLS, from empty dock to complete
ship in just 33 days.
Who
would have thought that a 15 degree temperature drop and a stray welder's arc
strike could destroy a ship as effectively as a German torpedo? Could a 29,000
ton ship be that fragile? How could the US Government build 5000 ships with such
a flaw?
When
an average person is subjected to a "Disaster", the memory of the emotion
is long, but the memory of details is short. Mention TITANIC and the immediate
response is "Sank by Iceberg". This is a normal defense reaction. It
is perfectly acceptable to even the simplest mind that a mammoth iceberg could
sink an "unsinkable" gigantic steel ship or an errant missile could
bring down a 747. But if the answer is as simple as the water was too cold but
nobody knew or frayed insulation caused an arc and explosion, how can we trust
that all the other engineering masterpieces our lives depend on, everyday, are
not as fragile? The planes we fly in, the miles long bridges we drive across,
are they also susceptible to catastrophic failure by a simple quirk of Nature
the greatest minds of our civilization are not aware?
