FAQs
(Steel)

The current myth of "inferior steel" evolved from pure hindsight. It is true that the steel provided to Harland & Wolff by Dalzell and D. Colvilles & Co. was produced in acid-lined open-hearth furnaces, which allowed for impurities (such as sulphur and phosphorous) in the steel. These impurities led to low fracture resistance, especially in cold water conditions that reduced ductility (ability of the steel to deform without yielding), by reducing the amount of manganese present to bind to the residual sulphur. With insufficient manganese, the sulphur combined with the iron to form the ferrous sulphide, which created paths of weakness (especially along grain boundaries) along which fractures could propagate. The manganese-sulphur ratio of Titanic's steel recovered from the wreck site has been determined to be 6.8:1, low in comparison to steels produced today that have ratios as high as 200:1. The presence of phosphorous, even in minute quantities, also played a significant role in the initiation of fractures.

However, most of steel used by British shipyards during this period was produced using the open-hearth method; in fact, the metallurgy of the steel did not change significantly until after 1947, when wartime experiences prompted closer examination of the elemental properties of steel. At the time of her construction, Titanic's builders used top-quality steel that would remain the industry standard for years to come. The steel used in the R.M.S. Queen Mary, which survives to this day, was produced by the same mill that provided steel for Titanic and is essentially the same in composition. To accuse Titanic's builders of using "inferior steel" is unfair, as it would be decades before the minor elements of steel would be more fully understood.

Another factor in the break-up of the ship appears to have been crack propagation along rivet holes. For the Olympic-class ships, the rivet holes were cold punched through the steel plates prior to riveting the plates to the framing. This is an invasive process that creates micro-cracks around the periphery of the rivet holes. In addition, many of Titanic's rivets were hydraulically driven, which created residual compressive stresses that were not relieved, as the cooling of the rivets drew the plate tight against the framing. When the sulphide particles in the steel are subjected to stress, the micro-cracks can coalesce into macro-cracks, which provide pathways for fracture propagation. The British Admiralty subsidised the construction of the R.M.S. Mauretania and R.M.S. Lusitania, thereby enabling them to enforce their standing requirement for all rivet holes to be reamed in order to prevent the spread of micro-cracks. After Olympic's collision with H.M.S. Hawke in 1911, Harland & Wolff Naval Architect Edward Wilding noted that cracks had developed in plates that were not located within the immediate impact area. His concern was that the micro-cracks allowed fracturing to propagate and he urged that the Lloyd's Rules for hull surveying requirements be modified to include impact and notched-bar testing. However, even though he recommended that rivet holes be reamed as a precautionary measure, he acknowledged that it was an expensive proposition that would not be cost-effective for steamship companies to implement, given the anticipated loads a steamship might endure during her career.

By 1930, ship classification societies had fully disallowed the cold punching process because of experiences with steamships that were by then getting long in the tooth. Olympic, in particular, suffered greatly from stress crack propagation in her plating, as evidenced in a 1930 hull survey. As mentioned above, the Queen Mary used essentially the same steel that the Olympic-class ships used, but she suffers less from crack propagation because her rivet holes were drilled, then reamed.

It wasn't until the T-2 tanker Schenectedy broke in half while fitting out in a shipyard in Oregon during the first part of January 1943 that a concerted investigation was launched into the mechanics of ductile-brittle behaviour at or around freezing temperatures. What we know today about steel embrittlement during cold temperatures comes from the failure rates of Liberty ships and T-2 tankers during World War II — the builders of the great transatlantic liners simply did not understand the relationship between temperature and ductility. Even so, plates recovered from the Titanic wreck site show a relatively low ductility in some, but not all, plates. There is not enough evidence to say that embrittlement played a significant role in the initial flooding of the ship. It did, however, play a significant role in the break-up of the hull, as will be explained later.

Actually, they did. Even though Olympic's structure was completely riveted, someone made the decision at some point to use welded joints in the area of the two expansion joints for the following hull. This was first discovered as change notes on the original builder's plans, and subsequently confirmed by David Livingstone of Harland & Wolff during one of the dives to the Titanic wreck site. It appears this change was made to Britannic, as well. The technique of welding steel plate was first demonstrated to Harland & Wolff management by the Thermite Company as early as 1907. Even so, neither riveted nor welded joints could have successfully resisted the massive stresses exerted on Titanic's hull during the sinking.

Practically none. The forward and aft expansion joints were designed to relive stresses in the superstructure brought on by longitudinal flexing of the hull in a seaway. The joints themselves did not penetrate B Deck, the strength deck for Titanic's hull. During the sinking, both expansion joints opened far beyond their normal limits, but this did not affect the integrity of the hull girder. The fact that they opened past their design limits does, however, provide an indication of the extreme bending moment acting on the hull at that point.

The exact nature of the collision is controversial, but it is my opinion that the ship briefly grounded on an underwater projection or shelf of the iceberg (for more detail, refer to "Grounding of the Titanic"). This strike was hard enough to open portions of the hull's double bottom to the sea and transmit shock damage up supporting members so that watertight integrity of the Fireman's Passage was compromised. In addition, as the ship's momentum carried the starboard side of the hull up farther onto the shelf, racking damage distorted shell plating on the starboard turn of the bilge, shearing rivets, breaking caulking and allowing the parting of strakes deep below the waterline, resulting in the inrush of water into Boiler Rooms Nos. 6 and 5 reported by eyewitnesses. The transverse bulkhead between Boiler Rooms Nos. 5 and 6 was weakened slightly as supporting longitudinals were distorted. The influx of water from multiple openings eventually overwhelmed the capacity of Titanic's pumps. The rate of flooding actually decreased from a high of approximately 400 tons per minute during the first hour of flooding, as the pressure began to equalize. The ship attained near equilibrium during the second hour of flooding, but as the loss of buoyancy in the flooded bow began to pull hull openings and non-watertight decks under the surface, flooding increased once again. The Titanic was doomed by this time, as Thomas Andrews had calculated.

At around 0200, events began to escalate. At this point, approximately 35,000 tons of water filled the submerged bow section. The forecastle was pulled under and Boiler No. 4 filled with sea water. There were now a loss of buoyancy forward equivalent to the 40,000 tons of water filling the bow, opposed to the weight of about 250 feet of unsupported hull as the stern rose clear of the surface. The stresses accumulated in the area abaft the third funnel, which happens to be a structurally weak spot, as the combination there of the engine casing, the after staircase and openings in the shell plating created discontinuities in the structure. The hull girder, already subjected to stresses well beyond the yield point of the steel, began to buckle. As the structure bent in a curve, a fissure developed along the top of the structure and spread downward toward the compressed keel. Ductile tearing of the shell plating was aided by increasing crack propagation along rivet holes and hull openings. The bow and stern sections began to separate, collapsing the two main transverse bulkheads framing Boiler Room No. 1. The deck structures subsequently failed, due to the lack of bulkhead support. The hull girder compressed further, destroying the inner bottom structure beneath the ship's machinery spaces. The cabling carrying electrical power was cut, along with the piping supplying steam to the dynamos. At some point under the surface, the double bottom structure finally gave way to compressive stresses and the hull broke into three major pieces. Freed from the dead weight of the flooded bow section, the stern settled back down onto the surface. Flooding began in the damaged lower compartments, upsetting the equilibrium of the stern and tipping it into a near-vertical position. The remaining buoyancy in the stern temporarily counteracted the advance of the flooding, until the trapped air was forced out through apertures in the hull. Tearing of the port-side shell plating or the manner of flooding caused the stern section to rotate counterclockwise about the vertical axis. Hydrostatic pressure systematically imploded damaged compartments in the stern section as it flooded and sank, which accelerated the rate of sinking towards the end.

In short, the impurities in her steel, the failure to ream the rivet holes prior to driving the rivets, the lower ductility of the steel due to the coldness of the water and the coarser grain structure of the shell plating would only serve to hasten the demise of Titanic. It was the depth and longitudinal extent of the impact damage that spelled doom for the ship, for it induced massive flooding that overcame the internal subdivision. The flooding itself created an estimated maximum bending moment of over 5 million foot-tons that grossly exceeded the yield strength of the steel. No ship, even a modern one employing A 36 steel and welded construction, could have withstood such excessive stresses.

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