Sunday, July 26, 2009

Cracked Hull Considerations not a Laughing Matter

USS Toledo (SSN-769), a Los Angeles-class submarine was built by Northrop Grumman Corporation's Newport News Shipbuilding and Drydock Company and commissioned in 1995.


Had Toledo really been sent to Scotland for repairs on 15 August 2000, three days after the tragic Kursk incident[2]? In December 2006, Toledo commenced a protracted depot modernization period completed in March 2009.


Cracks have recently been detected in Toledo's outer deck and pressure hull. The Naval Sea Systems Command is continuing its investigation, which could conclude other Grumman-worked submarines are at risk and suggest some well-deserved penalties in connection with lucrative SSN work; or on the otherhand, Systems Command may simply cite a rare circumstance that befell Toledo alone. The latter finding might involve defective metallurgy (standby HY-80 producer) or Teredo worms. Quite believable? Rather doubtful.


Were Longitudinal Stresses at Issue during Drydock or Earlier Shock?

The most likely failure mode of the pressure hull as a whole is an overall whipping response, because the structure being designed primarily for circumferential stress is not longotudinally stiffened. (from Concepts in submarine design October 1995; By Roy Burcher, Louis Rydill)


Were Rigorous Quality Inspections Performed?

The combination of elements to produce an alloy with great strength is only half the story of producing submarine hulls. The second factor in the manufacturing process is the tempering of the steel and shaping of the plates into a final form. Once again, the basic concept is that a slow-cooling steel tends to be resilient and a quick cooling steel tends to be brittle. ...


The next weld layer is placed on top of the deeper layer. As the process continues and the wedge shaped trough widens, more and more beads are placed side by side to fill the trough. Many hundreds of beads are required to bring the level of beading to the surface of the abutting hull sections. It is a long and tedious job and quality inspections are constant. ...


Time destroys the hull from several directions. The metal itself fatigues over time. Additionally, the sea takes its toll with corrosion eating at the metal. Hull modifications requiring welding, heat the hull and thereby reduce the effectiveness of the initial tempering. from Bulletin No. 31 Test Depth and High Yield; excerpts from "Steep Angles and Deep Dives".


Submarines are always silent and strange.



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