Submarine ARA San Juan only had a Weak Hull (eg. 100 Meter Operating Depth)

From November 18, 2017 to December 1, 2018 Submarine Matters reported many aspects of the loss of the Argentine submarine ARA San Juan. San Juan remains lost without a trace, even though several countries continue to look for it.

On January 30, 2017 International Business Times reported  :

" The ARA San Juan was “’limited’ in its operational depth at 100 meters...because at greater depth [it] could not ‘guarantee its watertightness’, according to the document" [the document may be from the Comprehensive-Nuclear-Test-Ban-Treaty-Organization (CTBTO) or US Naval Intelligence (?)]

The new internal document may be able to shed light on what happened to the ARA San Juan. Officials still had not determined the cause of the submarine’s disappearance, though a report released in January by SaveTheRoyalNavy(dot)org said it was likely that all crew on board died from an explosion on the vessel.

An acoustic signal was detected the day the submarine disappeared that authorities said was consistent with the sound of an implosion of pressure inside the ship at a depth of 388 meters... The report stated the explosion was equivalent to 5,669 kilograms of TNT which would have destroyed the hull in 40 milliseconds." [this is according to a CTBTO and/or US Naval Intelligence report]

COMMENT

By setting a safe operating depth of 100 meters the Argentine naval authorities must have decided that San Juan had a severely weakened pressure hull. Only a 100 meter safe operating depth is surprisingly shallow. Even German Type XXI submarines built in 1943 had "Test" (ie. operating) depths of 240 meters (see sidebar). A weak pressure hull may be due to one or several factors including:

-  age (San Juan was completed 35 years ago in 1983). A 25 to 30 year operating life for a well
   maintained submarine is considered standard.
-  age in conjunction with too many deep immersion cycles (repeated deep diving, then surfacing
   gradually causes metal fatigue in the pressure hull over a number of years).
-  the Argentine Navy is notorious for poor maintenance
-  extensive and/or improper hull cutting for engine maintenance (cutting or welding pressure hulls
   weakens them) and/or
-  too much rust and saltwater corrosion of the pressure hull shell and of strengtheners.

In general the newer the submarine the stronger its steel alloy pressure hull and the deeper it can safely dive (see here and here). Titanium alloy permits much deeper diving (eg. Russian Alfa class submarines) but titanium is more expensive to process, weld, use in construction and repair.

Pete