Apr 6, 2013

Loss of Nuclear Vessel USS Thresher - Lessons from 50 Years Ago

Periodically I attend Australian Standards meetings where I am a member of several Quality related committees and also a committee on Pressure Equipment. These can be dry of course but the Quality one's were often enlivened with yarns by Bob Innes, retired ANSTO & Steelplant engineer. One of the most evocative stories from Bob was that of the loss of the USS Thresher, which occurred 50 years ago in April 1963.
From US Navy

She was the first of a new class of nuclear submarine,  and was lost with her 129 men, inspiring the movie Grey Lady Down. But there was no happy ending & her lessons still apply eg in Australia with incidents such as those of the HMAS Westralia & HMAS Kanimbla naval vessels.

(Note - A memorial service was held in April 2013 Portsmouth USA to mark the 50th anniversary of the tragedy.)
From http://www.submarinehistory.com/Thresher.html

The Thresher sank off Cape Cod during her first descent to her 400m test depth, pushing beyond previous experience, in April 1963. It was believed back then that ...

Ice formed, bursting an engine room seawater pipe (weakened by dealloying or failed silver brazing?). Icy seawater poured in creating a foggy mist, with the control valves scattered about the room. She could not blow her ballast tanks, due to an unauthorised change – a strainer, causing icing up by a venturi cooling effect. Water soaked electrical circuits caused a power outage, the reactor shut down. Losing forward momentum, she slowed, drifted down; her hull bent, twisted, imploded and then split into three sections. 

Why? Political pressure to deploy new weapons systems & so standards were relaxed, due to an over confidence with submarine successes in WW2. They ignored the loss of 52 of 288 submarines, some possibly due to shoddy workmanship, including defective welding. Inspectors didn’t believe that the high standards were necessary. Indeed she was designed & built to 2 different standards ie nuclear power plants were constructed to veryexacting tolerances, while the design criteria in non-nuclear areas were seen only as goals. 

Later review found too many penetrations of the hull, with defects detected ultrasonically in many of the silver-brazed joints on pipes penetrating the hull. But the shipyard commander did not pursue new U/S inspection, considering it wasn’t a dangerous situation. Less accurate x-ray was the usual test & he was only required to try U/S methods. At that time there were no clearcut procedures for correcting the faulty joints. He was trying to meet a deadline, seeking to avoid pipe unlagging delays & increased costs.

Navy procedure allowed the shipyard commander to make such decisions as he was on-site, ostensibly having hands-on knowledge of the ships. In fact, he wanted to test only the repaired joints. But the Bureau of Ships would not allow so minimal a testing program. They compromised however – requiring the testing of only those joints that time would allow & were easily accessible. He did not immediately report the ultrasonically detected defects to his superior officer. The test report did not arrive at the Bureau of Ships until after the sinking.

Later some joints on the Thresher were found to not be brazed at all! Although a brazed  joint on the Barbel had failed earlier, this was not shared, so procedures for the Thresher were not reviewed, nor the Portsmouth shipyard’s Quality Control issues.

”The high performance required of these ships, the exotic materials being used, the pushing of older materials to greater limits, means the Navy cannot afford not to use higher standards throughout”. These were the words of Admiral Rickover, father of the US Navy’s Nuclear Submarine Program, in an address in 1962, before the sinking. Overriding these concerns, his senior officers feared tougher standards would add to costs. Some non-nuclear standards were even lowered. They were working at the limits of technology and not knowing the consequences of not knowing those limits.

Lessons learned from the subsequent Inquiry included:
1. Give equal weight to design & construction of nuclear & non nuclear submarine parts.
2. Cost & time pressures must not override safety in design, construction & overhauls.
3. Communicate near miss events to resolve weaknesses or flaws to avoid future tragedies.
4. Test equipment & parts on receipt & under operating conditions to assess suitability.

For many years the above was the accepted scenario of failure - however in recent years there has been some re-thinking - and utlising evidence now available that was classified at the time. According to an article from the website for Mass Live, it is now postulated that :

"the initial Thresher casualty as an electrical bus failure, which shut down the submarine's main coolant pumps causing the instant reactor scram. Unable to rapidly restart the reactor to regain propulsion, and unable to blow ballast, the Thresher slowly sank toward the ocean floor — a depth of 8,400 feet — with 129 men on board. " '

Regardless of which scenario prevailed back then, we can read how lessons were drawn from the loss - see the Mass Live article   ...

' "The Navy accelerated safety improvements and created a program called "SUBSAFE," an extensive series of design modifications, training and other improvements. People involved in the SUBSAFE program are required to watch a documentary about the Thresher that ends with an actual underwater recording featuring the eerie sounds of metal creaking and bending as a U.S. Navy submarine breaks apart with the loss of all hands.

"Every job we do, we need to have in the back of our minds that we have the lives of the sailors in our hands. It's that critical and it's that literal," said O'Connor, president of the Metal Trades Council.'

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