The Ultrasonic Inspection of Submarines
January 29, 2010
As a quality assurance inspector for more than 30 years, one of my favorite tasks is performing ultrasonic inspections (UT). For eight of the 20 years I spent performing nuclear submarine inspection, I was stationed in Guam.
First of all, the great thing about Guam is the separation from all the conveniences we take for granted on the mainland when it comes to repair and overhaul work. In Guam, we could not get on the phone in the evening and have a technical representative to our shop by morning to help us solve our problems. We had to completely understand technical manuals, be able to read drawings, and fully understand intent and application of standards, methods and acceptance requirements. It was during this time that I gained a significant amount of knowledge related to the problem solving techniques unique to Guam.
The most common methods of inspection I performed during my time in the U.S. Navy were ultrasonic shear wave and straight beam. The prevention of catastrophic events was perhaps the most important concern when it came to keeping our submariner mates safe. The Navy’s planned maintenance schedule of inspections is very effective. Even O-Rings were replaced at intervals to ensure there was no failure in operation.
My favorite inspection is the UT weld. This is perhaps because I did hundreds of feet of inspections as a shear wave weld inspector. To a layman, the view of a weld through an oscilloscope simply looks like lines jumping up-and-down and side-to-side. However, experienced ultrasonic inspectors, who evaluate the weld’s heat effective zone (HAZ), or the fusion of weld to base material, the root penetration area and fusion area between weld beads, are looking for lack of fusion, porosity, cracks or any anomalies that could render the weld rejected or in question. When we find a questionable discontinuity, we typically employ another nondestructive test (NDT) method to ensure the questionable condition is positively identified as either accepted or rejected. Then we take the appropriate action.
Most people do not realize that the actual submarine hull is not the tube shape they see in pictures. The actual pressure hull is shaped to incorporate ballast tanks used to surface and dive the submarine, mud tanks to hover the submarine in one spot and sonar array transducers to give the submarine sight under water.
Fiberglass Nose When someone sees a submarine in a dry dock, they realize it is like an iceberg where only about 5% is visible. For UT inspection, we enter the ballast tanks to perform weld inspections from the bottom of the submarine between the blocks that are holding the submarine up. Other locations on the submarine are accessed from inside, or other points of entry inside the outer hull.
During my service as a nuclear submarine inspector, occasionally there would be a collision from running silent, and we would have to inspect the fiberglass nose for fractures. Because of the array of sonar transducers in the bow, or front, of the submarine, if there was damage to the fiberglass or de-lamination, the sonar could not exit the fiberglass or be refracted in an angle not planned. This would give a 6,145-ton submarine sight problems.
For example, in 2005 the USS San Francisco (SSN-711) had a problem, and collided with an undersea mountain, damaging the submarine’s forward ballast tanks and sonar dome. The result of this collision was devastating-23 crewmembers injured and one death due to injuries during the accident. Following the investigation, the U.S. Navy attributed the incident to complacency on the part of the submarine’s commander and six crewmembers. According to Navy reports, these individuals did not adhere to “critical navigational and voyage planning procedures,” and were found guilty of “hazarding a vessel and dereliction of duty.”
Following the collision, the submarine was brought back to Guam, my old stomping ground, where temporary repairs were made prior to sending the vessel to the Puget Sound Naval Shipyard in Washington State, for more extensive repairs, where UT inspection obviously played an integral role in ensuring that the submarine would be ready and able for duty.