BREMERTON, Wash. –
A team of innovation-minded professionals from Shop 26, Welders, and Code 138, Weld Engineers & Non-Destructive Test Examiners, at Puget Sound Naval Shipyard & Intermediate Maintenance Facility, developed a new process for aircraft carrier rudder bore repair that cut the overall repair time by more than half.
According to Travis Yanda, Shafting & Rudder assistant project superintendent, Code 312, Aircraft Carrier Program Office, Shop 26 and Code 138 worked closely together for a year to refine and improve the rudder repair and refurbishment process, which included research and development, as well as comprehensive mock-up training. This effort reduced the Lower Rudder Thordon Bearing Repair, which is informally referred to as a rudder bore repair, from 99 days on USS Carl Vinson (CVN 70) to 34 days on USS Theodore Roosevelt (CVN 71).
While the basic process did not change, the team was able to fine-tune the use of mechanized welding and precision machining to ensure the repair work was completed without any rework.
When a rudder is removed from an aircraft carrier during a docked availability, the rudder bores are usually built back up to a precise dimension with both ferrous and non-ferrous materials so the rudder stock holding the rudder fits precisely.
Skeeter Judd, welding engineer, Code 138.2, said mechanized pulsed gas metal arc welding, known as GMAW-P, is used to build the steel back up to specification. After steel build-up is complete, the newly qualified mechanized pulsed gas tungsten arc welding, or GTAW-P, equipment is installed to perform the Monel cladding in certain areas over the steel. Monel cladding is a nickel alloy layer that is more resistant to corrosion than steel is. It is placed between the steel on the rudder bore, in areas where seawater touches.
Ron Cenicola, non-nuclear director, Shop 26, said the process satisfies two objectives. The first objective is to repair corrosion of the rudder bore casting. The second objective is to add non-ferrous (corrosion-resistant) material to the inner diameter to prevent future corrosion of critical surfaces.
“Previously, the practice was to hand weld the inner diameter,” said Cenicola. “This was very hot and uncomfortable for repair personnel and did not result in as smooth of a surface as the mechanized welding does. This increased the amount of time it takes to machine the welded surfaces to final dimensions. This is not the first time Shop 26 used a mechanized welding system to perform weld build up. Unfortunately, previous attempts were not as fine-tuned and resulted in numerous deficiencies during final inspections.”
According to Judd, the overall improvements were the result of much testing and the creation of step-by-step standard work documents.
“Shop 26 put in a lot of effort to ensure welders were properly trained, including the creation of standard workbooks,” recalled Judd. “Shop 26 and Code 138 had months' worth of mock-ups and troubleshooting that went into the standard workbooks and welding procedure that was used in production for the steel build-up.”
“For the new mechanized GTAW-P welding procedure, Shop 26 and Code 138 had even more time spent on development and procedure qualification work before being able to write a procedure and start qualifying welders/operators,” Judd continued. “Without the qualification, the Monel bands would have had to be welded by hand again (semi-automatic).”
Once the steel is built up and the Monel bands are created, the bore is machined to a precise specification that will help reduce the amount of wear and tear on the bore from sediment and salt water getting into the spaces between the bore and rudder.
“After welding, Shop 38, Marine Machinery Mechanics, will machine the bearing bore to maintain a .002-inch tolerance over the almost six-foot length of the bore,” said Yanda.
That tolerance is about the diameter of a human hair, and is about the same tolerance used on high-performance V8 engines.
According to Judd, new equipment alone will not always result in big wins, when trying to create savings throughout a process. Combining the capabilities of equipment with skilled people is where the best results can be achieved.
“The equipment used for this work is very valuable and can provide a huge benefit, but only when it is used correctly,” Judd said. “Success like we had recently on CVN 71 boils down to the people portion of the work. The people using the equipment were the reason things went well. Qualified and well-trained welders, machinists and NDT inspectors are what allowed this awesome example of first-time quality.”
Yanda said the benefit achieved by the team might not have come easily, but the year-long process improvement effort was worth it.
“Never stop trying to improve,” he said. “It may not always work on the first attempt, but keep learning and looking for ways to improve; whether it be a process change, new tooling or challenging requirements.”