CHERRY POINT, N.C. --- If a V-22 squadron needs a titanium hydraulic or fuel line tube for one of its aircraft, Fleet Readiness Center East is the source to call. That’s because FRCE is the only U.S. military aircraft repair facility to have perfected the orbital welding process required to produce these critical components.
V-22 fuel lines and hydraulic tubes are made of titanium to withstand the high operating pressures and degree of vibration the aircraft experiences in flight. FRCE engineers and artisans first began working to establish capability to weld titanium for fuel line and hydraulic tubes about 10 years ago, but results were uneven and customer demand was low. About two years ago, however, the U.S. Air Force requested that FRCE resume welding fittings onto the titanium tubes.
Welding fittings onto a titanium tube without defects proved to be extremely difficult to achieve. Mark Sapp, welding engineer with the FRCE Materials Lab, said that in spite of its strength, titanium is unforgiving of defects.
“It could be a matter of touching the surface with rubber, a scratch only three-thousands of an inch deep, or a fatigue characteristic – there are a lot of metallurgical considerations that could damage a titanium tube,” Sapp said. A crack, a scratch or a void in the weld on one of these tubes could compromise its integrity. If the strength of the titanium is weakened, the fuel line or the hydraulic line could fail.
Sapp said much of the knowledge gained in FRCE’s first attempt at welding the tubes had been lost by 2017, but one rule guided the team’s new quest for a perfect Class A weld.
“Clean, clean, clean was our mantra,” Sapp said. “It took quite a few evolutions before we could get our cleaning process down.”
Erik Quinn, overhaul repair supervisor, said each step in the welding process was evaluated to determine if it was adding value or creating contamination.
“The requirement of a clean, contaminant-free atmosphere when it’s in the chamber is what allows us to achieve a Class A weld,” Quinn said. “After it completes the welding process, it goes through a nondestructive inspection process, and … there are very strict requirements that have to be met through X-ray, as well. When you do this process, and it makes it all the way through successfully, you have just created the cleanest, strongest weld possible.”
Part of the process includes acid etching the fittings before they are attached to the tube to ensure they are free from contaminants. This process was previously completed by materials engineers, who had to fit the process into their schedules. Now, welders have been certified to etch the fittings, which cuts several hours from the process.
Once the fittings are etched, they are then lined up precisely with the tube in the orbital welder to ensure a strong, clean weld.
Robert Warmack, welder at FRCE, said the orbital welder uses argon gas to purge any contaminants from the system, and then the welding begins.
“Once the arc hits and starts welding, it’s a continuous weld that goes from one end all the way around the tube to the other,” he explained. “The welder makes one continuous orbit around the tube from start to finish. The fitting itself has a little bit of extra metal, that way it fuses on to the tube itself.”
Sapp said that, because FRCE is the only DOD repair point for the flight-critical V-22 fuel and hydraulic lines, the team maintains close control over the welding process.
“If we make a mistake or if there’s a failure in our production process we have to immediately go back and find that point of failure and get it corrected and make sure all who are involved understand what had taken place and what to look for,” Sapp said.
Quinn said as the welding team refined its process, their reliability rate has steadily increased from a 30 percent pass rate two years ago to 85 to 90 percent today. Quinn credited the perseverance of the project team with the ultimate success of the project.
“When you consistently see that you’re failing, you can easily get deterred and lose your drive to continue through,” Quinn said. “These individuals stayed vigilant, they stayed relentless, and they stayed on top of this to achieve what they’ve done. They have all done a wonderful job proving this process out.”
FRCE is North Carolina's largest maintenance, repair, overhaul and technical services provider, with more than 4,000 civilian, military and contract workers. Its annual revenue exceeds $835 million. The depot generates combat air power for America’s Marines and naval forces while serving as an integral part of the greater U.S. Navy; Naval Air Systems Command; and Commander, Fleet Readiness Centers.
Click here for a related June 14 story on the FRCE’s involvement in F-35 component maintenance.