Detecting danger: NDI shop evaluating new technology to find cracks in parts
By John Parker, Staff Writer
/ Published April 01, 2016
TINKER AIR FORCE BASE, Okla. --
A 548th Propulsion Maintenance Squadron unit is evaluating new technologies with the potential to detect dangerous cracks in metal jet engine parts that current methods may be missing, squadron officials said.
Finding those fractures is the job of the 548th PMXS's 53-member Non-Destructive Inspection shop. The Oklahoma City Air Logistics Complex shop examines more than 200,000 jet engine parts a year, including those that power B-52 and B-1 bombers that are crucial to the nation's 24/7 nuclear deterrence.
NDI inspectors currently rely on five industry-standard technologies to detect microscopic cracks in metal parts. When found, inspectors and engineers evaluate whether the fissures are serious enough to potentially cause the part to fail under the high pressures, stresses and temperatures of an operating jet engine. Problem parts are either repaired or declared unusable.
The NDI shop's current detection methods include using X-rays, magnetism, electrical eddy currents and other energy sources to reveal part flaws. Two new promising technologies could potentially improve finding critical fissures.
"The goal is to do be able to perform a truer, more accurate inspection," said Scott Sawyer, 548th Propulsion Maintenance Squadron flight chief. "There's always new technology coming, so we've always got to be looking to the future to figure out if there a better, cheaper, more effective and faster way of doing this that will achieve the same result or a better result."
One technology under evaluation bombards a part with ultrasonic sound waves. The waves cause the crack faces to rub together, generating heat. The minute difference in temperature is then detected by a highly sensitive infrared sensor that reveals the fracture.
A second technology would improve how eddy current sensors are used to discover cracks. In one existing method, for example, inspectors use a handheld device with a slender rod-like coil sensor less than the width of a pencil. The rod often has to be moved around a large part to take single readings in dozens of areas. A new method places multiple sensors in a flexible ribbon that can be attached to the part to test a wider area simultaneously.
"The present method is slow, tedious and time-consuming because each swipe is basically a very narrow width of inspection," 548 PMXS process engineer Ernesto Nieto said. "The time is up to 60 hours on some parts, but with this new technology you can contour the ribbon in a dovetail inspection, for example, and perform the inspection in three or four swipes as opposed to several dozen."
Although a new technology can look promising, engineers and managers must evaluate myriad factors before it can become part of the inspection processes, Sawyer said.
Will the process slow down production by finding more cracks that are actually harmless? Will it find dangerous fissures that older methods would have missed? Is the method good for all or just some types or parts?
Engineers, for example, are conducting a probability of detection study on the sonic/infrared technology to discover how well the potential new process finds cracks compared to current methods.
"Ultimately you want to eliminate any and all risk, if possible, of missing a crack in that part escaping," Sawyer said. "We're looking into other technologies to continuously improve our processes."
If approved, the new testing methods are scheduled be incorporated into NDI practices next year, Nieto said.