Production X-ray Inspection of Turbine Blades
November 18, 2014
Most would agree that manufacturing a modern jet engine is certainly a challenging task. These machines are constantly evolving and are required to be more fuel efficient, lighter weight, more powerful, while becoming quieter and cleaner for the environment. This is an extremely difficult combination to achieve.
A critical part at the heart of these amazing inventions is the High Pressure Turbine blade (HPT). These are specially cast, nickel based superalloy parts designed to operate in an environment hotter than their own melting temperature. These parts are located in the most hostile area of an aircraft engine, and it isn’t any easier for the surrounding blades in the low pressure and compressor areas.
High Pressure Turbine blade location in a typical jet engine (courtesy of Wikipedia)
Special manufacturing techniques, such as Directional Solidification and Single Crystal production methods combined with sophisticated cooling designs, turbulators and coatings, allow these parts to survive in this brutal environment, all the while spinning at tens of thousands of RPM.
As with most complex, safety-critical parts, the more daunting the manufacturing task, the more vital the testing process. Failure of these parts while in service is not an option. These are intricate castings subject to porosity, cracks, inclusions, shrinkage, gas holes, etc., and they're vulnerable to challenges in machining, like merged holes and over shots in the laser drilling process.
Using destructive versus non-destructive testing
Destructively testing the critical inner structures of these parts is an option, however it requires large sample sizes, is time consuming, is expensive and can’t be accomplished on 100% of the parts. It is just not practical for every case.
Using X-ray technology to nondestructively test these parts has been proven to be a valuable tool and a viable option for many years. X-ray images allow the inspector to validate and control the manufacturing process, verify dimensional requirements (both before and after machining), and even allows them to check welding quality for in-service maintenance procedures.
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