High-precision ultrasonic inspection for aerospace industry

The use of non-destructive inspection of components is an important core element in the aerospace industry. Due to the extreme stress of the installed security-related components, assuring their flawlessness is essential for safe aerospace missions.

Fig1: Immersion Inspection System LS 200, Scanmaster 

VOGT Ultrasonics provides a safe inspection solution with high-performance ultrasonic inspection systems. One of these high-performance ultrasonic in-spection systems was installed by Vogt at ASTRIUM GmbH in Ottobrunn-Germany. With 18000 employees ASTRIUM is the third largest company of the space industry. An inspection was performed on the VINCI-thrust chamber of the upper stage of the Ariane V. Besides the LS 200 ScanMaster immersion technique inspection system, installed in 2013 by VOGT, the inspection system of the same type which was installed by VOGT 12 years ago is used. The motto of those responsibles of inspection at ASTRIUM is to be seen in the context of the Ariane missions: “We do not ever want to see our components again.” Thus already in the development process a close collaboration between engineering and quality assurance takes place.

The VINCI thrust chamber is the heart of the high-performance engine of the European carrier rocket Ariane 5. The upper stage thrust chamber primarily consists of a Copper-Silver-Zircon-liner (CuAg3Zr05) with up to 468 cooling channels, milled into from the external side, and a subsequently applied Nickel coating. Additionally the intake and outtake ring at the top and the bottom as well as the nozzle flange are welded by an electron beam.

Within an incoming inspection the 1,2 m high and 320 kg heavy raw part is inspected on interior material defects by an 100% volumetric inspection. The area of inspection is hereby 30 mm, whereby the main focus is on the defects in the area of the hot gas wall of the final- turned Cu-liner. The inspection is performed in accordance to AMS-STD 2154 with a permissible defect size of 0,8 mm flat bottom hole (FBH).

fig. 2: Electron beam welds on VINCI thrust chamber

Up to 468 cooling channels are milled into the final-turned Copper liner. The milled channels have a width of 0,7 -1,2 mm depending on their position and a depth up to 15 mm. The residual wall thickness (hot gas wall) to the future thrust combustion chamber measures just 0,5 mm in the slimmest area. The permissible deviation is only 0,05 mm. On seven defined positions in the design drawing the wall thickness is measured via ultrasound. To get a precise result, each position is scanned with 10 scan lines in immersion technique, so that for each of the 468 channels 10 run time measurement values are determined. After-wards the average value is determined out of these single values via an Excel based special thrust chamber evaluation program and displayed as a protocol.

After filling the cooling channels with wax, a Copper/Nickel layer is applied in a galvanic process over a period of several weeks which closes the open channel side and forms the outer cover of the thrust chamber for stabilization. Now the linking area between Copper and Nickel are inspected via 100% ultrasonic inspection to detect adhesive flaws. To assure that there are no connections between the channels, existing flaws on the channel bridges are not permitted. Additionally various electron beam welding seams are inspected via ultrasound. The usually used material pairing is Nickel/Inco 718. The defect size to be determined is in accordance to the relative load [e.g. 0,5 mm FBH – (Flat Bottom Hole)].

The installed immersion technique inspection system is defined by its precise and practice-orientated scan mechanism as well as the high-performance scan- and process software. All inspection tasks could be fulfilled to the full satisfaction of the customer, ASTRIUM Aerospace Infrastructure in Ottobrunn/Germany by VOGT Ultrasonics as their partner in Germany.