Corrosion Damage Control Testing of Load-Bearing Aircraft Gliders

·Home
·Table of Contents
·Aeronautics and Aerospace

Corrosion Damage Control Testing of Load-Bearing Aircraft Gliders

V. Shaternikov, A. Maximov, P. Shkatov, Y. Mikolaitchook,
Moscow State Academy of Instruments Engineering and Computer Science (Moscow).
F. Shur,
Lufthansa (Hamburg).
Contact

Corrosion damage of load - bearing aircraft gliders elements is one of the dangerous factor that influences on glider strength as a whole and reduces aircraft's durability and safety. Non-destructive testing in aviation is very important at the initial stage of operation when there is no serious reduction of construction strength and there is an opportunity in order to carry out reconditioning of detected corrosion places. Nowadays corrosion damage control testing is a high priority task in Russia because a great number of aircraft is used more than 20 years in intensive operation and extreme environment (Africa, Asia regions, etc.).

Russian Federal Aviation Service worked out the plan of measures for solving complex problems dealing with corrosion damages of civil aircraft. According to the plan "Passport of aircraft (helicopter) corrosion condition" was designed in 1999 and introduced as a compulsory document. All information about:

aircraft individual service peculiarities,
registration of detected corrosion results in accordance with the testing rules of existing engineering specifications,
additional corrosion protection,
elimination of any corrosion damage,
repairing of construction should be put down in this document.

Now corrosion testing control of gliders elements is insufficiently introduced (adopted) due to the absence of testing means. The authors had investigated the opportunity to apply different methods of non-destructive corrosion damage and came to conclusion that complex testing method which merged eddy-current and ultrasonic ones was the most optimal. At the initial stage the testing and rejecting are made by low-frequency eddy-current defectoscope (such types as: "ZOND VD-96", "Corrotest" or "Alotest" can be used) with subsequent gauge ("Bulat-1" or "UT-93P"). The above mentioned technology was recommended for aircraft repairing and special methodical recommendation were worked out. Such factor that influence greatly on testing results as irregular gaps between stringer and skin; sealing and glue presence on the opposite side of skin, surface roughness and unparalleled surface on the phase boundary of non-corroded metal-product corrosion and many other items were took into account in the methodical recommendation. This devices are described to give positive results after applying for corrosion testing in practice. There are the wholesome effects of using eddy current flow detector "ZOND VD-96" (our Academy) and ultrasonic thickness gauge "Bulat 1" ("Constant", Saint-Petersburg). "ZOND VD-96" was successfully verified and recommended for the applying as corrosion indicator.

Under the floor fuselage part: stringer, skin, beams of luggage floor, elements of fixing of stringers to airframe (most concentration in area of toilet facilities);
Above the floor fuselage part: beams of passenger floor and skin near by toilet facilities and buffet (snack bar), the top panel of (centreplane)
(Hermetic) Tight wall: bilge, rays, section, threshold;
Lantern skeleton of navigator cabin;
Lantern of pilot cabin;
Parts of undercarriage (landing gear);
Pipeline (of hydraulic and fuel systems);
Varnished external surface parts of glide skin;
Installation recess of storage battery (accumulator).

The application of this universal eddy-current probe (transducer) based on the new principle gave an opportunity to conduct high-productive testing and at the same time to detect small corrosion damages in a form of pores as well as rough under surface damages and corrosion between vanish coat metal sheets of 5-6 mm depth and sealing with the thickness of 6-8 mm.

In this case all aspirates, roughness, curvature quantity of testing objects and the lift off (gapes) between metal sheets don't have effect on the testing results. The device is completed with special eddy-current probes and testing patterns which have simulation depth corrosion damage instrument. It enables to bring out the depth of corrosion damages up to 6-8% of metal layer thickness.

The more accurate measurement of the residual corrosion metal thickness was made in steps 0.01mm by the ultrasonic thickness gauge.

Corrosion damages which were detected in the process of aircraft using or repairing proved to be typical for all main models of aircraft.

Figure 1 shows the main types of corrosion and places of its origins for different Russian aircraft classes.

Fig 1: The basic zones of corrosion origin and extension.

According to the tasting results the special passport of corrosion damages is issued for every aircraft. The passport was designed by Russian Federal Air Service.