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If scratches are down to the sheet metal or if the paint is crazed, swollen or flaked, the surface affected must necessarily be stripped. For this purpose, use a paint remover.
After stripping followed by abundant flushing, it is urgent to procede to the surface repainting or to the application of protective treatment to avoid continued corrosive activity by the paint remover.
Increased protection of painted, varnished or lacquered surfaces can be obtained by applying a glossing and protecting product as mentioned above to deposit a fine, shiny insulating film and ease subsequent wiping.
NOTE : If the sheet metal underneath is already affected by corrosion, the paint removal should be completed by appropriate metal treatment before painting.
Surfaces exposed to acid electrolytes or their vapors
After cleaning and neutralization, the surfaces exposed to an acid attack must be treated with a protection product (TB 05-918) or a lacquer (TB 05-931) against acids.
Dissimilar metals in close contact
Whenever an electrolytic couple could start between dissimilar metals, a sufficient number of primer coats (zinc chromate or fay sealants) should be applied.
Metal surfaces covered with water-repellent product
Leather, neoprene and miscellaneous fabric coverings as well as soundproofing materials absorb moisture and create corrosion spots. The protection of the mating surfaces may be ensured by applying one or several coats of zinc chromate primer.
WA
Validity : S / N 1 - 9999
20-00-04 Page 202
20
(BA) JUN 02
2. CORROSION DETECTION
A. Visual inspection
Visual inspection remains, in most cases, a simple and often efficient method for corrosion detection.
It presupposes that the maintenance personnel has the right spirit, search willpower and is also capable of
identifying corrosion evidence. Chapter 20-00-04, page 1 outlines the various types of corrosion that can be seen.
B. Borescope inspection As a specific form of visual inspection, this method can be used to inspect hardly accessible or fully
inaccessible areas with a borescope. The borescope consists of a rigid, semi—rigid or flexible tube with optical and illumination equipment for straight sight, or at an appropriate angle.
1 C. Penetrant inspection
This method consists, after obtaining a good surface condition by etching and cleaning, in spreading penetrant product on a part. The excess penetrant is removed with a solvent before applying a developer. The penetrant /developer combination permits visualizing any cracks or defects.
This method has two variants which only differ in the facilities and products used :
— dye—penetrant visible under daylight,
II - fluorescent penetrant visible under UV light.
Disadvantages :
— personnel safety instructions for hygienic considerations (masks, gloves, etc),
— complete stripping of the part to be inspected is necessary,
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TB20 MAINTENANCE MANUAL 20 STANDARD PRACTICES AIRFRAME TB20飞机维护手册 20 标准施工机体(33)
