Figure 5-2. Corrosion Under Chipped and Loose Paint on Wing Skin Figure 5-3. Corrosion Indicated by Blistering of Paint in Fuel Cell 5-4
Figure 5-4. Popped Rivet Heads Resulting from Corrosion Products Figure 5-5. Skin Bulging Around Fasteners Caused by Pressure from Corrosion Products 5-5
Figure 5-6. Corrosion Cracking Between Fasteners on a Wing Spar Figure 5-7. Faying Surface Corrosion on Wing Spar Chord with Corrosion Cracking Also Visible 5-6
Figure 5-8. Severe Crown Stringer Corrosion 1060 Figure 5-9. Spar Chord Corrosion 5-7
5-8 Figure 5-10. Removal of Fillet Seal from Internal Edge of Lap Joint Exposed Full Extent of Corrosion Fi gure 5-11. Removal of Insulation Blankets Exposed Corrosion
5-9 Figure 5-12. Corrosion Developed Under Leveling Compound Installed During Previous Repair of Overwing Exit Fi gure 5-13. Corrosion Behind a Structural Component on a Wing Spar
Figure 5-14. Severely Corroded Lap Joint WiL 59. 24 outba 36r. 12-18 Figure 5-15. Severely Corroded Lap Joint 5-10
Figure 5-16. Local Paint Removal Required to Expose Full Extent of Corrosion Figure 5-17. Corroded Area After Paint Removal from Wing Skin 5-11
5-12 Figure 5-18. Bonderite 1200 Treatment Prior to Painting May Highlight Presence of Remaining Corrosion or Cracks
5.4.1.2 O ther Methods. There are several NDI methods which may be valuable in detecting corrosion, such as liquid penetrant, magnetic particle, eddy current, x ray, ultrasonic, and acoustical emission. These methods have limitations, and only qualified and certified NDI personnel should perform them. Eddy current, x ray, and ultrasonic inspections require properly calibrated per-use equipment and a reference standard to obtain reliable results.
5.4.1.2.1 Li quid Dye Penetrant. Inspect large stress-corrosion or corrosion fatigue cracks on nonporous ferrous or nonferrous metals using this process. The dye will enter cracks, fissures, or other small openings by capillary action when applied to a clean metallic surface. After absorption by any surface discontinuities, remove excess dye and apply a developer substance to the surface. A developer acts like a blotter and draws the dye from the cracks or fissures back to the surface of the part, giving visible indication of faults on the surface. The magnitude of the fault is indicated by the quantity and rate of dye on the surface after developer application.
5.4.1.2.2 Magnet ic Particle Inspection. Use this inspection method to detect cracks or flaws on or near the surface of ferromagnetic metals, or metals attracted by magnetism. A portion of the metal is magnetized and coated with finely divided magnetic particles, either in liquid suspension or dry. Surface faults will create discontinuities in the magnetic field and cause the particles to congregate on or above these imperfections, pinpointing their location.
5.4.1.2.3 Eddy Current Inspection. This method detects thinning due to corrosion and cracks in multi-layered structures. Low-frequency eddy current testing can, to
5-13 some degree, detect or estimate corrosion on the hidden side of aircraft skins because it can measure an uncorroded material’s thickness when used with a reference standard. Low-frequency eddy current testing can estimate corrosion in the underlying structure because the currents will penetrate through into the second layer of material with sufficient sensitivity for approximate results.
High-frequency eddy current testing is most appropriate for detection of cracks which penetrate the surface of the structure on which test personnel place an eddy current probe, including flat surfaces and holes.
5.4.1.2.4 X Ray Inspection. Because it is difficult to obtain the sensitivity required to detect minor or moderate corrosion, x ray inspection has somewhat limited use for detecting corrosion. Briefly, this method passes high-energy x rays through a material; a special film on the opposite side of the material registers the passage of the x rays. Areas of high density display as underexposed areas, while areas of 1ow density show up as overexposed areas. Moderate to severe corrosion or cracks using x ray inspection can be detected. However, this method, like other NDI methods, requires a qualified and certified operator to obtain reliable results.
5.4.1.2.5 U ltrasonic Inspection. Ultrasonic testing provides a sensitive detection capability for corrosion damage when access is available to a surface with a continuous bulk of material exposed to the corrosion. Personnel commonly use ultrasonic inspection to detect exfoliation, stress-corrosion cracks, and general material thinning. However, ultrasonic digital thickness gauges are not reliable for determining moderate or severe damage prior to removing corrosion. Trained personnel should conduct the examination to derive useful information from indicating devices.
5.4.1.2.6 A coustic Emission Testing. This method uses heat-generated emissions to detect corrosion and moisture in adhesive-bonded metal honeycomb structures. Acoustic emission testing can detect corrosion initiation as well as advanced corrosion.
5.5–5.99. RESERVED.
6-1 CHAPTER 6. CORROSION REMOVAL TECHNIQUES SECTION 1. SAFETY PROCEDURES
6.1 General. The following general safety precautions contain guidelines for handling materials with hazardous physical properties and emergency procedures for immediate treatment of personnel who have inadvertently come into contact with a harmful material.
Materials with hazardous physical properties are referenced to pertinent safety precautions and emergency safety procedures. All personnel responsible for using or handling hazardous materials should be thoroughly familiar with the information in the following paragraphs.
6.1.1 Safety Precautions. When required to use or handle solvents, special cleaners, paint strippers, strong alkalis or acids, etchants, corrosion removers containing acids, or surface activation material, such as Bonderite 1200, observe the following safety precautions:
1. Avoid prolonged breathing of solvent or acid vapors. Solvents and acids should not be used in confined spaces without adequate ventilation or approved respiratory protection;
2. Never add water to acid. Always add acid to water;
3. Mix all chemicals per manufacturer instructions;
4. Clean water for emergency use should be available in the immediate work area before starting work;
5. Avoid prolonged or repeated contact of solvents, cleaners, etchants, acid, or conversion coating material, such as a Bonderite solution, with skin. Wear rubber or plastic gloves when using solvents, cleaners, paint strippers, etchants, or conversion coating materials. Wear goggles or plastic face shields and suitable protective clothing when cleaning, stripping, etching, or conversion coating overhead surfaces;
6. When mixing alkalis with water or other substances, use containers made to withstand chemical heat generated by this process;
7. Wash any paint stripper, etchant, or conversion coating material immediately from body, skin, or clothing;
8. Promptly flush out materials splashed in eyes with water, and get medical aid for injured persons;
9. Do not eat or keep food in areas where the food may absorb poisons. Always wash hands before eating or smoking;
10. Verify that areas are clear and remain clear of all potential ignition sources within 50 feet of any cleaning or treating operations where materials with a flash point of 140 °F or below are in use;
11. Suitable fire extinguishing equipment should be available to the cleaning/treating area;
6-2
12. Where any flammable materials are in use, equipment should be effectively grounded;
13. If materials such as acid, alkali, paint remover, or conversion coatings are spilled on equipment or tools, treat immediately by rinsing with clean water if possible, or neutralizing acids with baking soda and alkalis with a 5 percent solution of acetic acid in water;
14. Do not use solvents with a flash point below 100 °F, such as methyl ethyl ketone (MEK) and acetone, in confined locations;
15. Clean all equipment after work is complete;
16. Implement all company safety precautions;
17. Check local environmental regulations for restrictions on the use of solvents, primers, and topcoats; and
18. Dispose of waste material per local environmental requirements.
6.1.2 E mergency Safety Procedures .
Note: Personnel should be thoroughly familiar with the following emergency safety procedures before using any materials referenced to an emergency safety procedure paragraph.
6.1.2.1 If exposed to physical contact with any of the following materials:
Methyl alcohol Xylene Methyl ethyl ketone Petroleum naphtha Methyl isobutyl ketone Chromates Toluene Dichromate Trichloroethylene Acetates Epoxy resin Cyclohexanone Methylene chloride Cellosolve Brush Bonderite Carbon tetrachloride
6.1.2.2 Treat as follows:
• If splashed into eyes, do not rub.
• Flush eyes immediately with water for at least 15 minutes. Lift upper and lower eyelids frequently to ensure complete washing.
• If splashed on clothing or large areas of the body, immediately remove contaminated clothing and wash body with plenty of soap and water. Also wash clothing before wearing again.