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
F igure 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
F igure 5-13. Corrosion Behind a Structural Component on a Wing Spar
Figure 5-14. Severely Corroded Lap Joint WBL 53. 24 outba SEr. 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. Alodine 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 Liquid 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 Magnetic 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-la yered 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 Ultrasonic 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 Acoustic 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 alodine 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 an alodine 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;
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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 Emergency 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 Methyl ethyl ketone Methyl isobutyl ketone Toluene Trichloroethylene Epoxy resin Methylene chloride Brush alodine Xylene Petroleum naphtha Chromates Dichromate Acetates Cyclohexanone Cellosolve Carbon tetrachloride 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.
• If splashed onto an easily accessible part of the body, immediately wash with soap and water.
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• If suffering a headache or other obvious symptoms resulting from overexposure, move to fresh air immediately.
• If vapors are inhaled and breathing has slowed down or stopped, remove person from exposure and start cardiopulmonary resuscitation (CPR)/automated external defibrillator (AED) procedures at once. Call local emergency services and continue this treatment until emergency services arrives.
6.1.2.2 If exposed to physical contact with any of the following materials:
Hydrofluoric acid Nitric acid Phosphoric acid Phenol Cresols Tricresyl phosphate Treat as follows:
• If splashed into eyes, quickly wipe eyelids with a soft cleaning tissue and immediately flush eyes with a gentle stream from a drinking fountain, cup, or other convenient water outlet while holding lids open. Call local emergency services and continue this treatment until emergency services arrives.
• If splashed onto an easily accessible part of the body, immediately drench affected area with water until ambulance arrives.
• If splashed onto clothing or large area of the body, immediately drench body and remove clothing while drenching until ambulance arrives.
• If taken internally, begin the following treatment immediately:
• If the person is conscious, cause vomiting by placing finger in back of the person’s throat. Encourage the person to drink large quantities of water and repeatedly wash out the mouth.
• If the person is unconscious, do not give any liquid. Start CPR/AED procedures at once. Continue until an emergency service arrives. Use the procedure above if the person regains consciousness before emergency services arrives, use the procedure above for a conscious person.
6.2 General Corrosion Control Work Procedures. The effectiveness of corrosion control depends on following basic work procedures. We recommend the following common work practices:
6.2.1 If rework procedures or materials are unknown, contact the aircraft manufacturer or authorized representative before proceeding.