(ii) Flush eyes immediately with water for at least 15 minutes. Lift upper and lower eyelids frequently to ensure complete washing.
(iii) If splashed on clothing or large areas of body, immediately remove contaminated clothing and wash body with plenty of soap and water. wash clothing before rewearing.
(ïv) If splashed onto an easily accessible part of the body, immediately wash with soap and water.
If suffering 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 artificial respiration at once.
Call ambulance and continue this treatment until ambulance arrives.
(2) If exposed to physical contact with any of the following materials:
Hydrofluoric acid Phenol Nitric acid Cresols Phosphoric acid Tricresyl phosphate Treat as follows:
If splashed into eyes, quickly wipe eyelids with a soft cleaning tissue and immediately flush eye with gentle stream from a drinking fountain, cup, or other convenient water outlet while holding lids open. Call an ambulance and continue the flushing procedure until an ambulance arrives.
(ii) If splashed onto an easily accessible part of body, immediately drench affected area with water until ambulance arrives.
(iii) If splashed onto clothing or large area of body, immediately drench body and remove clothing while drenching until ambulance arrives.
(iv) If taken internally, begin following treatment immediately:
(A) 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.
(B) If the person is unconscious, do not give any liquid. Start artificial respiration at once. Continue until ambulance arrives. If person regains consciousness before ambulance arrives, proceed as in subparagraph (A).
Chap 6 Par 600 113
601. GENERAL CORROSION CONTROL WORK PROCEDURES. The effectiveness of corrosion control depends on how well basic work procedures are followed. The following common work practices are recommended:
a. If rework procedures or materials are unknown, contact the aircraft manufacturer or authorized representative before proceeding;
o. Ihe work areas, equipment, and components should be clean and tree of chips, grit, dirt, and foreign materials.
c. Do not mark on any metal surface with a graphite pencil or any type of sharp, pointed instrument. Temporary markings (defined as markings soluble in water or methyl chloroform) should be used for metal layout work or marking on the aircraft to indicate corroded areas.
d. Graphite should not be used as a lubricant for any component.
Graphite is cathodic to all structural metals and will generate galvanic corrosion in the presence of moisture, especially if the graphite is applied in dry form.
Footwear and clothing should be inspected for metal chips, slivers, rivet cuttings, dirt, sand, etc., and all such material removed before walking or working on metal surfaces such as wings, stabilizers, fuel tanks, etc.
f. Do not abrade or scratch any surface unless it is an authorized procedure. If surfaces are accidentally scratched, the damage should be assessed and action taken to remove the scratch and treat the area.
g. Coated metal surfaces should not be polished for esthetic purposes.
Buffing would remove the protective coating and a brightly polished surface is normally not as corrosion resistant as a nonpolished surface unless it is protected by wax, paint, etc. A bare skin sheet polished to a mirror finish is more resistant than a bare mill finished sheet when both are given regular maintenance.
h. Protect surrounding areas when welding, grinding, drilling, etc., to prevent contaminating them with residue from these operations. In those areas where protective covering cannot be used, action should be taken to remove the residue by cleaning.
i. Severely corroded screws, bolts, and washers should be replaced.
When a protective coating, such as a cadmium plating on boits, screws, etc., is damaged, immediate action should be taken to apply an appropriate protective finish to prevent additional corrosion damage.
602.-609. RESERVED.
Chap 6 114 through 120 Par 601
1/25/91 AC 43-4A SECTION 2. CORROSION REMOVAL TECHNIQUES GENERAL. When active corrosion is visually apparent, a positive inspection and rework program is necessary to prevent any further deterioration of the structure. The following methods of assessing corrosion damage and procedures for rework of corroded areas could be used during cleanup programs.
in general, any rework would involve the cleaning and stripping of all finish from the corroded area, the removal of corrosion products, and restoration of surface protective film.
a. Repair of corrosion damage includes removal of all corrosion and corrosion products. When the corrosion damage exceeds the damage limits set by the aircraft manufacturer in the structural repair manual, the affected part must be replaced or an FAA-approved engineering authorization for continued service for that part must be obtained.
b. For corrosion damage on large structural parts which is in excess of that allowed in the structural repair manual and where replacement is not practical, contact the aircraft manufacturer for rework limits and procedures.
STANDARD METHODS. Several standard methods are available for corrosion removal. The methods normally used to remove corrosion are mechanical and chemical. Mechanical methods include hand sanding using abrasive mat, abrasive paper, or metal wool, and powered mechanical sanding, grinding, and buffing, using abrasive mat, grinding wheels, sanding discs, and abrasive rubber mats.
is outlined in the following paragraphs. However, the method used depends upon the metal and the degree of corrosion. The removal method to use on each metal for each particular degree of corrosion
612. PREPARATIONS FOR REWORK. All corrosion products should be removed completely when corroded structures are reworked as the corroding process will continue even though the affected surface is refinished. Before starting rework of corroded areas, carry out the following:
rinsing of all surfaces. Position airplane in wash rack or provide washing apparatus for rapid
b. Connect a static ground line to the airplane.
c. Prepare the aircraft for safe ground maintenance.
and external hydraulic and electric power. (1) Remove the aircraft battery(s), LOX container (if installed),
(2) Install all applicable safety pins, flags, and jury struts.
d. Protect the pitot-static ports, louvers, airscoops, engine opening, chemical brightening agents. wheels, tires, magnesium skin panels, and airplane interior from moisture and
e. Protect the surfaces adjacent to rework areas from chemical paint strippers, corrosion removal agents, and surface treatment materials.
Спар 6 Par 610 121
7/25/91 AC 43-4A
613. PAINT REMOVAL.
using a medium grade abrasive mat. For larger areas, chemical paint removal is a. For small areas of metallic surfaces, paint may be removed by hand, the preferred method.
b. Phenolic and non-phenolic chemical paint removers containing methylene chloride are recommended for paint striping on metallic surfaces only.
Chemical paint strippers containing acid should not be used as hydrogen embrittlement on high strength steel and some stainless steels will occur. The following procedure is recommended when using chemical paint remover:
(1) Mask acrylic windows and canopies, other plastic parts, rubber noses, exposed wiring, composite surfaces, wheels and tires, and any other areas where the paint remover residue cannot be removed and refinishing cannot be accomplished;
(2) Remove sealants when required, by cutting away excess sealant with a sharp plastic scraper;
(3) Apply a thick, continuous coating of paint remover to cover the surface to be stripped;
(4) Allow paint remover to remain on the surface for a sufficient length of time to wrinkle and completely lift the paint. Reapply paint remover as necessary in the areas where paint remains tight or where the material has dried. Micarta scrapers, abrasive pads, or fiber brushes may be used to assist in removing persistent paint;
(5) Remove loosened paint and residual paint remover by washing and scrubbing the surface with fresh water and a stiff nylon bristle brush or an abrasive pad; and
(6) After thorough rinsing, remove masking materials and thoroughly clean the area with a solution of aircraft cleaning compound to remove paint remover residues.
c. For composite surfaces, paint removal should be done by mechanical removal techniques (scuff sanding) only. Composite surfaces include fiberglass, kevlar, carbon, graphite, and others. Due to the irregularities in composite surfaces (fiber weave), complete removal of the paint system can not be accomplished without surface fiber damage.
ine abre we used to prevent venoval of the base be required for removing corrosion from steel fasteners, side skins, or Chap 6 Par 613 122
7/25/91 AC 43-4A specified method for corrosion removal should be observed. irregularly shaped parts or surfaces. Whenever such special cases occur, the corrosion rework should be faired or blended with the surrounding surface. Fairing can be accomplished as follows: 615. FAIRING OR BLENDING REWORKED AREAS. All depressions resulting from
a. Remove rough edges and all corrosion from the damaged area. All TABLE 6-1.) dish-outs should be elliptically shaped with the major axis running spanwise on wings and horizontal stabilizers, longitudinally on fuselages, and vertically on vertical stabilizers. (SELECT THE PROPER ABRASIVE FOR FAIRING OPERATIONS FROM TABLE 6-1. ABRASIVES FOR CORROSION REMOVAL PROCESSED METALS OR MATERIALS TO BE RESTRICTIONS OPERATION ALUMINUM OXIDE ABRASIVE PAPER OR CLOTH CARBIDE SILICON GARNET ABRASIVE FABRIC OR PAD ALUMINUM STEEL STAINLESS PUMICE 350 MESH OR ABRASIVE WHEEL FINER ALLOYS FERROUS TO STEEL HEAT DOES NOT APPLY REMOVAL OR CORROSION 150 GRIT 180 GRIT FINE TO TREATÉD TO FAIRING FINER FINER ULTRAFINE
STRENGTHS TO 220,000 PSI AND FINISHING 400 ABOVE EXCEPT ALUMINUM ALLOYS SILICON CARBIDE ABRASIVE DO NOT USE FAIRING REMOVAL OR CORROSION FINER 150 GRIT OR 7/0 GRIT OR FINER ULTRAFINE VERY FINE AND CLAD ALUMINUM FINISHING 400 CLAD ALUMINUM SCRATCHES SANDING LIMITED TO THE REMOVAL OF MINOR FAIRING REMOVAL OR CORROSION 240 GRIT OR FINER 7/0 GRIT OR FINER ULTRAFINE VERY FINE AND × FINISHING 400 × ALLOYS MAGNESIUM CORROSION REMOVAL OR 240 GRIT VERY FINE AND
FAIRING FINER ULTRAFINE FINISHING 400 TITANIUM CLEANING 150 GRIT 180 GRIT
AND OR OR
FINISHING FINER FINER Chap 6 Par 614 123
7/25/91 AC 43-4A closely spaced multiple pits, intervening material should be removed to minimize catio of 20:1, length to depth (see Figures 6-1 and 6-2). b. Rework depressions by forming smoothly blended dish-outs, using a In areas having surface irregularity or waviness (see Figures 6-3 and 6-4). Steel nutplates and steel fasteners should be removed before blending corrosion out of aluminum structure. Steel or copper particles embedded in aluminum can become a point of future corrosion (see Figure 6-5). All corrosion products must be removed during blending to prevent reoccurrence of corrosion (see Figures 6-6 and 6-7).
removal of corrosion products by any method should be blended out to prevent C. In critical and highly stressed areas, all pits remaining after stress risers which may cause stress-corrosion cracking. On noncritical removal.
PIT HAS BEEN CLEANED UP TO THE EXTENT THAT ALL LOOSE CORROSION PRODUCTS HAVE BEEN REMOVED.
CORROSION DAMAGE BEFORE REWORK
LONGITUDINAL ROUGH EDGES HAVE BEEN SMOOTHED AND ALL CORROSION HAS BEEN REMOVED. HOWEVER, DISH-OUT AFTER BLENDING
DEPRESSION HAS NOT BEEN SHAPED FIGURE 6-1. BLENDOUT OF CORROSION AS SINGLE DEPRESSION Chap 6 Par 615 124
LOCATION OF CORROSION PITS WIDTH OF CLEANED UP AREA (10 TIMES DEPTH MIN)
VIEW LOOKING DOWN
VIEW IN TRUE PERSPECTIVE
DEPTH OF CLEAN UP OF CORROSION
LENGTH OF CLEANED UP AREA (20 TIMES DEPTH MIN)
CROSS SECTIONAL VIEW
NOT ACCEPTABLE ACCEPTABLE FIGURE 6-2. TYPICAL EXAMPLE OF ACCEPTABLE CLEANUP OF CORROSION PITS
- TRANSVERSE - BEFORE REMOVAL CORROSION DAMAGE "MIN . 10D
- LONGITUDINAL •
BOTTOM OF DEPRESSION
AFTER CORROSION REMOVAL
DAMAGE REMOVED AND SURFACE SMOOTHED
WITH SHALLOW ELLIPTICAL DISH-OUT FIGURE 6-3. BLENDOUT OF MULTIPLE PITS IN CORRODED AREA Chap 6 Par 615 125
- STIFFENE
IDGE FAC
ADJACENT STRUCTURE
STIFFENER
EDGE FACE FIGURE 6-4. PROFILE OF REWORKED CORRODED AREAS IN REGIONS OF LIMITED ACCESS FIGURE 6-5. STEEL PARTICLES FROM FASTENERS OR NUTPLATES MAY CAUSE FUTURE
CORROSION PROBLEMS IN ALUMINUM STRUCTURE Chap 6 126 Par 615
FIGURE 6-6. INCOMPLETE REMOVAL OF CORROSION PRODUCTS RESULTED IN
REOCCURRENCE OF CORROSION FIGURE 6-7. INCOMPLETE REMOVAL OF CORROSION PRODUCTS RESULTED IN
REOCCURRENCE OF CORROSION Chap 6 Par 615 127
616. CHEMICAL TESTING.
A serious problem encountered in corrosion control is the identification of the metal on which corrosion occurs. The importance of this identification arises from the fact that all metals possess certain chemical characteristics that are common only to themselves and which vary greatly from metal to metal and from alloy to alloy of the same metal. Since these characteristics are common to all metals and their alloys, chemical cleaning solutions and chemical protective films will react differently with various In some cases, this produces adverse reactions which can severely weaken or destroy the structural capabilities of the metal.
(1) The primary method of determining material identification is in the aircraft structural repair manual. When the structural repair manual is limited or when more information is required, 1.e., neat-treat and protective finishes, the best source of material identification is the aircraft manufacturer, where an aircraft drawing can be reviewed.
(2) Chemical testing can be used when all other methods have been exhausted and when the following precautions are followed:
Personnel should become thoroughly familiar with the safety precautions and emergency safety procedures, prior to performing any chemical testing.
(її) Chemical spot testing should be accomplished by qualified personnel only.
(iii) Fasteners should not be identified by chemical spot tests.
(iv) High strength steel should not be identified by chemical spot tests.
Chemical testing for each type of metal should be accomplished on test samples before any tests are accomplished on the actual part. The preliminary surface preparation and primary classification of the metal may be determined by the following procedure.
(1) On the surface to be tested, choose an area where there is no corrosion and remove paint (if present) from a 1-inch square. Paint may be removed using hand sanding or an approved paint remover.
CAUTION: ADEQUATE PRECAUTIONS SHOULD BE TAKEN TO PREVENT PAINT REMOVER FROM CONTACTING COMPOSITE PARTS.
(2) Clean area of surface to be tested.
(3) Tentatively identify the exposed metal surface by visually comparing it with samples of previously identified materials, if available.
Chap 6 128 Par 616
7/25/91 AC 43-4A on the exposed surface. (4) Identify the metal as ferrous or nonferrous by placing a magnet Magnetic attraction classifies the base metal as a ferrous magnetic material (iron or steel).
magnesium, etc.) metal as either an austenitic stainless steel or a nonferrous metal (aluminum, The absence of magnetic attraction classifies the base
(5) Hardness test magnetic metals by a qualified person prior to chemical spot testing. If the metal is nonmagnetic, proceed with paragraph 618.
CHEMICAL SPOT ANALYSIS OF MAGNETIC METALS. The magnetic metals usually employed in aircraft construction are ferrous alloys (high strength steels and some stainless steels). These magnetic alloys, when plated, are generally plated with either chromium, nickel, zinc, cadmium, silver, or with a
a. If a magnetic alloy has been plated with cadmium, zinc, or chromium, attraction even if the substrate or base metal is not magnetic. it will exert magnetic attraction. Nickel plating will show slight magnetic identification should be made after accomplishing a hardness test. If positive identification of the metal plating is necessary, the CAUTION: DO NOT PERFORM A CHEMICAL SPOT TEST ON STEELS HEAT-TREATED TO 220,000 PSI AND ABOVE.
c. Place a drop of 10 percent hydrochloric acid (HCL) on the prepared metal surface. Ensure that the surface is dry before applying acid.
metal is zinc. (1) A rapid reaction producing a dark deposit indicates that the chromium, nickel, or steel. (2) A slow or no reaction indicates that the metal may be cadmium, CAUTION: THE ADDITION OF SODIUM SULFIDE (Na,S) TO ACID PRODUCES A POISONOUS GAS. ADEQUATE VENTILATION SHOULD BE PROVIDED WHEN THESE TESTS ARE BEING PERFORMED. DO NOT ALLOW LARGE QUANTITIES OF SODIUM SULFIDE (Na,S) AND ACID TO BE MIXED.
d. After 1 minute, add a drop of Na,S to the drop of HCL.
(1) A white precipitate identifies the metal as zinc.
metal as cadmium. (2) A yellow ring formed around a white precipitate identifies the Chap 6 Par 616 129
(3) A black ring formed around a white precipitate identifies the metal as iron or steel.
(4) A black precipitate indicates that the metal is chromium or nickel.
Confirm the cadmium, zinc, iron, or steel test by placing a drop of 20 percent nitric acid (HNO,) on a fresh spot. After 1 minute, add a drop of NaS to the drop of HNO.
(1) A white precipitate identifies the metal as zinc.
(2) A yellow precipitate identifies the metal as cadmium.
(3) A black spot identifies the metal as iron or steel.
f. Confirm the chromium test by placing a drop of 10 percent HCL on a fresh spot. Add a drop of concentrated sulfuric acid (H,S04) to the drop of HCL.
A color change to green after 1 or 2 minutes identifies the metal as chromium.
g. Confirm the nickel test by placing a drop of dimethylglyoxime solution on a fresh spot. Add a drop of ammonium hydroxide (NOH) to the drop of dimethyiglyoxime solution. A pink to red precipitate identities the metal as nickel.
h. Clean and refinish as detailed in paragraph 620.
618. nonmagnetic metals used in aircraft construction are aluminum, magnesium, and CHEMICAL SPOT ANALYSIS OF NONMAGNETIC METALS. The most common austenitic steels (generally used as 18-8 stainless steel). The positive identification of these nonmagnetic metals is accomplished by the following procedure:
a. Place a drop of 10 percent HCL on the prepared metal surface and allow to stand for 1 minute. Ensure that the surface is dry before applying acid. (Zinc deposits on nonmagnetic metals will react with 10 percent HCL but will not produce a black spot.)
(1) A rapid or violent reaction that produces a black spot indicates that the metal is magnesium.
(2) A slow reaction indicates that the metal is aluminum.
No reaction indicates that the metal is an austenitic steel or a nonmagnetic plating material.
b. If a reaction did not produce a black spot as noted in paragraph
618.a. (1), determine if zinc is present as detailed in paragraph 617.e.
Chap 6 130 Par 617