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9/27/01 AC 43.13-1B CHG 1 CHAPTER 6. CORROSION, INSPECTION & PROTECTION SECTION 1. GENERAL 6-1. GENERAL. The purpose of this chap ter is to provide information that will help maintenance personnel prevent, control, iden tify, and treat various types of corrosion. (Re fer to AC 43-4A, Corrosion Control For Air craft for a more in-depth study on the detection and treatment of corrosion.) a. Corrosion is a natural occurrence that attacks metal by chemical or electrochemical action and converts it back to a metallic com pound. b. Four conditions must exist before electrochemical corrosion can occur. (See fig ure 6-1.) They are: (1) A metal subject to corrosion (An ode); (2) A dissimilar conductive material (Cathode), which has less tendency to corrode; (3) Presence of a continuous, conduc tive liquid path (Electrolyte); and (4) Electrical contact between the anode and the cathode (usually in the form of metal to-metal contact such as rivets, bolts, and cor rosion). c. Elimination of any one of these condi tions will stop electrochemical corrosion. (See figure 6-2.) NOTE: Paint can mask the initial stages of corrosion. Since corrosion products occupy more volume than the original metal, painted surfaces should be inspected often for irregu- larities such as blisters, flakes, chips, and lumps. 6-2. FACTORS INFLUENCING COR- ROSION. a. Some factors which influence metal corrosion and the rate of corrosion are: (1) Type of metal; (2) Heat treatment and grain direction; (3) Presence of a dissimilar, less corro dible metal; (4) Anodic and cathodic surface areas (in galvanic corrosion); (5) Temperature; (6) Presence of electrolytes (hard water, salt water, battery fluids, etc.); (7) Availability of oxygen; (8) Presence of biological organisms; (9) Mechanical stress on the corroding metal; and, (10) Time of exposure to a corrosive environment. (11) Lead/graphite pencil marks on air craft surface metals. b. Most pure metals are not suitable for aircraft construction and are used only in com bination with other metals to form alloys. Most alloys are made up entirely of small crystalline regions, called grains. Corrosion can occur on surfaces of those regions which Par 6-1 Page 6-1PDF Image | AFS-640
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