structure test 3, sem 2

is the deterioration of metal by chemical or electrochemical attack. It can take place internally and/or on the surface. Deterioration may change the surface, weaken the interior and damage, or loosen adjacent parts. •chemical deterioration •electro chemical deterioration

ELECTROCHEMICAL ATTACK

YES •water or water vapor containing salt combines with oxygen in the atmosphere to produce the main source of corrosion in the aircraft.

is an attack resulting from a direct exposure of a bare surface to caustic liquid or gaseous agents. (battery acid, residual flux deposits, entrapped caustic cleaning solutions)

4 CONDITIONS MUST EXIST BEFORE THIS CORROSION CAN OCCUR: 1. The presence of a metal that will corrode (ANODE) 2. The presence of dissimilar conductive material (CATHODE) which has less tendency to corrode 3. Presence of a conductive liquid (ELECTROLYTE) 4. ELECTRICAL CONTACT between the anode and cathode

• ANY MOISTURE - water (salt) • ACID (sulphuric, uric) • ALKALINE (cleaners)

anode

The greater the distance apart on chart, the FASTER the anode will corrode.

1. SIZE OF ANODE AND CATHODE • small cathode, large anode (slow corrosion) •large cathode, small anode (fast corrosion) 2. TEMPERATURE •More corrosion in tropical areas 3. TIME •Exposed to corrosive environment 4. TYPE OF ELECTROLYTE • any moisture-water (salt) • acid (sulphuric, uric) • alkaline (cleaners)

MOST COMMON FORM of corrosion. Characterized by corrosive attack (direct chemical attack) proceeding evenly over the entire surface area. •caused by the reaction of metallic surface with atmospheric contaminants and exposure to oxygen.

localized form of corrosion by which cavities or “holes” are produced in the material. This is most common on aluminum and magnesium. It penetrates deep into the surface and is likely the result of uniform surface corrosion. It usually appears as clumps of white powder or gray dots on surface.

also known as DISSIMILAR METAL CORROSION. This refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte.

A form of oxygen concentration cell corrosion. Often caused by wash primer not curing properly. Wash primer requires air to cure appears as a thread or wormlike lines. Sometimes looks like a puffiness under the skin. - Is first noticeable around rivet heads and along lap joints. There is no cure for this type of corrosion, short of a completely stripping and redoing the aircraft

A form of oxygen concentration cell corrosion. Often caused by wash primer not curing properly. Wash primer requires air to cure appears as a thread or wormlike lines. Sometimes looks like a puffiness under the skin. • Is first noticeable around rivet heads and along lap joints. There is no cure for this type of corrosion, short of a completely stripping and redoing the aircraft

extreme form of intergranular corrosion which occurs mainly in extruded parts (angles, channels) and along grain boundaries. Metals tend to separate or delaminate.

Occurs from the combined influence of tensile stress and a corrosive Environment (Intergranular cracking) •Commonly found between rivets and stressed skins, pressed in bushings, tapered fittings.

•causes smoking rivets • Combination of corrosion and wear. • Oxidation is the most common element. • Relative movement between 2 surfaces. • Metal oxides become trapped between 2 surfaces.

Found at the bottom of fuel tanks (dark sludge\slime). Caused by microbial growth and reproduction in aviation fuel

SURFACE CORROSION – RUST

PITTING CORROSION

DISSIMILAR METAL CORROSION

filoform corrosion

INTERGRANULAR CORROSION

EXFOLIATION CORROSION – METALS SEPARATE OR DELAMINATE

FRETTING CORROSION – “SMOKING RIVETS”

(aka STRESS CORROSION) - caused by pressurization and depressurization of the structure or cyclic stress. This occurs between lap seams and fasteners.

PREVENTIVE MAINTENANCE • Frequent cleaning • Detailed inspection for corrosion • Quick treatment of corrosion and touchup of damaged paint areas • Keeping drain holes free of obstruction • Daily wipe down of exposed critical areas • Make maximum use of protective covers • Store in well-ventilated areas

• BATTERY COMPARTMENTS - Fumes • LAVATORIES, BUFFETS, AND GALLEY Spills • EXHAUST TRAILS - Exhaust deposits are corrosive • BILGE AREA - Lowest part fuselage • WHEEL WELLS - Exposed to environment • HINGE AREAS - Moving parts/Fretting corrosion • LEADING EDGES - Exposed to environment • EXTERNAL SKINS – Exposed to environment • FLEXIBLE HOSE ASSEMBLIES – Moving parts

COLLAR

•BLIND RIVETS “are used when there is access to only one end of the rivet” • POP RIVETS • CHERRY MAX • RIVNUT

called a PRESSED FIT or FRICTION FIT • fastener has a larger diameter than the hole so force is needed for installation

o HI LOKS o HI SHEAR RIVETS o TAPER

1 and 3

ALLEN KEY

•DIAMETER = 32nds •LENGTH = 16ths

COWLING and FAIRINGS Camloks consist of three parts: • studassembly • grommet • receptacle