Filiform Corrosion in Materials and Hardware - CASA Part 66
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Questions and Answers

What happens to the strength of the metal affected by exfoliation corrosion?

  • It becomes more flexible
  • It remains the same
  • It greatly decreases (correct)
  • It increases

    • What is the recommended remedy when exfoliation corrosion is evident on the metal surface?

  • Polishing the surface
  • Heating the metal
  • Complete removal of the affected sections (correct)
  • Applying a protective coating

    • Where do microbiological growths in aircraft fuel tanks primarily live and feed?

  • Inside the fuel lines
  • In the air
  • On the metal tank structure
  • In the water collected in the tanks (correct)

    • What type of organic bodies are microbes found in aircraft fuel tanks?

    <p>Fungi</p> Signup and view all the answers

    What do microbes in aircraft fuel tanks produce that promotes corrosion?

    <p>A scum</p> Signup and view all the answers

    What flight conditions contribute to water condensation in aircraft fuel tanks?

    <p>High-altitude, low-temperature</p> Signup and view all the answers

    What type of corrosion is described as an extreme case of intergranular corrosion?

    <p>Exfoliation corrosion</p> Signup and view all the answers

    In fretting corrosion, what destroys the protective film that develops on surfaces?

    <p>Continued rubbing action</p> Signup and view all the answers

    What visual indication can appear around rivets in skin if fretting corrosion is occurring?

    <p>Dark deposits around rivet heads</p> Signup and view all the answers

    Which type of materials are most susceptible to exfoliation corrosion?

    <p>Extruded materials</p> Signup and view all the answers

    Why must rivets showing signs of fretting corrosion be replaced as soon as possible?

    <p>To prevent further damage to the parts</p> Signup and view all the answers

    What characteristic makes exfoliation corrosion distinct from other types of corrosion?

    <p>Causes the material to separate or delaminate along grain boundaries</p> Signup and view all the answers

    What happens if prompt treatment is not provided when white, puffy areas are discovered on a structure?

    <p>The corrosion will penetrate through the structure</p> Signup and view all the answers

    In what type of environment does the natural oxide-carbonate film on magnesium alloys not provide sufficient corrosion protection?

    <p>Mild environment</p> Signup and view all the answers

    What is a consequence of titanium absorbing gases at high temperatures from the surrounding air?

    <p>It becomes very brittle</p> Signup and view all the answers

    What effect can chlorides and some chlorinated solvents have on certain titanium alloys?

    <p>Induces stress corrosion cracking</p> Signup and view all the answers

    What does the oxide film that forms on titanium surfaces provide?

    <p>Protective barrier against corrosion</p> Signup and view all the answers

    Why is electrical insulation necessary between titanium and other metals?

    <p>To prevent galvanic corrosion</p> Signup and view all the answers

    What is a common application of pure nickel?

    <p>Electroless coating</p> Signup and view all the answers

    How does the stress corrosion resistance of stainless steel alloys change with increasing nickel content?

    <p>Increases</p> Signup and view all the answers

    In what areas are nickel-based alloys commonly used?

    <p>High-temperature areas like engines</p> Signup and view all the answers

    What is a common application of copper and copper-based alloys in avionics systems?

    <p>Contacts, springs, leads</p> Signup and view all the answers

    What is a common sign of copper corrosion on a part?

    <p>Accumulation of blue-green corrosion products</p> Signup and view all the answers

    What can lead to flaking of the nickel coating?

    <p>Pitting corrosion of the nickel</p> Signup and view all the answers

    Why is tarnish removal critical on gold components?

    <p>To prevent corrosion on the less noble metals underneath</p> Signup and view all the answers

    What is the result of gold corrosion over silver or copper in thin layers?

    <p>Darkening of the silver or blue-green deposits on the copper</p> Signup and view all the answers

    What is 'Purple plague' in the context of gold-aluminium compounds?

    <p>A brittle gold-aluminium compound formed when bonding gold to aluminium</p> Signup and view all the answers

    Which metal offers the best combination of solderability and corrosion resistance?

    <p>Tin</p> Signup and view all the answers

    What tends to grow 'whiskers' on tin-plated wire and other plated applications?

    <p>Tin</p> Signup and view all the answers

    Why is corrosion accelerated over less noble metals when gold plated over them in thin layers?

    <p>Due to the formation of darkening deposits</p> Signup and view all the answers

    What determines whether a power header or a hand beading tool is used to accomplish beading of a tube?

    <p>The diameter and wall thickness of the tube</p> Signup and view all the answers

    What is the purpose of the inner liner in a flexible hose used in aircraft fluid systems?

    <p>To carry the fluid and offer least resistance to flow</p> Signup and view all the answers

    Why does the inner liner of a flexible hose need to be chemically compatible with the material being carried?

    <p>To ensure it does not corrode or degrade</p> Signup and view all the answers

    What is the main function of an outer cover in the construction of a flexible hose?

    <p>To protect from physical damage</p> Signup and view all the answers

    What is essential for the inner liner of a flexible hose in terms of porosity?

    <p>It must have minimal porosity</p> Signup and view all the answers

    Why is flexibility throughout an entire range of operating temperatures essential for the inner liner of a flexible hose?

    <p>To allow smooth flow of fluid</p> Signup and view all the answers

    What is the angle of the external flare in AN fittings?

    <p>37°</p> Signup and view all the answers

    What material are AN steel fittings colored as for identification purposes?

    <p>Black</p> Signup and view all the answers

    What type of tube is used with flareless fittings?

    <p>Straight-cut tube</p> Signup and view all the answers

    Which metal base alloys are flared-tube fittings made of?

    <p>Aluminium and steel</p> Signup and view all the answers

    What color are AN aluminium fittings for identification?

    <p>Blue</p> Signup and view all the answers

    How many parts does a flared-tube fitting consist of?

    <p>Three parts</p> Signup and view all the answers

    Which synthetic compound is best suited for carrying phosphate ester-base hydraulic fluids?

    <p>Butyl</p> Signup and view all the answers

    Which synthetic rubber is more suitable for carrying petroleum products than neoprene?

    <p>Buna-N</p> Signup and view all the answers

    Which synthetic compound breaks down if used with petroleum products?

    <p>Butyl</p> Signup and view all the answers

    Which synthetic compound has an extremely broad operating temperature range and offers minimum resistance to fluid flow?

    <p>Teflon</p> Signup and view all the answers

    Which synthetic rubber is used with petroleum-based fluids and is abrasion resistant?

    <p>Neoprene</p> Signup and view all the answers

    Which compound has a unique chemical structure that leads to less volumetric expansion than rubber?

    <p>Teflon</p> Signup and view all the answers

    What is the purpose of O-rings in some applications of banjo fittings?

    <p>To replace aluminium gaskets</p> Signup and view all the answers

    What feature allows the banjo to rotate before the bolt is torqued during installation?

    <p>Positive visual engagement</p> Signup and view all the answers

    In which fluid systems are quick-disconnect couplings commonly used?

    <p>Fuel, hydraulic, and water/waste servicing adaptors</p> Signup and view all the answers

    What is the primary function of the sliding collar in some quick-disconnect couplings?

    <p>Snap-lock attachment</p> Signup and view all the answers

    What type of lines are typically joined using rubber hoses and screw-type hose clamps?

    <p>Large-diameter lines carrying low-pressure fluids</p> Signup and view all the answers

    What is the advantage of having a built-in shutoff valve in quick-disconnect couplings?

    <p>No-spill connection</p> Signup and view all the answers

    What is the purpose of the outer cover in a hose?

    <p>To provide protection from physical damage</p> Signup and view all the answers

    What information can be found on the lay line of an aircraft flexible hose's outer cover?

    <p>The MIL-SPEC number, hose size, manufacturer's details, and manufacturing date</p> Signup and view all the answers

    Why are reinforcement layers essential in hoses?

    <p>To reduce the pressure-induced dimensional changes in the hose</p> Signup and view all the answers

    What is generally marked on the outer cover of an aircraft flexible hose?

    <p>A lay line with identification information</p> Signup and view all the answers

    How can one determine if a hose is twisted during installation?

    <p>By observing the lay line on the outer cover</p> Signup and view all the answers

    What materials are commonly used for reinforcement layers in hoses?

    <p>Cotton, rayon, polyester fabric, and steel wire braid</p> Signup and view all the answers

    Study Notes

    Corrosion and Metal Strength

    • Exfoliation corrosion reduces the strength of metals, leading to structural integrity issues.
    • Recommended remedies include removing the affected areas and applying protective coatings.

    Microbiological Growth in Aircraft Fuel Tanks

    • Microbial growths primarily thrive in water present in aircraft fuel tanks, feeding on hydrocarbons.
    • Microbes often consist of bacteria and fungi that derive energy from fuel components.
    • These microorganisms produce acids and other byproducts that accelerate corrosion.

    Conditions Leading to Corrosion

    • Water condensation due to temperature changes and humidity contributes to corrosion in aircraft fuel tanks.
    • Exfoliation corrosion is an extreme form of intergranular corrosion, affecting the metal's grain boundaries.

    Fretting Corrosion

    • In fretting corrosion, mechanical movements destroy protective films on metal surfaces.
    • Visual signs of fretting corrosion include white, powdery deposits around rivets.

    Material Susceptibility

    • Aluminum and its alloys are highly susceptible to exfoliation corrosion.
    • Rivets showing fretting corrosion must be replaced promptly to prevent further deterioration.

    Unique Characteristics of Corrosion

    • Distinct characteristics of exfoliation corrosion include the formation of layers that can flake off.
    • White, puffy areas, if unaddressed, can lead to severe material failure over time.

    Corrosion Protection in Magnesium Alloys

    • The natural oxide-carbonate film on magnesium alloys fails to protect in highly corrosive environments.

    Titanium Behavior

    • Titanium's absorption of gases at high temperatures can lead to embrittlement.
    • Chlorides and chlorinated solvents can negatively impact certain titanium alloys.

    Titanium Oxide Film

    • The oxide film on titanium surfaces serves as a protective barrier against corrosion.
    • Electrical insulation between titanium and other metals prevents galvanic corrosion.

    Nickel and Alloys

    • Pure nickel is commonly used in various applications, offering good corrosion resistance.
    • Increased nickel content in stainless steel alloys enhances resistance to stress corrosion cracking.

    Applications of Copper and Alloys

    • Copper and copper-based alloys are often used in avionics systems for electrical connections.
    • Signs of copper corrosion include greenish-blue staining or patina on components.

    Nickel Coating Issues

    • Flaking of nickel coatings can occur due to improper surface preparation or adhesion issues.
    • Removal of tarnish on gold components is crucial to maintain electrical conductivity and prevent corrosion.

    Gold-Aluminium Compounds

    • 'Purple plague' refers to the formation of a brittle layer between gold and aluminum alloys that can lead to failure.
    • Gold plating provides excellent solderability and corrosion resistance, but thin layers can exacerbate issues with whiskers.

    Flexible Hose Construction

    • The inner liner in flexible hoses ensures fluid compatibility and prevents leaks.
    • It is crucial for the inner liner to withstand various operating temperatures without compromising flexibility.

    Fitting Types and Identification

    • AN fittings have a 37-degree external flare angle.
    • Identification colors for AN fittings: steel fittings typically have a cadmium plating, while aluminum fittings are colored blue.

    Hose Reinforcement and Indicators

    • Reinforcement layers in hoses prevent bulging and rupture under pressure.
    • The lay line on a hose's outer cover contains essential information, including specifications and operating limits.

    Additional Hose Aspects

    • Quick-disconnect couplings are widely used in hydraulic systems for rapid maintenance and safety.
    • A built-in shutoff valve in quick-disconnect couplings prevents fluid leakage during disconnection.

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    Description

    Learn about fretting corrosion in materials and hardware from the training materials for CASA Part 66. Understand how surfaces erode when they fit tightly together but can move relative to each other, leading to the destruction of the protective film due to rubbing action.

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