Nickel and Chromium Alloys Nickel and chromium alloys are also used as protective agents in the form of electroplated coatings. Also, they are used as alloying constituents with iron in stainless steels, such as the wear surfaces of aircraft struts. Nickel and chromium plates protect by forming a physical, noncorrosive barrier over the steel. Electroplated coatings, particularly chromium on steel, are slightly porous, and corrosion eventually starts at these pores or pin holes unless a supplementary coating is applied and maintained. Titanium Titanium is often used in engine exhaust areas. Titanium is a highly corrosion-resistant metal. However, it can greatly accelerate corrosion of dissimilar metal coupled to it. Insulation between titanium and other metals is necessary to prevent dissimilar metal attack on the other metal. Maintenance personnel must frequently inspect such areas to make sure that insulation failure has not allowed corrosion to begin. Q59. Q60. Q61. Q62. Q63. Q64. Q65. Q66. Q67. Q68. What publication should you refer to for information about structural corrosion? Hydrated ferric oxide is commonly known as what kind of corrosion? What are the three types of aluminum surfaces insofar as corrosion removal is concerned? How should you remove corrosion from clad aluminum surfaces? What is the primary type of aluminum used on naval aircraft? What are the approved tools for cleaning anodized aluminum surfaces? Who should evaluate any loss of structural strength in critical areas of an aircraft? What manual should you refer to for tolerance limits for dimensions of critical structural members? Copper and copper-based alloys are used in avionic systems for what purpose? Where is titanium most often used on a aircraft? CORROSION REMOVAL AND TREATMENT LEARNING OBJECTIVE: Describe the methods of removing and treating corrosion. Once corrosion is detected, a specific and immediate program for corrective treatment is required. A complete treatment involves paint removal and cleaning of all corroded areas, removal of corrosion products,   restoration of protective, surface-treatment films, and immediate application of protective coating and paint finishes. Each type of corrosion has its own peculiarities and requires special treatment. Corrosion should always be removed by the mildest means available. CORROSION REMOVAL Before starting any corrosion removal, you must conduct an inspection and evaluation of the suspected area. When you inspect an aircraft or a particular area of an aircraft for corrosion, you should follow the steps listed below. 1. Clean the area thoroughly. 2. If an area is suspected of having corrosion, visually inspect the area by using a magnifying glass. 3. To preclude metal damage, remove paint chemically from areas suspected of having underlying hidden corrosion. Use abrasive paint removal techniques only when corrosive products are observed. 4.   After removing the paint, use a magnifying glass to determine the extent of the damage, especially if there is evidence of corrosion on critical parts. Corrosion cracks must be detected as early as possible. 5. Refer to the applicable structural repair manual (SRM) or MIM for damage limits. Metal loss damage is accumulative. When assessing corrosion damage, consider prior metal loss, including areas on the opposite side of the part. Propellers and helicopter blades have critical balance requirements. Refer to the propeller and blade manuals that apply for the evaluation and repair limits of corrosion, erosion, and abrasive damage. After the aircraft or aircraft part has been inspected, the extent of the corrosion damage must be correctly evaluated. The severity of corrosion damage is grouped into the following categories: Light corrosion. This type of damage is defined as a protective coating that is scarred or etched by light 4-39