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SAE ARP4118 1994 Edition, June 1, 1994
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Isolation and Corrosion Protection of Dissimilar Materials
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AIA/NAS Aerospace Standards
This SAE Aerospace Recommended Practice (ARP) provides methods and guidelines for isolating dissimilar repair patch materials from carbon composite structure during a repair operation.

These procedures are applicable to any repair procedure for carbon composite parts in which the repair patch is a metallic alloy that can form a galvanic cell with carbon in the presence of moisture or other electrolytes. The principal patch materials addressed are aluminum, titanium, and stainless steel.

The procedures are primarily concerned with bolted repairs that introduce the most severe, potential corrosion problem but bonded repairs are also considered.

The procedures are also applicable to repairs that involve reinstallation of metallic inserts into a carbon composite part.

Fiberglass and aramid composites do not have galvanic reactions with other materials, and the procedures outlined herein are, therefore, not essential with these materials. The sealing procedures covered herein are still recommended, however, as a means of preventing moisture entry. Boron filaments can produce a galvanic reaction by contact between the tungsten core of the fiber and adjacent metal, particularly in a bolted repair where the metal fasteners can contact cut fibers. Thus, the procedures outlined herein are advisable for bolted repairs of boron composites.

Generic materials and parts are described herein with no specific vendor identifications. All materials used in the procedures outlined herein shall be accompanied by a Material Safety Data Sheet (MSDS) and shall be handled in accordance with MSDS instructions.

Safety-Hazardous Materials:

While the materials, methods, applications, and processes described or referenced in this specification may involve the use of hazardous materials, this specification does not address the hazards which may be involved in such use. It is the sole responsibility of the user to ensure familiarity with the sage and proper use of any hazardous materials and to take necessary precautionary measures to ensure the health and safety of all personnel involved.