fatigue—the process of progressive localized permanent structural change occurring in a material subjected to fluctuating stresses less than the ultimate tensile strength of the material that may culminate in cracks or complete fracture after a sufficient number of fluctuations.
fatigue strength—the maximum stress that can be sustained for a specified number of cycles without fracture.
fault current—a current that flows from one conductor to ground or to another conductor as a result of an abnormal connection (including an arc) between the two. A fault current flowing to ground may be called a ground fault current.
feather edging—see feathering.
feathering—reducing the thickness of the edges of an undamaged coating film, such as adjacent to a damaged coating or rusted area, by abrasion or sanding to produce a smoothly tapered transitional area prior to re-coating.
ferrite—the body-centered cubic crystalline phase of iron or iron-based alloys.
ferritic stainless steel—stainless steel whose micro structure at room temperature consists predominantly of ferrite.
ferritic steel—a steel whose micro structure at room temperature consists predominantly offer rite.
fiberglass-reinforced plastic—a resin-rich coating or lining into which layers of fiberglass reinforcement have been incorporated to produce mechanical and physical properties superior to the base resin itself.
filiform corrosion—corrosion that occurs under some coatings in the form of randomly distributed thread like filaments.
film—a thin, not necessarily visible layer of material.
finish coat—see topcoat.
fisheye—a small dimple or crater with a visible defect or contaminant in the central area resembling a fish eye that forms in a wet-applied coating. [see crater]
forced drainage—drainage applied to underground or submerged metallic structures by means of an applied electromotive force or sacrificial anode.
foreign structure—any metallic structure that is not intended as a part of a system under cathodic protection.
fouling—an accumulation of deposits. (This includes accumulation and growth of marine organisms on a submerged surface and the accumulation of deposits on heat exchanger tubing.)
fractography—descriptive treatment of fracture, especially in metals, with specific reference to photographs of the fracture surface.
fracture mechanics—a quantitative analysis for evaluating structural reliability in terms of applied stress, crack length, and specimen geometry.
free corrosion potential—see corrosion potential.
free machining—the machining characteristics of an alloy to which an ingredient has been introduced to give small broken chips, lower power consumption, better surface finish, and longer tool life.
fretting corrosion—deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory slip between the two surfaces.
furan—type of resin formed by the polymerization or polycondensation of furfuryl, furfuryl alcohol,or other compounds containing a furan ring.