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Definitions F-G

Failure Analysis: The process of collecting and analyzing data to determine the cause of a failure and how to prevent it from recurring. It is an important discipline in many branches of the manufacturing industry where it is a vital tool used in the development of new products and for the improvement of existing products. Failure analysis is also used to determine liability where personal injury or property damage has occurred.

Fatigue Striations: Marks left on a fatigue fracture surface as a result of the advance or growth of the fatigue crack resulting from one load application. To visualize a single fatigue striation or even a series of fatigue striations requires extremely high magnifications. Individual striations are often visible at high magnifications in a scanning electron microscope (SEM). The yellow marker in the SEM pictured below traverses approximately 13 fatigue striations. Each striation is 9.8 micro inches (9.8 X 10-6 inches or 0.0000098 inches) in width.

SEM example of fatigue striations
  Fatigue striations seen through a SEM

Faying Surface: The contact surface between two, three or more joined objects.

Ferrite: Pure iron at room temperature is called ferrite. Ferrite is soft and ductile.

Ferrite Line: A region within an ERW weld where ferrite is formed along the weld centerline. The ferrite line is in fact a three dimensional plate of ferrite (pure iron) grains.

Filament: a conducting wire or thread with a high melting point, forming part of an electric bulb and heated or made incandescent by an electric current. 

Fillet: A corner with a radius to smooth the transition between adjacent pieces or components. As the fillet radius increases, the ability of the fillet to effectively transfer stress, without stress concentration, is increased.

Fillet Weld: A weld of approximately triangular cross-section as used in a lap joint, joining two surfaces at approximately right angles to each other.

Finite Element Analysis (FEA): A computerized method of analyzing the stress that results from a given load or multiple loads in the object of interest. The results of FEA are displayed in a multicolored pattern on the surface of a model of the object of interest.

Fish or Fishing: A metallurgical term of art referring to an object that has been unintentionally dropped and lost down the wellbore. Fishing is the process where specialized tools are used to retrieve the object or fish.

Fit-up: The initial positioning of pieces before welding or fastening.

Fit-up Gap: A space between pieces when they are being positioned for welding. The gap may remain after welding or it may be filled by the weld.

Flashback: The regression of a flame front from a torch tip back along the fuel hose which normally transports the gas from the high pressure gas cylinder to the torch.

Flashback Arrester: A device commonly used in oxygen/fuel brazing, welding or cutting which will stop burning gas from flashing back into equipment resulting in damage and/or an explosion.

Flaw: An undesirable alteration of the metal structure. Flaws can be internal, i.e., inside the metal objects or located on an external surface. Internal flaws are not visually observable. These flaws may be porosity (holes), inclusions (extra included non-metals/oxides), laminations (external surfaces rolled into the interior of the metal), etc. The most troublesome flaw is a crack. Cracks usually, but not always, initiate at a free external surface and grow or propagate into the metal structure. Cracks or discontinuities can be of insufficient size to create a problem or failure and as such are classified as flaws not defects.

Flexible Hose: Hose connecting the torch to the acetylene or oxygen tank. The acetylene hose is red. The oxygen hose is blue.

Flux: A non-metallic material, which melts during the welding process and protects the molten metal from oxidation while in liquid state.

Fourier Transformed Infrared Spectroscopy (FTIR): A type of laboratory equipment which allows the analysis of infrared radiation source from an unknown compound or compounds.

Fractography: The interpretation of visual evidence that is presented by the failed part and/or the failed parts fracture surface. Examples: brittle fracture, chevron marks, clamshell/beach marks, ductile fracture. (see Fracture Surface Analysis)

Brittle Fracture
Brittle Fracture

Chevron Marks
Chevron Marks


Ductile Fracture   

Ductile Fracture

Fracture Surface Analysis: When a metal or any other object fails or breaks, a surface is created by that fracturing process. In fact, usually two identical, mirror image fracture surfaces are created by a fracturing process. Analysis of the fractured surface of a component can be conducted at several levels. Visual examination can give clues or evidence of the fracture mechanism or process. Visual examination of the macroscopic fracture features can give a strong indication of the fracturing process. This is the science or art of fractography. Fractography can give a variety of clues or evidence about the fracture process. Fracture surface evaluation using the SEM is a common practice in metallurgical failure analysis. Some examples of unique fracture surface characteristics are referred to as dimple rupture, cleavage, intergranular fracture, and metal fatigue. These fracture surface characteristics or typographies are fingerprints which remain after the fracture has occurred. These fingerprints are unique witness marks to stress and/or environment and/or material condition at the time of the fracture.

Fracture surface evaluation using the SEM is a common practice in metallurgical failure analysis. Some of the common fracture modes are:

1) Cleavage

2) Dimple Rupture

3) Intergranular

4) Metal Fatigue

5) Progressive Stepwise Fracture

6) Quasi-Cleavage

7) Transgranular

Fracture Toughness Testing: A test where a notched specimen is loaded so that a defined pre-existing notch or crack is forced open. This test measures a material’s resistance to fracture.

Fretting Corrosion: Fretting is a mechanical damage process that occurs when the high points (asperities) on one surface are moved over and adhere to the asperities of another surface. Although a metal surface may look flat, and even if it has been polished, when magnified especially at very high levels of magnification, small peaks and valleys exist on the surface. When two pieces of metal slide or are rubbed over each other those peaks contact each other. The result is that metal from one surface is rolled up, broken off and sometimes is transferred to the other surface. Thus, fretting is categorized as a corrosion process. Fretting corrosion occurs when one surface of two metal objects moves over the other, usually without lubrication, then sticks or adheres to the other surface and results in metal transfer. Under some circumstances the small pieces of fretted metal merely become oxidized and appear as a powder or dust.

Friction: Mechanical resistance to the motion of one surface with respect to the other.

Galvalume: A metal alloy coating that is composed of aluminum, zinc and silicone.

Galvanization Thickness (t): Thickness expressed in inches, of the zinc (Zn) layer deposited on the I.D. and O.D. of the subject pipe.

Grain Size and Grain Boundary: Metals are made up of individual grains, much like a sandcastle is made up of individual sand grains. In metal, these grains all are very tightly bonded together, not like sand grains in a sandcastle. The edge of each metal grain, where it meets another grain, is referred to as a Grain Boundary. In order to have uniform metal properties, metals will usually possess or be made up of grains of equal or approximately equal size. Castings that are cooled uniformly produce a uniform grain size throughout the casting. Large variations in metal grain size are an indication of a lack of uniformity of mechanical properties within the metal.

Gusset: Triangular metal piece added to a corner to increase strength of the joint.

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Dallas, Texas 75287

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