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1. • CommentAuthorDr. Zee
   • CommentTimeFeb 4th 2007

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   General Failure Analysis Protocol consists of the following:
   
   I. Determine when, where and how the failure occurred. It is important to visit the failure site in the field if possible. All persons involved in the failure should be interviewed personally. Determine what the conditions were at the time of failure. Were there prior indications suggesting failure was about to occur? Was the failure gradual or catastrophic? These and all other appropriate questions should provide a basis for the investigation.
   
   II. Collect samples for laboratory examination. Samples selected should be characteristic of the material and contain a representation of the failure or possible corrosive attack. For comparative purposes, both failed and sound, normal areas should be examined.
   
   Sampling handling is a paramount issue on which the whole remaining analysis depends. Fracture surfaces must be protected from damage during shipment by rigorously careful packaging. Surface chemistry must not be contaminated by careless handling.
   
   Materials specifications and service history reveal much about the nature of failure. If submitting a sample for analysis some background information will need to be provided.
   
   III. Take on-site photographs. Photographs should be taken of the failed piece of equipment in place, if possible. The dimensions of the sample, the date the failure occurred, and the date of the photographs should be noted.
   
   IV. Visually examine the sample. Examine the sample with unaided eye, hand lens and low magnification light microscopes. Note the condition of the accessible surface documenting all sorts of anomalies, searching for cracks, corrosion damage, the presence of foreign material, erosion or wear damage, or evidence of impact or other distress. Also consider the condition of protective coatings. Manufacturing defects are likely to be extremely important.
   
   V. Identify defects Non-Destructively. Search for material imperfections with radiography, magnetic particle, ultrasonic, liquid/dye penetrant, eddy current, leak, and/or acoustic emissions non-destructive testing procedures.
   
   VI. Conduct appropriate chemical analyses. Chemical analysis should be conducted on the original material to determine if the material was of proper type and grade, whether it met appropriate standards, and whether deviation from the specifications contributed to the fracture, wear, breaks, corrosion and failure.
   
   VII. Confirm material composition and identify contaminants through EDS analysis. EDS (Energy-Dispersive Spectroscopy) is an analytical method based on the differences in energy of the characteristic x-rays emitted by the various elements. It is used in conjunction with scanning electron microscopy (SEM) to identify the elements present at a particular spot on a sample. Advantages of EDS are that it is easily performed and is reliable as a qualitative method. Limitations are that it is only marginally useful as a quantitative method.
   
   VIII. Analyze via Fractography., Fractography is used to determine the mode of fracture (intergranular, cleavage, or shear), the origin of fracture, and location and nature of flaws that may have initiated failure. With this information, the answer as to why a part failed can usually be determined. The chief use of fractography is to reveal the relationship between physical and mechanical processes involved in the fracture mechanism. The size of fracture characteristics range from gross features, easily seen with the unaided eye, down to minute features just a few micrometers across.
   
   IX. Analyze via Metallography. Prepare a laboratory specimen with care not to remove inclusions, erode grain boundaries or compromise the sample in some other way. Study structural characteristics in relation to its physical and mechanical properties at low and high magnification. Take careful note of grain size, shape, and distribution of secondary phases and nonmetallic inclusions. Segregation and other heterogeneous conditions also influence the mechanical properties and behavior characteristics of metal.
   
   Metallography for the analyst may be concerned with pit depth, intergranular corrosion, hydrogen attack and embrittlement, caustic embrittlement, stress corrosion cracking (intergranular or transgranular), and corrosion, mechanical or thermal fatigue. Also, within limits, an almost complete history of the mechanical and thermal treatment received by a metal is reflected in its microstructure.
   
   X. Determine the cause of failure. Failures can spring from a wide range of causes. In general, the failures can be attributed to:
   
    deficiencies in design;
    material selection;
    imperfections in materials,
    both internal and surface defects;
    processing deficiencies;
    errors in assembly; or
    improper service conditions.
   
   For more specifc or complex failures you should contact Dr. Zee at 412-788-1263