Metallurgical failure analysis


Metallurgical failure analysis

Metallurgical failure analysis is the process by which a metallurgist determines the mechanism that has caused a metal component to fail. Typical failure modes involve various types of corrosion and mechanical damage. It has been estimated that the direct annual cost of corrosion alone in the United States is a staggering 276 billion, approximately 3.1% of GDP.[1]

Metal components fail as a result of the environmental conditions to which they are exposed to as well as the mechanical stresses that they experience. Often a combination of both environmental conditions and stress will cause failure.

Metal components are designed to withstand the environment and stresses that they will be subjected to. The design of a metal component involves not only a specific elemental composition but also specific manufacturing processes such as heat treatments, machining processes, etc.… The huge arrays of different metals that result all have unique physical properties.[2] Specific properties are designed into metal components to make them more robust to various environmental conditions. These differences in physical properties will exhibit unique failure modes. A metallurgical failure analysis takes into account as much of this information as possible during analysis.

Analysis of a failed part can be done using destructive testing or non-destructive testing. Destructive testing involves removing a metal component from service and sectioning the component for analysis. Destructive testing gives the failure analyst the ability to conduct the analysis in a laboratory setting and perform tests on the material that will ultimately destroy the component. Non destructive testing is a test method that allows certain physical properties of metal to be examined without taking the samples completely out of service. NDT is generally used to detect failures in components before the component fails catastrophically.

There is no standardized list of metallurgical failure modes and different metallurgists might use a different name for the same failure mode. The Failure Mode Terms listed below are those accepted by ASTM,[3] ASM,[4] and/or NACE[5] as distinct metallurgical failure mechanisms.

Contents

Metallurgical Failure Modes Caused By Corrosion and Stress

Metallurgical Failure Modes Caused By Stress

Metallurgical Failure Modes Caused by Corrosion

  • Erosion Corrosion
  • Oxygen Pitting
  • Hydrogen Embrittlement
  • Hydrogen Induced Cracking (ASM term)
  • Corrosion Embrittlement (ASM term)
  • Hydrogen Disintegration (NACE term)
  • Hydrogen Assisted Cracking (ASM term)
  • Hydrogen Blistering
  • Corrosion

References

  1. ^ ‘Corrosion Costs and Preventive Strategies in the United States,’ Report FHWA-RD-01-156, contact the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161; phone: 703/605-6000.
  2. ^ M&M Engineering Conduit Fall 2007 “Ferrous Metallurgy 101,”
  3. ^ “Standard Terms Relating to Corrosion and Corrosion Testing” (G 15), Annual Book of ASTM Standards, ASTM, Philadelphia, PA.
  4. ^ ASM-International Metals Handbook, Ninth Edition, Corrosion, ASM-International, Metals Park, OH
  5. ^ NACE-International NACE Basic Corrosion Course, NACE-International, Houston, TX
  6. ^ M&M Engineering Conduit Fall 2007 “Chloride Pitting and Stress Corrosion Cracking of Stainless Steel Alloys,” [1]

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