Typically an engineering root-cause failure analysis (RCFA) is performed for one of two purposes. These are for use in litigation or for internal use in various industrial and related organizations. 

In the legal arena RCFA’s are part of the input that an engineering expert witness contributes to define the physical circumstances that caused the accident, injury or other loss in question. Litigation may also develop out of subrogation that an insurance company makes following a property and casualty claim. After the RCFA, the retaining attorney gains definitive information on liability for his or her case. The expert obtains a solid basis for offering fully objective opinions during sworn testimony. 

The second use of a RCFA is in several types of organizations where a physical failure often involves a financial loss but no legal action is involved. Here the objective is to gain a fundamental understanding of the failure so as to make changes that will prevent a reoccurrence. An organization that employs the engineer, either in-house or as an outside consultant, is most interested in practical recommendations to prevent a future failure of the given equipment. By contrast, the attorney in a legal case likely will concentrate primarily on the cause(s) of the incident as a basis for assigning liability and not what the best “fixes” might be.

When starting any failure investigation the engineer should consider just what is a “failure” in the given situation. Essentially it is whatever the owner or user of the device, system or process defines as a failure. For materials and mechanical design applications this might include such conditions as fracture, permanent deformation or dimensional change, inadequate service life, unacceptable appearance, contamination of the process stream or excessive vibrations during operation. 

Completing a RCFA typically follows the scientific method. This entails defining the specific problem or failure to be evaluated; proposing alternative hypotheses, i.e., causes in the case of failures; testing or evaluating each alternative; and, finally, forming a conclusion based on which alternative or cause is best supported by the total evidence assessed.  

For failures of engineering materials or mechanical designs the sequential steps in a thorough RCFA will generally flow as follows: 

• Gather and protect for analysis all possible physical evidence and information. If possible this should include samples of failed parts, similar but unaffected parts, i.e., exemplars, any relevant documents (drawings, manuals, etc.) and verbal descriptions of the circumstances from the best-available sources. Take digital photos of “everything” using macro and close-up views for comparison. Always take more photos than you think you will need,
• Complete detailed, non-destructive visual examinations of all physical evidence. Assess these macro-scale results in terms of all written, photographed and verbal information gathered. Often it is advisable to seek more facts about the general type of equipment or process in question for comparison to the verbal and written data provided by those persons directly involved in the failure, 
• Define the most probable cause (and/or contributory causes) of the failure and develop a plan for doing specific analyses. The goal of the planned work is to support or refute the possible cause(s) defined. The actions in the analysis plan should always proceed from the least to the most destructive level of destruction of the physical evidence,
• Carry out the analysis plan. Various laboratory tests often are used,
• Integrate all findings and information obtained and come to a conclusion about the most probable and contributing causes of the failure,
• For industrial failures, complete sufficient research to establish practical recommendations to minimize the chances of future failures. Generally it is advisable for the engineer to offer different corrective actions in a written report – each alternative with its own probability of success and cost – along with his professional opinion as to which best meets the needs of the given client.                       

Posted in: Industrial/Training Services