In the real world, components fail. There are many reasons why. If a premature failure occurs, it is important to evaluate all possible causes and then isolate a root cause that can be corrected to assure that the problem will not reoccur. Let's learn more.
Failures that occur during testing on the factory floor in controlled laboratory conditions or during product manufacture can be classified as "regular" failures, ones in which a significant amount of resources (people and test equipment) can be brought to bear on the problem. By contrast, field failures are those in which an assembly has failed in its normal working environment, often remote to the manufacturer, and where resources for analysis can be limited and must be transported to the jobsite. Field failures are particularly challenging. To help, here are some simple suggestions.
A Baker's Dozen1. Have a plan. Failure analysis starts with documented procedures and good training. Anticipate your needs. Don't be surprised or confused with what has to be done. Do not attempt to investigate a failure in a haphazard way. 2. Set up a team composed of representatives of all disciplines (management, purchasing, engineering, service, metallurgy, manufacturing, quality and legal). Meet to discuss the problem and review the facts (this step is often overlooked but can be invaluable if someone is able to recall details of this circumstances surrounding how the part was originally manufactured). Make recommendations as to the type and extent of the analysis that should be performed in the field. Understand the implications of the failure and the potential liability exposure of the company. 3. Use your time efficiently. Be prepared for the inspection. Plan your work carefully to obtain as much evidence as possible. Gather the right people and tools. Don't become distracted. 4. Inspect failed components immediately. Information relating to the failure should be compiled as soon and as thoroughly as possible. A "rapid response team" should be in place. Know that the longer the time between the failure and the inspection, the greater the risk that external influences will induce error into the analysis process. 5. Preserve the evidence. The ideal situation is to have information gathered on-site by a person or team familiar with failure analysis methods. If you can't get to the failure site, have someone at the site you can trust report the situation to you or follow your explicit instructions. Photograph everything (especially in this age of digital photography), even details that seem like incidentals. Try to emphasize the importance of having quality tools at the jobsite (especially the right digital camera-the ones we use can photography up to 1.2 in. away from an object with 8 megapixal resolution). 6. Evaluate if field disassembly is a good idea. In a perfect world, the assembly that failed would be undisturbed when the people assigned the task of field failure analysis arrive on the scene. Often, however, the assembly has already been taken apart; which, admittedly, may have been necessary to determine which component had failed. In some instances, the equipment has already been placed back into service. This usually makes the job of determining the root cause of failure much more difficult.
Prior to arrival, if asked by field personnel for permission to disassemble and return equipment to service before a thorough inspection by the failure analysis team takes place, resist the urge to say yes. It may be necessary to ship the assembly back to the factory in one piece for a more controlled analysis where more specialized resources may be available. If field disassembly is required, the failure analysis team should participate and not defer "hands on" work to technicians or less qualified individuals.
And remember, failures occur for a variety of reasons including:
- Overloading: tensile stresses, torsional forces and shear forces
- Impact: mechanical shock, thermal shock
- Wear: abrasive, adhesive, fretting, cavitation damage, erosion
- Fatigue: vibration
- Corrosion: uniform, pitting, galvanic, crevice, intergranular
- Stress corrosion cracking: hydrogen embrittlement, sulfide embrittlement
- Heat Treatment: improper hardening, tempering, quenching, cryogenic treatment