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RISK ANALYSIS OF INTERNAL COMBUSTION ENGINE 39
VALVE PRODUCTION USING FMEA METHOD

 A basis for in-flight troubleshooting procedures and for locating performance
monitoring and fault-detection devices.

 Criteria for early planning of tests.

From the above list, early identifications of SFPS, input to the troubleshooting procedure and
locating of performance monitoring / fault detection devices are probably the most important
benefits of the FMEA. In addition, the FMEA procedures are straightforward and allow orderly
evaluation of the design.

4. 3. Limitations of FMEA

While FMEA identifies important hazards in a system, its results may not be comprehensive and
the approach has limitations.[8][9][10] In the healthcare context, FMEA and other risk
assessment methods, including SWIFT (Structured What If Technique) and retrospective
approaches, have been found to have limited validity when used in isolation. Challenges around
scoping and organizational boundaries appear to be a major factor in this lack of validity.[9]

If used as a top-down tool, FMEA may only identify major failure modes in a system. Fault tree
analysis (FTA) is better suited for "top-down" analysis. When used as a "bottom-up" tool
FMEA can augment or complement FTA and identify many more causes and failure modes
resulting in top-level symptoms.

Additionally, the multiplication of the severity, occurrence and detection rankings may result in
rank reversals, where a less serious failure mode receives a higher RPN than a more serious
failure mode. The reason for this is that the rankings are ordinal scale numbers, and
multiplication is not defined for ordinal numbers. The ordinal rankings only say that one
ranking is better or worse than another, but not by how much. For instance, a ranking of "2"
may not be twice as severe as a ranking of "1," or an "8" may not be twice as severe as a "4,"
but multiplication treats them as though they are. See Level of measurement for further
discussion.

4. 4. Some of the Risks and Results of Them for Manufacturing Valves

 Wrong material for stem/head
 Wrong dimensions
 Cracks on any step of production
 Visual defects
 Hardness value may not match the desired value
 Material structure may be wrong
 Welding stress relief can be incorrect
 Porosity or bonding on stellite surface

And results may be:

 Engine failure due to low mech. properties
 Wrong dimensions may lead low performance, premature failure of engine, also wrong

dimensions may lead machine failures while valve is being produced
 Cracks may lead premature fracture on valves, can damage engine

Sayı 5, 2016 GiDB|DERGi