Page 34 - Handbook of Materials Failure Analysis

1 Introduction 27

1. Wrong material selection
2. Shortcomings in product designing approach
3. Non-engineered manufacturing
4. Unexpected environmental conditions
5. Unscheduled and nontechnical maintenance approaches
The optimum materials selection for a particular component, the design necessitates
specific characteristics of materials and prescribes a set of conditions for safe operation.
The inadequate mechanical properties, microstructural characteristics, nonuniform
alloying elements distribution, and imperfections in the materials are detrimental to
the performance of a product or an equipment. Other factors i.e. cost, availability,
and fabricability of a material also play a vital role in the selection process. The inca-
pable materials are selected due to unawareness of materials characteristics, non-
certified materials, or compromise of the procurer with the quality of the product over
cost. The safety and longevity of any component is assured at the designing step of a
component. The intelligent approach and consideration of surrounding effects on the
designed component is the key responsibility of the designer. The factor of safety
should be limited to restrict overdesigning but should be enough to withstand severe
conditions throughout its designed life. Design-oriented failure problems may also
arise if anisotropy of materials, ignoring service conditions, that is, temperature, pres-
sure, corrosivity of the environment, fluctuating mechanical stresses, and presence of
residual stresses are not considered carefully [3]. The conceptual design is always
required for critical consideration of sharp notches, abrupt geometry changes, over-
looking the compatibility of thick and thin sections with the operational stresses,
and chemical/electrochemical attack to avoid failures. The manufacturing of
components and fabrication of equipment is equally important as designing. Any
wrong action during fabrication or deviation from the mandatory requirements of
the adopted standard could also lead to premature failure. The efficient fabrication
methods, proper heat-treatment procedures, precise testing, and expert approach to cer-
tify equipment for intended application is also needed at the manufacturing stage. It
should be considered carefully that unexpected conditions may arise during service
beyond the designed limits, it is therefore proper material selection, the best designing
approach, and standardized fabrication procedures are essential. This could be benefi-
cial to enhance the service life of a component and or an equipment. During service of
the equipment, the standard operating procedure should be strictly followed. The
scheduled shutdowns and proper maintenance is required to ensure the integrity of
the component and to assess the remaining life [4]. The negligence at any stage or tol-
erating even minor requirement could lead to failure in a process industry which
imposes huge economic burden additive to replacement cost by loss of product, pro-
long shutdowns, contamination of the product, and decrease in production rate. Oper-
ation beyond the prescribed limits of design to acquire large production in short time
could also be a threat to the safety of equipment even if all the steps from designing to
manufacturing are carefully considered.
One of the major reasons of metallic components failure would be environmental
deterioration during service. This may include stress-induced cracking, selective