Page 480 - Corrosion Engineering Principles and Practice

446 C h a p t e r 1 1 M a t e r i a l s S e l e c t i o n , Te s t i n g , a n d D e s i g n C o n s i d e r a t i o n s 447

of finding an appropriate candidate material that will meet traditional
requirements while providing a required level of corrosion resistance.
The disadvantage is that such an analysis is generally more costly.
For highly important decisions with strict deadlines, analyzing
multiple materials simultaneously would be the most efficient
approach as it would minimize the impact on a project schedule.

11.4.2 Screen Materials Based on Past Experience
After choosing the material(s) to be initially considered, the next step
is to look at whether there have been corrosion problems in applications
similar to the system being designed, and to ascertain the nature of the
causes of these problems. It is usually expedient to eliminate from
consideration any material that has caused corrosion problems in a
similar application in the past, especially those problems that could
not be controlled using affordable corrosion prevention and control
practices. The sources of information that should be consulted at this
point will depend on many factors and vary greatly with organizations.
Access to a good library with pertinent reference documents and on-
line documentation is always a convenient starting point.
It is also important to consult any personnel that might have been
involved with the materials considered for similar applications or
consult maintenance records if these exist. Computer technologies
are used extensively by large organizations to track and manage
maintenance activities often supported by computerized technical
drawings, parts lists, and detailed part descriptions. Figures 11.10 to
11.13 illustrate how such information technology can provide an easy
graphical access to historical aircraft maintenance data [15].
11.4.3 Conduct Environmental Assessment
The next step in the materials selection process is to discount the
forms of corrosion that are unlikely to occur. For example, if the
application being designed will not be exposed to a flowing fluid,
then erosion–corrosion would not be considered. To determine the
more likely forms that will occur, the analyst should examine the
factors responsible for initiating each corrosion mode and then
determine which ones are present in the application. Chapters 6 and
7 provide descriptions that could be quite useful for this phase of the
selection process.
After candidate materials have been selected, the next step is to
analyze the environment in which a system will operate. When
considering the operational environment many may automatically
consider exposure to atmospheric, industrial, or marine conditions as
the corrosion inducing factors. While important, such a global or
“macro” view may be too limited since conditions imposed by the
configuration and operation of a system may result in the formation
of corrosion cells and of particularly corrosive microenvironments.