Page 38 - Handbook of Materials Failure Analysis

2 How to Conduct Failure Investigation 31

2.2 ONSITE INVESTIGATION
The field visit of a failure analyst at the accident site is always helpful to examine the
extent of damage and in collecting evidences. Otherwise the failure study is always
dependent on the information provided by the client, operators, and observers.
Before conducting survey of accidental site, the analyst should have updated infor-
mation and have sufficient knowledge about the equipment and other integrated
components of the system. For an analyst, the field inspection could be beneficial
to narrow down the possibilities of failure causes. Also the documentation of failure
site, that is, photography, sketching, and dimensional measurements could be helpful
later on during the study. The examination of failure site, “something is considered
insignificant sometimes” or even some aspects are overlooked which could become
essential afterward. However, adequate photography gives assistance to capture
clues and signs of failure stimuli. It is also important to include photographs in
the final report of failure as evidence of narrative description. It would be useful
to decide collection of important parts or wreckage of the failed components [32].
It provides judgment to the investigator for selecting proper samples which need
to be further examined in a laboratory. The careful examination of the failed com-
ponents, surroundings, and condition of connecting facilities is also essential. All
these intelligent efforts made at the accident site are always beneficial to predict
the factors involved in failure. To know about any variation in the process parameters
or alarming situation before failure, the interview with operators and discussion with
eye witnesses could also be helpful to predict probable cause.

2.3 SELECTING THE SAMPLES
For detailed study of the failed component, if possible, the whole system should be
transported to the laboratory. Otherwise, the failed part should be separated by cut-
ting sufficiently away from the sound region. If the cracks are present at numerous
sites, the samples should be selected which apparently had experienced severe but
different operating conditions. If the failure happens by fracture, the mating surfaces
should be cut well away to avoid any thermal or mechanical damage of the fractured
surface which may obscure the failure evidence [32,33]. The failed samples should
be carefully stored in air-tight bags to prevent contamination or oxidation by the
environment during transportation to the laboratory.

2.4 EXECUTION OF LABORATORY TESTING
Laboratory testing is an important step in the process of failure analysis. The selec-
tion of test methods is very much critical as the results are depictive of materials
properties. It is well known that man, machine, and method combination should
be experienced, calibrated, and standardized, respectively.
In corrosion failure analysis, the laboratory testing depends on the type of envi-
ronmental conditions and surface features of failed component. In laboratory, the