During the construction of a 56km long 16 in. carbon steel sour gas pipeline, repetitive surface
preparation failures were detected during visual inspection of pipeline girth weld internal surface prior to
coating application. Such failures represented 67% of the total pipeline girth welds and were manifested
by excessive sharp-edges at the root pass. To identify the failure causes, an investigation was
performed through reviewing the pipeline, fabrication and coating application specifications and
procedures, quality control records and performing an extensive visual inspection through an advanced
video robotic crawler on all pipeline girth welds made. Upon investigation analysis, the failures were
caused by sharp-edges in the root pass which were attributed to improper practices during
manufacturing, field fabrication and pre-coating quality control. The failure analysis indicated that the
mechanized Gas Metal Arc Welding process, with the parameters used, was not suitable for internal
girth weld coating application. In addition, a more stringent requirement should be applied to the
acceptable pipe-end diameter tolerance and pre-coating quality control to ensure absence of similar
premature surface preparation failures. The pre-coating quality control can be improved through
utilization of robotic laser contour mapping crawler for precise detection and sizing of unsatisfactory
surface weldment defects, including sharp edges.

Conducting a materials failure analysis requires a carefully planned series of steps intended to
arrive at the cause of the problem. Consistent with the current trend towards better accountability
and responsibility, failure analysis purpose has been extended in deciding which party may be
liable for losses, be they loss of production, property damage, injury, or fatality [1]. Hence it
increases the importance of proper implementation of characterization tools in failure analysis to
rightly identify the failure mode.
Present work discusses a few case studies to shed light upon the importance of the metallurgical
characterization tools and techniques in identification of correct failure mode. Some typical case
studies where metallography plays a very important role have been discussed, such as improper
welding joints which led to premature failure, sensitization and stress corrosion cracking in S.S.,
improper heat treatment and forging indicated the microstructures which led to the premature
failure. These cases are examples of only a few laboratory based investigations which justify that
without metallography it is not possible to diagnose the causes of premature failures.
Generally, examination of failed components commence with the low-power stereomicroscope
whereas hand-held magnifying lenses are still in wide use by experts to study fractures mostly
limited now for field purpose [2]. Metallographic examination typically is performed after nondestructive
and macroscopic examination procedures while using the light optical microscopy
which helps to assess the failure mode with respect to material defects, shortcomings in
processing, metallurgical changes etc. Since light optical microscopy has limited value for direct
observation of fracture surfaces (more limited for metals than non-metals), with still more factual
information can be gathered by scanning electron microscopy at higher magnification.