Metallurgical analysis is used in the practice of failure analysis to assist in the identification of material problems and to ascertain fracture mechanisms.  A metallographic cross-section through failed parts provides information regarding the suitability of weld procedures used, and the degree of penetration achieved.  This type of analysis is especially useful in the determination of manufacturing defects or service related material problems.

A fabricated structural mast section incorporated a steel lug welded to a 1 ½” thick steel plate as an end connection.  During use, the lug separated suddenly from the underlying plate, through-thickness, resulting in a catastrophic failure.  Metallographic examination of the plate material found a gross non-metallic subsurface plane to be present.  The presence of this material defect was unexpected and resulted in brittle behavior in the thick plate when it was loaded in the through-thickness direction.

A large mobile trailer structure had been fabricated and delivered to the client for use.  Early in the life of the trailer, however, failure of several welds occurred resulting in downtime and additional costs.  Metallographic examination of the assembly welds found the vertical passes to be performed using gas metal arc welding (GMAW) and no penetration or fusion was achieved.  This manufacturing defect was subsequently pursued with the fabricator.

Fire tubes used in separator vessels were experiencing severe cracks throughout their welded connections.  Metallographic examination of some of these cracks revealed them to be the result of thermal fatigue.  Subsequent modification to the fire tube support design minimized the cyclic thermal stress components and improved the service life of these parts.

Zeus Engineering Ltd.
www.zeuseng.com