In this presentation, Roger Costanzi discusses a tubular aluminium single column pantograph disconnecting arm from an 82kV disconnector, that was received for examination following failure adjacent to the weld joining the tubular arm to a clevis.
Failure of the disconnector arm was a result of exfoliation corrosion arising from the formation of precipitates in the weld heat affected zone (HAZ) joining the extruded tubes to a cast aluminium alloy clevis. Corrosion attack was exacerbated by the presence of drilled holes adjacent to the welds that exposed the end grain of the tubes to the environment. The disconnector was operating in an industrial substation located approximately 13km from the coast and at the time of failure was understood to have had a service life of approximately 17 years. While this arm was the first to have fractured it was understood that inspection had found thirty six (36) joints to exhibit external blistering of the surface adjacent to the weld. The tubes had been extruded from 2014 aluminium alloy and exhibited a hardness of 112HB suggesting the T4 heat treatment condition.
Roger Costanzi (Burea Veritas)
Roger Costanzi is the Manager of the Materials Science & Engineering Group of Bureau Veritas, a position he has held since 2007. The group provides a broad range of technical support and failure analysis investigations of plant and equipment used in the Australian mining, transport, manufacturing, power and process industries.