Failure Analysis Case History No. 019

Industry: Chemical
Specimen Description: Failed Scaffold Clip
Material: Carbon Steel
Environment: Atmosphere
Welds attaching a scaffold clip to a scaffold failed causing the scaffold boards to fall to the bottom of a API 650 tank.
Time in Service: ~ Less than a week.
The as-received scaffold clips were made by fillet welding one side of a bent bar onto the I.D. of the tank wall with approximately one-inch of weld. On one sample, the clip still remained. On the other sample both welds attaching the bar to the tank wall had failed. Visual observation of the fillet welds showed that they had been made with the SMAW process and apparently without removing rust, etc. from the tank wall or the bar. The weld fracture appeared dendritic and contained significant voids. SEM examination of a fractured weld revealed significant unfused areas amongst areas of ductile overload. A polished and etched profile of the unfailed clip showed that the weld contained large interdendritic cracks and a large untempered weld heat-affected zone. The weld microstructure contained many interdentric cracks suggestive of hot tear cracks.


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