Failure analysis of stud bolt with cracks

Elkem received a sample for examination in a scanning electron microscope (SEM). This particular bolt was known to have cracks in the thread roots.

The analysis discovered two visible cracks in the root referred to as “Root 1” in the left picture. The longest crack was approximately 370 microns.

In the bottom of the crack we found evidence of zinc (Zn) and oxides (O).

Zink in the bottom of crack indicates that the bolt was fractured before galvanizing, therefore not during torquing of the bolt.