Failure Analysis of Reed Switch Glass Failure

Glass expert performed a root cause failure analysis on failed reed switches. The upper left photograph shows the type of reed switch that was failing. This switch consists of two ferromagnetic "blades" that are enclosed in glass. At either end are leads that pass through glass-to-metal seals. The sealed tube is filled with inert gas which is introduced through a side tube that is heat sealed after the gas has been introduced. The switch is activated magnetically. The glass expert performed a glass failure analysis and determined that the glass envelopes were cracking due to the presence of mechanical damage (i.e. scratches) on the outer surface of the glass. All the cracks initiated at a flaw and then proceeded circumferentially till the two halves of the crack met on the opposite side from the origin. It is believed that the source of the failure stress was thermal stress generated by heating during potting and assembly. WIthout the pre-existing flaw on the outer glass surface, the switch would not have failed. The center photograph shows the initial crack leaving the origin in two directions. These two halves of the crack eventually meet on the side opposite the origin. The upper right photograph shows the surface flaw where the crack originated. These switches failed as a result of a manufacturing defect.

Failure Analysis Expert Witness Analyzes a Pipe Fatigue Failure

Failure analysis expert analyzes a pipe failure. In this case the failed brass pipe supported a gauge. The gauge was cantilevered on the 6" long pipe and valve assembly. This assembly was attached to a pump, and the pump vibrations acted on the assembly and caused a metal fatigue failure to initiate ar the root of the male pipe thread where the thread exited the 'T' fitting. This is the most vulnerable point. The moment is maximum at this point and the root of the thread was a stress concentrator that magnified the stresses caused by the vibrations. The photographs above summarize the failure. Upper left shows an overview of the failure. The pipe failure occured where the pipe entered into the 'T' fitting. Upper right is an 8X photomicrograph ofthe fracture surface. The fatigue failure initiated at the root of the pipe thread. It then proceeded to the left as shown by the arrows. Fundimentally, the vibrating weight of the cantilevered, unsupported gauge caused the failure.