When a PVC fitting with female pipe thread is coupled with male brass pipe threads, the PVC half is put into tension (i.e. hoop stress). The threads are tapered, and when the two halves are joined to produce a leak free joint, the PVC is put into tension and has the probability to fail over time. This situation is worsened if a brass hose bib is screwed into the PVC. Normal use of the valve, such as tightening or pilling of a hose. The present sample had been in use for over 10 years before it failed. Since the circumstances of this failure are known, it is worthwhile to examine the fracture surface.
The failure mode is low cycle fatigue. This is indicated by the striations accompanied by overload failure.
