A measuring cone made of borosilicate glass mounted in a flowmeter failed after a life¬time of only a few months. Therefore, a failure analysis was conducted which revealed that the reason for failure was a too high flow rate. The high flow rate made the float touch the upper float stop. When contacting the stop, the float started to rotate in an unstable manner and as a result was hitting and grinding along the inner cone wall which resulted in cracks, micro-chipped surface areas and grinding marks. One of the longitudinal cracks then grew subcritically till final failure occurred.