Glass Cookware Failure Analysis: Pyrex Pie Plate Failure

Fracture Surface at One Failure Origin

Assembled Pie Plate Showing Several Failure Origins

Read Consulting Failure analysis lab performed a glass failure analysis. An annealed borosilicate glass Pyrex baking dish failed as a result “thermal shock”. There were multiple origins for the failure, and these all initiated at damage sites on the bottom of the Pyrex baking dish. Because the bottom of the pie plate was convex, setting the dish down and moving it on hard (abrasive) surfaces such as tile counter tops created a “rim” of damage. When the hot dish was placed on a cold surface,thermal shock created tensile stress  on the bottom of the dish, and this caused the failure to initiate at the several preexisting damage sites. This baking dish is appears old and shows signs of heavy use. 

"Scuff" Damage on the Pie Plate Bottom

Failure Analysis of Glass Pot: Visions Cookware

A failure analysis  was performed on a broken 5 quart stove top glass pot. The origin was determined with optical microscopy, and the broken pot was assembled to show how cracking proceeded. The re-assembled pot is shown upside down in the upper left photograph. The failure originated at a preexisting "chip" on the interior at the top rim of the pot. In this case, the the Wallner lines indicated that, initially, the crack grew as a result of bending forces. Although the user had claimed that there was no impact involved in the failure event. The physical evidence indicates that this pot had been "bumped" on the outside near the top rim. It is important to realize that table top glass cook ware is just as fragile as normal annealed glass. It just has a much lower thermal coefficient of expansion. A large pot such as the one in this investigation is heavy, and a minor "bump" to the pot can generate high enough forces to cause failure and potential injury to one holding the pot. It is not unusual to have chips on the inner rim of such a pot due to the fact stainless steel spoons can be used to stir the contents. This failure analysis eliminated the possibility of a product defect or a manufacturing defect.