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.

Porcelain Toilet Tank Failure Analysis

A failure analysis was performed on a toilet tank that had caused water damage to a residence. This failure initiated at a hold down bolt hole. This tank was 14 years old. Originally it was proposed that thus porcelain failure was the result of a manufacturing defect. The root cause failure analysis shows that the tank was subjected to forces that were transfered to the porcelain through the hold down bolts. This toilet tank failed as a result of undue forces. It is not the result of a product defect.

California Coating Expert Performs Failure Analysis of Epoxy Paint

A California coating expert was confronted with a municipal water tank with a rubbery epoxy coating. The complaint was that the epoxy paint was not properly mixed, and it had not cured properly. During the coating failure analysis, the study showed that the epoxy paint was aliphatic amine cured. In addition, the tank was painted in the winter, and it cured at 50°F. Prior to filling with water, the tank interior was given a final inspection. During the inspection the paint layer was found to be rubbery on the sunny side of the tank. Because epoxy is thought to be "cross linked" all were surprised that the paint was rubbery. and they were concerned that the paint adhesion had been compromised. Adhesion tests were positive. The fact is many epoxies 'soften' above their initial cure temperature. In this case, the epoxy paint had cured at or below 50°; thus, on a warm day (T> 70°F) the epoxy will initially be soft. However, over time, the paint will "re-cure" and harden at the higher temperature. The failure analysis demonstrated that there was no product defect.

Failure Analysis Expert Examines a Corrosion Failure

Corrosion engineer performed a metallurgy failure analysis to determine the cause of prematurely failing burners in a particular brand of gas grill. The burners in question would fail completely after two or three years of service. The failure analysis of the burner revealed that the grill manufacturer made the subject gas burners from an inferior grade of stainless steel. They used a relatively obscure alloy (J1). This alloy is a variation on 304 stainless steel. The 304 alloy contains 18% chromium (Cr), 8% nickel (Ni) and 2% maximum manganese (Mn), and it allows a maximum of 0.08% carbon (C). The J1 alloy allows the same amount of C but contains only 15% Cr; it also has 4% Ni and 8% Mn. Because the Cr is the active ingredient for the corrosion resistence of stainless steel, the J1 alloy will perform poorly in a corrosive environment. A by-product of burning propane in a gas grill is water. In addition, the burner is hot with other contaminants on it; a corrosion expert would state that this is a corrsive environment. Upper left is a photograph of a burner that failed prematurely. Upper right is an unetched metallugraphic sample of a piece of this burner. One can clearly see that the burner surface shows grain bounbary corrosion. It is believed that the low level of Cr and the presence of water and carbon makes the J1 alloy susceptable to stainless steel corrosion and unsuitable for gas grill burners. This product defect analysis indicates that this is a not a manufacturing defect but design defect.

Glass Expert Performs Bottle Failure Analysis

A glass failure expert witness performs a failure analysis on a failed cosmetic bottle. As received, the top of the bottle had broken off. Upper left is a photograph of 'as receceived' failed bottle. Approximately one half of the bottle finish had broken off. Read Consulting performed a glass failure analysis to determine if this failure was a manufacturing defect, or it failed as a result of shipping damage. The upper right photomicrograph is 30X view of the failure origin. The failure initiated at a bruise (small impact damage) on the top of the finish. Three of nine bottles from the same molding cavity also had damage to the top of the finish. In this shipping lot there were over thirty five bottles from other cavities, and none of these showed damage. Thus, the glass failure analysis expert witness believes that this product defect occured during manufacturing. However, both the shipping methods and the manufacturing proceedures will be reviewed for product liability improvement.

Grinding Wheel Failure Analysis

Failure analysis expert witness performed a failure analysis on a broken grinding wheel. This is part of a product liability case where it was claimed that the wheel broke apart during normal use and injured the user. Examination of the wheel showed that the wheel had been broken by someone clamping it and breaking off a piece. The upper left photograph shows the failed wheel. this wheel has the paper label bent over. This indicates that the wheel did not spontaneously fail. Upper right is a photomicrograph of the paper label opposite the break. Visible is a linear array of marks indicating that this wheel had been held in a clamp (such as a vice). This evidence shows that the subject grinding wheel did not fail spontaneously as described by the injured user. There was no product defect or manufacturing defect with respect to this wheel.

Product Liability, Chair Failure Analysis

Failure analysis expert witness examined a failed hospital chair. The chair failed during a breast X-ray examination. The chair had been altered 3 years prior to the failure, and the machine shop that had made the alterations was accused of causing the fatigue failure. Examination of the chair discovered hammer marks on a critical region of the chair. The chair owner had performed repairs two days prior to the accident. The nature of the repairs was such that the hammer marks would have been appropriate. Therefore, the failure was attributed to user error. This fatigue fracture was not the result of a product defect. Therefore, product liability was not in question.

Glass Bottle Failure Analysis

Glass failure analysis expert performed a root cause failure analysis on a bottle failure. The cap on this bottle had not been removed. The failure analysis revealed a manufacturing defect on the bottle interior. On the upper left photo is a 30X photomicrograph of a portion of the origin on the fracture surface. The arrows show the travel direction of the crack exiting the origin. On the upper right is a 30X photonicrograph of the origin as it appears on the interior surface of the bottle. There is a "chip" associated with the origin; therefore, this is a product defect on the bottle interior.

Glass Expert Analyzes Wine Bottle Defect

A glass expert was asked to examine poor quality bottles received by a winery. The issue was whether this product defect would significantly lower the strength of the bottle and would present a product liability problem. The photo on the upper left is a photograph of the manufacturing defect. It is a 4 inch horizontal "gash". The center picture is a photo-micrograph of the defect cross-section. The cross-section shows that the edges of the defect are rounded. This is a molding defect that occured when the glass was at or above the its softening point. The edges of the defect are rounded; therefore, in the opinion of a manufacturing engineer, they are unlikely to cause a low stress bottle failure. The picture on the upper right is a photo-micrograph of the top of the defect. There is a thin sheet of glass over the center mound of the defect. It is believed that this defect was formed in the blow molding step of the bottle manufacturing process.

Beer Bottle Impact Failure Analysis

Glass failure expert analyzed a failed beer bottle to determine if there was a product defect. It was stated that the bottle exploded when it was put into a cooler filled with ice. The failure analysis revealed that the bottle had been hit with a sharp object. The photograph on the left is the bottle after re-assembly. The photograph in the center is a closeup of the failure origin from the outside of the bottle, The photo on the right is the failure origin from the inside of the bottle. The hertzian cone from the impact is readily visible. It is obvious that this bottle broke after it was hit on the side. Thus there are no product liability issues or manufacturing defects associated with this failure.