Brass Plumbing Failure Analysis Stress Corrosion Cracking (SCC)

California failure analysis expert witness has analyzed numerous plumbing failures involving yellow brass (i.e. brass with more than 30% Zn in the alloy). The two major brass failure modes in yellow brass are dezincification and stress corrosion cracking. Above are two samples of stress corrosion cracking. Sress corrosion of yellow brass commonly involves the presence of ammonia along with the presence of stress. Upper left is a photo of a brass ferrule that cracked. The stress came from the clamping force of the ferrule on the rubber hose. These ferrules were covered with an expanded foam insulation that was painted with latex paint. At a minimum the latex paint contained ammonia; it is also believed that there was residual ammonia in the rubber foam insulation. Upper right is a failed flexible bathroom water supply line. The stress in this pipe failure is residual stress from non-uniform bending. It is believed that the ammonia came from houshold cleaners used on the plumbing. In both cases, the cracking is inter granular cracking and is attributed to stress corrosion cracking.

Plumbing Failure Analysis: Failure Analysis of a Water Flow Indicator

A California failure analysis expert performs a failure analysis on a broken water flow indicator. This flow indicator was in a large building, and as a result of the failure, there was substantial damage. The flow indicator consisted of a glass dome clamped into a metal housing.The failure originated where the flange of the glass dome contacts the interior wall of the metal housing. The failure initiated at the “half thickness” of the flange on the glass dome and spread left and right. This failure was caused by misalignment of the glass dome with respect to the interior of the glass housing. From this perspective, this is an assembly defect. From another perspective, this is a design defect. The absence of a compliant spacer between the edge of the flange and the wall of the metal housing allows misalignment. A design improvement would be to add a compliant “ring” spacer between the glass dome flange and the interior wall of the metal housing. This failure should be considered a product defect.