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.

Failure Analysis Expert Witness Analyzes a Pipe Fatigue Failure

Failure analysis expert analyzes a pipe failure. In this case the failed brass pipe supported a gauge. The gauge was cantilevered on the 6" long pipe and valve assembly. This assembly was attached to a pump, and the pump vibrations acted on the assembly and caused a metal fatigue failure to initiate ar the root of the male pipe thread where the thread exited the 'T' fitting. This is the most vulnerable point. The moment is maximum at this point and the root of the thread was a stress concentrator that magnified the stresses caused by the vibrations. The photographs above summarize the failure. Upper left shows an overview of the failure. The pipe failure occured where the pipe entered into the 'T' fitting. Upper right is an 8X photomicrograph ofthe fracture surface. The fatigue failure initiated at the root of the pipe thread. It then proceeded to the left as shown by the arrows. Fundimentally, the vibrating weight of the cantilevered, unsupported gauge caused the failure.