Sewer Pipe Failure Analysis

 Failure expert performs a failure analysis on a cracked drain pipe removed from a high rise building. The pipe drained rainwater from the roof down to the ground This 2 3/4" OD cast iron pipe began to fail after approximately 12 years of service. The upper left photo is an overview of a piece of the pipe. The predominant failure mode is a single linear crack parallel to the pipe axis. The crack opening is 1/4" wide, and this opening indicates that there are residual tensile stresses in the pipe that are contributing to the failure. The photograph on the right show the fracture surface created when a section of the pipe is broken open. The outer layer of the pipe is white cast iron, and the interior portion of the pipe is gray cast iron. It is believed that because the outer portion of the pipe is chill cast, there are high residual casting stresses that are driving this stress corrosion failure.

Glass Expert Witness Discusses Tempered Glass Fracture Surface

California failure analysis expert witness examines two distinct fracture surfaces for tempered glass failures.
According to the tempered glass expert witness, the surfaces of tempered glass are under compressive stress. This stress is balanced by an "equivalent" tensile stress in the center of the glass. Tempered glass failures are really the end result of self destruction. The mid-plane tensile stresses take control of any defect that enters the center of the glass pane and drives the crack to the point that the original piece becomes a large number of almost cubic diced pieces. , under normal conditions, the fracture surface consists of two sets of Wallner lines separated by a central zone of mist hackle (upper  photo-micro-graph). The fracture surface for a tempered glass piece that failed as a result of bending is distinct. The fracture surface shows a shift of the central mist hackle toward the convex side of the bend. In this case, the Wallner  lines have essentially disappeared (lower photo-micro-graph).