Large Diameter HDPE Reducer Fitting Failure
The reducer fitting pictured above was removed from a large irrigation project in Rwanda due to an in-service failure. No information was provided on the manufacturer of the fitting. The fitting was fabricated by butt fusion joining together multiple sections. The smallest diameter (top) of the fitting assembly was 22 inches (560 mm) in diameter. The largest diameter (bottom) of the fitting assembly was 26 inches (660 mm) in diameter. The intermediate diameter (middle) of the fitting assembly was approximately 24 inches (610 mm) in diameter. The planar fracture encircled approximately 80% of the fitting body in the middle diameter region of the fitting approximately one inch below a factory butt fusion weld (outer beads removed). The approximate 20% of the intact fitting body circumference was cut within approximately the same plane as the fracture and perpendicular to the main axis of the fitting to reveal the fracture surface was contaminated with orange soil trapped within the fracture and separating the fitting into two sub-sections; a top and bottom. Our analysis revealed the fracture initiated at a sharp notch machined into the fitting inner wall and exhibited multiple independent slow crack growth initiations (shown below by red arrows) at the inner wall consistent with slow crack growth initiation. The fracture was brittle with small areas of ductile tearing observed at the extreme outer diameter of the fitting . In some locations, a second distinct texture was observed in the fracture surface toward the outer radius which was interpreted as illustrating fast fracture in the same plane as the slow crack growth. This fitting was manufactured by machining an interior diametrical change into the fitting creating an inappropriately sharp notch. This sharp notch acted as a site of stress concentration on the inner wall of the fitting assembly in the plane of machining under service pressures and initiated multiple independent brittle fractures which propagated through the fitting wall resulting in the observed failure.
The reducer fitting pictured above was removed from a large irrigation project in Rwanda due to an in-service failure. No information was provided on the manufacturer of the fitting. The fitting was fabricated by butt fusion joining together multiple sections. The smallest diameter (top) of the fitting assembly was 22 inches (560 mm) in diameter. The largest diameter (bottom) of the fitting assembly was 26 inches (660 mm) in diameter. The intermediate diameter (middle) of the fitting assembly was approximately 24 inches (610 mm) in diameter. The planar fracture encircled approximately 80% of the fitting body in the middle diameter region of the fitting approximately one inch below a factory butt fusion weld (outer beads removed). The approximate 20% of the intact fitting body circumference was cut within approximately the same plane as the fracture and perpendicular to the main axis of the fitting to reveal the fracture surface was contaminated with orange soil trapped within the fracture and separating the fitting into two sub-sections; a top and bottom. Our analysis revealed the fracture initiated at a sharp notch machined into the fitting inner wall and exhibited multiple independent slow crack growth initiations (shown below by red arrows) at the inner wall consistent with slow crack growth initiation. The fracture was brittle with small areas of ductile tearing observed at the extreme outer diameter of the fitting . In some locations, a second distinct texture was observed in the fracture surface toward the outer radius which was interpreted as illustrating fast fracture in the same plane as the slow crack growth. This fitting was manufactured by machining an interior diametrical change into the fitting creating an inappropriately sharp notch. This sharp notch acted as a site of stress concentration on the inner wall of the fitting assembly in the plane of machining under service pressures and initiated multiple independent brittle fractures which propagated through the fitting wall resulting in the observed failure.
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