Fracture Surface Analysis
Observation Example of Fracture Surface: Breakage and Falling-off of Aerator Blade Shaft
Observation example of fracture surface
| Product: | Breakage and falling-off accident of aerator blade shaft |
|---|---|
| Material: | JIS SUS 304 Blade- φ2,280 mm (broken part: t25 mm, φ480 mm) |
| Circumstances: | Aerator blade which had been used for agitation (32.8 rpm) in activated sludge tank of water treatment plant in a steel works for about 25 years was fallen off from the root of mounted portion. A few fine cracks were also found at weld near the fractured portion and stress concentration area such as difference-in-level portion. |
| Cause of breakage: | Stress corrosion cracking was verified based on fracture surface observation and sectional microstructure observation. As separation of industrial effluent had been performed in this sludge tank, chlorine (Cl) was found there. It is presumed that stress corrosion cracking due to chlorine ion (Cl-) is the cause of the fracture. |
