Abstract
The failure reasons of the circulating pump shaft in the upper section of the quench tower were analyzed by means of chemical composition analysis, macroscopic observation, metallographic examination and fracture section analysis. The analysis result shows that the calcium-silicate inclusions in the surface of the pump shaft cause the microcracks and the parallel fatigue sources, which leads to the fatigue cracks propagation under alternating load and finally the shaft is fatigue fractured.
Highlights
In order to confirm whether the material of the pump shaft is consistent with the original design, the chemical composition of the shaft material is analyzed, as shown in Tab
The middle step is the step formed by the interface of the three crack sources, while the lighter step on the fracture section is the step at the junction of 2# crack source and 3# crack source
The fatigue crack source is formed on the surface, and the fatigue crack growth is connected with the external environment, so the surface of the fatigue crack growth zone is dark brown due to oxidation or corrosion, while the final fracture zone usually tears quickly and appears the color of metallic luster
Summary
A sudden abnormal sound was detected in the circulating pump with the type of p-107S in the upper section of the quench tower of an acrylonitrile unit in Shanghai in 2019, and the circulating pump was stopped and lift for inspection. The pump shaft was found fractured, and other parts were basically intact. The fractured part of the pump shaft was at the keyway of the shaft shoulder, where the structure of the pump shaft was discontinuous, as shown in Fig.. The pump was a single-stage double-suction centrifugal pump with the flow rate of 10,000m3/h, the head of delivery of 62m, the power of 2100kW, and the speed of 590r/min. The sealing type was packing seal, and the bearing lubrication type was grease lubrication. The impeller was the type of closed double-suction, and the coupling was the type of laminating coupling. The design material of the pump shaft was the austenitic steel forging of 06Cr17Ni12Mo2Ti (according to NB/T 47010-2010 ‘Stainless and heat-resisting steel forgings for pressure equipments’). The diameter of the pump shaft was 215mm, and the keyway width was 10mm
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