Failure analysis of mechanical seal of nitrobenzene sulfuric acid pump

Sulfuric acid pumps serving in the nitrobenzene process failed many times due to the mechanical seal's failure in a chemical plant. To clarify the failure reasons, damage characteristics were examined by visual inspection, scanning electron microscopy, and energy dispersive spectros-copy. Moreover, the possibility of the galvanic corrosion was confirmed by the designed tests, and the effects of the pure sulfuric and mixed acid on the corrosion were also clarified by the im-mersion tests. The results show that the material degrades in the form of intergranular corrosion. The most severe damage locates in the sealing gland, in contact with the static ring seat. Galvanic corrosion is mainly responsible for the failure. The differences in the chemical compositions and the microstructure play an important role in galvanic corrosion. Moreover, some suggestions are provided to alleviate the corrosion based on the analysis above.

Automated summary

Sulfuric acid pumps have failed multiple times in a chemical plant's nitrobenzene process due to mechanical seal failure. Through examination of the damage characteristics and corrosion effects, it was found that galvanic corrosion, particularly in the sealing gland in contact with the static ring seat, was the main cause of failure. Additionally, suggestions were provided to mitigate the corrosion.