Corrosion Failure Analysis And Improvement Measures Of The Plates In Evaporator Applied In Waste Heat Boiler

Waste Heat Boilers Used in Liquid Waste Disposal Unit are one of the significant equipments in engineering areas like petrochemical, metallurgy, and so on. However, owing to the variability of the process media and the complexity of the service conditions, e.g., as well as high temperature and high pressure, such evaporators applied in waste heat boiler are always encountered with premature failures. As a result, the lifetime of the whole equipments would be shortened, great economic losses would be suffered, and even safety accidents would be engendered. Several failure resulted from severe corrosion occurred on plates in evaporator have found in inspection in one petrochemical plant. Based on the typical failure incidents, this thesis will deeply investigate the premature failure behaviors of the support plate in the evaporator, and will also study the relevant failure mechanisms and propose the pertinent prevention methods. Achievements of this research will have a reference value for failure prevention of the in-service evaporators that operate under similar service conditions.In this thesis, the fundamental theory, testing technique and evaluating analysis method were comprehensively utilized to systematically investigate into four aspects were then carried out, including matrix materials, process media, service conditions, and maintenance management. On one hand, the chemical compositions, the metallographic structures, and the hardness properties of the sample of in-service plates were inspected. The results showed that the materials quality of these support plates met the requirements of corresponding standards, in other words, the failure was induced by external factors rather than the plates themselves. On the other hand, microscopic morphologies and chemical compositions of the corrosion surfaces were observed and detected by SEM (scanning electron microscope),3D-SM (3-dimensional stereo microscope), XRD (X-ray diffraction), and EDS (energy disperse spectroscopy); then the shedding on the plate surfaces were collected and studied by OM (optical microscope), XRD (X-ray diffraction), and TGA (thermo gravimetric analysis). The results showed that high-temperature oxidation and high-temperature melting was the foremost corrosion’ mechanism; a momentary overheating temperature owing to improper operation is the root cause of premature failure of the support plate. The strong thermal resistance of the scale substances makes heat to accumulate on the surface of evaporator, and the corrosion will accelerate with the rising of temperature.Subsequently, the relevant corrosion failure mechanisms were deeply discussed, and both the effective pertinent countermeasures and the prevention measures were put forward as well. Based on this incident analysis, the initiating factors and prevention methods of potential failures of the steel supporting plates operating under similar service conditions were commanded, which would play an important role in safe and smooth operation of the whole evaporators in engineering applications.