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Degradation: Any substance in contact with the container surface, whether organic or inorganic components, wastewater or fresh water, steam or air, can cause degradation on the container surface. The forms of degradation can be electrochemical, chemical, mechanical, or a combination of these three. Deterioration may be caused by temperature, stress, fatigue (including fatigue resulting from vibrations and pressure changes), impact, high-speed erosion, or turbulence. Corrosion is the main cause of material degradation in pressure vessels, and it can occur in any part of the vessel. The severity of degradation is influenced by the concentration of corrosive substances in the medium, temperature, properties, and the corrosion resistance of the material. The most common internal corrosion agents in refineries are sulfide and chloride compounds, caustic alkalis, inorganic acids, organic acids, water (especially water with a low pH), sediments, or loose corrosive chemicals; other chemicals used in specific processing operations can also cause corrosion of containers. For example, stress corrosion cracking caused by the combined effect of caustic alkalis and stress, severe graphitization corrosion, pore-type and interlayer zinc loss corrosion, deposit blockage, and corrosion beneath deposits. External corrosion, especially within the insulation layer, accelerates as humidity increases; this type of corrosion is also accelerated by pollutants present in the air environment. It is particularly prone to corrosion under the environmental conditions in industrial areas and coastal regions. Erosion refers to the loss of surface material caused by the scouring of solid particles or liquid droplets on a material surface; it often occurs at throttle points, where the flow direction changes, or in areas with high flow velocities resulting from turbulence. Typical erosion occurs at the nozzles at the inlets and outlets, internal pipelines, baffles or tray baffles, the vessel wall opposite the inlet nozzle, internal support plates, and the baffles subjected to impact. Changes in structure and composition: When pressure vessels operate under conditions that may cause changes in the material’s microstructure and metallographic structure, such changes often affect the mechanical properties of the metal and can lead to cracks or other forms of degradation. Microstructural changes can be caused by errors in heating and cooling the metal, as well as by changes in the metal’s chemical composition. Examples of these changes include graphitization, hydrogen embrittlement, carbon compound precipitation, intergranular corrosion, and embrittlement.