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Corrosion protection design refers to the measures taken during the design phase to prevent corrosion. These include the proper selection of materials, analysis of material properties, cost estimation, requirements for material and corrosion testing, verification that the structural strength meets corrosion protection standards, ensuring that the shape of structures and components is suitable for corrosion resistance, selection of appropriate manufacturing methods for the materials, measures to prevent changes in the material properties during operation, consideration of potential corrosion or damage to the materials, as well as determining the expected lifespan during the design phase and the maintainability of the device. Material selection: Since pressure vessels are generally in contact with various corrosive chemical media, and there are many such media, the corrosion behavior varies depending on factors such as temperature, concentration, and pressure. If the materials are not selected properly, it has a significant impact on performance, particularly in terms of the device’s long operational life, safe operation, and issues related to leaks. Therefore, it is very important to establish the right balance in the design – ensuring that the initial investment does not increase significantly, while at the same time preventing frequent unplanned shutdowns due to corrosion issues after operation begins, as well as avoiding costly repairs and replacements. This requires careful consideration by equipment designers, along with comparative analysis of various options, in order to achieve this goal. When using corrosion prevention techniques such as equipment lining, coatings, composite materials, electrochemical protection, or corrosion inhibitors, the design must select appropriate anti-corrosion measures based on the properties of the medium, temperature, concentration, pressure, flow rate, and structure. Of course, the economic viability of various methods also needs to be taken into account. Corrosion-resistant structural design: Among all the aspects of corrosion control, the structural design of equipment is a crucial element, its importance possibly second only to the choice of materials. A reasonable structural design can not only fully utilize the corrosion resistance of the material but also compensate for any deficiencies in its inherent properties. Many types of local corrosion, such as erosion corrosion, abration, cavitation corrosion, galvanic corrosion, crevice corrosion, etc., are caused by unreasonable structural design or are related to it. Equally important is the fact that these local corrosion problems can be effectively and economically resolved most easily through proper structural design improvements. A reasonable structural design includes two basic requirements: on one hand, it is necessary to eliminate or minimize irregularities in the design and the surrounding environment as much as possible ； On the other hand, it is necessary to consider what anti-corrosion techniques to use at the design stage and to create the conditions for implementing these techniques. The specific requirements for the design of anti-corrosion structures are as follows: ① Avoid stress concentration. Ensuring as uniform a stress distribution as possible is one of the basic requirements in structural design. The uneven stress distribution increases the likelihood of the formation of corrosion cells; the areas with stress concentration often become the anode of these corrosion cells, thereby exacerbating corrosion. Worse still, in certain environments, high stress can also lead to stress corrosion cracking (static) and corrosion fatigue (alternating). Therefore, the structure is required to be as simple as possible, with a surface that is uniform, smooth, and clean. The shape of the components should be streamlined, with the largest possible radius of curvature. Try to avoid cuts, sudden changes in cross-section, sharp edges, grooves, etc ； Alternatively, these uneven areas can be placed in low-stress regions and appropriate measures can be taken, such as using rounded transitions or filling in internal corners. If gaps are unavoidable, they can sometimes be welded shut or appropriately enlarged to prevent geometric conditions that lead to closure, thereby avoiding gap corrosion. ②Avoid liquid accumulation. This is not only because liquids are generally more corrosive than gases, but also because the accumulation of liquids leads to the concentration of corrosive substances and the formation of dirt. The design of the equipment should facilitate the flow of water, with drainage holes provided in areas where water may accumulate. The internal shape of storage tanks and containers should facilitate liquid discharge. The inside of the pipeline system should be streamlined, with an appropriate inclination downstream to ensure smooth flow. ③Avoid the formation of turbulence, vortices, and fluid impacts. In a flow system, the flow velocity should be appropriate; the flow direction and cross-sectional area must not change suddenly, and obstacles to the flow should be minimized as much as possible. The air flow and liquid flow should not strike the vessel walls directly. Bubbles and solid suspended particles entrained in liquids, as well as liquid droplets entrained in gases, all increase the intensity of wear and corrosion; therefore, measures for separation and removal should be considered. If turbulence and impact are inevitable, measures such as increasing the thickness of the components subjected to impact, upgrading the local materials, installing baffles, and enlarging the flow area can be considered. ④Avoid local overheating. An increase in temperature generally increases the corrosion rate of materials, and in some cases can lead to rapid corrosion damage. On the other hand, for high-temperature gases, it is necessary to prevent the formation of \"cold spots\" in certain parts of the equipment, which requires special attention during the design of the equipment’s insulation. ⑤Prevent liquid from flowing along the vessel walls and from splashing, which could lead to increased local concentrations. Uneven concentration can lead to intensified local corrosion conditions. The feed pipe extending into the container must be at a sufficient distance from the housing. The distance from the liquid surface should be very small, or it should be inserted into the solution. ⑥Avoid the formation of a gas-liquid interface in shell-and-tube heat exchangers. Here, concentration of harmful substances, uneven temperature, and erosion by corrosive gases can easily occur. For the cooler, the liquid level should be raised to fully submerge the tube bundle ； For reboilers, the volume of the gas phase space should be increased appropriately to reduce the gas flow rate and thereby alleviate the corrosion conditions. The gap at the junction of the tubes and the tube sheet in shell-and-tube heat exchangers is also a common problem. Expanding joints are commonly used between tubes and tube sheets, but this creates many gaps ； Expansion welding can prevent gaps from forming on the tube side, but gaps still exist on the shell side ； Deep-hole seal welding yields excellent results, but it is difficult to manufacture and costly. ⑦Regarding corrosion fatigue and stress corrosion issues, the results of analytical design can be utilized to reduce the actual stress levels in the equipment, enabling it to operate under low-stress conditions. Increasing the thickness of the load-bearing element always reduces its actual stress level.