Problems with shell-and-tube waste heat boilers

Some manufacturers install expansion joints regardless of whether the linear expansion coefficients of the materials used for the heat exchange tubes and the shell are similar. Is it reasonable? I’m not familiar with this type of equipment; I hope experts can offer some guidance!

I’m not familiar with the first two, so I can only give a brief explanation. 1. The shell temperature can be calculated based on the water temperature, from which the degree of shell expansion can be determined. By taking into account the temperature drop of the flue gas, an integral can be calculated to determine the expansion amount in the tube side. If the two expansion amounts are similar, that’s fine; but if there is a large difference, the data must be used to convince the client. 2. SH refers to petrochemical standards, while GB refers to national standards. All standards specify their scope of application, so it’s important to read them carefully. Just because the operating pressure falls within the specified range doesn’t mean the standard applies. I’m familiar with the third one, so I can elaborate more on it. 3. First, I recommend that you look at the construction drawings for the refractory material used in the high-temperature end seal of shell-and-tube waste heat boilers – this will help in convincing the client. There are two main reasons for using corundum sleeves here: firstly, to protect the welds. If no corundum sleeves are used at the ends of the pipes, the flue gas will directly affect the welds between the pipes and the orifice plates. Since these are pressure vessels with high internal pressures, this can easily lead to weld failure. Once a weld fails, leakage can occur, forcing the entire boiler to be shut down urgently; in severe cases, the boiler may even become unusable. The corundum sleeve protects the initial section near the weld, preventing wind from reaching that area; thus, even if the pipe warms up and deforms in certain areas, it won’t have a significant impact. Additionally, the coefficients of thermal expansion of refractory materials and metals differ greatly. When refractory materials are placed directly on the orifice plate, at the locations where holes are present in the pipe, a boundary layer between metal and refractory material forms. Due to these differences in thermal expansion, gaps can appear at high temperatures, allowing hot smoke and air to penetrate and damage the surface of the orifice plate or blow away the refractory material on its surface. The coefficient of thermal expansion of the corundum sleeve is the same as that of refractory materials. By installing the corundum tube and then covering it with refractory materials, the orifice plate can be protected from air leakage, provided that the construction meets the required standards. For a boiler that costs several million, it’s really not worth putting it at risk of being scrapped just because of corundum sleeves that cost only tens of thousands of dollars.