Aluminum pipes are used for pipelines carrying 97% concentrated nitric acid. What standards should be followed for selecting the pipe diameter, flanges, and gaskets?

You can download this abstract from Baidu; it’s paid, but if you really need it, you don’t have to worry about the cost

The best stainless steel materials and equipment available at present for resisting corrosion by concentrated nitric acid are as follows: 1. High-purity aluminum; 2. High-silicon iron; 3. Teflon; 4. Special high-silicon stainless steel. Among these materials, high-purity aluminum exhibits excellent resistance to corrosion by concentrated nitric acid at room temperature; however, problems often arise in the welds of equipment made from this material. In particular, the welds used in pipelines for transporting concentrated nitric acid are most prone to issues, as the quality of these welds cannot be guaranteed during on-site construction. This is a problem that many users of nitric acid frequently encounter. Secondly, when the temperature of concentrated nitric acid exceeds 40°C, high-purity aluminum is significantly susceptible to corrosion by it. High-silicon iron exhibits excellent resistance to corrosion by concentrated nitric acid at various temperatures. However, due to its fragile nature, it has poor mechanical properties, which hinders its use in equipment designed for handling concentrated nitric acid. Tetrafluoride is also resistant to corrosion by concentrated acids at various temperatures; however, it has certain drawbacks due to its properties, such as relatively soft mechanical strength and susceptibility to aging. These also limit its use in nitric acid equipment. Currently, it is mainly used for mechanical seals and gaskets. Made with its equipment, the performance is not very good. Among these materials, special high-silicon stainless steel has the best overall resistance to corrosion by concentrated nitric acid. Its corrosion resistance is superior to that of high-purity aluminum, and it is similar to that of high-silicon iron; moreover, its mechanical strength and machinability are beyond comparison with those of high-purity aluminum and high-silicon iron. This material is relatively expensive, requiring a high initial investment, but it has good corrosion resistance and a long service life. It has good mechanical properties, a high safety factor during use, and is easy to maintain; this allows for minimal or no downtime in production, thereby improving the efficiency of the entire production line. Taking all the above factors into account, the overall operating cost of special high-silicon stainless steel is relatively low. Therefore, at present, the special high-silicon stainless steel has the best corrosion resistance to concentrated nitric acid.

What process requires such a high concentration of nitric acid? Is it the fueling line for rocket propellant?

Pipelines and fittings are made of high-silicon austenitic stainless steel (00Cr14Ni14Si4), known as C4 steel (also called KY704), while gaskets are made of tetrafluoro material.