-Selection of calcium chloride saline pipelines at 20°C

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Dear experts: I am facing the challenge of selecting a suitable material for pipes used in calcium chloride solutions at -20°C, and I have the following questions: 1. In the design standards for petrochemical pipelines, it is specified that grade 20 steel can be used at temperatures ranging from -20°C to 425°C. However: For steel grades used in low-temperature pipelines with a design temperature of -20°C or lower, except those with a carbon content of less than or equal to 0.01% ； Furthermore, for standard chromium-nickel austenitic stainless steels, no low-temperature impact test is required when the material temperature is not lower than -196°C; all other materials must undergo a Charpy (V-notch) low-temperature impact test. The test requirements shall comply with the current provisions of GB150 for Steel Pressure Vessels. And: the carbon content of 20-grade steel is 0.2%. Taking all the above conditions into account, steel grade 20 is not suitable for use in calcium chloride saline delivery pipelines at -20°C. Has anyone used grade 20 steel as the material for such pipes? In actual use, will the pipes become brittle due to low temperatures? What is the lifespan? 2. The operating temperature for 16MnD (Q345D) is -40~350°C. However: the carbon content of (Q345D) is 0.17–0.23%, which also fails to meet the requirement that the carbon content be less than or equal to 0.01% ； Based on the comprehensive criteria for material selection, can’t 16MnD (Q345D) be used either? Is there something wrong with this standard? 3. In practical engineering applications, 16MnD (Q345D) is often used for low-temperature pipelines; however, if the standards are followed strictly, it seems not to meet those requirements, which is quite surprising. 4. Could everyone recommend what material should be chosen? I would appreciate it if the experts could answer each of these 4 questions one by one. Thank you! ! ! !