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The design temperature T of a pipeline refers to the temperature of the pipeline material that it may reach under the corresponding design pressure during normal operation. The professionals in the process system select the pipeline design temperature based on the operating temperatures under various conditions during normal operation, as provided by the chemical process specialists, following the \"pressure-temperature combination under the most severe conditions\". The pipe design temperature proposed by the process systems team (in this section, it refers to the highest operating temperature of the medium in the pipe) can be determined in accordance with the following principles. ①The pipe wall temperature at the highest operating temperature of the medium, as determined through heat transfer calculations or actual measurements, is used as the design temperature. ②In situations where heat transfer calculations or actual measurement of the tube wall temperature are not feasible, the positive value of E is used as the highest (or lowest) operating temperature of the fluid during the process, and this value serves as the design temperature for the pipeline. a. Metal pipes i. Uninsulated pipes with a medium temperature of less than 38°C, T = maximum medium temperature. ⅱ. For pipes with a medium temperature of not less than 38°C, T = 95% of the maximum medium temperature. Ⅲ. External insulated pipe, T = maximum temperature of the medium. Ⅳ. Internal insulated pipe (lined with insulating material), T = wall temperature calculated for heat transfer or the wall temperature measured experimentally. V: The medium temperature is not greater than 0°C, where T is the lowest temperature of the medium. b. Non-metallic pipes and metal pipes with non-metallic linings: i. Pipes not affected by ambient temperature, T = highest temperature of the medium; ii. Pipes installed in an environment where the ambient temperature is higher than the highest temperature of the medium (except those for which protective measures have been taken), T = ambient temperature. ③For the normal operating conditions specified in the chemical engineering process field, the design temperature is determined by taking the normal temperature of the medium plus (or minus) a certain margin; it can be calculated using the following formula: a. When the normal operating temperature of the medium is between 0 and 300°C, T ≥ Normal operating temperature of the medium + 30°C. b. When the normal operating temperature of the medium is greater than 300°C, T ≥ Normal operating temperature of the medium + 15°C. ④When the temperature of the fluid medium approaches the upper limit of the operating temperature permitted for the selected material, the design temperature should be chosen carefully based on the specific circumstances, in order to avoid increased costs or reduced safety. For example, if the calculations outlined in point ③ above require the use of a higher-grade material, from an economic perspective it is permissible to reduce the additional 15°C allowance as specified by the engineering requirements; however, measures must be put in place to ensure that the temperature does not exceed the allowed limits during operation. ⑤When there are various conditions or periodic changes in working pressure and corresponding operating temperature, process system designers should list all the condition data provided by the chemical process specialists and provide explanations to the pipeline material specialists.