Dear forum member, where do the values for the design temperature of the pipes below come from?

The design temperature of a pipeline is usually based on the highest temperature that the pipeline material can withstand under specified operating conditions. The selection of the design temperature requires taking into account the highest temperatures that the pipeline may encounter during normal operation, startup, shutdown, or in case of failures, while also allowing for a certain safety margin. The temperature value table you provided may originate from a specific engineering standard or industry specification. Different ** and industries may have varying requirements and standards regarding the design temperature of pipelines. For example, ASME B31.3 is a process piping standard issued by the American Society of Mechanical Engineers, while GB 50251 is a piping design standard issued in China. These standards typically detail how to determine the design temperature based on different operating conditions and pipe materials. The design temperature settings specified in the above rules are applicable to the specific conditions and engineering requirements described in the specifications. - When the operating temperature is between -20°C and 0°C, the design temperature is the operating temperature minus 5°C, but it must not be lower than -20°C. - When the operating temperature is between 0°C and 100°C, the design temperature is set at 120°C, which provides a safe upper limit for normal operating temperatures. - When the operating temperature is between 100°C and 350°C, the design temperature is the operating temperature plus 20°C to account for thermal expansion and other factors. - When the operating temperature exceeds 350°C, the design temperature is determined by adding a factor to the operating temperature, with this factor typically ranging from 5°C to 15°C. If you need to know the specific sources of standards or the applicable regulations, you should consult **or industry standard documents related to your project in order to obtain the most accurate and compliant methods for determining design temperatures. .

There is a claim that 120 takes steam purging into account; I also think there’s something wrong with this, so I’m asking about its source