Understanding the provisions on hot fastening and cold fastening in GB-50235

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Section 4.2.12 of both GB-50235 \"Code for Construction of Industrial Metal Piping\" and SH3501-2001 \"Code for Construction and Acceptance of Piping Systems for Toxic and Flammable Media in the Petrochemical Industry\" contains the following provisions. The excerpt is provided below for reference. 4.2.12 During the trial operation of the piping system, the connection bolts of high-temperature or low-temperature pipes shall be tightened hot or cold in accordance with the following provisions: 1 The temperature at which the bolts are tightened hot or cold shall meet the requirements specified in Table 4.2.12 ； Table 4.2.12 Temperatures for hot and cold bolt tightening operations (°C) Operating temperature, Temperature for first hot/cold tightening, Temperature for second hot/cold tightening: 250–350, Operating temperature –, >350; 350, Operating temperature, -70–-29, Operating temperature –, <-70; -70, Operating temperature 2. Hot or cold tightening should be carried out after the tightening temperature has been maintained for 2 hours ； 3 When tightening the pipeline connection bolts, the maximum internal pressure of the pipeline shall comply with the following requirements: a) When the design pressure is less than 6 MPa, the maximum internal pressure during hot tightening shall be less than 0.3 MPa ； b) When the design pressure is greater than 6 MPa, the maximum internal pressure during hot tightening shall be less than 0.5 MPa ； c) Cold tightening should be performed after depressurization. 4 Safety technical measures must be in place for bolt tightening to ensure the safety of operators. In the red-colored section, the requirement regarding thermal tightening specifies that the maximum internal pressure should not exceed 0.3 MPa. Based on this, it seems that at the operating temperature the system’s maximum pressure must not go above 0.3 MPa. However, thermal tightening is usually carried out under normal operating conditions. Please share your thoughts – how do you carry out thermal tightening in your practice?