The issue of temperature and frequency for cold, hot, and tight treatments
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The procedure states: heat-tighten once at temperatures below 350 degrees Celsius, and twice at higher temperatures. We have a major maintenance session next month, and the management requires three thermal tightening steps: at 150, 250, and 350. Are there any regulations or standards regarding the cold and hot tightening temperatures for equipment pipelines at the start of construction?
Generally, when the operating temperature is between 250 degrees and 350 degrees, heat tightening is performed once; when it is above 350 degrees but below 250 degrees, heat tightening is carried out once as well, followed by another round of heat tightening. The requirements for heat and cold tightening are specified in Table 7 on page 8 of standard SH3501-2002； Table 6.3.10 on page 16 of GB50235-1997 also has it
GB50235: Operating temperature of pipes, primary hot and cold tightening temperatures, secondary hot and cold tightening temperatures – 250～; Operating temperature –——— Above 350: 350; Operating temperature –20~－70: Operating temperature ———— Below –70: –70; Operating temperature