Cold tightening, hot tightening, loose-cold, loose-hot of pipes
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I saw a sentence in the regulations that says, \"Cold tightening can be carried out when it is necessary to reduce the thrust and torque exerted by the pipeline on the equipment during its initial operation.\" What does this sentence mean? What exactly is pipeline cold tightening, hot tightening, loose-cold tightening, and loose-hot tightening? What are their respective functions?
Cold tightening can reduce the thrust and torque exerted by the pipeline on the connecting devices or fixing points during operation, thereby preventing leaks caused by excessive bending moments at the flange connections. Cold tightening is a method that concentrates part of the thermal strain of a pipe in the cold state, thereby inducing an initial displacement and initial stress in the pipe during installation (in the cold state). When the cold tightening ratios of the pipeline in the X, y, and Z coordinate directions are different, the cold tightening value for each direction should be calculated based on the cold tightening in that specific direction. When there are several cold tightening points on the pipeline, the cold tightening values in the X, Y, and Z coordinate directions are respectively the algebraic sum of the cold tightening values of each point in those corresponding coordinate directions. When cold straining is used for pipes, the effective coefficient for hot-state cold straining is 2/3, and it is 1 for cold-state straining. Pipes connecting rotating equipment should not be tightened cold. The cold tightening ratio is the ratio of the cold tightening value to the total compensation amount. For pipes in which the material operates at the positive transformation temperature, the cold shrinkage ratio should be set at 0.7. For pipes in which the material operates at temperatures below the creep temperature, a cold tightening ratio of 0.5 is advisable. The remaining terms seem to have no relation to pipe stress.
Thank you for the reply from above; it was very helpful, ^_^ I’m new to this field and there’s still a lot I don’t understand. What do you mean by \"total compensation amount\"? Does it refer to the thermal displacement of the pipes? How should the effective coefficients for cold tightening in hot and cold conditions be interpreted? For example, does it mean that if I perform cold tightening by 1 meter, it can only compensate for a displacement of 0.7 meters in the pipeline?
In simple terms, the total compensation amount refers to the overall deformation from the installed state to the operating state； The effective cold tightening coefficient refers to the ratio of the actual effective cold tightening value to the theoretical cold tightening value.