Help explain a sentence
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In the \"Regulations on Safety Inspection of Pressure Piping\", there is a statement that reads: \"For pipes subjected to external pressure, the test pressure shall be 1.5 times the difference between the designed internal and external pressures...\" What does \"subjected to external pressure\" mean in this context? Under what circumstances is external pressure tolerated? Please give me some advice.
Previously, it was specified as 1.5 times the operating pressure; now the specification is more precise, with external pressure generally referring to atmospheric pressure. Generally speaking, pressure pipes are subjected to internal pressure, meaning that the operating pressure is positive and greater than atmospheric pressure. The pressure inside a vacuum tube is lower than atmospheric pressure, so the tube is subjected to external pressure. The pressure acting on the pipe is the difference between the internal and external pressures. There is one issue that requires flexible handling here: whether your operating pressure is absolute pressure or gauge pressure. If it is absolute pressure, following the regulations is sufficient; but if it is gauge pressure, the external pressure cannot be deducted any further, otherwise the test pressure will become too low. One must thoroughly understand the procedures and grasp their meaning in order to apply them flexibly.
Such as heat exchanger equipment, which has a tube side and a shell side; the tube side is subjected to both internal and external pressures.
A more typical type of pipeline that is subjected to external pressure is a vacuum pipeline. After all, the heat exchange tubes in heat exchangers are generally considered as TUBES rather than PIPES, and are not regarded as pressure pipelines
When the pressure in the innermost layer of a sleeve pipe is lower than that in the interlayer
The pressure inside the tube is less than one atmosphere
In the case of a vacuum tube, the internal pressure is negative while the external pressure is positive; the absolute value of the pressure difference between the inside and outside is greater than both the internal and external pressures. Is that correct?