Verification of external pressure stability for the hemispherical head at the floating head end of a floating head heat exchanger
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Regarding the external pressure stability verification of the hemispherical head at the floating head end of floating head heat exchangers, I believe it should be divided into two operating conditions: 1. Under operational conditions, the stability verification should be carried out using the design pressure of the shell side as the external pressure (assuming that the pressure on the tube side is 0)； 2. Verification of external pressure stability under hydrostatic test conditions. Our calculation software does not include a check for external pressure stability during hydrostatic testing, and the examples provided in the interpretation of GB151-1999 standard also do not cover this condition. I’d like to hear everyone’s opinions on this issue.
In my opinion, since the duration of the hydrostatic test is very short, it is not necessary to conduct a stability check on the external pressure under this condition; it is sufficient to perform only a stability check on the external pressure under operational conditions.
The hydrostatic test conditions do need to be taken into account; otherwise, the head may become unstable. If possible, use SW6 for verification; the design temperature should be the pressure test temperature, with a corrosion margin of zero.
I agree with the original poster’s view; stability verification should be carried out under the conditions of a hydrostatic test.
Instability often occurs in an instant; if the rigidity of the spherical head at the floating head end is insufficient, instability can still occur during the hydrostatic test. Therefore, during a hydrostatic test, it is necessary to perform an external pressure check on the spherical head at the floating head end. GB151 states that for spherical dome heads, external pressure calculations shall be carried out in accordance with GB150; when performing these calculations, the pressure Pc used should take into account the maximum pressure difference between various pressure chambers.