The issue of calculating the minimum pressure retention value to prevent the inner cylinder from becoming unstable during the jacket hydrostatic test
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This post was last edited by yechao25038 on 2019-4-2 at 16:06. If the inner cylinder becomes unstable during the jacket hydrostatic test, is the minimum pressure that can be maintained in the inner cylinder equal to the allowable external pressure for the inner cylinder minus the value resulting from the jacket hydrostatic test? As shown in the figure below (entered arbitrarily), the allowable external pressure for the inner cylinder is 0.8482, while the hydrostatic test value for the jacket is 1.0; the software indicates that the inner cylinder must maintain a pressure of at least 0.152. 0.152+0.8482≈1.0, right? It’s just as I thought. Now, looking at the calculations below (the calculation sheet has been uploaded): the allowable external pressure for the inner cylinder is 0.8548, while the allowable pressure for the inner cylinder’s head is 0.72. The pressure value required for the jacket’s hydrostatic test is 0.875. The software indicates that a pressure of at least 0.094 is necessary for the inner cylinder’s head in order to prevent instability of the inner cylinder itself. So the question is: since the allowable external pressure for the inner cylinder, which is 0.8548, is lower than the value required for the jacket’s hydrostatic test, how can it still pass the verification? The pressure retention of the inner cylinder head is 0.094 + 0.72 = 0.814, which is also less than the value obtained from the jacket hydrostatic test. Everyone, take a look at what’s going on here Is it the software, or is there something wrong with my understanding? Edit: I was confused. The temperature during the test was different from the design temperature~~ Haha, I get it now
The formulas for calculating internal and external pressures are different from those used for pressure test verification; under internal and external pressures, the stress must be less than the allowable stress, while under pressure testing it must be less than 0.9ReL. Simple comparison of pressure addition and subtraction is not accurate
This post was last edited by yechao25038 on 2019-4-2 at 14:34. Thank you, I understand now. The difference in temperature between the hydrostatic test and the design conditions was ignored. Haha, my head can’t keep up. Haha, struggling since this morning until now: lol
In the calculation of external pressure, for oblong cylinders, it is the elastic modulus of the material that affects the allowable external pressure due to temperature changes; it has nothing to do with the allowable stress.
Mm-hmm. At first, I thought the allowable stress would be the same, so the external pressure calculation should also be the same. I finally understand now: lol