Issues with the discharge pressure parameter in safety valve calculations

Thread Content

When calculating safety valves, there is a parameter called Pf, which is the discharge pressure. On 150, the discharge pressure (absolute pressure) of the relief device is indicated, which includes both the design pressure and the overpressure limit. On page 18 of 150, it is stated that the overpressure limit for containers should not exceed 10% of the design pressure, or the larger of the two values: 20 kPa. To give an example, the design pressure of the container is 1.5, while the set pressure of the safety valve is 1.45. Now there is a problem: according to the calculation guidelines provided by the engineers in the office for such safety valves, the discharge pressure is calculated as 1.1*1.45+0.1. My question is why 1.5 times the design pressure is not used, but rather 1.45 times the set pressure? Isn’t this different from what’s stated in the book? Another scenario involves a maximum allowable operating pressure. For example, if the design pressure of the container is 1.5, the maximum allowable operating pressure is 1.7, and the setting pressure of the safety valve is 1.6, then is my discharge pressure equal to 1.1*1.7+0.1 or 1.1*1.6+0.1? Because the book states that when the maximum allowable operating pressure is specified, it is possible to use the maximum allowable operating pressure of the container in place of the design pressure. I hope someone who knows about safety valves in computing can help me figure this out.