Pressure issues in pressure vessels
Thread Content
The pressure shown on the pressure gauge of a pressure vessel is the operating pressure, which is equal to or less than the allowable operating pressure and the monitoring pressure. The pressure indicated by the gauge is either the actual current pressure or the working pressure as specified in the standards, that is, the maximum working pressure that may occur during the use of the container. During the use of pressure vessels, what is the relationship between the normal gauge pressure and the operating pressure, working pressure, as well as the permitted/monitoring pressure levels? Is the setting pressure of the safety valve determined based on the normal gauge pressure during vessel operation, or rather on the operating pressure, working pressure, or permitted/monitoring pressure levels? In my opinion, under normal circumstances, the gauge pressure is usually < operating pressure ≤ working pressure ≤ allowable/monitoring pressure. The problem lies in the ambiguity regarding the selection of the set pressure for the safety valve. There are many opinions on this; one is to use the normal gauge pressure and then multiply it by 1.05 to 1.1, while another suggestion is to use the operating pressure or the working pressure.
During the operation of pressure vessels, the gauge pressure observed under normal conditions refers to the current pressure inside the vessel. Meanwhile, the operating pressure, service pressure, and permissible/monitored pressure range are all pressure limits determined according to design requirements. The pressure indicated on the pressure gauge represents the actual current pressure value. The setting pressure of the safety valve should be selected according to design requirements, and it usually depends on the maximum allowable operating pressure of the container. A common practice is to select a suitable safety valve in practical use based on the pressure level inside the container, and set its setting pressure at around 1.1 to 1.2 times the maximum allowable operating pressure of the container. It is important to ensure that the set pressure of the safety valve reliably protects the vessel from damage caused by accidental overpressure. .
Where do so many terms come from? Operating pressure refers to the highest pressure at the top during normal operation; for example, if the pressure within the normal operating range is between 2.3 and 2.4 Mpa, then the operating pressure is 2.4 Mpa. The setting pressure of the safety valve is determined based on the operating pressure, with a value of 1.05 to 1.1 times that amount (the 2011 version still specifies this value; the draft for comments has adjusted the range for calculating this setting pressure). The design pressure should be slightly greater than or equal to the setting pressure
Really, you’ll understand after working for a few more years; don’t take on management positions right from the start. For such a simple opening pressure, go to all this trouble.
Hahaha, I initially calculated it based on the working pressure, but they insisted on using gauge pressure. There are surely fluctuations during operation, which confused me, so I came to ask. I asked several people from other companies, and they all said that working pressure should be used, not the usual gauge pressure. The strength check is the same; they also use the normal gauge pressure indicated by the pressure gauge.
Do not mislead others; the setting pressure of the safety valve must not be higher than the design pressure (it should be noted that when the maximum allowable operating pressure is specified, it must not exceed that value)
This post was last edited by AtlantisH on 2023-6-8 09:07. Isn’t the gauge pressure usually the operating pressure? The working pressure indicated on the container’s nameplate refers to the highest pressure that may occur at the top of the container under normal conditions. There is no specific requirement regarding how the set pressure of a safety valve must be calculated. It is not considered non-compliant to determine it using other methods, provided that it does not exceed the design pressure. Specifically, when the maximum allowable working pressure is specified, the set pressure must not exceed this value; and when a monitored operating pressure is indicated following periodic inspections, it must not exceed that monitored operating pressure. Of course, people generally use the formulas recommended by the standards for calculations, with the working pressure serving as the basis for those calculations ； Some large companies or those with strong capabilities generally have their own regulations for projects, and calculations are carried out in accordance with these rules; of course, these rules are also based on the level of work pressure, though the coefficients are more specific. (For example, for pressures below 1.8 MPa, the coefficient is +0.18 MPa; for pressures between 1.8 and 4.0 MPa, the coefficient is 1.1; for pressures between 4.0 and 8.0 MPa, the coefficient is +0.4 MPa; and for pressures above 8.0 MPa, the coefficient is 1.05.) As long as the piping system connected to the container can handle the pressure and the safety valves do not activate frequently, that is sufficient. If the setting pressure of the safety valves is set too high, the design pressure will also have to be increased, which raises the manufacturing cost of the container.
How can you talk about work stress and gauge pressure together?