Does the maximum allowable pressure include negative pressure?
Thread Content
I recently encountered a controversial issue: is the maximum allowable pressure included negative pressure? If the device experiences -0.1 and positive pressure, should -0.1 be listed as the maximum allowable operating pressure in the parameter table? Is there any basis if I want to write something?
It is necessary; this maximum allowable operating pressure includes both the maximum positive pressure and the maximum negative pressure. Generally, tanks are under positive pressure, so only the parameters related to positive pressure apply.
Is there any evidence? I can’t persuade my colleagues right now. ;P
-0.1 is used as the design pressure parameter
Why is there a maximum allowable operating pressure? Simply put, one must not exceed this level of stress at work. To put it more directly, how can we ensure that this stress level is not exceeded? Definitely, things like safety valve rupture discs are used to ensure that. The negative pressure has been set to 0.1; so how can it exceed this value in the case of a single-layer container? For the entire device, safety valves are installed only to handle positive pressure, and no safety valves are provided for negative pressure... If it’s a single-layer container with a pressure of -0.1, it makes no sense to specify a maximum negative pressure value
It seems there’s no way to directly achieve a pressure of -0.1 at the moment, right?
Regarding this issue of negative pressure, it was already indicated indirectly when determining the design pressure or calculated pressure for 150 and larger capacity ratings – that the negative pressure will not exceed 0.1 (for vacuum vessels). Therefore, specifying a maximum value for negative pressure is meaningless; of course, it’s not wrong to include such a value either……
The maximum allowable operating pressure is specified in order to enable the installation of safety devices; the pressure released plus any deviations must not exceed this maximum allowable operating pressure, but it must be higher than the design pressure in order to ensure airtightness……
From a large-scale perspective, indeed the maximum allowable operating pressure is set merely to ensure airtightness
The maximum allowable working pressure (MAWP), as defined in GB150, is the maximum load that can be sustained by the effective thickness of all pressure-bearing components, with the lower value being taken. In other words, the maximum allowable pressure (MAWP) is determined by using the effective thickness of each component; the MAWPs of all components are then compared, and the lowest value is taken as the MAWP for that equipment. The difference is that TSG21 requires that the MAWP be calculated when ensuring airtightness (or at the user’s request, in which case it’s likely that the user wants to use the equipment beyond its specified limits), while under normal circumstances it’s optional not to calculate it, in which case the default MAWP is the design pressure. In terms of design, calculating the MAWP is also useful; if there is a large difference in the MAWP of various components, then the design is either unreasonable or uneconomical. ASME believes it is reasonable to use the MAWP of main components such as the cylinder as the limiting value; in other words, the MAWP of other components needs to be higher than that of the cylinder. Therefore, many experienced engineers add an additional reinforcement ring to the calculation results for a properly reinforced opening, or they increase the wall thickness by one grade. This is the reason why.