Maximum allowable working pressure of liquefied petroleum gas storage tanks
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This post was last edited by yangkangning on 2019-5-5 10:29. The design pressure of the liquefied petroleum gas storage tank is 1.77, MPa. The medium is moderately hazardous and explosive. It is a Category III low and medium pressure vessel. The equipment is equipped with a safety valve and requires a pressure test and an air tightness test. The maximum allowable working pressure is marked on the drawings and product nameplate. Therefore, the maximum allowable working pressure of each part needs to be calculated in the strength calculation book, and then the minimum value is taken to determine the maximum allowable working pressure of the container. An interesting problem was discovered during recent work - the maximum allowable working pressure value given in the strength calculation book for individual containers (taking the minimum value of each part) is inconsistent with the maximum allowable working pressure in the technical parameter column of the drawing. The maximum allowable working pressure value in the technical parameter column of the drawing is lower than the maximum allowable working pressure value in the strength calculation book. Is this design reasonable? Why?
I am not a designer. I discovered it at work and communicated with the designers. I have two opinions.: Some designers believe that the maximum allowable working pressure in the technical parameter column on the drawing should be consistent with the maximum allowable working pressure in the strength calculation book, for example: After calculation, the minimum value taken from each part is 1.92MPa. Then, the maximum allowable working pressure in the technical parameter column of the drawing should be marked as 1.92MPa. ； Another group of designers believe that the maximum allowable working pressure in the strength calculation book should be between the design pressure and the maximum allowable working pressure value calculated in the calculation book (the minimum value is taken after each part is calculated separately), that is, between 1.77MPa~1.92MPa, for example, 1.83MPa (considering that the safety valve opening pressure deviation does not exceed ±3%, 1.77×1.03≈1.83MPa). I ask my seniors for advice on how to consider this issue correctly.
The concept is confusing. First, our country's software SW6 does not have the ability to calculate MAWP and cannot give accurate MAWP. Second, assuming that the software can calculate it, the software takes a small value and marks it on the drawing. The drawing should be consistent with the calculation book. The safety valve set pressure and MAWP should be separated. You are right to consider the deviation, but the method of handling it is wrong.
Liquefied petroleum gas storage tanks are equipment that require the maximum allowable working pressure to be marked in the technical parameter column of the drawing.
The MAWP takes the lowest value of the reinforcement of each component and opening as the MAWP of the entire equipment. Have you calculated the reinforcement of the connection? See attachment
Back calculation and verification are required, especially for non-standard parts.
You can directly determine a maximum allowable working pressure (greater than the set pressure of the safety valve), and perform strength calculations and opening reinforcement calculations based on this.
We calculate based on the maximum allowable working pressure, including reinforcement calculations. This will ensure that the material strength is up to standard.
Under the rule design, only the effective wall thickness can be used and the pitch diameter formula can be used to back-calculate the MAWP of the rotating shell components that bear primary overall film stress, such as convex heads, shells, and circular nozzles. The minimum MAWP value of these components is taken as the MAWP of the entire container. This MAWP is then used to calculate components or parts with bending stress and edge effects, and determine their thickness. Such as flanges, flat heads, openings and reinforcements.
Generally speaking, we are not willing to take this risk. Our usual approach is to take the design pressure as the maximum allowable working pressure. The leak test does not require an air tightness test, but uses ammonia leak testing to avoid this pressure problem.