Question: Under high vacuum, can air outside the storage tank penetrate through the tank wall and enter the tank?

There are very strict standards for the design, manufacturing, and inspection of pressure vessels; if everything meets these standards, then there are no issues of the kind mentioned.

The tank body should be divided into separate zones; air cannot pass through the steel material of the tank body itself； However, for the welded joints, threads, flanges, or other connection points of the tank, air may pass through. For equipment with high requirements for airtightness, leak tests are generally conducted. As long as the leakage test at the corresponding level passes, the above problems will not occur.

Reply to 3# 6mkl: Bubbles forming in flanges, welds, and similar areas is due to gaps at the connection points as well as molecular gaps within the material structure at the welded areas. Whether gas can pass through the material depends on its gas permeability. I’m wondering where I can find information regarding the gas permeability of materials such as carbon steel (The requirement for vacuum level is very high; attention must be paid to the breathability of the material as well as any bubbles within it. Please provide your answers! ）

Reply to 3# 6mkl: Additionally, the current airtightness tests, as well as inspections and evaluations, are rather crude and based on visual checks; in my opinion, they do not take into account the gas permeability of the container materials!

Ammonia leak detection, halogen leak detection, and helium leak detection can be used; these gases all have high permeability. Ammonia leak detection is carried out using pH test strips ； Halogen leak detection and helium leak detection are both performed using instruments. Please refer to these standards……

Does outside air enter the tank through the steel? I have never heard of such a precedent; aside from leaks at the weld joints and sealing surfaces, the base material itself cannot allow air to pass through, otherwise storing tanks containing extremely hazardous substances would be dangerous. Furthermore, I personally believe that it is unlikely for air from pores in the steel to leak into the tank. Under high temperature and pressure conditions, hydrogen atoms may penetrate the steel and gather to form high-pressure bubbles. The negative pressure in vacuum equipment certainly cannot be higher than the positive pressure in hydrogenation units, nor will the temperature be that high. I have heard that hydrogen has a high solubility in steel at high temperatures and a low solubility at low temperatures; if the temperature drops while pressure remains high, hydrogen will escape from the steel and cause bulging. I have never heard of pores in steel escaping into the tank due to vacuum. And as mentioned by the person on floor 6, helium has the highest permeability, which is why it is used for leak detection tests where the highest level of airtightness is required. Its air permeability is much lower than that of He, H, and NH3. The above are purely my personal guesses; please feel free to correct me

Reply to 7# realben: First of all, thank you for your comment; I think it’s very reasonable! Secondly, I would like to point out that, still taking carbon steel as an example, its internal crystal structure does indeed contain voids, and theoretically, permeability does exist. Moreover, since the structure of steel is not uniform, there are areas where the gaps are quite large; this situation should indeed occur. The conditions required for this to happen are high pressure and high temperature, but to what extent should these temperatures and pressures be?

Reply to 8# miaotao1984: By penetration, I mean the infiltration of hydrogen into the steel at high temperatures in the hydrogenation unit, as well as the release of hydrogen after cooling, which leads to the formation of bubbles between the grains. It does not mean that hydrogen can penetrate through the steel and leak outside the tank; in my opinion, that is unlikely, and I have never heard of any such cases. However, I cannot assert anything definite about exactly how this process works.

It’s impossible; I’ve operated a Roots vacuum pump that achieved a vacuum level of nearly -0.1 Mpa

The requirement for vacuum level is very high, with a maximum of –0.1 MPa. One should not assume that hydrogen embrittlement, which occurs under high pressures of 10 MPa and temperatures above 300 degrees Celsius, can also occur in a vacuum.