If the pipe wall has ventilation openings, is it still necessary to install a breathing valve on the top of the tank?

Sorry, I mistakenly wrote “tube wall” instead of “tank wall” in the title.

I’m not entirely sure; I’ve seen it as well. It seems that the vent window is primarily used for ventilation and allowing excess gas to escape. The breathing valve and flame arrester, when used together, serve a certain purpose. If the vent window could completely replace the breathing valve, then there would indeed be no need to install a breathing valve at all! I’m an amateur too

A breathing valve prevents accidents caused by sudden overpressure or vacuum inside the tank due to accidental events, which could otherwise lead to damage to the tank; it also serves a safety and fire prevention function, acting as a device to protect the tank. In internal floating roof tanks, the internal floating disk covers the oil surface, thereby virtually eliminating the gas space, so evaporation losses are minimal. As a result, no mechanical breathing valves or safety valves are required on the top of such tanks. However, in practice, leaks of oil and gas still occur at the ring gaps on the floating roof or at other joints of attachments. To prevent the accumulation of oil and gas to dangerous levels, ventilation holes are provided on both the top and sides of the oil tank.

Vent hole: In storage tanks with internal floating roofs, the oil level is completely covered by the internal floating disk; therefore, no breather valve is installed on the tank top. However, in practical use, oil and gas still leak from the annular gaps or joints between other components; to prevent the accumulation of oil and gas, ventilation holes are provided around the tank top and tank walls. The vent on the top of the tank is installed in the middle of the tank’s roof; it has a rain cover and a metal mesh inside. The vent holes in the tank wall are installed around the topmost layer of the tank wall, at a distance of 700 mm from the top edge. The circumferential spacing between each hole should not exceed 10 m; each oil tank should have at least 4 such holes, arranged symmetrically. A metal protective cover is installed at each ventilation opening ； It also serves as an overflow function when the oil storage level is excessively high and the automatic alarm system fails. The phenomenon you mentioned basically does not exist in internal floating roof tanks

A breathing valve is installed to prevent the negative or positive pressure inside a storage tank from exceeding certain limits; it must activate under conditions of negative or positive pressure. If vents are provided on the tank walls, the pressure inside the tank is balanced with that of the atmosphere, and the breathing valve then becomes ineffective

Adding a breather valve to a tank that already has vents is unnecessary!

You might have misseen it; some internal floating roofs are equipped with a nitrogen seal, and they don’t have ventilation holes around them, which is why a breathing valve is used

Vent holes are provided around the walls of internal floating roof tanks; in addition, a rain cover similar to a vent valve is usually installed on the tank top, with a metal mesh inside that serves as a fire barrier. In fact, installing a breathable rain cover on the top of the tank is not unnecessary; it serves to create a convective environment for the gases inside the tank, by allowing ventilation through the vents in the tank walls, taking into account changes in temperature and differences in height. This enables the gases accumulated inside the tank to be discharged outside through convection.

The original poster might have misunderstood; what appears to have a semicircular dome on top of the tank is actually just a ventilation hole equipped with a rain cover, and it’s not a breathing valve, although it does look similar. A floating roof tank with ventilation windows on its side walls will absolutely not be equipped with a breather valve, as it serves no purpose; even if the design team lost their sense common sense, they wouldn’t do such a thing.

So, for an internal floating roof tank with six vent windows on its side walls, and a naphtha tank with a capacity of 3,000 cubic meters, is it still necessary to use a nitrogen blanketing system?

For pure internal floating roof tanks, a breather valve is not required on the tank top that has ventilation windows in its wall； However, storage tanks with internal floating roofs and nitrogen seals should be equipped with breather valves as well as emergency pressure relief manholes!

The storage tanks designed for the irrigation system in our factory were probably the result of the designer’s poor judgment; such tanks have a breathing valve on their roofs as well.

If there is already a ventilation window, there’s no need to add a breathing valve anymore, as the breathing valve would then be completely ineffective. By the way, if the tank wall has ventilation windows, is it necessary to seal those windows when installing a nitrogen seal? Is it essential to change the ventilation openings on the top of the tank into breather valves?

If a nitrogen seal is to be applied in the modification of an internal floating roof with ventilation windows, those ventilation windows must be sealed; otherwise, the positive-pressure nitrogen will leak into the atmosphere, and the nitrogen seal function will not be achieved. Similarly, the ventilation openings on the filling port should also be sealed or replaced with breather valves. With a nitrogen seal in place, a vent valve or pressure relief valve must be installed

The lighting openings are usually closed and are only opened during inspection and maintenance for lighting and ventilation purposes.

The internal floating roofs I’ve come across have breather valves equipped with flame arresters.