In many applications, these tanks must also comply with strict hygienic standards to prevent contamination and maintain product integrity. Typically constructed from stainless steel with sanitary finishes, atmospheric tanks are engineered with an emphasis on cleanliness, smooth internal surfaces, and configurations that enable effective cleaning or sterilization.
Because they are not subjected to significant internal pressure, atmospheric tanks are not subject to the same stringent requirements as pressure vessels, which are designed to handle fluids at pressures significantly above or below atmospheric levels.
By comparison, a pressure vessel certified to American Society Of Mechanical Engineers (ASME) is generally required for pressures above 15 psi (1 bar), or 0.5 barg and higher under European Pressure Equipment Directive (PED) regulations. Atmospheric tanks typically operate at pressures no greater than 1 psi (0.07 barg).
Nonetheless, pressure remains a critical factor. Even at low levels, atmospheric tanks must be equipped with proper venting systems to prevent excessive vacuum or overpressure that can arise from temperature fluctuations or during filling and emptying cycles. Without proper venting, a tank can collapse under vacuum or rupture due to overpressure.
Even normal ambient temperature variations, particularly in vessels installed outdoors or exposed to daily temperature cycles, can cause significant changes in internal pressure. Although many fluids are stable under atmospheric pressure, when placed in a closed container even normal fluctuations in ambient temperature or equipment operation can generate overpressure (as temperature rises) or vacuum (as temperature falls).
Safety concerns extend to fire prevention and vapor control, particularly when flammable or volatile liquids are stored. Standards such as NFPA 30, published by the National Fire Protection Association, specify requirements for the safe storage of combustible and flammable liquids in atmospheric tanks.
A fire case addresses the danger of a pressure build-up in a tank or vessel caused by an external fire. The heat from the fire raises the temperature of the tank shell and its contents, causing the liquid to expand and vaporize. This increases internal pressure, which, if not relieved, can rupture the tank.
To prevent structural failure, the tank must include emergency pressure relief sized for fire exposure conditions. API 2000 provides detailed formulas for determining the required emergency venting capacity. The goal is to release vapor fast enough to prevent the internal pressure from exceeding the tank’s design limits during a fire.
“Once a low-pressure-rated vessel or tank is sealed, it is necessary to provide protection against both overfilling, rapid emptying which can lead to vacuum, and exposure to external fire. In a fire case, internal pressure can rise rapidly, so a properly designed rupture disk is essential to manage that emergency condition safely,” says Geof Brazier, Director of Development, BS&B Safety Systems, LLC.
According to Brazier, protecting vessels from vacuum collapse or minor overpressure typically requires a rupture disk sensitive enough to activate at only a few inches of water column—just a fraction of a bar.
To address the need for a more streamlined approach for low pressure applications, Brazier tasked BS&B’s R&D department to develop a simpler, more efficient design. The result is a new type of rupture disk, called the GHI™, which is capable of providing one-way or two-way (pressure and vacuum) relief. The disk is engineered to operate reliably at pressures so minimal they are comparable to the force of an ordinary sneeze.
The GHI (Gasketed Hi/Lo) rupture disk activates at extremely low burst pressures as low as 12.5 mbar/5 in water column in 4 in/100 mm sizes.
“Low-pressure rupture disks have traditionally required a separate safety head that adds cost, complexity, and weight. To achieve the desired low burst pressure also often requires the use of an oversized rupture disk and an adapter that makes the entire device even bigger and heavier,” explains Brazier, adding that the size and complexity of the combined component parts inevitably increase the material, installation, and maintenance costs.
The GHI rupture disk eliminates the need for a safety head. It is a self-contained assembly that installs directly between sanitary piping connections using industry-standard clamps and fittings. This also serves to simplify installation and replacement.
By combining high sensitivity at low pressures with a simplified installation process, the BS&B GHI rupture disk design addresses longstanding challenges related to safety, efficiency, and compliance within industries that demand hygienic conditions for very low burst pressures. The result is a simplified safeguard for process integrity, helping facilities maintain consistent operations even under fluctuating temperature or pressure conditions.
