Atmospheric Storage Tanks

Atmospheric storage tanks are engineering marvels designed for the safe and efficient storage of liquids and some gases in industrial facilities at a pressure close to or equal to atmospheric pressure. They form the cornerstone of operational continuity and product quality in a wide range of sectors such as oil and gas, chemical, food and beverage, water treatment, and power plants. These tanks are specially designed and manufactured according to the properties of the product they contain, the storage volume, and environmental conditions. Atmospheric storage tanks, particularly those used for storing flammable, combustible, or environmentally sensitive liquids, aim for maximum safety and minimum product loss by being manufactured in compliance with international standards (API, EN, etc.). Cryotanx, a leading firm in the sector, provides the most suitable atmospheric storage tank solutions for its customers’ needs, executing turnkey projects from the design phase to field assembly and periodic maintenance, thanks to its deep engineering knowledge and experience. The main purpose of these structures is to protect liquids from external factors, minimize losses such as evaporation, and increase operational efficiency. The success of a storage solution depends on selecting the correct tank type, using quality materials, and flawless manufacturing processes. Therefore, it would not be wrong to consider these tanks operating under atmospheric conditions as works of engineering art.

Atmospheric storage tanks, by technical definition, are closed or open vessels designed to operate at internal pressures very close to atmospheric pressure (approximately 101.3 kPa or 14.7 psi), generally only a few kilopascals above or below this value. The fundamental distinguishing feature of these tanks is that they are not designed to withstand high pressures. Therefore, they do not fall into the pressure vessels category, and their design, manufacturing, and inspection are subject to different standards, particularly codes like API 650 and API 620 published by the American Petroleum Institute (API). The operating principle is based on fundamental laws of physics. When the liquid level inside the tank rises (filling) or falls (emptying), the volume of gas (air or product vapor) at the top of the tank changes.

Similarly, changes in ambient temperature also cause the vapor inside the tank to expand or contract. To balance these volume and pressure changes, atmospheric storage tanks have “breathing” mechanisms. These mechanisms are typically special equipment called pressure/vacuum relief valves (breather valves). When the pressure inside the tank exceeds a predetermined positive value, the valve opens, allowing excess vapor to be released into the atmosphere in a controlled manner, thus protecting the tank from overpressure. Conversely, when a vacuum is formed inside the tank due to liquid emptying or a temperature drop, the valve draws in air from the outside to prevent the tank from collapsing inward (vacuum damage). This simple but vital function preserves the structural integrity of the tank. The Cryotanx firm provides the most reliable storage solutions by considering the properties of the stored product and operational requirements at every stage, from the selection of this critical equipment to its assembly.

These atmospheric systems are ideal for storing petroleum products with low volatility, such as water, diesel, and fuel oil, and many chemical substances. For products with higher volatility, such as gasoline or crude oil, more advanced designs like floating roof tanks are preferred to minimize evaporation losses. In summary, atmospheric storage tanks are far more than simple vessels; they are sophisticated engineering structures that respond intelligently to dynamic changes in internal and external conditions, prioritizing safety and efficiency.

Atmospheric storage tanks are the most commonly used and structurally diverse type of structure for industrial liquid storage needs. These tanks are designed in different configurations depending on factors such as the type of product stored, its volatility, storage capacity, and environmental regulations. This diversity makes it possible to find the most cost-effective and safest solution for every application. Specialist firms like Cryotanx work closely with the customer from the very beginning of the project to determine the most suitable tank type and carry out manufacturing in compliance with international standards. Fundamentally, atmospheric storage tanks are classified according to their roof structures. This classification is the most important design decision that directly determines the tank’s performance, cost, and environmental impact.

The most common storage tank types include fixed cone roof tanks and floating roof tanks. Each tank type offers certain advantages and disadvantages, and their fields of use differ. For example, a more economical fixed roof atmospheric tank may suffice for storing water or less volatile chemicals, while using floating roof tanks is of critical importance for storing valuable and volatile products like crude oil or gasoline to prevent evaporation losses and emissions. Therefore, selecting the correct tank type when starting a storage project is a fundamental step for both the economic and environmental success of the project.

Fixed cone roof tanks, as the name suggests, are a model of atmospheric storage tanks that have a cone-shaped roof welded to a cylindrical shell. They are one of the most frequently encountered tank types in the industry due to their structural simplicity and relatively low initial investment costs. The roof is generally supported by internal rafters or truss systems to bear its own weight and environmental loads (snow, wind, etc.), but self-supporting (unsupported) roof designs are also possible for smaller diameter tanks.

The most fundamental feature of these tanks is that they have a fixed vapor space regardless of the liquid level inside. This vapor space is the main source of operational losses and emissions. When the tank is being filled, the product vapor and air mixture in the vapor space is compressed as the liquid level rises and is vented to the atmosphere via the pressure/vacuum valve. This is known as “filling loss”. Similarly, when the temperature inside the tank increases, the vapor expands and is released into the atmosphere. Due to these losses, fixed cone roof tanks are generally preferred for storing liquids with very low or no volatility. Water, fire-fighting water, diesel, fuel oil, and certain chemical substances are ideal storage products for these tanks.

Cryotanx carries out the engineering, fabrication, and erection of fixed cone roof storage tanks made of high-quality carbon steel or stainless steel materials, compliant with the API 650 standard, according to the needs of its customers. These tanks offer a highly effective and reliable atmospheric storage solution in situations where evaporation losses do not pose an economic or environmental concern. However, if volatile products like gasoline are to be stored, they are generally equipped with additional systems like an internal floating roof to prevent these losses.

Floating roof tanks are advanced engineering varieties of atmospheric storage tanks designed specifically to prevent volatile organic compounds (VOCs) from evaporating and mixing with the atmosphere. The basic principle of these tanks is that they have a roof that floats directly on the liquid surface inside the tank and can rise and fall according to changes in the liquid level. In this way, the large vapor space, which is the main source of evaporation in fixed roof tanks, is almost completely eliminated. This design dramatically reduces both economic losses (product evaporation) and environmental pollution (air emissions). Therefore, they have become the industry standard for storing large volumes of crude oil, gasoline, jet fuel, and other petroleum derivatives.

Cryotanx has deep expertise in both internal and external floating roof tanks. Floating roof tanks are divided into two main categories: internal floating roof tanks (IFRT) and external floating roof tanks (EFRT). In the internal types, the floating roof is placed under a fixed cone or dome roof that protects the tank from weather conditions. This protects the floating roof from external factors such as snow, rain, and wind and allows for the use of more sensitive sealing systems. In the external types, there is no fixed roof over the tank; the floating roof is directly exposed to the atmosphere. Therefore, they must have special drainage systems for rainwater and more durable seal systems that ensure a tight fit between the roof and the tank shell. These seal systems are vitally important for the tank’s efficiency and safety.

An investment in a floating roof storage tank is a strategic atmospheric storage solution that pays for itself through the long-term environmental and economic benefits it offers.

The success of an atmospheric storage tanks project depends on the meticulousness and expertise demonstrated in every stage of the design, fabrication, and erection processes. These processes represent much more than a simple metal construction job; it is a complex discipline that requires strict adherence to international standards, advanced engineering calculations, precise fabrication techniques, and careful site operations. Cryotanx manages the entirety of these processes with its experienced staff of engineers and technicians, offering its customers the highest quality, safe, and long-lasting storage solutions. Each atmospheric tank is designed specifically according to the chemical and physical properties of the product to be stored, the seismic and wind load conditions of the site, and the operational requirements of the customer.

This holistic approach ensures that the tank meets not only today’s needs but also future requirements. The process begins with detailed engineering work, continues with precise fabrication in the factory environment, and finally concludes with erection and testing on-site, where safety is kept paramount. Each of these three fundamental stages has a critical impact on the overall quality of the project, and thus no detail can be overlooked. Especially in projects involving large volume tanks, logistics and site management become at least as important as engineering and fabrication.

The atmospheric storage tanks design process is the most critical stage that forms the foundation of the project. All engineering work carried out in this phase directly determines the tank’s safety, durability, and operational efficiency. The most common and accepted standard in the sector for welded steel tanks used for petroleum storage is API 650, developed by the American Petroleum Institute. This standard details the minimum requirements and calculation methods for all structural components of the tank, such as shell thickness, bottom plate design, roof structure, nozzle placement (connection opening), and reinforcements.

Engineers calculate the thickness and geometry of each element of the tank using parameters such as the density of the stored liquid, the design temperature, and the yield and tensile strength of the material. Furthermore, environmental factors such as the seismic activity and maximum wind speed of the geographical location where the project will be realized are also included in the design. These loads require special calculations to ensure the tank is resistant to overturning, sliding, and structural damage. The API 620 standard is used for atmospheric storage tanks that operate at slightly higher pressures (but still below the pressure vessel limit).

The Cryotanx engineering department performs these complex calculations with high precision by utilizing state-of-the-art design and analysis software (e.g., Finite Element Analysis – FEA). This software allows for the simulation of the tank’s behavior under various loads, enabling potential weak points to be detected and reinforced while still in the design stage. Correct standard selection and strict adherence to these standards are both a legal requirement and an indispensable element for facility safety. A successful storage system begins with a strong, standard-compliant engineering design behind it. Designing these tanks is a matter of experience and foresight, going beyond merely performing calculations.

Building an atmospheric storage tank is only the beginning of the project. The ability of these massive structures to serve safely and efficiently for decades depends on regular maintenance, professional inspection, and properly planned repair activities. Over time, corrosion, environmental effects, and operational wear can threaten the tank’s structural integrity. Managing these risks is vital for facility safety, personnel security, and environmental protection. Cryotanx serves not only as a tank manufacturer but also as a reliable solution partner throughout the entire life cycle of these structures. With its teams specializing in API 653 (Tank Inspection, Repair, Alteration, and Reconstruction) standard, it offers comprehensive services that extend the life and increase the performance of existing storage assets. An effective maintenance and repair program prevents unexpected failures and associated production losses. Furthermore, the safety of a storage tank is not just about its metal structure.

Critical safety equipment like pressure relief systems, overfill prevention mechanisms, and fire protection systems are integral parts of the tank. These systems must also be periodically checked and kept in working order at all times. In summary, the management of atmospheric storage tanks requires a proactive approach. Focusing on planned maintenance rather than reactive repairs offers a safer and more economical operating model in the long run.

Periodic maintenance and inspection programs for atmospheric storage tanks are the cornerstone of managing the safe life of these assets. The industry standard in this area is API 653, which sets out all the requirements, procedures, and evaluation criteria for out-of-service and in-service inspections. This standard provides tank owners and operators with a clear roadmap on when and how their tanks should be inspected. Cryotanx certified API 653 inspectors have the necessary knowledge and equipment to manage this complex process. Inspections are fundamentally divided into two: in-service and out-of-service inspections. In-service inspections are carried out while the tank is operational and generally include external visual checks, ultrasonic thickness measurements, and the examination of critical areas such as the base-shell joint region.

These inspections aim to detect problems such as obvious corrosion, leaks, deformation, or foundation settlements at an early stage. Out-of-service inspections are much more comprehensive. For this inspection, the tank must be emptied, cleaned, and degassed. Inspectors then enter the tank to perform detailed examinations on the bottom plates, internal shell surfaces, and structural elements. Advanced testing methods such as Magnetic Flux Leakage (MFL) scanning are used to map corrosion on the bottom plates. Shell and roof plate thicknesses are precisely measured with ultrasonic tests.

Weld seams are checked for cracks using non-destructive testing (NDT) methods like magnetic particle or penetrant testing. As a result of these inspections, the current condition of the tank is reported in detail, corrosion rates are calculated, and the remaining life is estimated. If repair or alteration is necessary, this report provides a basis for the work to be done. Regular API 653 inspections are like an insurance policy for an atmospheric storage tank; they prevent potential disasters and ensure the sustainability of the facility. This is the most responsible operating practice of a storage facility.

Purchasing a cryogenic storage tank is not a one-time transaction, but the beginning of a long-term responsibility. For the tank to continue operating safely, efficiently, and lawfully throughout its life, it depends on regularly applied professional maintenance and periodic control procedures. Just as a car needs regular maintenance, these high-tech pressure vessels must be inspected against potential problems that could cause wear or affect their performance over time. These controls are not just a recommendation, but also a legal obligation in many countries and part of the employers’ duty to ensure the safety of life and property.

As Cryotanx, we not only sell tanks to our customers but also provide the necessary information, service, and support to protect the lifelong safety and performance of these tanks. It should be remembered that even the best-designed tank can turn into a safety risk if its maintenance is neglected.

Legal Obligations and Inspection Frequency

Cryogenic storage tanks are classified as “pressure vessels” because they contain potentially hazardous liquids under high pressure. In Turkey, the safe use of such equipment is strictly regulated by the “Occupational Health and Safety Law” No. 6331 and the “Regulation on Health and Safety Conditions in the Use of Work Equipment” enacted under this law. According to this regulation, having the periodic control and inspection of cryogenic tanks carried out is a legal responsibility of the employer. The Regulation also clearly specifies the frequency of these checks: Unless otherwise stated in the standards, periodic checks must be performed at least once a year (at intervals not exceeding 12 months). These checks cannot be carried out by just anyone. The Regulation also defines the competence of the individuals who will perform the inspection: These individuals must be mechanical engineers, mechatronics engineers, related technical teachers, or machine technicians/high technicians who have been trained in the relevant field and are registered in the ministry’s database (with an Ekipnet number). As a result of the inspection, a detailed report is prepared by the authorized institution stating the condition of the tank, the deficiencies identified, and whether it is compliant, and is presented to the employer.

Vacuum Level Control and Maintenance

The heart of a cryogenic storage tank’s insulation performance is the vacuum between the inner and outer shells. This vacuum directly affects the “boil-off” rate of the liquid inside the tank. Over time, this vacuum level can slowly degrade due to microscopic gas leakage (outgassing) from materials or small leaks. The degradation of the vacuum means a drop in insulation performance, i.e., more heat penetration and consequently more product loss through evaporation. This situation is both an economic loss and a factor that stresses the safety systems more by causing the pressure inside the tank to increase faster. Therefore, regularly checking the tank’s vacuum level is critically important. It is generally recommended that this check be performed at least twice a year (every 6 months). Tanks are equipped with a special vacuum measurement port for this measurement to be performed. A thermocouple vacuum gauge is connected to this port to read the pressure value in the annular space. If it is determined that the vacuum level has exceeded the determined limits (i.e., the vacuum has degraded), a “re-evacuation” procedure must be performed. This procedure first requires the tank to be completely emptied and brought back to normal temperature. Then, a powerful vacuum pump is connected to the system to evacuate the gases from the annular space again, and the insulation performance is restored to factory settings. This process is an important maintenance procedure that extends the tank’s life and ensures its efficient operation.

The most fundamental and inevitable challenge of cryogenic storage is the continuous product loss due to “boil-off,” or evaporation. Even the most perfect insulation systems cannot completely prevent heat leakage, and every unit of heat that enters causes some amount of cryogenic liquid to vaporize. This situation constitutes a serious economic loss and a logistical problem, especially in long-term storage or the storage of extremely valuable and volatile liquids like liquid hydrogen. In conventional tanks, this vaporized gas is vented to the atmosphere via safety valves when the pressure reaches a certain level. This is where Zero Boil-Off (ZBO) technology comes in, a revolutionary approach developed to eliminate this waste. The basic logic of ZBO is to accept the limits of passive insulation and add an active cooling element to the system. This system contains special miniature refrigerators called “cryocoolers” that operate inside the tank or in a loop connected to it. These cryocoolers continuously pump the heat leaking into the tank out and, more importantly, capture the vaporized gas (boil-off gas), cool it back down to liquefy it, and return it to the tank. Thanks to this closed loop, theoretically no product loss occurs, and the tank can remain sealed for years. This technology is vital, especially for future long-duration space missions. For example, storing the liquid hydrogen needed for a 3-year mission to Mars in a passive tank would mean almost half of the fuel would evaporate on the way, while the ZBO system can reduce this loss to nearly zero. Experiments like NASA’s ZBOT (Zero Boil-off Tank) conducted on the International Space Station are testing the performance of this technology in a microgravity environment and shaping the future space infrastructure.

As the world shifts toward clean energy sources to combat climate change and reduce reliance on fossil fuels, the concept of the “hydrogen economy” emerges as the energy paradigm of the future. In this vision, hydrogen, especially when produced from renewable sources (solar, wind), is a clean, efficient, and universal energy carrier used to store and transport energy. However, one of the biggest technological hurdles facing the hydrogen economy is storing hydrogen safely, densely, and economically. Hydrogen, under normal conditions, is the lightest gas in the universe, and therefore its volumetric energy density is very low. Various methods have been developed to overcome this problem, but one of the most volumetrically efficient methods is storing hydrogen by liquefying it at −253∘C (LH2). Liquid hydrogen occupies much less space than its gaseous state, making it an attractive fuel, especially for mobile applications such as heavy-duty vehicles, ships, and aircraft. However, LH2 storage is the most challenging frontier faced by cryogenic technology. Hydrogen’s extremely low boiling point pushes the limits of conventional insulation materials and makes active cooling technologies like ZBO almost a necessity. Furthermore, the very small size of hydrogen molecules increases their tendency to permeate through materials. To overcome these difficulties, the aerospace industry is conducting intensive research on cryogenic storage tanks made of composite materials, which are much lighter and potentially more insulating than traditional metal tanks. As the hydrogen economy grows, the demand for these advanced LH2 storage solutions will multiply exponentially.

The world of cryogenic storage is far from being a stagnant field of technology. From the efficiency revolution brought by ZBO systems to the massive new markets created by the hydrogen economy and innovative solutions like composite materials, the sector is in continuous evolution. This future requires not only better insulation materials or stronger steels but also smarter systems. The cryogenic storage tank of the future will evolve into a mechatronic system equipped with sensors, control units, and software that actively manages its temperature and pressure. This transformation presents both a great opportunity and a serious technological challenge for manufacturers. As Cryotanx, we are not just spectators of this future, but we are actively working to shape it. Our investments in R&D, our commitment to follow the latest material science and insulation technologies, and the continuous development of our engineering team are preparing us for the requirements of this new era. What we offer our customers is not only today’s proven and reliable technology but also a vision and partnership that will ensure they are ready for the challenges and opportunities of tomorrow. Whether it is making your current operations more efficient or transitioning to next-generation energy sources like hydrogen, Cryotanx has the knowledge, expertise, and technology to take you into the future. With us, you don’t just buy a tank; you invest in the technologies of the future.