Understanding Modern Storage Tank Design & Fabrication

Ever wonder how industries manage to store massive amounts of liquids, gases, and even powders? The answer lies in some pretty impressive storage tanks and pressure vessels.

In the expansive world of powder and bulk solids handling these storage systems are sophisticated, well-engineered solutions that are integral to maintaining product integrity, ensuring efficient material flow and worker safety. Custom-fabricated storage tanks, reactors, and pressure vessels are widely utilized across chemical, pharmaceutical, food processing, and energy production sectors.

As technology, industry standards, and certifications evolve, it is crucial for manufacturers to partner with experienced fabricators who can handle projects of any scale and complexity.

Design Principles of Modern Storage Tanks

Storage tanks come in many configurations, the two most common designs are flat-bottom tanks with conical tops and elevated tanks with support legs. The choice between flat-bottom and elevated tanks depends on various factors, including the properties of the stored material, discharge requirements, available space, and specific industry regulations.

Flat-Bottom Tanks

These cost-effective tanks are often built to API (American Petroleum Institute) standards and feature a flat bottom and a conical top. The flat bottom provides stability and even weight distribution, while the conical top allows for efficient rainwater runoff and helps minimize vapor space. Typically constructed from stainless steel, this design is particularly well-suited for storing large volumes of liquids at atmospheric or low pressures.

Elevated Tanks

Elevated tanks are supported by legs and offer unique advantages, particularly when gravity-fed discharge is required which reduces the need for pumps. These tanks can be designed with either a conical or dished bottom, depending on the specific application requirements and can be designed to optimize space in facilities with limited floor area. Additionally, the elevation allows for easier maintenance access underneath the vessel.

This ROSS 3,000-gal 304/304L stainless steel-type elevated tanks with dished bottom are ASME stamped and designed for 200 psi with full vacuum up to 200˚F (Charles Ross & Son Co.)

This ROSS 4,500-gal 304/304L stainless steel-type flat-bottomed tank is ASME stamped and designed for 25 psi with full vacuum up to 400˚F (Charles Ross & Son Co.)

Materials & Fabrication Considerations

Material selection is crucial in tank design, with stainless steel being a popular choice due to its corrosion resistance and durability. However, other materials such as carbon steel, aluminum, and various alloys like Monel, Hastelloy, and Inconel are also used, depending on the specific requirements of the application.

Fabrication limitations are another important consideration, especially for shop-fabricated tanks. Typical maximum dimensions for shop-fabricated tanks are around 12 feet in outer diameter and 30 feet in length, yielding capacities of up to 30,000 gallons. Larger vessels can be fabricated but may require special transportation arrangements, including permits and escorts, which can impact project timelines and costs.

Industry Standards & Compliance

The design and fabrication of storage tanks are governed by various industry standards and codes, ensuring safety, reliability, and consistency across different applications. Some of the most prevalent standards include:

ASME Code

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, particularly Section VIII, Division 1, is widely used for the construction of pressure vessels. This code provides guidelines for materials, design, fabrication, inspection, and testing of pressure vessels.

API Standards

The American Petroleum Institute (API) has developed several standards relevant to storage tanks, including:

* API 650: Welded Steel Tanks for Oil Storage

* API 620: Large, Welded, Low-Pressure Storage Tanks

Other important standards include:

* USFDA (U.S. Food and Drug Administration) regulations for food-grade tanks

* BISSC (Baking Industry Sanitation Standards Committee) for the baking industry

* ABS (American Bureau of Shipping) for marine applications

* UL142 for aboveground storage tanks for flammable liquids

Customization & Special Features

Modern storage tanks can be highly customized to meet specific operational requirements. Some common customization options include:

Pressure & Temperature Ratings

Tanks can be designed to withstand specific internal pressures (from full vacuum to high pressure) and temperature ranges. For example, a tank might be rated for 50-psig internal pressure to full vacuum at 200°F.

Nozzles & Ports

Custom configurations of nozzles, manways, and other access ports can be incorporated based on operational needs.

Additional Features

Agitators such as high-speed dispersers, high shear rotor/stators, anchor agitators and other impeller types can be included depending on specific processing needs and viscosity requirements. Additionally, heating/cooling jackets, spray nozzles for cleaning, lifting lugs, ladders, handrails, and specialized coatings are available.

Control Systems

Control and data acquisition systems offer unprecedented accuracy and flexibility, monitoring a wide array of process variables while controlling essential parameters such as mixing time, agitator speeds, temperature and vacuum/pressure level. PLC-based recipe controls and various automation options improve worker safety by limiting exposure to hazardous chemicals and extreme temperatures.

The ROSS FDA-50-gal fixed tank dual-shaft mixer is equipped with two agitators: a high-speed disperser features two 6-in. sawtooth blades. The stainless steel-type 316 dished-bottom vessel and removable dished cover is ASME stamped and can accommodate internal pressures up to 100 psi (Charles Ross & Son Co.)

Quality Control & Testing

Ensuring the integrity and safety of storage tanks involves rigorous quality control measures and testing procedures:

Non-Destructive Testing (NDT)

Various NDT methods, such as radiography, ultrasonic testing, and magnetic particle inspection are employed to detect defects in welds and materials.

Hydrostatic Testing

Tanks are often filled with water and pressurized to test for leaks and structural integrity.

Surface Treatment

Interior surfaces may undergo thorough cleaning, drying, media blasting or mechanical polishing to ensure product purity and prevent contamination. Exterior surfaces often receive protective coatings to prevent corrosion.

Pre-Shipment Procedures

To maintain cleanliness during transportation, nozzles may be capped and tanks purged with inert gas like nitrogen.

Future Trends in Tank Design & Fabrication

As industries evolve, so do the requirements for storage tanks. Some emerging trends include:

The design and fabrication of storage tanks and vessels continue to advance, driven by industry needs, technological improvements, and evolving standards. From material selection to customization options and rigorous quality control measures, modern tank manufacturing combines engineering expertise with stringent safety considerations. As industries demand more from bulk material storage and process equipment, the importance of good design, fabrication workmanship, and deep manufacturing experience remain paramount.

Erin Dillon is media and marketing coordinator at Charles Ross & Son Co. (Hauppauge, NY) For more information, call 631-254-0500 or visit www.mixers.com.