STORAGE TANK SELECTION

In liquid and dry bulk storage, quality and value drives today's storage tank selection process. With advances in fabrication technology, engineering design, coating processes and field construction techniques, some storage products utilized in the past have become outdated, while other products have pushed to the front of the line in product development and field performance.

The process of selecting a liquid storage tank or a dry bulk storage silo starts with a series of questions that require answers before proceeding. This is one of the main problems witnessed in today's containment and storage markets. Many times storage tank selection is based on a preferred construction type in lieu of stored product performance requirements. Tank manufacturers tend to process customer information relative to their standard storage products and design parameters, which leaves the client responsible for the outcome. This is an archaic approach which is safe for the vendor, but often misses the mark in achieving a functional and efficient storage tank system that performs per your requirements.

The "top 10" list below includes basic considerations that should be addressed on every storage application. If the application under review is routine and no problem areas exist with the product/liquid stored, a standard storage tank quotation can be generated. If any items listed are a concern, a specialist in storage applications should advise you on the correct approach.

CONSIDERATIONS — DRY BULK SILOS

  • How much material will be stored in tons/cubic feet?
  • Are there any unique characteristics of the stored material to consider?
  • What materials of construction should be used?
  • What product density should be used for volume and design calculation?
  • Is material degradation a concern?
  • Is material segregation a concern?
  • What type of material discharge pattern is preferred or required for the application? (funnel flow, mass flow, expanded flow, etc.)
  • Is a hopper flow aid device required for reliable discharge?
  • Should my material be tested by a “flow specialist?”
  • Do I need a reliable performance guarantee from the silo supplier?

CONSIDERATIONS — LIQUID STORAGE TANKS

  • Capacity requirements in gallons/cubic meters?
  • Project design conditions (specific gravity, wind, seismic, snow loads, etc.)?
  • Are there any unique "storage process" requirements (agitation, digester, pressure/vac., etc.)?
  • pH and temperature of stored liquid?
  • What materials of construction should be used?
  • System interface responsibility?
  • Configuration type (flat bottom, sloped bottom, elevated, etc.)?
  • Corrosion allowance and/or cathodic protection requirements?
  • Foundation requirements (concrete ring wall with compacted fill, base setting ring, concrete slab, steel bottom with external saddles, etc.)?
  • Specific design code (AWWA, API 650, NFPA, FM, AISC, NSF, etc.) requirements?

You don't need to have all the answers, but you do need to know a reliable storage/containment specialist that can advise you in these areas. With the basics covered, the selection process can be narrowed for customer review and preference.

Example 1:

Liquid storage application requires 2 million gallons of wastewater storage. The PH of stored wastewater is relatively neutral. Tank construction evaluation is narrowed down to field-welded storage tank , concrete storage tank, and bolted storage tank designs. Bolted tank design is selected due to recognized field performance of non-leak design and factory applied powder coat system. Based on system configuration, two tanks are utilized.

Example 2:

We need to store 5000 cubic feet of hydrated lime. Based on the capacity requirements as detailed below, a bolted storage tank or shop-welded storage tank is correct for the application. Based on experience with the material and an extensive number of applications in the field, a flow aid device is required. A bin activator sized at half the tank diameter will provide reliable material discharge. A bin activator provides a funnel flow material discharge pattern. The material does not need to be tested. Material degradation should not be a concern.

Example 3:

Potable water storage tank application requires 1 million gallons of containment. A condensed field construction schedule is critical to the project. AWWA specification requirements are applicable. Tank selection is narrowed to bolted storage tank and field-welded storage tank construction. Based on expedited schedule requirements and superior performance of factory applied powder coat systems available for potable water storage, bolted storage tank construction is selected. International location — order to installation complete within 10-12 weeks.

Example 4:

Storage application requires 25,000 cubic feet of a granular product. It is desired to minimize material segregation during discharge. First we will note that size selection exceeds a shop-welded tank. This eliminates the shop-weld tank, unless we break the capacity requirements into a two tank package. The correct storage selection is a bolted smooth-wall storage tank. The correct flow discharge selected is mass flow. This does not mean we specify a silo designed for mass flow design loads. The correct request is to specify a storage silo designed for functional mass flow discharge. In order to provide reliable "functional mass flow" (FIFO) discharge, the material will need to be tested.

In general, storage tank applications that require a storage volume of less than 10,000 cubic feet (dry) or 30,000 gallons (liquid) will utilize a shop-welded or smoothwall bolted storage tank. Both products are used interchangeably in the industry. Shop-welded storage tank and bolted storage tank construction maintain advantages as listed above. Under review, the total installed costs (material + freight + field installation) are comparable between both products.

Bolted storage tanks, field-welded storage tanks, concrete storage tanks and hybrid storage tanks are typically utilized in large volume storage applications. All four designs are routinely specified in the power industry. In the industrial market, bolted tank and hybrid tank construction are the most cost efficient storage silo designs. Field-welded tank and concrete storage tank construction require extended field installation timeframes, which equates to higher installed cost.

Relative to "materials of construction" selection, bolted storage tanks, shop-welded storage tanks, and field-weld storage silos are available in coated carbon steel, stainless steel and aluminum construction. All storage tanks and storage silos are customized for the application and are available for installation at grade level or elevated. Typical storage tank accessories include manway accesses, level control nozzles, maintenance access platforms, agitators, heaters, insulation, caged ladders, spiral stairways, perimeter guardrails, and custom requirements for system integration. In summary, if the basics are covered in storage tank selection, years of trouble free containment can be expected. In today's industrial and municipal storage markets, a storage specialist should advise or confirm your selection. In all cases, a reliable storage tank system starts with a properly designed and configured tank/silo. Guesswork has been removed from the equation.

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