Guide to Selecting Liquid Storage Tanks

By Bill Neighbors

In liquid storage containment, quality and value drives today's tank selection process. With advances in fabrication technologies, engineering design, coating processes and field construction techniques, some storage products used in the past have become outdated, while other products have pushed to the "front of the line" in product development and field performance.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 water or wastewater storage tank starts with a series of questions and considerations. This is one of the main problems witnessed in liquid storage containment applications. Many times tank selection is based on a preferred construction type in lieu of field performance requirements. In reviewing different types of tank construction, always remember to start with the field performance requirements, which will lead you to define the "value attributes" of each type of tank construction. In most cases, a review of "value attributes" (the value aspects defined by your client as important, i.e., long life, low maintenance, cost efficient, etc.) and "life cycle costs" will guide and simplify your selection process.

Slip, Jump-Form, Wire-Wound Concrete Construction

The "top 10" list below includes basic considerations that should be addressed on every liquid storage tank application. If the application under review is routine and no special conditions exist, a standard quotation can be requested from a vendor of choice. If any items listed are a concern, a specialist in liquid storage applications should advise you on the correct approach.

Application Considerations

Capacity requirements in gallons/cubic meters?
Project design conditions and applicable codes (AWWA, API 650, NFPA, FM, AISC, NSF, other)?
Are there any unique "storage process" requirements (agitation, digester, pressure/vac., other)?
PH and temperature of stored liquid?
What materials of construction should be used?
System requirements/ interface responsibility?
Configuration type (flat bottom, sloped bottom, elevated, other)?
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, other)?
Performance guarantee and/or warranty requirements?

Bolted Smoothwall RTP (rolled, tapered panel) tank.

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.

Tank Styles

In general, water storage applications requiring a volume of less than 90,000 gallons will use a shop-welded or smoothwall bolted tank. Both products are used interchangeably in municipal and industrial applications. Both shop-weld and bolted construction have their own advantages. Under review, the total installed costs (material + freight + field installation) are comparable between both products.

Bolted RTP (rolled, tapered panel), field-weld, concrete and hybrid tank construction are typically used in large volume liquid storage applications. All four designs are routinely specified in the power industry. In industrial and municipal applications, bolted RTP and hybrid steel construction are the most cost efficient tank designs. Field-weld and concrete construction require extended field installation timeframes, which equates to higher installed cost.

Beyond the rhetoric of vendor promotion in the marketplace, when "value attributes" are reviewed and compared to installed costs and life cycle costs, some simple facts become pronounced in ground storage reservoirs:

Specifying a water or wastewater tank in or below ground . . . the best installed product is concrete tank construction with aluminum dome cover (as applicable).
Specifying a water or wastewater tank above ground . . . the best installed product is steel tank construction with steel or concrete bottom and aluminum dome cover (as applicable).
Specifying a cover over a concrete or steel tank . . . the best installed product is an aluminum dome cover.
Specifying bolted tank construction for water or wastewater storage . . . the best installed product is bolted RTP (rolled, tapered panel) steel tank construction with steel or concrete bottom and aluminum dome cover (as applicable).
Specifying field welded construction for water and wastewater storage . . . the best installed product is a field welded steel tank sidewall and bottom with aluminum dome cover (as applicable).

Bolted RTP construction was used in these anaerobic digesters.

Relative to "materials of construction" selection, bolted, shop-weld and field-weld tanks are available in coated carbon steel and stainless steel construction. All tanks are customized for the application and are available for installation at grade level or elevated. Typical 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.

Conclusion

If the basics are covered in tank selection, years of trouble free containment can be expected. Today, in industrial and municipal storage applications, there are steel storage tanks throughout North America that are over 100 years old. Based on proper maintenance of a storage tank and its coatings, a high quality, properly designed and installed steel storage tank can be maintained for an indefinite service life. Quality and value should drive your future tank selection process.WW

Liquid Tank Selection

Shop-Weld Construction

Applications: Potable water, fire protection, industrial liquids