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  Ask Tom! Column

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Welcome to Ask Tom!, a monthly column by our resident water treatment guru, Tom Keenan of National Environmental Services Agency (NESA).  Tom addresses the issues that bug you the most. And Tom knows!!  With 35 years experience in providing environmental support services to public and private sector clients on a wide range of environmental issues.
For past articles visit the Ask Tom! Archive.

Water & Wastewater – Liquid Tank Selection
by Bill Neighbors, Tank Connection

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design, coating processes and field construction techniques, some storage products utilized in the past have become outdated, while other products have pushed to the “front of the line” in product development and field performance.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 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.

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.

Considerations – Water, Wastewater & Industrial Liquid Storage Applications

- Capacity requirements in gallons/cubic meters
- Project design conditions and applicable codes
- Are there any unique “storage process” requirements
- pH and temperature of stored liquid
- What materials of construction should be used
- System requirements / interface responsibility
- Configuration type
- Corrosion allowance and/or cathodic protection requirements
- Foundation requirements
- Performance guarantee and/or warranty 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: Wastewater Treatment

Client application required multiple liquid storage tanks for wastewater treatment. Application required multiple clarifiers in sizes up to 2.4 million gallons each. The tank selection process is narrowed down to field-weld, concrete and bolted RTP (rolled, tapered panel) construction. Bolted RTP design is selected due to recognized field performance of non-leak design and factory applied powder coat system.


Example 2: Municipal Water Treatment

Application requires 5000 cubic feet of hydrated lime storage. Based on the capacity requirements, a shop-welded tank is selected for the application. Based on experience with the material stored 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 from the tank. A bin activator provides a “funnel flow” material discharge pattern. The material does not need to be tested. Material degradation is not a concern.

Example 3: Municipal Water Storage

Potable water storage application requires ~ 4.5 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 RTP (rolled, tapered panel) and field-weld construction. Based on expedited schedule requirements and superior performance of factory applied powder coat systems available for potable water storage, bolted RTP tank construction is selected. Specialized jacking process is utilized which allows the XL bolted tank to be built entirely from grade level.

Location: Singapore
Note: Field installation completed within 12 weeks.

Example 4: Standpipe Water Storage

Standpipe application required ~100,000 gallons of water storage. Welded, bolted RTP and API 12B tank construction were evaluated. RTP construction was selected based on advanced coating system, leak-free design and expedited schedule requirements.

Location: Dubai
Note: Standpipe was jacked in place from grade level. Field construction completed in 3 weeks.



Example 5: Anaerobic Digesters

Anaerobic digester application – Client review of bolted RTP design with LIQ Fusion 7000 coating system, glass coated tanks and field weld construction. Bolted RTP construction was selected based on perceived value of product quality, future low maintenance cost and advanced, safe field construction processes.

Locations: Global
Note: Field construction completed in less than half the time required for welded construction.

Example 6: Potable Water Storage

Application required water storage containment of ~ 600,000 gallons. Client specification requested a bolted steel tank with bolted steel bottom for placement on compacted fill with grade ban arrangement (no foundation). Bolted RTP and FP (flat panel) construction were reviewed. Bolted RTP construction was selected as precision design and premier installed quality.

Locations: Global
Note: Bolted steel bottoms allow flexibility in foundation requirements.

Example 7: Potable Water Storage

Bechtel project for Dept. of Energy requires two 250,000 gallon potable water tanks for Area 51 location. Specification requirement for field-weld construction with aluminum geodesic dome covers.

Location: U.S, Area 51
Note: Welded tank construction and field installation per AWWA D100.

In general, water storage applications requiring a volume of less than 90,000 gallons will utilize a shop-welded or smoothwall bolted tank. Both products are used interchangeably in municipal and industrial applications. Both shop-weld and bolted construction maintain advantages as listed above. 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 utilized 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).

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.

In summary, 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.

Contact our author:

Mr. Bill Neighbors
Tank Connection, LLC
1801 South 21st Street
Parsons, Kansas 67357
Telephone: 620-423-3010
Fax: 620-423-3999
Email: bill@tankconnection.com
Web site:  http://www.tankconnection.com/TankConnection



Help others by posting your comments, suggestions and experiences with water or wastewater treatment or any other concerns you may have on our On-Line Help Forum.  For past Ask Tom! Articles, visit the Ask Tom! Archive.

Guest articles for the Ask Tom! Column are always welcome, for more information please contact Tom Keenan directly at his email address:  info@nesa.ie


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