Aluminum Tanks

Aluminum tanks serve as versatile storage and process vessels in municipal water and wastewater treatment, housing everything from potable water to chemical solutions and biosolids. These lightweight, corrosion-resistant vessels work by providing contained environments for storage, mixing, or treatment processes, with welded seams and specialized coatings protecting contents from contamination. Typical municipal installations range from 5,000 to 500,000 gallons, with aluminum offering a strength-to-weight ratio approximately 35% better than steel. The primary trade-off is higher initial cost compared to steel tanks, though reduced foundation requirements and longer service life often justify the premium in lifecycle analysis.

• Chemical Storage and Feed Systems: Aluminum tanks serve as primary storage for liquid treatment chemicals like sodium hypochlorite, aluminum sulfate, and polymer solutions. Selected for corrosion resistance to these chemicals and lightweight installation advantages. Common sizes range 500-5,000 gallons for 0.5-50 MGD plants
• Backwash Water Storage: Used in filter backwash systems to store filtered water for cleaning media. Aluminum's corrosion resistance handles chlorinated water well, while lighter weight reduces structural requirements compared to steel
• Process Water Holding: Applied for temporary storage of treated water during maintenance operations or flow equalization. Selected when steel corrosion concerns exist and concrete isn't cost-effective for smaller volumes. Typical municipal installations range 1,000-10,000 gallons

Daily Operations: Operators monitor tank levels through SCADA systems, checking for proper fill/drain cycles and verifying chemical feed rates align with storage levels. Visual inspections include checking for leaks around nozzle connections and ensuring vent systems remain unobstructed. Level alarms require immediate response to prevent overflow or pump cavitation conditions.

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Maintenance: Monthly inspections focus on gasket conditions and connection tightness. Annual internal cleaning requires confined space entry procedures with proper ventilation and gas monitoring equipment. Aluminum's passivation layer requires specific cleaning agents - avoid caustic solutions that can cause pitting. Typical service intervals include gasket replacement every 3-5 years and internal coating inspection every 10 years.

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Troubleshooting: Common failure modes include gasket deterioration causing minor leaks and level instrument fouling from chemical deposits. Warning signs include unexplained level drops, discolored water around tank base, or erratic level readings. Proper installation typically provides 20-25 year service life, with replacement often driven by capacity increases rather than structural failure.

• Tank Shell: Welded aluminum plate construction, typically 5052 or 6061 alloy, 1/4" to 3/8" thickness depending on capacity. Sizing based on hydrostatic pressure and wind loads per AWWA D103 standards
• Inlet/Outlet Nozzles: Flanged aluminum connections, 2" to 12" diameter, positioned based on hydraulic requirements. Include vortex breakers for suction connections to prevent air entrainment
• Access Manholes: 24" diameter minimum with aluminum covers and gaskets. Required for cleaning and inspection access per local health department standards
• Level Instrumentation: Ultrasonic or pressure transmitters for continuous monitoring. Critical for automated chemical feed control and overflow prevention
• Venting System: Atmospheric vents with flame arrestors where required. Sized per tank capacity and filling rates to prevent vacuum formation during drawdown operations
• Foundation System: Concrete ring walls or full slabs designed for aluminum's thermal expansion characteristics and seismic requirements

• Tank Capacity: 10,000-5,000,000 gallons for municipal applications (0.5-50 MGD systems)
• Wall Thickness: 0.125"-0.375" for atmospheric tanks; 0.25"-0.5" for pressurized vessels up to 150 PSI
• Alloy Selection: 5052-H32 for potable water storage; 5454-H32 for wastewater applications requiring higher corrosion resistance
• Foundation Loading: 62.4 pcf for water plus tank weight (typically 2-4 psf additional); seismic design per ASCE 7
• Freeboard: Minimum 2 feet for atmospheric tanks; 6-12 inches for covered reservoirs
• Turnover Rate: 0.5-2.0 turnovers per day for potable water storage; contact time requirements drive sizing for chemical feed tanks
• Access Requirements: 24" minimum manway diameter; ladder spacing per OSHA 1910.27
• Pressure Rating: Atmospheric to 150 PSI for municipal applications; vacuum rating -14.7 PSI for suction tanks
• Temperature Range: -40°F to 180°F operational; thermal expansion joints required for tanks >50 feet diameter
• Seismic Design: Importance Factor 1.5 for essential facilities per ASCE 7; sloshing analysis required for tanks >100 feet diameter

• Atmospheric vs. Pressurized Configuration? Atmospheric tanks suitable for gravity-fed systems with static head <30 feet. Pressurized vessels required for system pressures >15 PSI or when space constraints prevent adequate elevation
• Fixed vs. Floating Roof Design? Fixed roofs acceptable for potable water and most municipal applications. Floating roofs required when vapor emissions are concern or for large diameter tanks (>120 feet) storing volatile chemicals
• Foundation Type Selection? Concrete ring wall foundations for tanks <100 feet diameter on competent soil. Full mat foundations required for poor soils or tanks >2 MG capacity. Pile foundations needed when bearing capacity <3,000 psf
• Alloy Grade and Coating Requirements? 5052-H32 adequate for pH 6.5-8.5 potable water. 5454-H32 required for wastewater or aggressive water chemistry. Interior coatings needed for pH <6.5 or >8.5

• Primary: Division 40 - Process Integration
• Section 40 05 00 - Common Work Results for Process Integration
• Secondary: Division 46 - Water

• Material/Equipment Verification: Mill test certificates for aluminum alloy grade (typically 5052 or 6061), welding certifications and NDT documentation, AWWA compliance verification for potable water contact
• Installation Requirements: Crane access planning for large panel assembly, foundation tolerance verification (±1/4" typical), weather protection during welding operations
• Field Challenges: Aluminum welding requires certified welders and inert gas protection, galvanic isolation details at steel connections critical
• Coordination Issues: 12-16 week lead times typical for custom municipal sizes, early structural coordination prevents field conflicts

• CST Industries - TechSpan aluminum covers and Complete Mix systems, strong municipal references including 15 MG clearwell covers in Ohio
• Caldwell Tanks - Pedesphere and column-supported designs, notable for 2.5 MG elevated tanks in Texas municipalities
• Tank Connection - RTP (rolled, tapered, pressed) aluminum storage tanks, popular for 0.5-5 MG municipal applications
• Pittsburgh Tank - welded aluminum construction, established presence in Northeast municipal markets

• Welded Steel Tanks - 20-30% lower initial cost but require ongoing coating maintenance; preferred for buried applications
• Bolted Steel Tanks - Glass-fused-to-steel options offer corrosion resistance approaching aluminum at 10-15% cost premium over standard steel
• Prestressed Concrete - Most economical for large storage (>2 MG) with 50+ year service life but limited to cylindrical geometries and requires specialized contractors

Establish relationships with manufacturer field service teams early - they provide invaluable installation support and warranty responsiveness. Specify aluminum walkways/platforms simultaneously with tank to ensure proper load distribution and avoid costly field modifications. Consider bulk purchasing with neighboring utilities for 15-20% cost savings on similar tank sizes. Always include spare gaskets and hardware in initial order.