Glass-lined Steel Pressure Tanks

Glass-lined Steel Pressure Tanks serve as corrosion-resistant pressure vessels for storing treated water, providing system pressure maintenance, and accommodating thermal expansion in municipal water distribution systems. These tanks feature a steel shell with a fused glass lining that creates an impermeable barrier against corrosion while maintaining structural integrity under pressure. Typical operating pressures range from 100-300 psi with storage capacities from 500 to 50,000 gallons for municipal applications. The primary trade-off is higher initial cost compared to epoxy-coated steel tanks, but significantly lower long-term maintenance requirements due to the glass lining's superior corrosion resistance.

• Hydropneumatic Storage Systems: Glass-lined tanks serve as pressure vessels in hydropneumatic systems for distribution pumping stations, maintaining 40-80 psi system pressure. Connected downstream of high-service pumps with pressure switches and air compressors. Selected for corrosion resistance in chlorinated water service and ability to handle pressure cycling without coating degradation.

• Chemical Feed System Storage: Used for storing liquid chemicals like sodium hypochlorite, ferric chloride, and polymer solutions under pressure for injection systems. Positioned upstream of chemical feed pumps with pressure relief valves and level controls. Glass lining prevents chemical attack on steel substrate while maintaining structural integrity under 150-300 psi operating pressures.

• Backwash Water Storage: Applied in filter backwash systems requiring pressurized water delivery at 15-25 psi. Connected between backwash pumps and filter underdrain systems. Glass-lined construction resists chlorine residuals in stored backwash water while steel shell provides pressure rating for rapid discharge cycles.

Daily Operations: Operators monitor system pressure via local gauges and SCADA, checking for proper cycling between cut-in/cut-out pressures. Air pressure requires weekly verification using tire-type gauge on charging valve. Water level monitoring through sight glass or electronic sensors ensures adequate liquid volume while maintaining air cushion ratio.

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Maintenance: Monthly inspection of pressure relief valve operation and quarterly air pressure adjustment. Annual internal inspection requires confined space entry procedures with proper ventilation and gas monitoring. Glass lining inspection uses bright lighting to identify chips or cracks. Typical service life 15-20 years with proper maintenance, requiring specialized glass-lining contractors for repairs.

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Troubleshooting: Rapid pressure loss indicates glass lining failure allowing water-steel contact and hydrogen gas generation. Short cycling suggests insufficient air cushion or undersized tank. Discolored water discharge indicates internal corrosion. Warning signs include unusual pressure fluctuations, metallic taste in water samples, and visible rust staining at connections.

• Glass Lining System: Fused silicate glass coating applied at 1600°F, typically 0.008-0.012 inches thick. Provides chemical resistance and prevents steel corrosion. Selection based on chemical compatibility and temperature rating (up to 400°F). Municipal tanks range 100-5,000 gallons capacity.

• Steel Shell Construction: ASME-coded carbon steel vessel, typically A516 Grade 70, designed for 150-300 psi working pressure. Wall thickness 3/16" to 1/2" depending on diameter (30" to 120" typical). Provides structural integrity while glass lining handles corrosion protection.

• Nozzle Connections: Flanged or threaded connections with glass-lined surfaces. Standard configurations include 2-8 inch inlet/outlet, 1-2 inch drain, pressure relief, and instrumentation ports. Sized based on flow requirements and piping system design.

• Air Charging System: Includes air valve, pressure gauge, and relief valve assembly. Maintains proper air cushion (typically 30-40% of tank volume) for pressure regulation. Pre-charged to system requirements during installation.

• Operating Pressure Range: 150-300 PSIG typical municipal service, with design pressures to 350 PSIG. Standard ratings include 150, 200, 250, and 300 PSIG working pressure.

• Tank Capacity: 120-20,000 gallons for municipal applications. Common sizes: 315, 525, 1,050, 2,000, 4,000, and 8,000 gallons for systems serving 0.5-50 MGD plants.

• Temperature Range: 32-180°F operating, with glass lining rated to 400°F. Municipal water applications typically operate 40-120°F.

• Drawdown Capacity: 25-40% of total tank volume depending on pre-charge pressure settings. Higher drawdown requires lower pre-charge ratios.

• Flow Rate Sizing: Peak demand flow rate determines minimum tank size. Rule of thumb: 1 gallon capacity per GPM peak flow for residential systems, 0.5-0.75 gallons per GPM for municipal distribution.

• Pre-charge Pressure: Typically set at 60-80% of cut-in pressure. For 60 PSIG cut-in, pre-charge at 38-48 PSIG.

• Cycle Rate: Maximum 10-12 starts per hour for pump protection. Tank sizing must limit cycling frequency during normal demand variations.

• Connection Sizes: 2"-12" flanged connections standard, with 4"-8" most common for municipal applications.

• What is the required drawdown volume versus total tank capacity? Municipal systems need 300-1,200 gallons drawdown for 0.5-5 MGD plants. Insufficient drawdown (below 25% of tank volume) causes excessive pump cycling and premature failure. Engineers need peak hourly demand data and acceptable pump cycle frequency limits.

• Should the tank be horizontal or vertical configuration? Horizontal tanks offer better drawdown efficiency and easier maintenance access but require more floor space. Vertical tanks save footprint but may have 10-15% less effective drawdown. Decision depends on available space, crane access, and drawdown requirements above 1,000 gallons.

• What operating pressure range optimizes system efficiency? Higher operating pressures (200-250 PSIG) provide better drawdown ratios but increase energy costs and stress on distribution components. Lower pressures (150-175 PSIG) reduce pumping energy but require larger tanks. Engineers need distribution system hydraulic analysis and energy cost projections.

• Is redundancy required for critical service applications? Single tank failure can interrupt service to entire pressure zone. Dual tank systems with isolation valves cost 40-60% more but eliminate single points of failure. Decision requires service criticality assessment and acceptable downtime analysis.

• MasterFormat 40 22 13 - Packaged Water Treatment Equipment - Primary section for pre-engineered pressure tank systems with controls

• Alternative: 33 11 00 - Water Utility Distribution Piping for field-erected installations

• Material/Equipment Verification: Glass lining thickness certification (typically 0.008-0.012"), AWWA D103 compliance documentation, Cathodic protection system specifications

• Installation Requirements: Concrete pad design for full tank loading, Proper grounding for cathodic protection, Access clearances for inspection manholes

• Field Challenges: Glass lining damage during shipping/handling, Coordination with electrical for cathodic protection, Foundation settlement preventing proper support

• Lead Times: 12-16 weeks typical, 20+ weeks for larger custom tanks

• A.O. Smith Water Systems: Aquastore glass-lined tanks, municipal references include Aurora, IL and Plano, TX installations

• CB&I (McDermott): Aquastore series with 25-year glass lining warranty, serving facilities like Mesa, AZ

• Wessels Company: WTA series hydropneumatic tanks, common in smaller municipal applications

• Tank Connection: Glass-fused-to-steel technology with bolted construction options

• Welded Steel with Coating: 30-40% lower initial cost but requires recoating every 8-12 years. Suitable for budget-constrained projects with maintenance capability.

• Concrete Tanks: Best for large storage (>500,000 gallons) with 50+ year life expectancy. Higher initial cost but lowest lifecycle expense.

• Composite/Fiberglass: Excellent corrosion resistance, 20-25% premium over glass-lined steel. Preferred for aggressive water chemistry or coastal installations with high chloride exposure.

Installation Insight: Specify factory-applied external coatings rather than field-applied to avoid adhesion issues. Many operators report 20+ year service life when properly maintained versus 8-12 years for standard steel tanks.

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Manufacturer Relations: Establish preferred vendor agreements with local representatives - they often provide free technical support for sizing and troubleshooting. Consider standardizing on one manufacturer's connection details to simplify spare parts inventory and operator training across multiple facilities.