Top OEMs for Aluminum & Stainless Covers and Walkway Systems

1. INTRODUCTION

In municipal and industrial water and wastewater treatment facilities, the containment of process basins, channels, and reservoirs is a critical engineering discipline. While historically treated as secondary accessories, cover systems and associated walkways have evolved into essential components for odor control, process stability, safety compliance, and algae mitigation. The shift from heavy concrete or degrading steel structures to lightweight, corrosion-resistant materials—specifically aluminum and stainless steel—has become the standard for modern facility design.

Aluminum and stainless steel cover systems serve multiple functional roles. In wastewater applications, particularly in headworks, primary clarifiers, and thickeners, the primary objective is often the containment of hydrogen sulfide (H₂S) and other odorous compounds to facilitate efficient extraction to scrubbers or biofilters. A well-engineered cover system minimizes the volume of air requiring treatment (headspace), directly impacting the capital and operating costs of the odor control system. If a cover leaks or fits poorly, the HVAC sizing must increase to maintain negative pressure, driving up lifecycle energy costs.

In potable water applications, covers over clearwells, flocculation basins, and filters are mandated to prevent contamination from debris, wildlife, and atmospheric pollutants. Furthermore, opaque covers are crucial for blocking sunlight to prevent algal growth, which can foul weirs, increase turbidity, and contribute to taste and odor issues. For open channels and UV disinfection systems, covers provide necessary thermal protection and prevent UV degradation of surrounding equipment.

Walkway systems, often integrated with or independent of the covers, provide essential operator access. These structures must meet stringent deflection criteria and slip-resistance standards while surviving in highly corrosive atmospheres. The selection of the Original Equipment Manufacturer (OEM) for these systems is not merely a procurement detail; it dictates the structural integrity, integration with civil works, and long-term maintenance burden of the plant. A poorly fabricated aluminum cover can suffer from galvanic corrosion at anchor points, structural failure under snow loads, or seal degradation that renders odor control ineffective.

This article provides a comprehensive engineering analysis of the leading OEMs specializing in aluminum and stainless steel covers and walkway systems. It examines the technical nuances of material selection, structural design, and the specific capabilities of the industry’s most prominent manufacturers. The focus is strictly on long-term operability, specification compliance, and the realities of installation and maintenance in harsh treatment environments.

2. HOW TO SELECT THIS SYSTEM OR EQUIPMENT

Selecting the appropriate cover and walkway system requires a multi-dimensional analysis that balances structural requirements, corrosion resistance, accessibility, and budget. Engineers must move beyond generic specifications to address the specific environmental and operational constraints of the facility.

Functional Role and Process Integration

The first step in selection is defining the primary function. Is the cover intended for odor containment, algae blocking, temperature retention, or fall protection?
Odor Control: For H₂S containment, the seal integrity is paramount. Flat covers with gasketed joints are typically preferred over arched covers because they minimize the headspace volume, reducing the CFM requirements for the odor control fans. The interface between the cover and the concrete wall or steel tank rim must be designed to accommodate thermal expansion while maintaining a gas-tight seal.
Algae and Debris Control: In potable water, the cover must be opaque and fit tightly enough to prevent insect intrusion. However, gas tightness is less critical than in wastewater, allowing for different joint designs.
Walkways and Access: If the cover serves as a walking surface, it must meet OSHA and local building code requirements for live loads (typically 50-100 psf). Integrating handrails, kick plates, and non-slip surfaces is mandatory. The engineer must determine if the entire cover needs to be walkable or if dedicated walkways over a non-walkable cover are more cost-effective.

Materials of Construction: Metallurgy Matters

Aluminum (6061-T6): This is the dominant material for modular covers due to its high strength-to-weight ratio and natural corrosion resistance. The formation of a passive oxide layer protects the metal in standard pH ranges. However, in highly alkaline or acidic environments, or where direct contact with concrete occurs, additional protection (anodizing or bituminous coatings) is necessary to prevent severe pitting or galvanic corrosion.
Stainless Steel (304 vs. 316/316L): Stainless steel is generally reserved for environments where aluminum cannot survive (e.g., extreme pH swings or extremely high H₂S concentrations leading to sulfuric acid formation) or where extreme structural rigidity is required in a thin profile. 316L is the standard for wastewater due to its molybdenum content, which offers superior resistance to pitting and crevice corrosion compared to 304.
Design Considerations: Engineers must specify the alloy grade clearly. “Stainless Steel” is insufficient; “ASTM A240 Type 316L” is a specification.

Structural Loads and Deflection

Covers must be engineered to withstand a combination of loads:

• Dead Load: The weight of the cover itself.
• Live Load: Personnel and equipment (typically 50 psf for maintenance access, higher for heavy traffic).
• Snow and Ice Load: Critical in northern climates. Accumulation in channels or between trusses can lead to catastrophic failure.
• Wind Load: Uplift forces can be significant for large flat covers or domes. Secure anchoring is vital.
• Deflection Limits: Standard specifications often call for L/240 or L/360 deflection limits. Stiffer covers (L/360) feel more secure to walk on and reduce seal fatigue over time.

Common Failure Modes and Mitigation

Galvanic Corrosion: The most common failure occurs when aluminum covers are anchored to concrete using carbon steel or even stainless steel anchors without isolation. An electrolyte (wastewater mist) completes the circuit, eating away the aluminum. Mitigation: Specify strict isolation utilizing EPDM gaskets, neoprene washers, and bituminous paint at all dissimilar metal interfaces.
Seal Degradation: Gaskets dry out, crack, or compress permanently (compression set), leading to odor leaks. Mitigation: Specify high-quality EPDM or Viton gaskets with UV inhibitors. Ensure the design allows for easy gasket replacement without disassembling the entire structure.
Seizing of Hatches: Hinges and latches seize due to corrosion. Mitigation: Specify 316 stainless steel hardware for all moving parts, regardless of the cover material. Use nylock nuts and anti-seize compounds during assembly.

Lifecycle Cost and Maintenance

While aluminum systems often have a higher upfront material cost than fiberglass (FRP), they typically offer lower lifecycle costs. Aluminum is UV stable (unlike FRP, which can bloom and degrade), non-combustible, and fully recyclable at the end of its life. Maintenance is minimal, primarily involving seal inspection and cleaning. Engineers should evaluate the Total Cost of Ownership (TCO) over 20-30 years, factoring in the cost of coating repairs (for steel) or UV protective sealing (for FRP), neither of which are required for raw aluminum.

3. COMPARISON TABLE

The following table compares the top OEMs specializing in aluminum and stainless steel covers. Engineers should use this matrix to align project requirements—such as span length, load capability, and specific process applications (e.g., launders vs. large basins)—with the manufacturer’s core strengths. Note that “System Integrator” roles are less common in this category; these entities are primarily direct manufacturers (OEMs).

OEM Name	Core Specialization	Typical Applications	Strengths	Limitations	Best-Fit Scenarios
Hallsten	Modular Aluminum Deck Systems	Large basins, oxidation ditches, clearwells, trickling filters	Proprietary interlocking plank design; high load-bearing capabilities; seamless integration of walkways and covers.	Primarily focused on flat, walkable deck styles; less focus on small, intricate hatch work compared to others.	Large surface area coverage requiring full walkability and high structural integrity.
Golden Harvest	Custom Metal Fabrication & Gates	Channels, pump stations, valve vaults, weird geometries	Exceptional custom fabrication; ability to integrate covers directly with gate/valve assemblies; deep engineering support.	Can be cost-prohibitive for simple, commodity-grade standard covers; lead times reflect custom nature.	Complex retrofits requiring covers, gates, and structural supports to be designed as a single unit.
NEFCO Systems	Launder & Weir Covers (Process Optimization)	Clarifier launders, UV channels, density current baffling	Specialized designs that improve process performance (algae blocking, density current mitigation); Density Current Baffle Systems.	Niche focus on clarifier and channel components rather than massive clearwell decking.	Clarifier rehabilitation projects focusing on algae control and TSS reduction.
Whipps	High-Grade Stainless & Aluminum Fab	Gate-integrated covers, heavy-duty hatches, corrosive environments	Industry-leading leakage rate standards; high-precision stainless steel welding; robust hatch mechanisms.	Focus is heavily tied to their gate portfolio; strictly high-spec, may be over-engineered for basic shelter needs.	Projects where water control gates and access covers must share the same high-spec material standards.
McWane Plant & Industrial	Comprehensive Water Infrastructure	Plant-wide coverage, heavy industrial applications, valve vaults	Massive manufacturing scale; broad portfolio including iron, steel, and aluminum; strong distribution and support network.	Large corporate structure can sometimes lack the agility of smaller specialty shops for one-off custom prototypes.	Large-scale municipal projects requiring a single source for valves, gates, and cover systems.

4. TOP OEMs / SYSTEM INTEGRATORS

The following detailed analysis covers the five approved OEMs for aluminum and stainless steel cover systems. Each profile examines the manufacturer’s technical approach, specific product lines, and suitability for municipal and industrial specifications.

Hallsten

Overview: Hallsten is widely recognized as a pioneer in aluminum deck cover systems. Unlike manufacturers that adapt general metal fabrication techniques to covers, Hallsten developed a proprietary interlocking extrusion system specifically designed for the water and wastewater industry. Their focus is almost exclusively on spanning structures that serve dual purposes: containment and access.

Technical Differentiators:
The core of the Hallsten system is the aluminum plank design. These extrusions are engineered to interlock, creating a continuous, high-strength surface that can span significant distances without intermediate supports. This design eliminates the need for a separate structural skeleton in many applications, reducing dead load and simplifying installation.

• Structural Efficiency: The deck itself acts as the structural beam. This “stressed skin” or integrated beam approach allows for high live loads (pedestrian to vehicular) with a relatively low profile.
• Modularity: Hallsten covers are modular, allowing individual planks or panel sections to be removed for basin access. This is superior to welded plate systems where access is limited to specific hatches.
• Surface Traction: The extrusions typically feature knurled or ribbed surfaces integrated directly into the aluminum die, providing permanent slip resistance that does not wear off like grit paints.

Engineering Considerations: Hallsten systems are ideal for covering large rectangular basins, such as aeration tanks or chlorine contact chambers, where operators require unrestricted walking access across the entire surface. Engineers should verify span tables carefully; for extremely wide spans, Hallsten utilizes deep-profile trusses or beams to support the deck.

Golden Harvest

Overview: Golden Harvest is a premier name in the water control industry, known primarily for sluice gates and slide gates. However, their metal fabrication capabilities extend significantly into high-end aluminum and stainless steel covers. Their approach is one of custom craftsmanship, often tackling complex geometries that standard modular systems cannot accommodate.

Technical Differentiators:
Golden Harvest excels in the integration of covers with mechanical equipment. Because they manufacture the gates and actuators, they can design covers with precise penetrations, actuator pedestals, and access hatches that align perfectly with the underlying equipment.

• Material Versatility: While many competitors focus solely on aluminum, Golden Harvest has deep expertise in 304 and 316 stainless steel fabrication. This is crucial for environments with pH extremes or where chloride stress corrosion cracking is a concern for aluminum.
• Custom Geometry: Their shop is set up for bespoke fabrication. They can produce circular covers, trapezoidal shapes for odd channels, and covers that interface with existing, irregular concrete works common in retrofit projects.
• Hatch Design: Their access hatches are robust, often featuring heavy-duty stainless steel hardware, gas-spring lift assists, and safety grates that comply with the strictest safety standards.

Engineering Considerations: Use Golden Harvest when the cover is not just a lid, but a mechanical interface. For example, in a pump station or valve vault where the cover must support actuator stands or allow for the removal of large pumps, their custom fabrication capabilities ensure a seamless fit.

NEFCO Systems

Overview: NEFCO Systems occupies a specialized niche within the cover market. While they produce general-purpose covers, their reputation is built on “Process Performance” covers—specifically designed for clarifier launders and UV channels. They are the industry leader in density current baffles (Stamford baffles) and launder cover systems that actively improve treatment quality.

Technical Differentiators:
NEFCO’s designs are driven by fluid dynamics and biology as much as structural engineering. Their launder covers are designed to exclude sunlight to prevent algal growth, which significantly reduces maintenance (cleaning weirs) and improves effluent quality (lower TSS).

• Launder Covers: These are typically low-profile, hinged covers that fit over the effluent troughs of circular or rectangular clarifiers. They are lightweight for easy operator access and opaque to stop photosynthesis.
• Density Current Baffles: Often sold in conjunction with covers, these fiberglass or aluminum baffles mount on the tank wall to redirect density currents, improving the settling efficiency of the clarifier.
• Weir Systems: NEFCO integrates the cover mounting with the weir and scum baffle supports, providing a single-source responsibility for the entire effluent assembly.

Engineering Considerations: NEFCO is the “Go-To” for secondary clarifiers and chlorine contact tanks. Specifying NEFCO is often justified on an O&M basis: the reduction in labor hours required to scrub algae from weirs can pay for the cover system within a few years. Engineers should look for their “swing-open” designs which allow operators to inspect weirs without fully removing the cover.

Whipps

Overview: Similar to Golden Harvest, Whipps is a major player in the water gate market that leverages its high-precision manufacturing for cover systems. Whipps is renowned for the quality of their stainless steel welding and their rigorous adherence to leakage standards. Their cover systems are often found in critical applications where seal integrity is non-negotiable.

Technical Differentiators:
Whipps brings a “machinist” mentality to fabrication. Their tolerances are typically tighter than general structural fabricators.

• Seal Integrity: Whipps focuses heavily on the gasket and sealing interface. They utilize high-grade EPDM seals and precise corner construction to ensure that odor control covers are truly gas-tight.
• Gate Interface: For channels equipped with Whipps slide gates, the company can provide covers that bolt directly to the gate frame, eliminating the need for complex intermediate concrete work.
• High-Grade Alloys: Whipps is comfortable working with duplex stainless steels and other exotic alloys if the application demands it (e.g., industrial wastewater with high chlorides).

Engineering Considerations: Whipps is an excellent choice for headworks and grit chambers where H₂S levels are lethal and containment is critical for safety. Their ability to deliver “flat top” covers with integrated safety hatches ensures that operators are protected from falls while the gas is contained.

McWane Plant & Industrial

Overview: McWane is a conglomerate with a massive footprint in the water infrastructure world. Through their various divisions and acquisitions, they offer a comprehensive range of plant solutions. Their entry into the cover and fabrication market brings industrial-scale manufacturing efficiency and financial stability to the table.

Technical Differentiators:
McWane’s strength lies in their breadth and capacity. They can package cover systems with valves, pipe, and iron products, offering a holistic supply chain advantage.

• Heavy Duty Applications: McWane systems are often over-designed for durability. They are well-suited for traffic-rated valve vaults and deep pump stations where structural loads are substantial.
• Support Network: Being a large entity, McWane has an extensive network of field engineers and support staff, ensuring that installation issues can be resolved quickly.
• Standardization: They offer standardized designs for common municipal structures (e.g., standard manhole or valve vault sizes), which can reduce lead times and engineering costs compared to fully custom shops.

Engineering Considerations: McWane is ideal for large greenfield projects or major plant expansions where supply chain reliability and vendor reduction are priorities. Their systems are robust and specification-compliant, making them a safe choice for public works projects requiring long service lives.

5. APPLICATION FIT GUIDANCE

Selecting the right OEM often depends on the specific unit process being covered. The following guidance aligns the capabilities of the discussed manufacturers with common facility areas.

Municipal Wastewater Headworks (Screens & Grit)

Challenge: High H₂S, high humidity, corrosive sulfuric acid condensate, need for frequent access to remove screenings.

Recommendation: Whipps or Golden Harvest. Their ability to integrate tight-sealing hatches with slide gates is crucial here. The covers must be gas-tight to make odor scrubbers effective. Stainless steel (316L) is often preferred over aluminum here due to the aggressive acid attack potential, or aluminum with a high-performance coating.

Primary & Secondary Clarifiers

Challenge: Algae growth on weirs, density currents affecting settling, large surface areas.

Recommendation: NEFCO Systems. Their launder covers and density current baffles are specifically engineered for this application. The focus is on process improvement (blocking UV light) rather than just containment. The covers are typically lightweight aluminum to allow easy lifting by a single operator.

Aeration Basins & Oxidation Ditches

Challenge: Massive surface areas, need for walkability to service mixers/aerators, thermal retention in cold climates.

Recommendation: Hallsten. Their modular deck system excels at spanning large rectangular basins. The ability to make the entire surface a safe walkway provides immense operational flexibility. The aluminum oxide layer performs well here as H₂S is typically stripped out or lower concentration than headworks.

Valve Vaults & Pump Stations

Challenge: Heavy live loads (sometimes vehicular), integration with actuators, security.

Recommendation: McWane Plant & Industrial or Golden Harvest. For standard vaults, McWane provides robust, heavy-duty solutions. For complex pump stations requiring custom actuator cutouts and split covers for pump removal, Golden Harvest’s fabrication skills are superior.

Potable Water Clearwells

Challenge: Absolute contamination prevention (Sanitary Seal), large spans, security.

Recommendation: Hallsten. The interlocking plank design minimizes gaps and provides a secure, walkable surface for inspection. The system effectively seals the tank from bird droppings, insects, and rain while allowing for necessary venting.

6. ENGINEER & OPERATOR CONSIDERATIONS

Beyond selecting an OEM, the engineering specification and operational procedures determine the success of the installation. The following considerations are derived from field experience and forensic engineering of failed systems.

Installation & Commissioning Risks

Concrete Interface: The most common installation issue is the mismatch between the theoretical drawings and the “as-built” concrete reality. Concrete walls are rarely perfectly straight or parallel.
Best Practice: Mandate field verification of dimensions before fabrication begins. Specifications should require the OEM to provide adjustable anchoring systems or “field-trim” allowances to accommodate ±1 inch of concrete variance.

Anchor Bolt Selection: Never allow galvanized or zinc-plated anchors in submerged or headspace environments. Specify Type 316 stainless steel adhesive anchors.
Best Practice: Ensure the anchor design accounts for the edge distance in the concrete. Retrofitting covers often involves drilling into old, spalling concrete; pull-tests on anchors may be required.

Maintenance Access & Ergonomics

Hatch Weight: Operators will not open a hatch that is too heavy or dangerous.
Best Practice: Specify a maximum lift force of 30-50 lbs for any manual hatch. Mandate 316SS gas struts or spring-assist mechanisms for anything heavier. Ensure the hold-open arm engages automatically and requires a deliberate action to disengage (preventing wind from slamming the hatch shut).

Fall Protection: When a hatch is open, a fall hazard exists.
Best Practice: Specify hinged safety grates (aluminum or orange powder-coated stainless) underneath the main cover. This allows the operator to open the lid for visual inspection or airflow without exposing themselves to a fall.

Long-Term Durability & Spare Parts

Gasket Memory: All rubber gaskets take a “set” over time, losing their elasticity.
Best Practice: Design covers so that gaskets are attached to the removable panel, not the fixed frame. This allows the panel to be taken to a workshop for gasket replacement rather than requiring work over an open tank.

Isolation Materials: Bituminous paint is the bare minimum for isolation.
Best Practice: For aluminum-to-concrete contact, specify a heavy-duty EPDM or neoprene pad in addition to bituminous coating. This provides a physical capillary break, preventing wicking of moisture into the joint.

Ventilation & Airflow Management

Vacuum Protection: Flat covers can be destroyed by vacuum forces if a basin is drained rapidly without adequate venting.
Best Practice: Ensure the cover design includes properly sized mushroom vents or gooseneck vents. The OEM should verify the vent capacity against the maximum withdrawal rate of the pumps to prevent structural collapse.

7. CONCLUSION

The selection of aluminum and stainless steel cover systems is a critical decision that impacts plant safety, odor control efficiency, and long-term maintenance budgets. It is no longer acceptable to treat covers as generic “miscellaneous metal” items. The interaction between corrosive gases, structural loads, and operator ergonomics demands a specialized engineering approach.

The OEMs highlighted in this article—Hallsten, Golden Harvest, NEFCO Systems, Whipps, and McWane Plant & Industrial—represent the tier-one standard for the industry. Each possesses distinct strengths: Hallsten dominates in large modular decking; Golden Harvest and Whipps excel in high-precision, gate-integrated fabrication; NEFCO leads in process-enhancing launder systems; and McWane provides industrial-scale reliability.

For the consulting engineer and plant manager, the goal is to match these strengths to the specific application. A one-size-fits-all approach rarely works in water and wastewater treatment. By strictly defining the functional requirements—whether it be gas-tightness for H₂S, opacity for algae control, or walkability for maintenance—and specifying the correct metallurgy and isolation details, utilities can ensure their cover systems provide decades of trouble-free service.

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