Key Points for Anti-Corrosion and Thermal Insulation of Underground Integrated Equipment

I. Corrosion Mechanisms of Underground Integrated Equipment

Submerged integrated sewage treatment equipment is buried underground for extended periods, making the tank and pipeline systems highly susceptible to electrochemical, microbial, and chemical corrosion due to factors such as soil moisture, groundwater infiltration, microbial activity, and stray currents.

Primary Corrosion Types:

• Electrochemical corrosionAs soil acts as an electrolyte, potential differences form across different sections of the metal tank, creating a galvanic cell effect.
• Microbiologically Influenced CorrosionMicrobial metabolites, such as those from sulfate-reducing bacteria in soil, accelerate metal corrosion.
• Chemical corrosionSoil pH, chloride ions, sulfides, and other chemicals directly corrode metal surfaces.
• Stress corrosionResidual stress generated during equipment manufacturing, transportation, and installation, acting synergistically with corrosive media.

II. Selection of Anti-Corrosion Coating Systems

1. Epoxy Coal Tar Enamel Coating

• Features: Strong adhesion, excellent water resistance, and moderate cost
• Suitable for: General soil conditions, neutral to slightly acidic or alkaline environments.
• Structure: Primer + multiple topcoat layers, dry film thickness ≥ 400 μm

2. Epoxy zinc-rich primer + Epoxy micaceous iron intermediate paint + Polyurethane topcoat

• Features: Dual protection with cathodic and shielding systems; excellent weather resistance
• Suitable for: highly corrosive soils, coastal areas, and industrial zones
• Structure: Three-layer composite system, total dry film thickness ≥ 500 μm

3. Polyurea elastomer anti-corrosion coating

• Features: fast curing, high strength, wear-resistant, and durable.
• Suitable for: demanding engineering projects and complex geological conditions
• Benefits: Single-spray application creates a seamless, monolithic protective layer for superior overall protection.

4. Fiberglass anti-corrosion coating

• Features: Excellent corrosion resistance, high strength, and lightweight.
• Suitable for: highly acidic/alkaline soils, areas surrounding chemical industrial parks
• Construction: Fiberglass-reinforced resin, thickness ≥3mm

3. Selection and Construction of Insulation Materials

1. Polyurethane foam insulation

• Low thermal conductivity (≤0.024W/m·K) with excellent insulation performance
• High closed-cell rate (≥90%), excellent waterproof performance
• Foamed in place, securely bonded to the tank.
• Suitable for: Cold northern regions and winter equipment operation

2. Rock wool/glass wool insulation

• Class A fire-resistant material with excellent high-temperature performance
• High water absorption; requires a waterproofing layer.
• Lower cost and easy to install
• For use in areas requiring fire resistance

3. Extruded Polystyrene (XPS) Insulation

• High compressive strength, ideal for scenarios with heavy soil loads
• Low water absorption; stable long-term insulation performance
• Joining required; seal all seams.

IV. Key Points for Anti-corrosion and Thermal Insulation Construction Processes

1. Surface Treatment

• Sandblasting rust removal grade reaches Sa2.5; surface roughness Rz40-70 μm.
• Remove oil, dirt, and welding slag
• Complete primer coating within 4 hours after treatment to prevent rust reversion.

2. Coating Application

• Mix the two-component coating strictly according to the product manual's ratio.
• Apply using airless spray or brush to ensure an even coating.
• Allow the specified interval between each coating layer as per technical requirements.
• Measure total coating thickness with a thickness gauge; deviation ≤ 10%.

3. Insulation layer installation

• Polyurethane Foam: Control raw material and ambient temperatures to ensure foam quality.
• Insulation panels: tight seams, staggered joints, and secure fastening
• Waterproofing layer: Lap width ≥ 100 mm, firmly bonded, no damage.

4. Protective layer construction

• Fiberglass protective layer: fully resin-saturated, no bubbles or delamination
• Polyethylene Heat-Shrinkable Sleeves: Uniform heating, tight shrinkage
• Cement mortar protective layer: uniform thickness, properly cured

5. Quality Control and Acceptance

1. Process Inspection

• Perform visual inspection and roughness testing after surface treatment.
• Measure wet film thickness after each coat application.
• Conduct dry film thickness inspection and spark testing after coating curing.
• Verify density, thickness, and moisture content after insulation layer installation.

2. Final Acceptance

• Coating: Smooth appearance, no sagging, no pinholes, no peeling
• Thickness: Meets design requirements; allowable deviation: -10% to +20%
• Adhesion: Passes 1 or 2 grade per cross-cut test.
• Insulation Layer: Thermal conductivity, density, and water absorption rate meet design requirements.

6. Maintenance and Repair

Daily Inspection:Regularly inspect the equipment exterior, inspection ports, and pipe connections. Promptly address any coating damage or insulation loss.

Local fix:Clean small-area damage and touch up using the original process; for large-scale damage, reapply surface treatment and full protection.

VII. Conclusion

The corrosion and thermal insulation quality of buried integrated equipment directly impacts its service life and treatment performance. Scientific material selection, standardized construction, and rigorous acceptance are critical to ensuring engineering quality. Shandong Zhongnan Environmental Protection Equipment Co., Ltd. provides tailored corrosion protection and thermal insulation solutions based on local soil conditions, climate characteristics, and operational requirements.