The shield plates, anchorage components, and bolts of pneumatic shield dams are constantly exposed to alternating wet and dry conditions and siltation. Therefore, corrosion protection directly determines the actual service life of the project. Based on the SL/T793-2021 and SL105 standards for corrosion protection of hydraulic metals, this paper analyzes the entire corrosion protection process for pneumatic shield dams, specifically for inland rivers, silty rivers, and coastal brackish water rivers, to avoid common construction pitfalls.

Pneumatic shield dams, as a new generation of ecological water-retaining structures, are widely used in urban river management and landscape water storage projects. Many projects operate normally initially, but after 3~5 years, rust appears on the shield plates and bolts become stuck and cannot be removed. The root cause is often not poor steel quality, but rather inadequate selection and construction of the corrosion protection system. Areas with fluctuating water levels are the most susceptible to corrosion; therefore, corrosion protection plans must be developed for the shield plates, anchorage components, and fasteners according to their location and the specific river conditions.

I. Anti-corrosion Treatment for Shield Plate Main Body (Q355 Carbon Steel is Most Commonly Used)

Basic Hard Requirements: Steel must be sandblasted to Sa2.5 grade with a roughness of 40~100μm. Primer application must be completed within 8 hours of rust removal; direct painting after manual grinding is prohibited. Weld slag at weld seams must be thoroughly cleaned, and the coating should be thickened.

1. Ordinary Inland Freshwater Landscape River Channels

• Mainstream Cost-Effectiveness, Design Life 10~15 Years: 120~160μm thermal spray zinc, epoxy sealing primer, 120μm epoxy micaceous iron oxide intermediate coat, 80μm polyurethane topcoat, total dry film thickness ≥320μm.
• Prioritized for Rivers with High Sediment Flow Velocity: Apply pure polyurea ≥2mm to the upstream side and water level fluctuation zone for resistance to sediment abrasion; the downstream side uses thermal spray zinc+sealing+micaceous iron oxide+polyurethane topcoat. Polyurea's resistance to water flow impact and alternating wet and dry conditions is far superior to ordinary paint, making it the preferred option for rivers with high sediment content.

2. Coastal brackish water and rivers with high chloride ion content

• Carbon steel shield plate: 160μm thermal spray zinc-aluminum coating + sealing primer + epoxy micaceous iron oxide + fluorocarbon topcoat, with added sacrificial anode cathodic protection, designed life 15-20 years.
• If budget allows, directly use 304/316L stainless steel shield plates, with welds treated by pickling and passivation, minimizing later maintenance workload.

In coastal environments, ordinary paint will only result in coating blistering and rusting after 3-5 years; this is not recommended.

II. Anchorage parts and bolts (the most easily overlooked weak link)

1. Embedded steel plates: Exposed metal parts have the same corrosion protection standard as shield plates; embedded components only require Sa1 level rust removal, followed by application of cement slurry before pouring concrete. Painting embedded parts before pouring concrete is strictly prohibited, as it will reduce the concrete bond strength.

2. Bolts, Washers, and Fasteners

Inland freshwater channels: Grade 8.8 high-strength bolts, hot-dip galvanized with a zinc layer ≥85μm.

Coastal saltwater channels: 316 stainless steel bolts are directly used. Ordinary hot-dip galvanized bolts are prone to rusting and seizing within 2-3 years, making later maintenance and disassembly impossible.

III. Special Anti-corrosion Points for Metal Components Around the Airbag

The bladder rubber must not come into direct contact with rusty or sharp metal. After the anti-corrosion treatment of the inner side of the shield plate, flange, and limit clamp is completed, a 5mm rubber pad should be laid to isolate the airbag; 304 stainless steel should be preferred for the limit clamp to prevent carbon steel rust from falling and damaging the airbag rubber layer.

IV. Operation and Maintenance Management Points

1. On-site welding will damage the finished anti-corrosion layer. Welded areas must be sandblasted to remove rust and the entire coating must be reapplied.
2. Conduct inspections every 2~3 years, focusing on the coating in areas of water level fluctuation. Repair any peeling or damage promptly.
3. Polyurea spraying has strict requirements on environmental humidity; construction is prohibited in rainy or high-humidity environments.

V. Common Engineering Mistakes in Lightning Protection

1. Applying only a simple epoxy zinc-rich primer and topcoat, without thermal spraying/polyurea reinforcement, leads to widespread corrosion in areas with fluctuating water levels within 5~8 years;

2. Using ordinary hot-dip galvanized bolts in coastal conditions results in eventual seizure, making dam maintenance impossible;

3. Painting embedded parts before directly pouring concrete creates a risk of anchorage failure.

Different river conditions require different anti-corrosion solutions. Early selection based on water quality, sediment, and salinity can significantly reduce later maintenance costs and extend the overall service life of the pneumatic shield dam.