Corrosion Protection Coating Systems for Steel Structures in Aquatic Environments

1.GBT 30790.2-2014: Paints and Varnishes – Protective Coating Systems for the Corrosion Protection of Steel Structures – Part 2: Environmental Classification

 

The type of water (freshwater, brackish water, or seawater) has a significant impact on the corrosion of steel.

 

Corrosiveness is also influenced by the oxygen content in water, the types and quantities of dissolved substances, and water temperature. Additionally, biological growth from animals or plants can accelerate corrosion (the maintenance of weathering steel also requires attention to this aspect).

 

Three distinct areas can be defined for structures submerged in water:

 

– Submerged Zone: This area is permanently immersed in water.

 

– Tidal Zone (Water Level Fluctuation Zone): This area experiences changes in water levels due to natural or anthropogenic influences, leading to increased corrosion from the combined effects of water and atmosphere.

 

– Splash Zone: This area is wet due to wave action and splashing, which creates very high corrosion stress, particularly in the presence of seawater.

 

For structures submerged in water or buried in soil, corrosion is typically localized, making it difficult to define a corrosion severity level.

 

Despite this, the aim of this section is to provide a classification for various environments. Table 2 lists three different environments along with their symbols.

 

Note: In many cases, cathodic protection should be considered.

2.GBT 30790.5-2014: Paints and Varnishes – Protective Coating Systems for the Corrosion Protection of Steel Structures – Part 5: Protective Coating Systems

 

Paints are formulated by mixing three primary components:

1.Pigments: Finely ground inorganic or organic powders that provide color, opacity, film adhesion, and, in some cases, barrier or corrosion-inhibiting protection, such as micaceous iron oxide (MIO) or flake aluminum.

 

2.Binders: Typically resins or oils, but can also include organic compounds like two-component epoxy resins or inorganic compounds like soluble silicates. The binder is the film-forming component of the paint.

 

3.Solvents: Used to dilute the binder and facilitate the application of the paint. Solvents are usually organic liquids or water.

 

Coating Options:

– Coating Option 1: Anti-corrosive coatings.

– Coating Option 2: Thermal spraying + anti-corrosive coatings.

 

Environmental Classifications:

– Im1: Immersion in freshwater.

– Im2: Immersion in brackish or seawater.

 

Seawater immersion in tidal zones is typically divided into four areas:

 

1.Splash Zone: Just above high tide, typically the most corrosive, with an average corrosion rate of approximately 75 μm/a.

 

2.Tidal Zone: The area between high and low tide, often covered with marine organisms or debris, with a corrosion rate of about 35 μm/a.

 

3.Low Water Zone: Below low tide, exhibiting similar corrosiveness to the splash zone (75 μm/a).

 

4.Permanent Immersion Zone: Extending from low water to the seabed, with a lower corrosion rate of about 35 μm/a.

 

Freshwater Immersion: The corrosion rate in freshwater is lower than in saltwater, ranging from 30 to 50 μm/a.

 

3.GBT 28699-2012: General Technical Conditions for Protective Coatings on Steel Structures

 

4DBJ 46-057-2020: Technical Standards for Corrosion Protection of Building Steel Structures in Hainan Province

 

The durability of corrosion protection systems can be categorized as medium-term, long-term, and ultra-long-term:

 

1.Medium-term (M): 8 to 15 years.

2.Long-term (H): 16 to 25 years.

3.Ultra-long-term (VH): 26 years and beyond.

 

5.SL 105-2007: Specifications for Corrosion Protection of Hydraulic Metal Structures

 

5.3.1 The thickness of the metal coating in metal thermal spraying composite protection systems can refer to Table 5.3.1 for selection.

 

5.3.2 The sealing coating should be compatible with the metal sprayed layer, have lower viscosity, and possess certain corrosion resistance. It is advisable to use epoxy sealing coatings; for pH > 7 water environments, phosphating primers may be selected.

 

5.3.3 The type and thickness of intermediate and topcoats should be referenced according to the usage environment.

 

6.JTS153-3-2007: Technical Specifications for Corrosion Protection of Steel Structures in Port Engineering

 

6.1.3 Corrosion protection measures should be determined based on structural location, protection lifespan, construction, maintenance management, safety requirements, and technical-economic benefits, and must comply with the following provisions:

– 6.1.3.2 For the splash zone and water level fluctuation zone, it is advisable to use heavy-duty anti-corrosion coatings or metal thermal spraying layers with a sealing coat for protection; resin mortar or coated organic composite layers, as well as composite corrosion-resistant metal layers, may also be used.

 

– 6.1.3.3 For the submerged zone, cathodic protection can be used in conjunction with coatings or employed independently. When using cathodic protection alone, measures for corrosion protection during the construction phase should be considered.