Aux 2 Unit 17 Q3

Surface preparation is a crucial step in the painting process of a vessel’s hull in dry-dock. Proper surface preparation ensures that the new coating adheres effectively to the hull, enhances the durability of the paint system, and improves the vessel’s overall performance by protecting it from corrosion, fouling, and wear. Below are the key stages of surface preparation for painting a vessel’s hull in dry-dock:

1. Cleaning the Hull Surface

• Purpose: The hull must be free of any contaminants, such as marine growth (e.g., barnacles, algae), dirt, salt, grease, oil, and loose paint, before any surface preparation begins. This ensures proper adhesion of the new coating.
• Methods:
  • High-Pressure Water Blasting: A high-pressure water jet is used to remove dirt, marine growth, and salt deposits from the hull. This method is often the first step in cleaning, ensuring that the surface is free from any large debris or buildup.
  • Degreasing: Any oily or greasy areas are treated with appropriate cleaning agents to remove residues that may affect paint adhesion.

2. Abrasive Blasting (Grit Blasting or Sandblasting)

• Purpose: Abrasive blasting is used to remove old paint, corrosion, and any remaining contaminants from the hull’s surface. It also roughens the surface to create a suitable texture for the new paint to adhere to.
• Methods:
  • Grit Blasting: This is the most common method for surface preparation. Abrasive materials, such as steel grit or sand, are propelled at high velocity onto the hull’s surface, stripping away old paint, rust, and corrosion.
  • Shot Blasting: In some cases, round steel shots are used to clean and prepare the hull surface, especially if a smoother finish is required.
• Surface Profile: The roughened surface, or “profile,” created by abrasive blasting, is essential for the paint system to properly adhere. The surface profile must be within the manufacturer’s specifications for the chosen paint system.
• Blasting Standards: The cleanliness level achieved by blasting is often measured according to international standards such as ISO 8501-1 (Standards for surface cleanliness) or the Society for Protective Coatings (SSPC) standards. A common standard for ship hull preparation is SA 2.5 or Near-White Metal Blast Cleaning, which removes almost all rust and old coatings.

3. Mechanical Cleaning

• Purpose: In areas where abrasive blasting is not possible (e.g., due to space constraints or the sensitivity of equipment), mechanical tools can be used to clean the hull surface.
• Methods:
  • Power Tools: Tools such as grinders, wire brushes, and needle guns are used to manually remove rust, scale, and old paint from smaller areas or tight spaces.
  • Chipping Hammers: These can be used to break away heavy layers of rust and old paint, particularly in localized spots.
• Application: Mechanical cleaning is often used as a supplementary process to prepare areas that cannot be reached by abrasive blasting.

4. Rust and Corrosion Treatment

• Purpose: Any remaining rust or corrosion on the hull, especially in areas that are difficult to reach with abrasive blasting or mechanical tools, must be treated to prevent further degradation.
• Methods:
  • Rust Converters: Chemical rust converters are sometimes applied to convert remaining rust into a stable compound that can be painted over.
  • Spot Blasting: In cases of localized rust, small areas may be subjected to focused abrasive blasting or wire brushing to eliminate the corrosion.

5. Surface Roughness Check

• Purpose: After abrasive blasting or mechanical cleaning, the surface roughness or profile must be checked to ensure it meets the requirements for the paint system being applied.
• Methods:
  • Surface Profile Gauge: Instruments like a surface profile gauge or replica tape are used to measure the depth of the profile created by blasting. The ideal profile depth depends on the paint system but typically ranges from 50 to 100 microns.
• Importance: If the surface profile is too smooth, the paint may not adhere properly. If it’s too rough, the paint may not form a uniform protective layer.

6. Surface Cleanliness Check

• Purpose: After blasting or mechanical cleaning, the surface must be checked to ensure it is free from contaminants such as dust, salt, or loose debris that may have settled during the preparation process.
• Methods:
  • Blowdown: Compressed air is used to remove any remaining dust or debris on the hull surface after blasting.
  • Tissue or Tape Test: A tape or cloth can be pressed onto the hull to check for dust or debris. If too much residue is present, the surface must be cleaned again.
  • Salt Test: Surface salt contamination can be measured using methods such as the Bresle test or other salt detection kits. High salt content can lead to poor paint adhesion and premature coating failure.

7. Priming (If Required)

• Purpose: In cases where the hull may be exposed to the atmosphere for extended periods before painting, a primer may be applied to protect the cleaned surface from flash rusting or oxidation.
• Methods:
  • Temporary Primer: A temporary primer, sometimes referred to as a holding primer, can be applied to protect the steel until the full paint system is applied.
  • Surface Tolerance Primers: If blasting does not achieve the desired cleanliness, a surface-tolerant primer may be used that can bond effectively to less-than-ideal surfaces.

8. Final Inspection Before Painting

• Purpose: A final inspection is conducted to ensure that the surface preparation meets the necessary standards before the application of the paint system.
• Inspection Criteria:
  • Surface Cleanliness: Ensure that there is no loose debris, rust, or contaminants.
  • Surface Profile: Verify that the surface roughness is within the recommended range for the coating system.
  • Environmental Conditions: Check that humidity, temperature, and surface moisture levels are within the acceptable limits for painting to proceed (e.g., relative humidity should generally be below 85%, and the surface temperature should be above the dew point).

Conclusion:

Surface preparation for painting a vessel’s hull in dry-dock is a multi-step process that involves cleaning, abrasive blasting or mechanical cleaning, checking for corrosion, and ensuring the proper surface profile for paint adhesion. The effectiveness of this preparation is critical to ensuring the durability and performance of the paint system, preventing corrosion, and optimizing the vessel’s efficiency. Proper surface preparation ensures that the new coating adheres well, providing long-term protection against the harsh marine environment.

Abrasive blasting is a widely used method for surface preparation, especially in marine applications, to clean and prepare surfaces before coating. It involves propelling abrasive material (such as sand, grit, or steel shot) at high velocity to remove rust, old paint, and other contaminants. While it is highly effective, there are several advantages and disadvantages associated with abrasive blasting.

Advantages of Abrasive Blasting:

1. Efficient Cleaning and Surface Preparation
   • Advantage: Abrasive blasting is one of the most effective and efficient methods for removing old paint, rust, corrosion, and other contaminants from metal surfaces, especially large areas such as ship hulls.
   • Benefit: It allows for rapid and thorough surface cleaning, ensuring the surface is properly prepared for the application of new coatings.
2. Creates an Ideal Surface Profile
   • Advantage: Abrasive blasting roughens the surface, creating a profile that enhances the adhesion of paint or other coatings. This surface roughness is essential for achieving a strong bond between the substrate and the coating.
   • Benefit: A properly profiled surface ensures better coating adhesion, leading to longer-lasting protection.
3. Removes Rust and Corrosion
   • Advantage: Abrasive blasting effectively removes rust and other forms of corrosion from metal surfaces, stopping the corrosion process and preparing the surface for protective coatings.
   • Benefit: It extends the life of the surface by preventing further corrosion, especially in harsh marine environments.
4. Fast and Time-Saving
   • Advantage: Compared to manual cleaning methods (such as wire brushing or grinding), abrasive blasting is significantly faster and can cover large areas in a short amount of time.
   • Benefit: This efficiency makes it a preferred method for large-scale surface preparation, reducing downtime during maintenance operations.
5. Versatile and Adaptable
   • Advantage: Abrasive blasting can be used on various surfaces, including steel, aluminum, concrete, and fiberglass. Different abrasive materials can be selected depending on the surface and the level of cleaning required.
   • Benefit: The versatility of abrasive blasting makes it suitable for various industries, including marine, automotive, and construction.
6. Effective for Hard-to-Reach Areas
   • Advantage: Abrasive blasting can reach into corners, crevices, and other hard-to-reach areas where manual cleaning methods may be insufficient.
   • Benefit: It ensures that even areas that are typically difficult to clean are properly prepared for coating.
7. Environmentally Friendly Options
   • Advantage: With modern advancements, certain abrasive materials, such as water or eco-friendly abrasives (e.g., crushed glass or garnet), reduce the environmental impact of blasting.
   • Benefit: These options help minimize environmental pollution while still achieving effective cleaning results.

Disadvantages of Abrasive Blasting:

1. Health and Safety Hazards
   • Disadvantage: Abrasive blasting can generate significant amounts of dust, which may contain harmful materials such as silica or lead from old paint coatings. This dust poses health risks to workers, including respiratory issues, lung diseases (e.g., silicosis), and eye injuries.
   • Drawback: Stringent safety measures, including proper ventilation, dust collection systems, and personal protective equipment (PPE), are required to mitigate these risks.
2. Environmental Concerns
   • Disadvantage: Abrasive blasting can release large amounts of dust and waste material into the environment, particularly if conducted in open areas. This can lead to contamination of nearby water bodies, soil, and air.
   • Drawback: Additional containment measures, such as tarps and dust control systems, may be necessary to prevent environmental pollution.
3. Surface Damage Risk
   • Disadvantage: If not done properly, abrasive blasting can damage the surface being cleaned. Excessive pressure or the use of inappropriate abrasive material can cause pitting, gouging, or warping of the metal or surface.
   • Drawback: Damage to the surface can increase maintenance costs and may require additional repairs or rework before painting.
4. High Equipment and Material Costs
   • Disadvantage: Abrasive blasting requires specialized equipment, including compressors, blast nozzles, and containment systems. The cost of abrasive materials (such as garnet, steel grit, or aluminum oxide) can also be high.
   • Drawback: Initial setup costs and ongoing operational expenses may be significant, particularly for large-scale operations.
5. Noise and Vibration
   • Disadvantage: Abrasive blasting generates high levels of noise, which can be hazardous to workers and nearby residents. The vibrations from the blasting process can also cause damage to surrounding structures or delicate equipment.
   • Drawback: Ear protection is necessary for workers, and measures to reduce noise pollution may be required in certain environments.
6. Waste Disposal
   • Disadvantage: Abrasive blasting produces large amounts of waste, including spent abrasive material, paint chips, rust particles, and other debris. Proper disposal of this waste can be challenging and costly, especially if the materials contain hazardous substances (e.g., lead-based paints).
   • Drawback: Waste disposal must comply with environmental regulations, which can add to the complexity and cost of the operation.
7. Surface Preparation Limitations
   • Disadvantage: Abrasive blasting may not be suitable for every surface or material. For example, softer metals like aluminum or delicate surfaces may require gentler cleaning methods to avoid damage.
   • Drawback: In these cases, other methods such as wet blasting or chemical cleaning may be preferred, which may not provide the same level of efficiency as abrasive blasting.

Conclusion:

Abrasive blasting is an efficient and versatile method for surface preparation, especially for large areas like ship hulls, due to its ability to quickly remove rust, old paint, and contaminants while creating an ideal surface profile for coatings. However, it comes with health, safety, environmental, and cost considerations. Proper precautions, such as safety equipment, containment measures, and waste management, are essential to mitigate the disadvantages and ensure a successful and safe blasting operation.

Hydroblasting, also known as water jetting or high-pressure water blasting, is a method of surface preparation that uses high-pressure water to remove rust, old paint, scale, and other contaminants from a surface. It is commonly used in marine, industrial, and construction applications. Hydroblasting can be done at various pressure levels, including low pressure, high pressure, and ultra-high pressure (UHP). Like any surface preparation method, hydroblasting has its advantages and disadvantages.

Advantages of Hydroblasting:

1. Environmentally Friendly
   • Advantage: Hydroblasting uses only water for cleaning, without introducing chemicals or abrasive materials into the environment. This minimizes the ecological impact, particularly in marine applications where contamination must be carefully managed.
   • Benefit: It is ideal for environmentally sensitive areas, as there is no risk of chemical pollution or contamination from abrasive materials.
2. No Abrasive Residue
   • Advantage: Since hydroblasting uses water instead of abrasives (like sand or grit), there is no abrasive residue left behind after the process. This reduces the need for post-blasting cleanup and eliminates disposal concerns related to abrasive media.
   • Benefit: Clean-up is easier, faster, and less costly compared to abrasive blasting, where abrasive particles need to be collected and disposed of.
3. Surface Preservation
   • Advantage: Hydroblasting is less aggressive than abrasive blasting and reduces the risk of surface damage. It can effectively clean surfaces without causing pitting, warping, or etching, making it suitable for more delicate surfaces, such as aluminum or softer metals.
   • Benefit: This method is ideal for surfaces that require cleaning without altering the underlying structure or causing damage to coatings that are not meant to be removed.
4. Removes Contaminants and Embedded Salts
   • Advantage: Hydroblasting is particularly effective at removing contaminants like salts and chemicals that may be embedded in the surface, especially in marine applications where saltwater exposure is common.
   • Benefit: Removing salts and contaminants ensures better adhesion of coatings, improves the lifespan of the new coating, and reduces the risk of corrosion under the paint layer.
5. Dust-Free Operation
   • Advantage: Unlike abrasive blasting, which creates dust and airborne particles, hydroblasting generates no dust. This makes it safer for workers and minimizes the need for dust control measures, particularly in enclosed or populated areas.
   • Benefit: It reduces health risks for workers, improves visibility during the cleaning process, and eliminates concerns about dust contaminating the surrounding area.
6. Effective in Removing Tough Contaminants
   • Advantage: Hydroblasting, especially ultra-high-pressure water blasting, can be extremely effective at removing tough contaminants such as thick rust, heavy marine growth, old coatings, and grease.
   • Benefit: It can quickly and efficiently clean surfaces, reducing the time required for surface preparation.
7. Works on Complex Surfaces
   • Advantage: Hydroblasting can clean irregular or complex surfaces that may be difficult to access with abrasive blasting equipment. The high-pressure water can reach into crevices and around corners.
   • Benefit: This makes it ideal for cleaning surfaces with intricate geometries, such as tanks, pipes, and confined spaces.

Disadvantages of Hydroblasting:

1. Water Management and Waste Disposal
   • Disadvantage: Hydroblasting uses large volumes of water, which can create significant wastewater that needs to be contained, treated, and properly disposed of. This can be challenging in certain locations or when dealing with hazardous materials.
   • Drawback: Wastewater management can add complexity and cost to the project, especially when the water contains contaminants like old paint, oil, or other hazardous materials.
2. Limited Surface Profile Creation
   • Disadvantage: While hydroblasting is effective at cleaning surfaces, it does not create a rough surface profile like abrasive blasting. The rough profile is critical for paint or coating adhesion in many applications.
   • Drawback: For surfaces that require a specific surface roughness to ensure proper coating adhesion, hydroblasting may not be suitable without additional surface profiling techniques (e.g., mechanical tools or abrasive blasting).
3. Equipment and Operational Costs
   • Disadvantage: Hydroblasting equipment, particularly for ultra-high-pressure applications, can be expensive to purchase or rent. Additionally, the energy requirements to pressurize the water can be high, adding to operational costs.
   • Drawback: The initial investment in hydroblasting equipment and ongoing operational expenses can be higher than those for other surface preparation methods.
4. Surface Drying Requirement
   • Disadvantage: After hydroblasting, the surface remains wet and must be thoroughly dried before the application of coatings or paints. This can extend the overall time required for surface preparation, especially in humid or cold environments where drying is slower.
   • Drawback: Delays in surface drying can extend project timelines, and if not dried properly, moisture trapped under the coating can lead to coating failure or corrosion.
5. Potential for Flash Rusting
   • Disadvantage: Once the surface has been hydroblasted and cleaned, especially in marine or humid environments, there is a high risk of flash rusting if the surface is not dried and coated quickly.
   • Drawback: Flash rusting can require additional cleaning steps or even re-blasting, which can delay the project and increase costs.
6. Limited Effectiveness on Certain Materials
   • Disadvantage: Hydroblasting may not be as effective on certain hard, tough coatings or heavy corrosion, especially at lower pressures. It may require multiple passes or higher pressure to achieve the desired cleaning result, which can be less efficient.
   • Drawback: This can reduce the overall productivity of the process compared to abrasive blasting, which may remove tough coatings more effectively.
7. Safety Concerns
   • Disadvantage: High-pressure water jets, especially in ultra-high-pressure hydroblasting, can pose significant safety risks to workers. The pressurized water stream can cause serious injuries if not handled properly.
   • Drawback: Workers must be trained and use proper protective gear, such as reinforced clothing, face shields, and gloves, to minimize the risk of injury, which can increase the operational complexity and cost.

Conclusion:

Hydroblasting offers several advantages, particularly in terms of environmental friendliness, dust-free operation, and its ability to clean surfaces without damaging them. However, it also comes with certain challenges, such as the need for effective water management, the inability to create surface roughness for paint adhesion, and the potential for flash rusting. Proper planning and consideration of the application environment, materials, and project requirements are essential for deciding whether hydroblasting is the best method for surface preparation.