Knowing the technical characteristics of these coatings, their classes and the correct preparation of the surface, avoids costly repairs due to corrosive phenomena.
Corrosion protection is a dominant requirement for all exposed structures in an offshore or offshore marine environment and although sometimes areas have been designed to withstand the dominant environment, most of them are protected with liquid coatings.
by: Alejandro Lagler*
The correct selection and use of these coatings is now recognized throughout the industry as a key requirement to prevent costly maintenance programs due to early coating system failure or premature collapse of the predicted service life.
The maintenance and repair of marine structures has always been a concern, especially with regard to the long-term operation of anti-corrosion paint systems. Therefore, it has become critical that performance tests for the evaluation of coatings (fitness in purpose of use) are performed with the environments that will be found in practice. The objective of this work will be to identify the appropriate coatings, the different types of surface preparations, an approach to the technical characteristics that the coatings must meet, the type of appropriate maintenance and the future of marine coatings.
Specifications
The environmental conditions at sea are relentless, exposing the weaknesses of the structures and protective systems, constantly trying to return the steel to its original state (rust).
The power of corrosion has caused catastrophic failures resulting in loss of human life, significant financial losses and serious environmental damage. Knowledge, good selection of corrosion protection systems, proper planning and good painting practices can prevent these problems from occurring.
There is no appropriate coating system for all situations. However, today corrosion protection technology focuses on corrosion protection, operational health protection, individual safety and environmental care.
Some technologies are gaining favor in the marine market, such as solvent-free coatings, 100% solid in volume, edge-retentive materials for tank interiors, high abrasion resistance coatings, high immersion resistance coatings, high adhesion resistance coatings of marine organisms and high resistance coatings to marine weathering.
Due to environmental concerns, organ-tin-based anti-fouling (anti-captivative) products are being eliminated. New biocide-free anti-vectors are available on the marine market from leading marine coating manufacturers.
New high-performance acrylic-based polysiloxane coatings and mixtures of epoxy resins with acrylics have seen a growing wave of use in the marine and industrial markets. Organic Volatiles (VOC) emission regulations as well as health and safety issues in many countries have forced coating manufacturers to develop new technologies to replace hazardous materials and develop new versions of friendlier and higher-performance products.
Characteristics of coatings for sides and superestructur:
- Excellent corrosion resistance at the air-water interface.
- Ease of maintenance.
- Low Solar Absorption (LSA) technology.
- Excellent weather resistance with high color retention.
- Higher yield per liter and decreased cost per square meter.
Characteristics of coatings for roofs:
- Covers and levels plate deformations with elastomer technology.
- Anti-skid finish resistant to impact and abrasion.
- High UV resistance and excellent color retention
- Easy maintenance and repair, Can be easily repaired.
Characteristics of coatings for tank interiors:
- Epoxy coating 100% solids.
- Free of solvents and coal tar, Reduces the risk of explosion to 0%.
- Excellent corrosion resistance.
- Luminicent and thixotropic.
- Uniform layer of high thickness in the edges of the steel, giving greater protection to it.
- Low maintenance costs and easy application.
- Resistant to a wide range of chemicals and petroleum derivatives (diesel, turbosin, etc.) for cargo tanks.
- ANSI/NSF Standard 61 certificate. For drinking water tanks.
Characteristics of Antifouling coatings (anti-adhesive):
- Excellent resistance to adhesion of marine organisms.
- Low toxicity and limited emission of biocides into the sea.
- Preferably without biocides, without tin salts, zero environmental impact.
- Attachment to document IMO AFS/CONF/26.
- Low interference with the speed of the boat, low coefficient of friction with water.
- Decrease in fuel consumption.
Types of Antifouling coatings (anti-vegetative):
- Soluble matrix antifouling agents
- Antifouling by contact.
- Self-polishing antifouling.
- Controlled detachment antifouling agents
- Non-stick without biocides or metal salts.
Characteristics of Preconstruction coatings:
- Excellent corrosion resistance due to galvanic protection.
- No interference with weld quality.
- Excellent resistance to bending, welding and plate cutting with oxyacetylene equipment.
- Wide compatibility with most types of coatings.
Surface treatments
The expected service life of a coating or coating system is directly proportional to the degree of surface preparation made prior to the application of the protective system.
1. The first objective of surface preparation is to remove from the substrate contaminants and surface imperfections that affect the performance of a coating, some of which are:
- Organic inlays.
- Oil and grease
- Salts, dust and dirt
- Rolling husk and rust (corrosion)
- Aged coatings
- Surface imperfections
2. The second objective is to provide an "anchor pattern" or "anchor profile", which improves the mechanical adhesion of a coating to the prepared surface.
3. Standards established to determine the correct preparation of the surface.
ISO International Standard
The Society for Protective Coatings (SSPC)
International Marine Hydroblasting Standard.
4. Most commonly used Preparation Methods
- Cleaning with solvents.
- Manual cleaning.
- Mechanical cleaning.
- Chemical cleaning.
- Cleaning with abrasive torching.
- Cleaning with hydroblast.
- Cleaning with centrifugal abrasive torch.
Hydroblast.
- Surface preparation that uses high-pressure water instead of solid abrasives.
- Removes firmly bonded contaminants, salts and aged coatings.
- Ultra High Pressure Hydroblast:
- It operates at pressures above 1,700 bar (25,000 i.s.p.), although most equipment operates between 2,000-2,850 bars (30,000-40,000 p.s.i.).
Selection of marine coatings
Some of the essential requirements can be summarized in the following:
Environment, Health and Safety:
Environmentally friendly systems
Low Content of Organic Volatiles (VOC's)
Free of metals and toxic materials (lead, chromium, coal tar, etc.)
IMO Legislation:
Anti-vegetatives with low or no biocide or tin content.
Comply 100% with IMO agreements. (International Maritime Organization)
Technology:
- Antifouling technology of the non-stick type for live work.
- Outdoor polysiloxane technology and weather resistance.
- Polyurethane elastomer technology for roofs.
- Epoxy-phenalcamine technology for multipurpose primary.
- Higher % of solids by volume (by high solids)
- Increased durability and long-term protection.
- Reduce onboard maintenance and fuel consumption, as well as indoor temperature in the side and superstructure sections.
- Extend the useful life of the boats.
Maintenance process
Ship maintenance painting is normally divided into two areas: onboard painting ("during the voyage") and dry dock painting.
On-board maintenance
Onboard maintenance painting is an endless process that must be planned from the new construction phase.
Each ship should have a maintenance paint best practices manual that includes product data sheets, material safety data sheets, and a coating program for each area. This document should also address the surface preparation required for various conditions and contain detailed and sharply illustrated instructions on how to mix and apply the necessary coatings.
Additionally, all necessary equipment must be on board, including spray equipment, mixers for two-component paints, and a paint cabinet containing the correct coatings and thinners. Placing a large poster in the closet demonstrating proper mixing techniques and correct use of solvents will help educate the crew.
It is not recommended to apply large areas with brush or roller because it is very difficult to match the appearance of the original layer applied by spray. It is also impossible to achieve the recommended film thicknesses for high-thickness epoxies and many two-component polyurethanes with one layer per brush or roller.
Sometimes a contractor's crew travels on board to perform those jobs that the ship's crew can't typically handle. This can be solved very well when the part of the boat to be painted will not be used during a particular crossing.
It is also common for a contractor to provide a small group of workers to perform standard maintenance painting when the ship's painters do not have time to do so.
Dry dock maintenance
Underwater hull inspection and major repair work are completed while the ship is in dry dock. Cleaning of indoor areas by abrasive blowtorch can be carried out in the yard without causing problems for the boat crew.
Planning and preparation are key to successful dike. The cost of having a ship out of service, added to the daily cost of the dock is very high. All materials and equipment must be on site prior to the ship's arrival.
Most marine coating manufacturers will supply enough material for the job and accept any leftover material after the work is completed. The port engineer and the coating supplier's technical service representative must maintain a daily report of the materials used and arrange for the return of the unused material.
*Cia. Mexicana de Pinturas Internacional
[email protected]
