Introduction to Ship Coatings and Standards

Paint Industry

Coating Industry:

Recently, the phrase "a light boat has crossed a thousand mountains" in Li Bai's "The Fastest Poem in the World" and "Early Departure of the White Emperor City" has resonated throughout the internet with the hot release of the domestic animated film "Three Thousand Miles in Chang'an".   

Early Departure from White Emperor City

Li Bai from the Tang Dynasty

Amidst the colorful clouds of the White Emperor, a thousand miles of Jiangling are returned in one day.

The sound of apes on both sides cannot be stopped, and the light boat has crossed the mountains.

Once upon a time, one could only cross the mountains by boat.

Now, the giant ship rides the wind and waves, singing and sailing far away.

A ship larger than an aircraft carrier! The world's largest 24116TEU container ship built by China Shipbuilding Group, with a total length of 399.99 meters, a molded width of 61.5 meters, a molded depth of 33.2 meters, and a maximum number of stacking layers of up to 25, capable of loading 24116 standard containers. It is currently the largest container ship type in the world with the largest loading capacity.

With the rapid development of modern industry, the modernization, high-speed, high-efficiency transportation, and environmental protection of ships are increasingly receiving widespread attention, and ship coatings are also constantly being updated. According to the different parts of the ship, ship coatings can be generally divided into bottom coatings, waterline, outboard, deck coatings, oil tank coatings, drinking water tank coatings, cargo tank coatings, ballast tank coatings, etc.

1、 Quality requirements for ship bottom coatings

The natural corrosion rate of steel in seawater is 0.1 mm/a. Marine organisms attached to the outside of the ship's bottom can also cause a decrease in navigation speed, resulting in an increase in fuel and removal costs. Therefore, it is required that the ship's bottom coating have excellent seawater resistance and anti fouling properties. Anti fouling paint is one of the important products of ship paint, which is composed of anti fouling agents in the paint film that slowly dissolve in seawater for a certain period of time, thereby preventing the attachment of marine organisms. For a long time, organic tin based antifouling paint has been widely used as a practical and effective protective coating for areas below the waterline of ship hulls. But with the widespread use of organic tin materials in anti fouling coatings, the pollution of organic tin to the marine environment has gradually attracted people's attention. The International Maritime Organization (IMO) requires a ban on the use of organic tin based antifouling coatings from January 1, 2003, and a complete ban on the use of such products on ships from January 1, 2008, gradually phasing out organic tin based antifouling coatings from the historical stage. The national standard GB/T 6822-2007 "Anti fouling and Anti rust Paint System for Ship Hulls" has been implemented since April 1, 2008. This standard stipulates that the total amount of tin in the anti fouling paint should be less than 2500mg/kg of dry paint samples. After the implementation of this standard, it will provide a practical and feasible national standard that is close to the international advanced level for various types of ship anti fouling coatings and supporting ship bottom anti rust coatings in China. In recent years, Chinese ship bottom anti rust paint production enterprises have increased their research and development efforts, and environmentally friendly anti fouling coatings have developed rapidly. One of them is the new Wuxi anti fouling coating with cuprous oxide as the main anti fouling agent.

2、 Quality Requirements for Waterline, Outboard, and Deck Coatings

The waterline, outer hull, and deck are subject to corrosion due to alternating dry and wet conditions, damage caused by wave impact, and aging caused by ultraviolet radiation. The coating on this area should have good seawater corrosion resistance, excellent physical and mechanical properties, wear resistance, impact resistance, and weather resistance. Due to the harm of carbon tetrachloride solvent to the atmosphere, it has been listed as restricted or prohibited, and the production of chlorinated rubber coatings using such solvents is gradually restricted or prohibited. Developing high chlorinated polyethylene and thermoplastic acrylic resin to replace chlorinated rubber for use in waterline paint; Develop modified epoxy paint, acrylic paint, and high-performance acrylic polyurethane paint for ship hulls; Developing deck anti-corrosion coatings with excellent wear resistance, weather resistance, and chemical resistance is a trend in the development of ship coatings. National standards such as GB/T 9260-2008 "Marine Waterline Paints", GB/T 6745-2008 "Hull Paints", and GB/T 9261-2008 "Deck Paints", which were newly formulated and revised in 2008, have put forward higher requirements for the performance of related products. Coating manufacturers should adjust their product formulas to improve their overall performance.

3、 Quality requirements for cargo oil tank coatings

Our country's cargo oil tank paint mainly uses pure epoxy paint and epoxy asphalt paint, both of which have good oil resistance, chemical resistance, and water resistance, and can meet the requirements of oil resistance and sea water resistance of cargo oil tanks. However, due to the large number of coating passes, this is more troublesome for the construction of ventilated compartments. In order to reduce the number of coating passes, simplify the construction process, reduce environmental pollution and harm to human health, it is necessary to develop thick film cargo oil tank coatings. The newly revised GB/T 6746-2008 "Marine Oil Tank Paints" and GB/T 9262-2008 "Marine Cargo Tank Paints" in 2008 have improved the requirements for salt spray resistance of the products. In addition, the International Maritime Organization (IMO) has completed the localization of the performance standards for protective coatings for ship empty holds and cargo oil tanks, namely GB/T 31820. The main performance requirements for coatings include resistance to carbon dioxide, sulfur dioxide and hydrogen sulfide gases, organic acid resistance, and heat resistance (70 ℃); The coating on the top surface of the oil tank is required to be able to withstand heat/cold cycling. In response to the new standard requirements proposed by IMO, Chinese ship paint manufacturers should make early preparations.

4、 Quality requirements for coatings for drinking water tanks

The coating for the drinking water tank requires that the coating has passed the water resistance test and is resistant to water. Domestic drinking water tank coatings are mainly pure epoxy coatings, which have good water resistance, oil resistance, and chemical resistance, and low toxicity. The disadvantage is that the coating film is difficult to cure when the construction temperature is below 5 ℃. The standard for domestic drinking water tank coatings is GB 5369-2008 "General Technical Conditions for Marine Drinking Water Tank Coatings", which is a mandatory national standard issued in December 2008 and implemented on December 1, 2009. The original standard physical and chemical indicators basically meet the usage requirements, but their hygiene requirements no longer meet the increasingly strict requirements of environmental protection and hygiene protection. For example, ships docked in the United States require the coating of drinking water tanks to obtain FDA certification, and some shipowners have proposed to conduct more detailed toxicological tests on the coating of drinking water tanks. The revised standard basically retains the characteristic physical and chemical indicators in the original standard, Significant changes and additions have been made to the hygiene requirements in accordance with the Ministry of Health's document No. 161 [2001]. The revised standard not only stipulates the need for sanitary testing of drinking water quality, but also stipulates that toxicological tests for LD50, Ames, and mammalian cell chromosomal aberrations in immersion water should be conducted. Therefore, paint production enterprises should further pay attention to the safety of their products, and developing solvent-free and water-based drinking water tank coatings is the future development direction.

In 2008, China newly formulated and revised the national standard GB/T 6823-2008 "Ship Ballast Tank Coatings". The technical indicators of this standard are equivalent to the relevant content of the "Performance Standard for Protective Coatings on the Double Sides of Seawater Ballast Tanks and Bulk Carriers for Ships" (PSPC) adopted by the Maritime Safety Committee (MSC) of the International Maritime Organization (IMO) on December 8, 2006, in accordance with Article II-1/3-2 of the revised SOLAS Convention. The main test methods and conditions of the standard are as follows: The evaluation indicators are consistent with the attachment "Coating Qualification Test Procedure for Coatings Used in Seawater Ballast Tanks and Double Sides of Bulk Carriers for All Types of Ships" in PSPC. On December 8, 2006, the Maritime Safety Committee (MSC) of the International Maritime Organization (IMO), in accordance with Article II-1/3-2 of the Revised Convention on the Safety of Life at Sea (SOLAS), adopted the Performance Standard for Protective Coatings (PSPC)/1/, titled "Coating Qualification Test Procedure for Coatings Used in Seawater Ballast Tanks and Double Sides of Bulk Carriers for All Types of Ships", which was mandatory in July 2008. This standard includes two parts: coatings, coating performance standards, and quality control requirements for the entire shipbuilding coating process. According to PSPC regulations, the target lifespan of coating protection for ship ballast tanks is 15 years. In the preliminary qualification test for coating selection, in addition to the general performance testing of coating system anti-corrosion, a 180 day test must be conducted according to the test procedure in Annex 1 "Qualification Test Procedure for Protective Coatings for Seawater Ballast Tanks and Double Sides of Bulk Carriers" or equivalent test procedure. At present, there is a significant gap between the product quality and actual coating status of domestic ballast tank coating production enterprises and shipyards and the requirements of the new coating standards. To meet the requirements of the new standards, significant investment and improvement are needed.

6、 Standard for ship coatings

7、 Detection of toxic and harmful substances in ship coatings

Ship coatings are mainly tested according to the GB 38469 Standard for the Limit of Harmful Substances in Ship Coatings, and the relevant testing standards are as follows:

8、 Several Terminology of Ship Coatings

1. IMO: International Maritime Organization, ships at sea will have an IMO number;

2. IACS: International Association of Classification Societies. All offshore vessels need to be classified, and some offshore platforms also need to be classified;

3. MSC: Maritime Safety Committee (IMO affiliated organization);

4. SOLAS Convention: Convention for the Safety of Life at Sea (mainly regulating the safety and pollution prevention of ships);

5. PSPC: Refers specifically to the IMO "Performance Standards for Protective Coatings on the Double Sides of Seawater Ballast Tanks and Bulk Cargo Ships for All Types of Ships". The 81st IMO Maritime Safety Committee (MSC81) approved the "Performance Standards for Protective Coatings on the Double Sides of Seawater Ballast Tanks and Bulk Carriers for Ships" (PSPC), and stipulated that this standard applies to all new shipbuilding projects with a total tonnage of 500 or more signed after July 1, 2008. In the common regulations of IACS, it is required that bulk carriers with a captain of 90 meters or more and oil tankers with a captain of 150 meters or more must comply with IMO's coating standards on or after the date of IMO's approval of the coating standards (expected to be December 8, 2006);

6. AFS: International Convention on the Control of Harmful Anti fouling Bottom Systems on Ships;

7. CCS: China Classification Society, LR: Lloyd's Register of Shipping, DNV: Norwegian Register of Shipping, GL: German Register of Shipping, ABS: American Register of Shipping.

9、 Representative ship coating standards

1. GB 5369 General Technical Conditions for Coatings for Marine Drinking Water Tanks

Freshwater tank coatings are required to be non-toxic and comply with national hygiene certification requirements; The leachable chlorine content in the coating used for stainless steel surfaces should not exceed 200mg/kg, and the coating does not contain zinc.

2. GB/T 6745 Shipshell Paint

This standard is applicable to coatings used on the exterior of buildings above the waterline of ships, as well as for coatings used on masts and lifting machinery. Unless otherwise specified, the product shall be tested after being coated for 7 days, and the dry film thickness of the sample shall be controlled within (50 ± 10) for the primer μ m. Shell paint finish (60 ± 10) μ m. Total dry film thickness (100 ± 10) μ M.

3. GB/T 6746 Marine Oil Tank Coatings

This standard is applicable to the dual component marine oil tank paint on the inner surface of petroleum hydrocarbon oil tanks, except for special oils such as aviation gasoline and aviation kerosene.

During the experiment, the sample is coated or sprayed. Unless otherwise specified, the product is tested after being coated and placed for 7 days. One coat is applied during the drying time (with a dry film thickness of 20-26 μ M); Adhesion is tested after matching the primer and topcoat (one bottom and one surface, with a coating interval of 24 hours, and a dry film thickness of 40-70 meters for both the primer and topcoat); Salt spray resistance, salt water resistance, and oil resistance tests are all conducted after matching the primer and topcoat (multiple coats can be applied, with a coating interval of 24 hours, and the dry film thickness of both the primer and topcoat is l50-175 μ m. Total dry film thickness 350~355 μ m) .

4. GB/T 6747 Marine Workshop Primer (normal production, type inspection once every 4 years)

This standard applies to workshop primers applied to ship steel plates, profiles, and formed parts after surface treatment with shot blasting (or sandblasting) to meet the required level. This workshop primer serves as a temporary anti rust primer for protecting steel. The standard divides the products into two types: Type I (containing zinc powder) and Type II (excluding zinc powder). In addition, based on the weather resistance of the workshop primer, the products are divided into three levels: I-12 (exposed to marine climate environment for 12 months, rust ≤ level 1), I-6 (exposed to marine climate environment for 6 months, rust ≤ level 1), and I-3 (exposed to marine climate environment for 3 months, rust ≤ level 1).

The standard requires that the primer products in the marine workshop should adapt to the needs of automated assembly lines, be able to dry in a short period of time, and have no more than 15% reduction in cutting speed. In addition, the product should also have a wide range of compatibility with the next coat of paint, and have good repainting performance against the old paint film of the workshop primer that has been exposed for a long time. The labor safety of the workshop primer should comply with the requirements of "CB 3881 Safety Regulations for Ship Painting Operations".

5. GB/T 6822 Hull Anti fouling and Anti rust System, several important type inspections include: shallow sea immersion test, dynamic simulation test, cathodic stripping resistance, and detection of prohibited substance content.

This standard refers to the US military standard MIL-PRF-24647 "Paint System Anti rust and Anti fouling Hull", and its scope of application is defined as "parts below the waterline of ship design for various materials and parts of the hull waterline".

For anti fouling coating products, two types of "I type (self polishing anti fouling paint) and II type (non self polishing anti fouling paint)" are defined, and then divided into two major categories and six sub categories based on the scope of application and the toxic materials contained.

Class 1: Paint system for metal substrates

Class 1A: Antifouling paint in the paint system contains copper based toxic substances;

Class 1B: Anti fouling paint in the paint system contains composite toxic substances;

Class 1C: Anti fouling paint in the paint system does not contain toxic substances.

Class 2: Paint systems for non-metallic substrates (such as fiber reinforced materials, rubber, etc.)

Class 2A: Antifouling paint in the paint system contains copper based toxic substances;

Category 2B: Anti fouling paint in the paint system contains composite toxic substances;

Class 2C: Anti fouling paint in the paint system does not contain toxic substances.

Finally, the product's lifespan was defined in detail according to three types: short-term efficacy (less than 3a lifespan), mid-term efficacy (more than 3a, less than 5a lifespan), and long-term efficacy (more than 5a lifespan).

For anti rust paint products, the new standard also defines two types: Type I (dual component paint) and Type II (single component solvent volatile paint), and divides Type I into Class 1 (room temperature curing, curing temperature usually ≥ 10 ℃) and Class 2 (low temperature curing, curing temperature usually<10 ℃) based on curing conditions. The shelf life is modified from the original first level (30 months), second level (18 months), and third level (12 months) to first level (5a and above), second level (3a and above, below 5a), and third level (below 3a).

In addition, contents such as "anti fouling agent, non volatility, color, flash point, shelf life, toxicity, polishing rate (or abrasion rate)" have been added to the technical indicators of anti fouling paint. Fineness indicators have been removed, and the "shallow sea immersion test" method for anti fouling paint has been updated. Two items, "anti fouling coating polishing performance" and "dynamic simulation test", have been added, In terms of rust prevention technical indicators, content such as "non volatile matter, density, viscosity, shelf life, anti foaming, and cathodic stripping resistance of paint" has been added, and salt water resistance indicators have been adjusted to add content related to cathodic protection.

The requirements for ship anti fouling and anti rust paint products are that they must not contain asbestos (or use pigments containing asbestos), mercury compounds, DDT, and chemical substances prohibited by relevant national departments. The total tin content in the anti fouling paint should be<(2500 ± 500) mg/(kg dry paint sample)>.

In terms of general technical performance of coatings, the solid drying time is uniformly required to be ≤ 24 hours. Other technical performance indicators such as anti fouling agent, nonvolatile matter, density, color, viscosity, flash point, surface drying time, shelf life, toxicity, polishing rate, or abrasion rate can be evaluated based on the technical requirements of the product.

6. GB/T6823-2008 "Paint for Ship Ballast Tanks"

Two important type tests:

- Simulated ballast tank condition test (6 months)

- Condensation chamber test (6 months)