What Product Standard Governs Hull Antifouling Paint Systems in China?
Hull paint testing in China is anchored in GB/T 6822-2024 Anti-fouling and Anti-corrosive Paint Systems on Ship Hulls (replacing the 2014 edition), which covers the coating system on the outer surface below the design waterline — both the anticorrosive (AC) layers that protect the steel and the antifouling (AF) layers that resist marine growth. GB/T 6822 is reported to be executed by nearly every marine coatings manufacturer in the domestic market, making it the de facto baseline for hull coating qualification.
The 2024 revision introduced a four-type classification of antifouling paint by biocide content and release mechanism:
| Type | Mechanism | How it works |
|---|---|---|
| Type I | Self-polishing (自抛光) | Hydrolysing acrylic copolymer ablates at a controlled rate, continuously exposing fresh biocide |
| Type II | Ablative / erosive (磨蚀型) | Surface erodes under seawater flow, releasing biocide as it wears |
| Type III | Foul-release (污损脱附型) | Low-surface-energy silicone/fluoropolymer; organisms detach under hydrodynamic shear |
| Type IV | Biocide-free (无生物杀伤剂) | No biocide; relies on surface properties alone |
Knowing the type up front determines which tests apply — a Type I self-polishing coating needs an erosion-rate measurement (GB/T 31411); a Type III foul-release coating does not, but needs a different adhesion and surface-energy test set. A test plan that does not state the type is not scoped correctly.
Two further standards sit on top of the product standard. GB 38469-2019 Limit of Harmful Substances in Marine Coatings is the mandatory VOC and heavy-metal ceiling — note that this standard is being integrated into GB 30981.2-2025 (effective June 1, 2026), which tightens VOC limits and adds SVOC controls for the first time. And the international convention layer — the IMO AFS Convention (which banned organotin/TBT antifouling globally from 2008) and IMO MSC.215(82) (performance standard for protective coatings) — applies to vessels in international trade regardless of flag.
How Is Antifouling Performance Verified by Shallow-Sea Immersion?
The shallow-sea immersion test is the definitive antifouling-performance test, because it exposes coated panels to the actual fouling community — algae, barnacles, tubeworms, mussels, bryozoa — over months or years. The method is GB/T 5370 Method for Testing Antifouling Paint Panels by Shallow-Sea Immersion.
Panels (typically steel, prepared and coated to a defined dry-film thickness) are mounted on a floating raft at a defined depth at a recognised test station in coastal waters. They are inspected at fixed intervals — typically monthly for the first period, then quarterly — and the fouling coverage on the panel surface is rated as a percentage and by fouling type. A panel that resists fouling for the rated period (commonly 12, 24, or 36 months depending on the coating's claimed service life) passes; a panel that fouls beyond the rated threshold before the period elapses fails.
The shallow-sea immersion test is the slowest test in the hull-paint panel — a 36-month immersion cannot be accelerated — and it is geographically specific. Fouling pressure varies dramatically by location, season, and water temperature: a panel in tropical Southeast Asian waters fouls far faster than one in the Yellow Sea. This is why a credible antifouling report cites the test station (Qingdao, Xiamen, Sanya) and the immersion period alongside the result — the same coating can pass at one station and fail at another. A report that states "passed 24-month immersion" without naming the station and its fouling severity is not interpretable.
For Type I and Type II coatings, the immersion test is paired with an erosion/polishing rate measurement per GB/T 31411 Determination of Erosion Rate of Ship Antifouling Paint. The coating thickness is measured at intervals; the rate of thickness loss, in micrometres per month, confirms that the coating is releasing biocide at the design rate — too slow and it fouls, too fast and it exhausts before its claimed service life.
How Is Biocide Release Rate and Copper Content Measured?
For biocide-based antifouling (Types I and II), the release rate of the active ingredient — most commonly copper (Cu²⁺), sometimes supplemented with organic boosters — is the property that determines both antifouling efficacy and environmental impact. Two tests apply:
Release rate (渗出率): the coating is exposed to flowing natural or artificial seawater under controlled conditions, and the copper concentration in the effluent is measured over time by atomic absorption or ICP-MS. The release rate, in micrograms per square centimetre per day (µg/cm²·d), must fall within the design window. Too high a rate wastes biocide and risks exceeding the local water-quality standard for copper (a regulatory issue in ports with poor flushing, like some recreational marinas); too low a rate allows fouling to establish. The release rate typically falls over the coating's life — the early "burst" phase settles to a steady-state release — so a report that quotes a single rate without stating whether it is initial or steady-state is incomplete.
Total copper content (总铜含量): measured per GB/T 31409 Determination of Total Copper Content in Ship Antifouling Paint. This is a regulatory and formulation check, not a performance test — it confirms how much copper is loaded into the coating as manufactured, which bounds the theoretical total release over the coating's life. With the post-TBT regulatory environment putting copper itself under scrutiny (some jurisdictions, notably parts of California and Washington State in the US, have capped or phased down copper-based recreational antifouling), the total-copper number is increasingly cited in procurement specifications, not just in environmental filings.
For biocide-free Type IV and foul-release Type III coatings, these tests do not apply — the performance mechanism is surface energy and modulus, not biocide release, and the relevant tests shift to contact-angle measurement, surface-energy calculation, and the fouling-release efficiency under shear (often a rotor or tunnel test).
What Adhesion and Coating-System Tests Apply?
The hull coating is a multi-layer system — typically anticorrosive epoxy primer, intermediate coat, and antifouling topcoat — and the layer-to-layer adhesion is what stops the system disbonding in service. GB/T 6822 includes adhesion as a key technical indicator, and the failure mode it is designed to catch is exactly the one documented in field-failure investigations: the antifouling coat peeling off the anticorrosive coat because the recoat window was missed.
Pull-off adhesion (拉开法附着力): a standard dolly is bonded to the coating surface and pulled perpendicular until failure; the failure load (MPa) and the failure locus (adhesive between coats, cohesive within a coat, or adhesive to substrate) are reported. For a hull system, a failure locus between the AC and AF layers at a load below spec is the fingerprint of a recoat-interval or surface-contamination problem — the same root cause identified in field failures where the AF coat applied after the AC coat's tack window expired disbonded spontaneously.
Cross-cut / X-cut adhesion: a qualitative screen used on-site, where an X or cross-grid is cut through the coating, tape is applied and removed, and the amount of coating removed is rated. It is faster and cheaper than pull-off and used for field acceptance, but pull-off is the defensible quantitative method.
Cathodic disbondment resistance (耐阴极剥离性): hulls protected by sacrificial anodes or impressed current create a cathodic environment at coating defects that can drive coating disbondment. The test applies a cathodic potential to a scribed coated panel in seawater for a defined period and measures the disbondment radius from the scribe. This is what separates a coating that survives the combination of seawater immersion and cathodic protection from one that survives immersion alone.
Blister and immersion resistance: long-term seawater immersion under pressure and temperature cycling, checking for blister formation (osmotic blistering from soluble salts trapped under or in the coating) and adhesion loss.
The diagnostic pattern: a hull system that passes adhesion but fails cathodic disbondment has a formulation issue; one that fails adhesion between specific coats at a specific recoat interval has an application issue. The field-failure literature shows that application defects (wrong mix ratio, missed recoat window, surface contamination) cause more disbondment than formulation defects — which is why the application-control standards below matter as much as the product standard.
What Application-Control Standards Govern Surface Preparation and Film Build?
The product standard defines what the coating must deliver; a parallel set of standards governs how the coating is applied — and application, not formulation, is where most hull-coating failures originate.
Surface preparation — ISO 8501-1 Visual Assessment of Surface Cleanliness: defines the blast-cleaning grades (Sa 2, Sa 2½ near-white, Sa 3) that the steel must meet before priming. Most hull specifications require Sa 2½ as the minimum. ISO 8501-3 extends this to welds, edges, and surface imperfections — the geometry where coatings fail first. The Chinese equivalent is GB/T 8923.
Surface contamination — ISO 8502-6 / 8502-9 (Bresle method): field measurement of water-soluble salts (chlorides, sulfates) on the prepared surface. Soluble salt left under the coating is the single most common cause of osmotic blistering in immersion service.
Dust — ISO 8502-3: assessment of dust on the prepared surface before coating.
Dry-film thickness — ISO 19840 Measurement and Acceptance Criteria for DFT on Rough Surfaces: the procedure for verifying that each coat has been applied to its specified DFT, including inspection-area logic, sampling frequency, and the acceptance rule (typically 80-20 or 85-15: 80 % of readings at or above spec, no single reading below 80 % of spec). A thin system leaves the substrate exposed; an over-thick system traps solvent, cracks, and brittles. DFT is not a cosmetic metric — it is a primary acceptance measurement.
Application climate: surface temperature, air temperature, relative humidity, and dew-point spread must be within the coating manufacturer's window before and during application. If the substrate temperature is within 3 °C of the dew point, condensation is likely and the workfront should not be released — moisture under the primer is a latent adhesion failure.
A hull-paint report that cites only the product-standard test results (adhesion, immersion, copper content) without the application-control records (surface grade, salt level, DFT logs, climate readings) is incomplete for a failure investigation — because the most common failure cause lives in the application record, not in the product test.
How Is VOC Compliance Tested, and What Changes in 2026?
VOC compliance is the regulatory gate that determines whether a hull coating can be legally sold and applied. The current standard is GB 38469-2019 Limit of Harmful Substances in Marine Coatings, which sets:
- VOC limit by coating type, calculated at the product's stated maximum dilution ratio. Maintenance coatings (used for in-service repair) are capped at a higher VOC (e.g. ≤ 600 g/L) than factory-applied new-build coatings.
- Restricted solvents: glycol ethers and certain other solvents are capped or banned.
- Heavy metals: lead, chromium, mercury, cadmium are capped.
The 2026 transition is the key operational fact. GB 38469-2019 is being integrated into GB 30981.2-2025 Limit of Harmful Substances in Coatings — Part 2: Industrial Coatings, effective June 1, 2026. The new standard:
- Merges the previously scattered standards (GB 30981-2020 industrial protective, GB 38469-2019 marine, GB 18581-2020 wood, GB 24409-2020 vehicle, GB 24613-2009 toys) into a single industrial-coatings framework.
- Tightens VOC limits for certain product types.
- Adds SVOC (semi-volatile organic compound) controls for the first time.
- Expands scope to coating auxiliary materials (putty, colorants, thinners, curing agents, paint removers).
For a hull-paint manufacturer or shipyard, the practical implication is that a VOC test report issued before June 2026 against GB 38469-2019 is valid for product on the market before the transition, but product manufactured or sold after the transition must report against GB 30981.2-2025 — and a coating that passed the old standard may fail the new one if its VOC sits in the tightened band or if it contains SVOCs newly brought under control. The laboratory request should specify which standard the report is for, because the test methods and limits differ.
Our Testing Capabilities
Beijing ZKGX Research provides hull paint testing against the GB/T 6822-2024 product standard, the GB 38469-2019 / GB 30981.2-2025 harmful-substance framework, and the ISO 8501/8502/19840 application-control suite.
Antifouling performance:
- Shallow-sea immersion (GB/T 5370) at coastal test stations, with fouling-coverage rating by period
- Erosion / polishing rate for self-polishing and ablative coatings (GB/T 31411)
- Biocide release rate (copper) by controlled seawater exposure + AAS/ICP-MS
- Total copper content (GB/T 31409)
Coating system properties:
- Pull-off adhesion with failure-locus reporting
- Cathodic disbondment resistance in seawater
- Blister and long-term immersion resistance
- Cross-cut / X-cut adhesion for field acceptance
Harmful substances and VOC:
- VOC content per GB 38469-2019 (current) and GB 30981.2-2025 (effective June 2026)
- Restricted solvents (glycol ethers)
- Heavy metals (Pb, Cr, Hg, Cd)
Application control (for failure investigation and acceptance):
- Surface preparation grade (ISO 8501-1 / GB/T 8923, Sa 2½ verification)
- Soluble-salt contamination (Bresle method, ISO 8502-6/9)
- Dry-film thickness verification (ISO 19840, 80-20 rule)
- Application climate and dew-point assessment
If you need a GB/T 6822 hull-paint qualification report, a GB 38469 / GB 30981.2 VOC compliance certificate for domestic sale, a shallow-sea immersion performance test, or a coating-failure investigation that combines product testing with application-control records — contact our laboratory with the coating type (Type I-IV), service-life claim, and target standard, and we will scope the test plan.
FAQ
What is the difference between the four antifouling types in GB/T 6822-2024?
Type I (self-polishing) hydrolyses in seawater to expose fresh biocide at a controlled rate. Type II (ablative) physically erodes to release biocide. Type III (foul-release) uses a low-surface-energy silicone/fluoropolymer so organisms detach under hydrodynamic shear, with no biocide. Type IV (biocide-free) relies on surface properties without the foul-release chemistry. Types I and II are biocide-based and need release-rate and copper-content testing; Types III and IV do not, and are tested by surface energy and shear-release efficiency instead.
Why does the shallow-sea immersion test station matter?
Because fouling pressure is geographically specific. Tropical waters (Sanya, Southeast Asia) foul panels far faster than temperate waters (Qingdao, North Sea) due to year-round warmth and biological productivity. A coating that resists fouling for 24 months at a temperate station may fail at a tropical station in 12. A credible immersion report cites the station, its fouling severity classification, and the immersion period — without these, the "passed" result is not interpretable or comparable.
What changes for hull-paint VOC Testing in 2026?
GB 38469-2019 is integrated into GB 30981.2-2025, effective June 1, 2026. The new standard tightens VOC limits for some coating types and adds SVOC (semi-volatile organic compound) controls for the first time. Product manufactured or sold after the transition must report against GB 30981.2-2025, and a coating that passed the old standard may fail the new one. A test request should specify which standard applies, because the limits and methods differ.
Why do hull coatings fail more often from application than from formulation?
Because the most common failure modes — inter-coat disbondment from a missed recoat window, osmotic blistering from soluble-salt contamination, pinhole and void defects from application outside the climate window, and DFT shortfalls from under-application — all originate in the application record, not in the coating chemistry. A coating with excellent laboratory test results will still disbond in service if applied over a contaminated surface, outside the recoat window, or below the specified DFT. This is why a failure investigation combines product-standard tests with the ISO 8501/8502/19840 application-control record.
Is copper-based antifouling still compliant?
Yes, in most jurisdictions including China. Copper is the dominant biocide in GB/T 6822 Type I and II coatings and is tested per GB/T 31409 (total copper content) and the release-rate method. The regulatory concern is local: some US states (Washington, California marina regions) have capped or phased down copper in recreational antifouling due to sediment accumulation in poorly flushed marinas. TBT (tributyltin), the previous dominant biocide, was banned globally by the IMO AFS Convention from 2008 — any coating testing positive for organotin is non-compliant regardless of other results.