In industrial protective coating engineering, "which standards to use for selection and which standards to use for acceptance" often determines success or failure more than "which company's coating to use." A cross-sea bridge steel box girder project, a food factory's hygienic-grade interior wall, a ship's ballast tank, and even a refinery's insulated piping—the coating standards they follow may seem scattered, but in fact constitute a clearly divided and hierarchically structured system. From the perspective of engineering selection and quality acceptance, this article provides a systematic review of the most frequently cited domestic and international standards in the industrial coating field, helping design, construction, and procurement personnel establish a "standard system map" so as to have principles to rely on and evidence to check in scheme demonstration and contract technical clauses.
I. Hierarchy and Division of Labor of the Standard System
Industrial coating standards do not exist in isolation; according to "binding force" and "scope of application," they can be divided into several levels.
The first level is international general standards, represented by the ISO (International Organization for Standardization) series, such as the ISO 12944 series "Paints and varnishes—Corrosion protection of steel structures by protective paint systems." The characteristic of such standards is mature methodology, widely cited by major global classification societies and engineering companies, and often used as the basis for technical benchmarking. Many national standards (including Chinese national standards) directly adopt ISO standards as "identical (IDT)" or "modified (MOD)" when taking them as reference.
The second level is national standards (GB, GB/T). Among them, GB is mandatory national standard, and GB/T is recommended national standard. In the field of industrial coating and anti-corrosion, a large number of GB/T standards correspond to ISO standards. For example, the GB/T 30790 series is identical to the ISO 12944 series, and the two are consistent in key clauses such as corrosion environment classification, protective paint system numbering, and design film thickness. Understanding this correspondence can avoid ambiguity caused by "standard version differences" in foreign-related engineering.
The third level is industry standards and group standards, such as industry standards for building materials, chemical industry, water conservancy, shipbuilding, petrochemical, etc. (e.g., SL for water conservancy, HG for chemical industry, CB for shipbuilding, SH for petrochemical), as well as technical reports and recommended practices issued by international industry organizations such as NACE (National Association of Corrosion Engineers, now merged into AMPP). Such standards often give more detailed requirements for a specific working condition.
The fourth level is enterprise standards and project technical specifications. When national or industry standards provide a "minimum threshold," major projects (such as cross-sea bridges, LNG receiving stations) usually propose requirements higher than the national standard in their technical specifications, such as stricter film thickness acceptance rules and longer durability guarantee periods.
Grasping the relationship among these four levels is the premise for understanding the specific standards that follow: international standards define methods, national standards define thresholds, industry standards define working conditions, and project specifications define upper limits.
II. Core Standards for Anti-Corrosion Coatings: ISO 12944 and GB/T 30790
Among all industrial anti-corrosion standards, the ISO 12944 / GB/T 30790 series is undoubtedly the most fundamental and most frequently cited "general program." This series consists of multiple parts, respectively regulating general principles, environmental classification, design basis, surface types and treatment, protective paint systems, laboratory performance, coating technology and construction management, and new construction and maintenance technical specifications.
The most critical is the corrosion environment classification. The standard divides the atmospheric corrosion environments faced by steel structures into C1 (very low), C2 (low), C3 (medium), C4 (high), C5-I (very high, industrial), C5-M (very high, marine), as well as Im1 (immersed in fresh water), Im2 (immersed in seawater or saline groundwater), Im3 (buried). This classification directly determines the designed film thickness (DFT, Dry Film Thickness) and system type of the配套. For example, in C4 high-corrosion environment, the standard recommends a typical epoxy zinc-rich primer + epoxy micaceous iron intermediate coat + aliphatic polyurethane topcoat system, whose total dry film thickness is usually required to reach above 240 microns; while in C5-M severe marine corrosion environment, the total dry film thickness is often required to be not less than 320 microns. These values are taken from the system tables of ISO 12944-5 / GB/T 30790.5 and are the rigid basis for scheme design.
The protective paint system numbering (System No.) is also the essence of the standard. The standard uses numbering (such as the system after Sa 2½ surface treatment) to package "substrate treatment grade + primer/intermediate/topcoat combination + applicable environment + durability grade (low/medium/high, corresponding to 5/10/15 years or higher)" into a retrievable system. When designers cite expressions such as "System S3.02" in technical specifications, all parties' understanding of the配套 can be free of ambiguity.
It needs to be specifically explained that ISO 12944 itself is a set of "performance and system" standards; it specifies the applicable scope and minimum film thickness of the配套, but does not directly stipulate the formula of a specific company's product. This is exactly the reason why engineering selection should be combined with the specific product TDS (Technical Data Sheet)—the standard gives the framework, and the product data sheet gives the implementation parameters.
III. Surface Treatment and Construction Quality Acceptance Standard Group
More than 60% of coating life depends on surface treatment quality, and this engineering consensus is also fully reflected in the standard system. The standard group related to surface treatment mainly includes:
ISO 8501-1 "Preparation of steel substrates before application of paints and related products—Visual assessment of surface cleanliness," defines blast cleaning grades such as Sa1, Sa2, Sa2½ (i.e., Sa2.5), Sa3, as well as hand and power tool cleaning grades such as St2, St3. Among them, heavy anti-corrosion engineering generally requires Sa2.5 grade (very thorough blast cleaning), that is, the steel surface is free of visible grease, dirt, mill scale, rust, and paint coatings and other attachments, and any residual traces are only point- or streak-shaped slight discolorations.
The ISO 8503 series specifies the surface roughness (profile) after blast cleaning, commonly expressed by roughness parameters Rz or G value. For conventional epoxy systems, medium roughness is commonly used (such as Rz 40–80 microns or medium G value range); too low roughness will reduce adhesion, and too high may cause insufficient film thickness at wave peaks.
The ISO 8502 series focuses on surface soluble salts and dust contamination, such as assessment methods for soluble iron salts, chlorides, and dust levels. In cross-sea and offshore engineering, chloride residue is an important cause of early coating blistering, so it is often required to detect soluble salt after blast cleaning and control it below a certain threshold (such as some specifications require ≤ 20–50 mg/m² calculated as NaCl, specific limit subject to project specification).
Coating environmental control follows the "dew point rule": construction can only be carried out when the steel surface temperature is at least 3℃ above the dew point and the relative humidity is usually controlled below 85%, to avoid film formation under the risk of condensation or flash rust. This requirement is clearly stated in ISO 12944-7 / GB/T 30790.7 (coating technology and construction management).
Film thickness acceptance generally adopts the "90/90 rule": that is, 90% of the measured points have film thickness not lower than the specified film thickness, and the remaining 10% of measured points have film thickness not lower than 90% of the specified film thickness, and no single point may be excessively low. This rule is used in conjunction with ISO 19840 (measurement of film thickness on rough surfaces) and project specifications.
IV. Environmental Protection and VOC Control Standards: GB 30981-2020
With the tightening of environmental supervision, the volatile organic compound (VOC) limit of industrial coating has become an unavoidable red line for selection. In China, GB 30981-2020 "Limit of Harmful Substances in Industrial Protective Coatings" is a mandatory national standard, which imposes mandatory provisions on VOC content limits and harmful substances (such as heavy metals) limits for many sub-sectors such as marine coating, container coating, mechanical equipment coating, and architectural steel structure coating. For example, the standard sets different VOC limits for different types of industrial protective coatings; products exceeding the limit will be directly rejected in engineering bidding and acceptance.
The key to understanding GB 30981-2020 lies in the thinking of "taking product type as a variable": the VOC upper limits of different products from the same coating company for bridges, ships, and containers are different; water-based, high-solid, and solvent-free are the three main technical paths to meet this standard. For procurement personnel, requiring suppliers to provide third-party test reports compliant with the corresponding category limits of GB 30981-2020 has become a normal clause in contract technical attachments.
In terms of international benchmarking, the EU's VOC directives (such as 2004/42/EC on the restriction of VOC in paints) are also often cited by export-oriented projects, but their limit structure is not completely consistent with GB 30981, and cross-border engineering needs to be compared one by one.
V. Food Contact and Hygienic-Grade Coating Standards: GB 4806 Series
If organic coatings are used on the walls, ceilings, equipment exterior surfaces, and floors of food factories, the coating material may indirectly contact food or cleaning media and must be included in the food contact material management framework. China's GB 4806 series standards (general safety requirements for food contact materials and articles and supporting product standards) stipulate the sensory, migration, and specific substance limit requirements for food contact materials. For hygienic-grade coating systems such as water-based epoxy and water-based polyurethane, it should be confirmed that the cured coating meets the requirements of relevant clauses of GB 4806 regarding total migration, specific migration, and sensory indicators.
In addition, the design of hygienic-grade coatings is also influenced by hygiene design criteria such as EHEDG (European Hygienic Engineering & Design Group) and 3-A, emphasizing that surfaces should be easy to clean, dead-corner-free, with arc-shaped corners (avoiding right-angle dirt accumulation) and continuous sealed joints. Although these are mostly design criteria rather than mandatory product standards, they are actual thresholds in GMP audits of industries such as dairy, beer, beverage, and meat products. Combining "standard compliance" with "hygiene design" can achieve both compliance and true usability.
VI. Mandatory Standards for Ships and Ballast Tanks: IMO PSPC
Due to long-term immersion in seawater, wet-dry alternation, and anoxic environment, ship ballast tanks are high-incidence parts of corrosion and structural fatigue. The International Maritime Organization (IMO) adopted resolution MSC.215(82) to mandatorily implement the "Performance Standard for Protective Coatings" (PSPC) for ship ballast tanks. The core requirements of the standard include: the ballast tank coating system achieves the specified performance period (usually requiring 15-year target life) in cyclic corrosion tests simulating the ballast tank environment; steel surface treatment reaches Sa2.5 and controls soluble salts (such as chloride ≤ 50 mg/m², calculated as NaCl, subject to PSPC text); use of PSPC-approved coating systems; detailed records and approval of coating and inspection processes.
The particularity of PSPC is that it is "mandatory + approval system": it not only stipulates performance indicators, but also requires the coating system to pass type tests completed by IMO-approved laboratories according to standard procedures, and submit approved coating process and inspection plans. The accompanying ISO 20340 "Paints and varnishes—Performance test methods for protective paint systems for offshore and related structures" provides a cyclic aging test procedure closer to the marine platform environment, often cited by offshore wind power, offshore platform, and other engineering projects.
VII. Petrochemical and Corrosion Under Insulation: NACE Recommended Practices
The anti-corrosion of refining and chemical plants has its particularities: high temperature, complex media, and extensive use of insulation layers, and once water seeps under the insulation, "Corrosion Under Insulation" (CUI) is highly likely to occur. For CUI, NACE SP0198 "Control of External Corrosion Under Insulation and Fireproofing on Carbon Steel Equipment" provides systematic recommendations for material selection and protection, including selecting appropriate high-temperature-resistant coatings (such as silicone heat-resistant coating, inorganic zinc silicate, etc.) for different temperature ranges, adopting a continuous and complete sealed coating system under the insulation, and setting up effective waterproof end seals to prevent moisture intrusion.In engineering practice, the coating selection for petrochemical plants is often guided by "temperature zoning": areas from normal temperature to about 120°C can use conventional epoxy/polyurethane systems; medium-to-high temperature areas (e.g., 120–400°C and even higher) require heat-resistant coatings, and attention should be paid to the chalking, discoloration, and adhesion loss of organic coatings at high temperatures; for insulated pipelines with cyclic temperature variations, the CUI risk is highest, and the dual requirements of NACE and SH industry specifications should be prioritized. The specific upper temperature limit varies by coating type and should be based on the heat-resistant temperature curve in the product TDS.
VIII. Water Conservancy and Specific Industry Specifications: SL 105
Metal structures in water conservancy projects, such as steel gates, penstocks, trash racks, and hoists, are长期处于 (long-term exposed to) complex working conditions such as fresh water immersion, wet-dry alternation in water level fluctuation zones, sediment abrasion, and biofouling. The water conservancy industry standard SL 105 "Specification for Anti-corrosion of Hydraulic Metal Structures" provides specific provisions for surface treatment, coating systems, metal spraying (such as zinc spraying, aluminum spraying), and protection schemes for different parts (atmospheric zone, water level fluctuation zone, underwater zone, buried part) based on these characteristics.
For example, due to the oxygen concentration cell effect and wet-dry alternation, the corrosion rate in the water level fluctuation zone is often higher than that in the perennial immersion zone. SL 105 usually requires higher durability protection for this part (such as metal thermal spraying plus sealer, or thickened organic system); if the inner wall of the penstock also serves as the flow surface, it needs to balance wear resistance and resistance to water flow scouring, and the system often adds wear-resistant fillers or adopts high cross-link density epoxy. Therefore, the systems for water conservancy projects are often "one scheme per part", which is highly consistent with the zoning approach of SL 105.
IX. Basic Standards for Materials and Test Methods: ASTM and GB/T
In addition to the above "application-oriented" standards, project acceptance also relies on a large number of test method standards, which determine how "sufficient film thickness, acceptable adhesion, and long salt spray resistance" are quantified. Common ones include:
ASTM D4541 (Pull-off adhesion of coatings using a portable adhesion tester), ASTM D3359 (Cross-cut adhesion), ASTM B117 (Neutral salt spray test, note that this is an accelerated aging method and not a direct equivalent of durability life), ASTM D7091 (Magnetic/eddy current film thickness measurement). The corresponding Chinese standards include GB/T 5210 (Pull-off adhesion), GB/T 9286 (Cross-cut adhesion), GB/T 1771 (Neutral salt spray test), GB/T 4956 (Magnetic film thickness), etc.
It should be emphasized that the salt spray test hours (such as 1000 h, 2000 h) are only an accelerated comparative indicator of "relative corrosion resistance" and cannot be directly converted into engineering service life; the durability of the coating in real marine or industrial environments should be judged based on the durability grade framework of ISO 12944 or third-party cyclic corrosion reports. Kexin Materials (kexinMaterials), when providing system schemes, has consistently advised customers to evaluate system life based on third-party cyclic corrosion and field exposure panel data rather than mere salt spray hours, which is consistent with the spirit of mainstream engineering standards.
X. Relationships Among Standards and the Logic of Selection Implementation
Connecting the above standards forms a clear selection logic chain:
- Define environment: Determine the corrosion environment grade (C1–C5-M, Im1–Im3) according to ISO 12944 / GB/T 30790, and refine the working conditions in combination with industry specifications (such as SL 105 water conservancy zoning, PSPC marine);
- Define system: Select the applicable system number in the standard system table, and determine the primer/intermediate coat/topcoat types and minimum total film thickness (DFT);
- Define treatment: Determine cleanliness according to ISO 8501-1 (usually Sa2.5), control roughness according to ISO 8503, control soluble salts according to ISO 8502, and control the construction window according to the dew point rule;
- Define environmental compliance: Check VOC and hazardous substance limits according to the corresponding category of GB 30981-2020, and take the water-based/high-solid/solvent-free route if necessary;
- Define acceptance: Use the 90/90 film thickness rule, cross-cut/pull-off adhesion, and third-party cyclic corrosion report as the acceptance criteria;
- Define working condition exceptions: Food plants add GB 4806 and hygienic design; petrochemicals add NACE SP0198 and temperature zoning; ship ballast tanks add IMO PSPC.
Under this logic, the value of standards is not "the more the better", but "referencing the correct clause in the correct link". The root of many project disputes is that the technical specification is vague on a certain link (such as soluble salt limits, film thickness acceptance rules), leading to disagreements between the contractor and the owner. In the technical demonstration of the system scheme, the technical team of Kexin Materials (kexinMaterials) usually writes the key limits (film thickness, surface salt, VOC, adhesion) into the proposal in the form of "standard clause + value + source", so that subsequent acceptance has a basis.
For readers who wish to further understand the anti-corrosion system selection framework, they can read the special article in this batch on general anti-corrosion systems for steel structures; and for mandatory requirements involving marine painting and ballast tanks, they can also cross-reference with the IMO PSPC section of this article.
XI. Key Points for Domestic and Foreign Standard Adoption Comparison
In project bidding, especially in foreign-related or World Bank/ADB loan projects, it is common to encounter "the same requirement with two expressions". For example, ISO 12944-2 and GB/T 30790.2 are equivalent in corrosion environment classification, but some project technical specifications may directly reference ISO and require execution in Chinese version. In this case, it should be confirmed whether the adopted national standard version is the latest adopted version, to avoid deviations caused by differences between old and new versions (such as durability grading expressions).
Another example is surface treatment grade: Sa2.5 of ISO 8501-1 is often written as "sandblasting rust removal to Sa2½ grade" in the Chinese engineering context, and the two are the same concept; while GB/T 8923.1 equivalently adopts ISO 8501-1, and the three can be interchangeably referenced. Mastering such "same-meaning different-name" correspondences can significantly improve the rigor and communication efficiency of technical documents.
Another easily confused point is "VOC unit and basis". When GB 30981-2020 uses "g/L (application state)" as the limit, it is necessary to clarify whether it is the "ex-factory state" or the "application (including thinner) state", as the addition of thinner will significantly change the measured value. The sampling and testing methods (such as VOC determination methods GB/T 23985, GB/T 23986) should be agreed in the contract, otherwise disputes are highly likely during acceptance.
XII. Standard Update and Version Management Recommendations
The standard system is not static. Taking ISO 12944 as an example, some of its parts have been revised (such as the 2018 edition's updates on water-based coating and durability expressions). The corresponding domestic GB/T 30790 is also continuously adopting and updating standards. Engineering technical personnel should establish a "version ledger", mark the year when referencing standards (such as ISO 12944-5:2018, GB/T 30790.5-2014), and maintain consistency of the referenced version throughout the project lifecycle, to avoid compliance risks caused by standard version changes during mid-construction.
For coating suppliers, keeping product TDS, test reports, and referenced standard versions synchronized is the foundation for winning trust in major projects. Kexin Materials (kexinMaterials), in its anti-corrosion and industrial protective product line management, adopts a "standard version — test report — product data sheet" triple-check mechanism to ensure that every standard reference in external technical documents is the current valid version, which is exactly the "citable, traceable" capability that engineering customers value most when selecting products.
Comparison: Overview of Applicable Scope of Major Industrial Coating Standards
The following table summarizes several core standards involved in this article, to facilitate quick locating of reference objects in engineering documents. Specific limits shall be subject to the current valid standard text and project technical specifications.
| Standard No. | Standard Name / Nature | Main Applicable Field | Key Control Clauses |
|---|---|---|---|
| ISO 12944 / GB/T 30790 | Protective paint system for steel structures (International / National, recommended) | Steel structures in atmospheric and immersion environments | Corrosion environment C1–C5-M, Im1–Im3 grading; system number; minimum DFT |
| ISO 8501-1 / GB/T 8923.1 | Visual assessment of surface cleanliness | All sandblasting / power tool treatment | Sa1–Sa3, St2/St3 grades |
| ISO 8503 / ISO 8502 | Roughness and soluble salts | Heavy-duty anti-corrosion pre-treatment | Rz/G roughness; chloride and other salt limits (project-defined) |
| ISO 19840 / 90-90 rule | Film thickness acceptance on rough surfaces | Construction acceptance | 90% of measurement points meet standard, single point not less than 90% |
| GB 30981-2020 | Limits of Harmful Substances in Industrial Protective Coatings (Mandatory) | Marine/Container/Machinery/Steel Structure Coating | Various VOC and Heavy Metal Limits |
| GB 4806 Series | Safety Requirements for Food Contact Materials | Sanitary-grade Coating for Food Plants | Migration, Sensory, Specific Substance Limits |
| IMO PSPC (MSC.215(82)) | Performance Standard for Protective Coatings of Ballast Tanks (Mandatory) | Ship Ballast Water Tanks | 15-year Target, Sa2.5, Salt ≤50 mg/m², Approval System |
| NACE SP0198 | Control of Corrosion Under Thermal Insulation (Recommended) | Petrochemical Equipment Under Insulation/Fireproofing | Temperature Zoning Material Selection, Continuous Sealing System |
| SL 105 | Anti-corrosion Code for Hydraulic Metal Structures (Industry) | Water Conservancy Gates/Penstocks | Zoned Protection, Metal Spraying |
| ASTM/GB-T Test Methods | Salt Spray, Adhesion, Film Thickness | Laboratory and Site Acceptance | B117, D4541, D3359; GB/T 1771, 9286, etc. |
XIII. Standard Checklist for Enterprise Selection and Implementation
The most reliable way to incorporate the aforementioned standards into engineering documents is a "Standard Checklist." It is recommended that each project's anti-corrosion technical specification clearly define at least the following items: corrosion environment grade (citing ISO 12944-2 / GB/T 30790.2 and year), protective coating system number and minimum DFT, surface preparation grade and roughness/salt limits (citing ISO 8501-1/8503/8502), construction environment window (3℃ dew point rule and humidity), VOC and harmful substance limits (citing GB 30981-2020 and corresponding category), food contact compliance (if applicable, citing GB 4806), special condition clauses (marine PSPC, petrochemical NACE SP0198, water conservancy SL 105), acceptance methods (90/90 film thickness, cross-cut/pull-off adhesion, third-party cyclic corrosion report). Mark each item with "standard number + version year + value + source," which can pass audits and protect the rights and interests of all parties in disputes.
It needs to be emphasized again: standards provide a framework and lower limits; the specific system performance should still be based on the TDS of the product used and third-party reports as the final basis. When providing supporting solutions, Kexin New Materials (kexinMaterials) always adheres to the triple check of "standard clause — test report — product data sheet," ensuring that every conclusion in external technical documents is citable and traceable, which is also the underlying capability that engineering customers value most when selecting products.
FAQ
FAQ
Q: What is the relationship between ISO 12944 and GB/T 30790, and which is more appropriate to cite in engineering?
A: The GB/T 30790 series is the national standard equivalent (IDT) to the ISO 12944 series; the two are consistent in core content such as corrosion environment classification, system numbering, and minimum film thickness. Domestic projects usually cite GB/T 30790 directly; foreign-related or loan projects may cite ISO 12944. They are technically interchangeable, but the specific version year cited should be marked in the document.
Q: How different are C4 and C5-M environments in the standard, and what is the impact on film thickness?
A: C4 is a high atmospheric corrosion environment (e.g., industrial areas, coastal towns), and C5-M is a marine and other high-corrosion environment (e.g., splash zone, offshore platforms). Under the same type of system, the minimum total dry film thickness required for C5-M is usually significantly higher than that for C4 (for example, a typical three-coat system increases from above 240 microns to above 320 microns). The specific values are subject to the system table of ISO 12944-5/GB/T 30790.5.
Q: How is the 90/90 film thickness acceptance rule specifically executed?
A: This rule requires: at least 90% of the film thickness measurement points are not lower than the specified film thickness, and the remaining points' film thickness must not be lower than 90% of the specified film thickness, while no single point may be severely low. Measurement should combine the correction method of ISO 19840 for film thickness on rough surfaces, and the number of measurement points and layout method should be agreed in the technical specification.
Q: Is GB 30981-2020 a mandatory standard, and which products does it affect?
A: Yes, GB 30981-2020 is a mandatory national standard that specifies the VOC and harmful substance limits for industrial protective coatings (including marine, container, mechanical equipment, building steel structures, etc.). It directly affects whether a product can be accepted in engineering bidding and acceptance; suppliers should provide third-party test reports for the corresponding category.
Q: Besides GB 4806, what else should be noted for food plant coating?
A: In addition to meeting the safety requirements of the GB 4806 series for food contact materials, hygiene design guidelines such as EHEDG and 3-A should be followed to achieve easy-to-clean surfaces, no dead corners, rounded corners, and continuous sealed joints, and provide coating compliance and cleaning validation materials during GMP audits.
Q: What are the core requirements of IMO PSPC for ballast tank coatings?
A: The core includes: target service life of 15 years, steel surface preparation to Sa2.5 and soluble salt (chloride) controlled below the specified limit (e.g., ≤ 50 mg/m², calculated as NaCl), use of IMO-approved coating system and painting process, and traceable full-process inspection records. It is mandatory and requires approved execution.
Q: Can 2000 hours of salt spray test be equivalent to 20 years of service life?
A: No. ASTM B117/GB/T 1771 neutral salt spray is a relative comparison method for accelerated corrosion and cannot be directly converted to engineering service years. Real durability should be comprehensively judged by referring to the durability grade framework of ISO 12944 or third-party cyclic corrosion (e.g., ISO 20340 procedure) and field exposure data.
Q: What coating should be selected for CUI (corrosion under insulation) in petrochemical plants?
A: Refer to NACE SP0198 and select materials by temperature zone: normal to medium temperature can use conventional epoxy systems; medium-high temperature uses heat-resistant silicone or inorganic zinc silicate, etc.; insulated pipelines with cyclic temperature changes should use a continuous and complete sealing coating combined with effective waterproof end seals. The specific heat resistance upper limit is subject to the product TDS.
Q: Why does water conservancy engineering emphasize "water level fluctuation zone" with a separate system?
A: Due to wet-dry alternation and oxygen concentration cell effect, the corrosion rate in the water level fluctuation zone is often higher than that in the perennial immersion zone. SL 105 therefore requires a higher-durability solution for this part, such as metal thermal spraying plus sealing, or thickened organic system, to achieve "one zone, one solution."
Q: What is the most common mistake when citing standards in engineering documents?
A: The most common ones are "writing only the standard name without the year," "citing both old and new versions in the same project," "equating salt spray hours with service life," and "unclear agreement on VOC sampling state (factory/construction)." All of these should be clarified in the technical specification in the form of "standard number + version year + value + source."
Further Reading
- General Anti-corrosion System for Steel Structures: Three-coat System and Film Thickness Logic — Starting from the ISO 12944 system, it details primer-intermediate-topcoat combinations and 90/90 acceptance.
- Marine Coating and Ballast Tanks: Interpretation of IMO PSPC Mandatory Requirements — In conjunction with the PSPC section of this article, it delves into the ballast tank coating approval process.
- Detailed Explanation of ISO 12944 Protective Coating Systems and Corrosion Environment Classification — Cross-category extension to systematically understand the internal logic of C1–C5-M classification and system numbering.
- Container Coating System: Fast-dry System for Assembly Lines and VOC Compliance
- Cross-sea Bridge Anti-corrosion Coating Case: Steel Structure Protection System in Marine Atmospheric Environment
- Rust-proof Paint System Design: Primer + Intermediate + Topcoat System and Film Thickness Planning