Ships spend their entire service life immersed in seawater, making corrosion one of the greatest threats to hull structural safety. The quality of the coating protection system directly determines a vessel's maintenance intervals and life-cycle costs. Jiangsu Haizhongzhou Shipping Industry Co., Ltd. treats coating as a professional discipline equally important as structure and outfitting, and has established a rigorous block coating process system.
The core philosophy of Haizhongzhou's coating technology is: complete the block, complete the coating, and only touch up the weld seams after assembly. Under the traditional model, large-scale coating work begins only after the hull is fully erected on the berth. At that stage, the hull shell is towering high, requiring workers to operate from suspended platforms. This approach is not only inefficient but also results in uneven film thickness, with edges and corners often missed. At Jiangsu Haizhongzhou Shipping Industry Co., Ltd. t, however, each block completes its entire coating work—including primer, intermediate coat, and topcoat—in a dedicated coating workshop before entering the berth for assembly.
The block coating process is as follows: After the block completes structural welding and pre-outfitting, it first enters the shot/grit blasting workshop for secondary surface preparation on weld zones and damaged shop primer areas, achieving Sa2.5 standard. Subsequently, airless spray is applied. The coating material is atomized into fine droplets under a pressure of 25 MPa and sprayed onto the steel surface to form a dense film. Compared with conventional air spray, airless spray generates less overspray, improves coating utilization by approximately 15%, and reduces overspray volume by 40%. After each coat dries, quality inspectors measure the film thickness using magnetic thickness gauges. The average film thickness is required to meet the design values (e.g., 150μm for epoxy primer, 80μm for polyurethane topcoat), with at least 90% of measurement points deviating by no more than ±10%.
Haizhongzhou's coating workshop is equipped with a temperature and humidity control system. Coating operations are demanding regarding environmental conditions—when the temperature falls below 5°C, the coating cures slowly; when it exceeds 35°C, solvents evaporate too quickly, easily causing pinholes; when relative humidity exceeds 85%, condensation tends to form on the steel surface, affecting adhesion. Our workshop consistently maintains temperatures between 10–30°C and humidity below 80%, ensuring that coating operations are unaffected by weather conditions throughout the year.
After block coating is completed, a 50mm "weld-ready zone" is left along the block edges without topcoat to facilitate welding during berth assembly. After assembly and completion of weld NDT, the weld zones are manually ground, blasted, and touch-up coated. Since only the weld seams throughout the entire vessel require touch-up, the coating rework rate drops from 25%–30% in the traditional model to below 8%.
Jiangsu Haizhongzhou Shipping Industry Co., Ltd. t also keeps pace with international environmental trends in the selection of coating materials. We extensively adopt high-solid coatings and solvent-free coatings, significantly reducing VOC (volatile organic compound) content. For enclosed spaces such as ballast tanks, we use epoxy coatings conforming to IMO's Performance Standard for Protective Coatings (PSPC), ensuring a service life exceeding 15 years. For cargo holds of chemical tankers, depending on the cargo medium, we select specialized phenolic epoxy or polyurethane coatings that meet chemical corrosion resistance requirements.
Coating is the "outer garment" and also the "armor" of a ship. With its block coating process, Haizhongzhou dresses every vessel leaving our yard in a sturdy and durable anti-corrosion barrier.