Anticorrosive coating materials and technology in large-caliber stainless steel pipe

The inner anti-corrosion layer (also known as coating) of stainless steel tube has a wide variety of materials, and the quality difference of similar products is also large. When users choose, they are often determined according to the comparison of various test parameters in the laboratory and the performance of on-site hanging sheets. There are no uniform standards for the protective performance indexes of oil and gas pipeline inner coatings, and users are required to apply to coating manufacturers as needed. After the laboratory's routine inspection indicators are approved, the following three indicators can be adopted for the acceptance of coated products: 1 Appearance - using endoscope or closed-circuit television - no runny, wrinkle, orange peel, blistering, fisheye, etc. Defects; 2 thickness - using a magnetic thickness gauge is generally not less than 250ym. Considering the wet anti-corrosion, the thickness of the anti-corrosion layer should be no less than 400F/m; 3 coating leakage point detection - using spark-splitting detection or resistance detection.

Most of the commonly used coatings are epoxy, epoxy novolac, polyurethane and urushiol. Primer coatings are usually mixed with iron and red, chrome yellow and other pigmented fillers with passivation properties, and the intermediate layer and surface coatings are often mixed with scales or glass beads.

With it to improve the resistance to penetration and so on. According to different purposes, select the appropriate pigments and additives to improve the performance of the coating. All of the above mentioned are the basic work of the stainless steel anti-corrosion coating formulation design and coating structure design range. For details, please refer to the related monograph. For water pipelines, cement mortar linings and polyolefin membrane linings are commonly used. The design or selection of coating process technology plays an important role in reducing coating cost and ensuring coating quality. The design of different coating materials and coating material structures requires the use of appropriate process technology. Painting process technology can usually be divided into five types.

Sandblasting technology is the best in stainless steel surface treatment. The general requirements are: surface cleanliness of SIS Sa2.5, roughness of 40 ~ 60fm. Chemical treatment can also be used, but the phosphating solution matching the primer should be selected, and the surface of the steel tube should be sufficiently dried after surface treatment before coating to ensure the quality of the coating. Generally, economic analysis shows that in the cost of coating, the surface treatment accounts for about 45% of the cost, which is the basic factor to ensure the quality of the coating. Therefore, the surface treatment process should be paid attention to during the design.

Most of the spraying processes have used rotary jets, such as electric rotary jets and pneumatic rotary jets. The rotation speed is 30,000 to 40,000 r/min. The paint is conveyed using a high-pressure airless pump, and the coating speed is mainly determined by the pump pressure and pump volume. The number of passes and the time between each coat depends on the performance of the coating.

Curing of the coating: 

he case of recoating of each coating, in order to facilitate the interfacial bonding between the coatings, the coating is required to be solid, or the coating of the next coating can be completed within a few hours. The resin base of large-diameter stainless steel pipe should be fully cross-linked and cured. The completeness of cross-linking curing depends mainly on temperature and time. For example, an epoxy-phenolic base material needs to be thermally crosslinked and cured under baking conditions. Room temperature curing coatings can also be used in order to shorten the curing time, improve the coating work efficiency and the performance of the coating.