When a new petrochemical plant is built, the processing pipeline is very complicated, with different media and temperatures. Generally, inorganic zinc silicate primer is used as a general anti-corrosion and high-temperature resistant coating. The zinc powder content in the dry film of the inorganic zinc silicate primer is 80%, which can withstand high temperatures of 400°C, and the dry film thickness is 50-75μm. It should not be too thick, otherwise, the coating film will crack due to the cold wall effect of the pipeline. The design of the coating system of the processing pipeline should consider the limitation of working temperature, the difference between insulation and non-insulation, and material/substrate.
Insulation is mainly to prevent energy loss. For the surface of non-insulated pipelines below 120℃, the matching coating system is epoxy/inorganic zinc silicate + epoxy coating + aliphatic polyurethane topcoat. Within 120℃, epoxy paint and polyurethane paint can be used. At 120-230℃, acrylic silicone or phenolic epoxy paint can be used. At 200-400°C, inorganic zinc silicate is used. At 400-600℃, organic silicon aluminum paint is the main choice. If the paint on the surface of stainless steel, zinc, or aluminum paint should not be used to avoid galvanic corrosion.
The outer wall of the buried pipeline is mainly corroded by the soil. When choosing the anti-corrosion coating, its corrosion characteristics must be considered comprehensively. At present, the corrosion protection of pipelines adopts anti-corrosion coating and cathodic protection. For buried pipelines in petrochemical plants, epoxy asphalt coatings, modified thick-build epoxy coatings, solvent-free phenolic epoxy coatings, polyurethane foam-polyethylene anticorrosive insulation layer are practically used.
The internal coating materials for natural gas pipelines mainly include epoxy powder coatings, liquid epoxy coatings, and phenolic epoxy coatings. When the epoxy resin coating is cured, the volume shrinkage is small, the thermal expansion coefficient is small, and the temperature and stress resistance is strong. It is suitable for high-pressure gas pipelines.
The outer wall coating system of steel sewage pipes used an epoxy coal tar two-cloth-five-oil FRP system. New types of anti-corrosive coating systems of buried pipelines commonly use epoxy zinc-rich paint as a primer. Epoxy coal tar mortar paint, modified high build epoxy paint, solvent-free epoxy glass flake, and vinyl ester glass flake paint are for the choice of topcoat. The coating system has no pinhole defects, needs no glass cloth, has excellent insulation, anti-microbial corrosion, and good chemical resistance. The coating film can reach the required film thickness with one time layer, with the advantages of a simple construction process, low surface treatment cost, and short construction period. The inner wall of the steel pipe can also be matched with the same coating system.