First. Epoxy coal tar anti-corrosion layer
1. Epoxy coal tar anti-corrosion layer is suitable for the outer wall corrosion protection of buried steel pipelines for oil, water, and gas transportation. The temperature of the medium it transports is required to be less than or equal to 110℃.
2. The raw materials are epoxy coal tar paint plus glass cloth, thin coating multi-layer structure, and cold coating on site. It is suitable for pipe sections with the same material as the pipe body for corrosion protection.
3. The advantage of epoxy coal tar is that it is easy to operate on-site and does not require heating; the disadvantage is that the coating has a long curing time and is not suitable for field operations. It is difficult to construct when the ambient temperature is below 10℃. Epoxy coal tar is mainly used for municipal gas pipelines, water pipelines, and factory pipelines. Long-distance pipelines are generally only patched and repaired in stations and anti-corrosion layer overhauls.

Second. Patching process and requirements for epoxy coal tar on-site
1. After the surface of the steel pipe at the patching site is pretreated, the primer should be applied within 4 hours. The primer should be evenly applied and no leakage should be allowed.
2. After the primer is dry, the topcoat and glass cloth can be applied. If the weld is higher than 2mm, mix the topcoat and talcum powder into a putty of appropriate consistency. After the primer is dry, apply it on both sides of the weld and scrape it into a transition curve. The overlap of the glass cloth and the pipe body anti-corrosion layer shall not be less than 100mm.
3. The anti-corrosion layer of the ordinary grade structure can be painted with a topcoat after the topcoat is dry. The thickness of the anti-corrosion layer should be greater than or equal to 0.2mm.

For the anti-corrosion layer of the reinforced grade structure, the glass cloth can be wrapped after the topcoat is applied. The glass cloth should be tightened, the surface should be flat, without wrinkles and bulges, and the edge width should be 30-40mm. After the glass cloth is wrapped, the topcoat should be applied immediately. The paint should be full and all meshes of the glass cloth should be filled with paint. After the topcoat is dry, the third topcoat can be applied. The thickness of the anti-corrosion layer should be greater than or equal to 0.4mm. The anti-corrosion layer of the extra-reinforced structure is applied in the order of one layer of topcoat and one layer of glass cloth as mentioned above. The winding directions of the two layers of glass cloth are opposite. The fourth layer of topcoat can be applied only after the third layer of topcoat is completely dry. The thickness of the anti-corrosion layer should be greater than or equal to 0.6mm.