Straight seam steel pipe refers to the welded steel pipe with the weld seam parallel to the longitudinal direction of the steel pipe. Mainly used for large-span grid engineering, building steel structure engineering, electric power and ultra-high voltage transmission and distribution engineering, mechanical engineering, sea-crossing bridges, bridges, municipal pipe networks, foundation piling, water and gas pipelines and highway construction and other supporting facilities. Therefore, the paint spraying of straight seam steel pipe is very important.

The principle of spraying of straight seam welded pipe is to isolate air, moisture and corrosive medium with paint film to protect the surface of steel pipe from corrosion. There are four kinds of painting techniques for straight seam steel pipe and equipment surface: manual painting, air spraying, electrostatic spraying and high-pressure spraying, but the following two are commonly used:

1. Manual painting
 
Manual painting is to dilute the paint to an appropriate consistency and then apply it in layers with a brush.This method is simple and adaptable, and can be used for the construction of various paints, but the work efficiency is low, the quality of painting is greatly affected by the technical level of the operator, and the paint film is not easy to be uniform. Manual painting should be carried out from top to bottom, from left to right, inside and outside, and the thickness of the paint layer should be uniform and consistent, and there should be no leakage and hanging.

2. Air spray

Air spraying is the use of compressed air to generate high-speed airflow through the spray gun to inject and mix the paint liquid in the paint storage tank into a mist, which is sprayed on the surface of the object. The air circulating in the air spray is 0.2-0.4MPa, generally 250-400mm away from the surface of the workpiece, and the moving speed is 10-15m/min. The air spray paint film has a uniform thickness, a smooth surface and high efficiency; but the paint film is thin, and it often takes several sprays to achieve the required thickness. In order to increase the thickness of the first spray film, thermal spray construction can be used, and the thermal spray coating is heated to about 70%.

According to the production process, straight seam steel pipes can be divided into high frequency straight seam steel pipes and submerged arc welded straight seam steel pipes; submerged arc welded straight seam steel pipes are divided into UOE, RBE, JCOE steel pipes according to their different forming methods. Mainly used in water engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction, etc.

Different from straight seam steel pipe, seamless steel pipe refers to a steel pipe that is perforated from a whole round steel and has no welds on the surface. Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames and steel scaffolding used in construction, etc.