A fluid pipe is a type of steel pipe with a hollow cross-section, without welds from beginning to end. Steel pipes have a hollow cross-section and are widely used as pipelines for transporting fluids such as oil, natural gas, gas, water, and certain solid materials. Compared with solid steel such as round steel, steel pipes are lighter in weight when their bending and torsional strength is the same. They are an economical section steel and are widely used in the manufacturing of structural and mechanical parts, such as petroleum drill rods, automotive transmission shafts, bicycle frames, and steel scaffolding used in construction.

Fluid pipes are specialized pipes used for conveying media with fluid properties. Media with fluid properties, in addition to liquid media such as water, oil, and solutions, solid media such as cement, grains, and coal powder can also flow under certain conditions. Fluid pipes can be made of steel, non-ferrous metals such as copper and titanium, and even non-metallic materials such as plastic. Fluid tubes (3 pieces) must have a hollow cross-section, but can also be square, triangular, or any other shape. Some equipment may be limited by conditions, so rectangular tubes must be used, but the vast majority still use circular tubes. A circular tube has the smallest circumference/area ratio among all geometric cross-sections, which means that the maximum inner section can be obtained under the same amount of material. Steel pipes are widely used in modern fluid transportation due to their low cost and high strength. Steel pipes are divided into two categories based on their production processes: seamless steel pipes and welded pipes. Welded pipes are further divided into high-frequency straight seam welded pipes (ERW), spiral welded pipes (SSAW), submerged arc welded pipes (UOE), etc. In the past, seamless steel pipes were traditionally used for fluid pipes. With the development and progress of material science, forming technology, and equipment, welded pipes have made great progress. Welded pipes have the advantages of better wall thickness uniformity, higher accuracy, lower energy consumption, and higher production efficiency compared to seamless pipes. They require high standards for oil and gas transportation pipes (API standards). In the past, almost 100% of seamless pipes were used, but today, more than 95% of them have been replaced by welded pipes in developed countries such as the United States, Japan, and Europe.

Fluid pipe usage:

① General boiler tubes are mainly used to manufacture water-cooled wall tubes, boiling water tubes, superheated steam tubes, superheated steam tubes for locomotive boilers, large and small smoke tubes, and arch brick tubes.

② High pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, air ducts, and main steam tubes for high-pressure and ultra-high pressure boilers. However, circular pipes also have certain limitations. For example, under the condition of planar bending, circular pipes are not as strong as square and rectangular pipes in terms of bending strength. Some agricultural machinery skeletons, steel and wood furniture, etc., commonly use square and rectangular pipes. Special shaped steel pipes with other cross-sectional shapes are required for different purposes. 1. Seamless steel pipe for fluid transportation (GB/T8163-2008) is a general seamless steel pipe used for transporting fluids such as water, oil, and gas.