The uniform deformation of the square rectangular tube is a simple case of object deformation. Its characteristics are: the plane and the line are still planes and straight lines after deformation. The parallel lines and parallel planes remain parallel after deformation and the cube is perpendicular to the strain axis. After uniform deformation, there is only linear scale change without shear deformation. If the deformed body is a spherical surface, it will be an ellipsoid after deformation.

It can be seen that the characteristic of uniform deformation is that the displacement of each point of the object is a linear function of the original coordinates, and uniform deformation has only three principal strains and no shear strain.

For square and rectangular tubes, in the evaluation of metal pressure processing, especially in the evaluation of rolling places, logarithmic strain is usually used to express uniform deformation. Logarithmic strain is a more accurate representation of the deformation level of an object than relative deformation systems.

Hot-dip galvanized square tube, also known as the welded tube, is a steel tube made of steel plate or steel strip after being crimped and welded. Welded steel pipe has a simple manufacturing process, high manufacturing efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe.

The quality of square and rectangular pipes is constantly improving, and the varieties and specifications of welded steel pipes are increasing day by day, and seamless steel pipes are replaced in more and more fields. Welded steel pipes are divided into straight-seam welded pipes and spiral-welded pipes according to the weld pattern. The manufacturing process of longitudinal welded pipe is simple, the manufacturing efficiency is high, the capital is low, and the development is rapid.

The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with a larger diameter can be manufactured with a narrower billet, and welded pipes with different pipe diameters can be manufactured with the same width billet. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the manufacturing speed is lower. Therefore, most of the smaller-diameter welded pipes use straight seam welding, and most of the large-diameter welded pipes use spiral welding.

The hot-dip galvanized rectangular tube for low-pressure fluid transportation is also called an ordinary welded tube, commonly known as a clarinet tube. It is a welded steel pipe used for conveying water, gas, air, oil, heating steam, and other common lower-pressure fluids and other purposes. The wall thickness of the steel pipe is divided into ordinary steel pipe and thickened steel pipe; the connection end mode is divided into unthreaded steel pipe and threaded steel pipe. The specification of the steel pipe is expressed by the nominal diameter, which is the approximate value of the inner diameter. It is customary to express in inches, such as 11/2, etc. In addition to being directly used to transport fluids, welded steel pipes for low-pressure fluid transportation are also widely used as raw pipes for galvanized welded steel pipes for low-pressure fluid transportation.