Tube is open at both ends and have hollow cross section, its length and around the larger steel, according to production methods can be divided into seamless and welded steel pipe, steel pipe size specifications with the appearance (such as the diameter or side length) and the wall thick that a wide range in size from very small diameter capillary until a few meters in diameter, large diameter pipe. Steel can be used for pipes, thermal equipment, machinery, petroleum geological exploration, container, chemical industrial and special purpose.  Classification of Steel: Seamless and welded steel points (pipe joints) two categories. By cross-section shape can be divided into tube and shaped tubes, round steel is widely used, but there are some square, rectangular, semi-circular, hexagon, equilateral triangle, octagon and other special-shaped pipe. For the steel pipe to withstand fluid pressure test should be conducted to test the pressure of hydraulic capacity and quality, the provision does not leak under pressure, wet or expansion of qualified, some steel but also according to the requirements of the standard or demand side, curling test , flaring test, flattening tests.