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Steel pipes are divided into two categories: seamless steel pipes and welded steel pipes (with seam pipes). According to the shape of the section, it can be divided into round tubes and special-shaped tubes. Circular steel tubes are widely used, but there are also some special-shaped steel tubes such as square, rectangular, semi-circular, hexagonal, equilateral triangle and octagonal.

For steel pipes subjected to fluid pressure, hydraulic tests are carried out to check the pressure resistance and quality. No leakage, wetting or expansion is allowed under the specified pressure. Some steel pipes are also subjected to the crimping test according to the standard or the requirements of the purchaser. , flare test, flattening test, etc.

Seamless stainless steel pipe is also called stainless steel seamless pipe. It is made of steel ingot or solid pipe blank through perforation and then made by hot rolling, cold rolling or cold drawing. The specifications of the seamless steel pipe are expressed by the outer diameter * wall thickness in millimeters.