Stainless steel pipe is a hollow, long, round steel bar widely used in industrial pipelines and mechanical components in the petroleum, chemical, medical, food, light industry, and instrumentation industries. Furthermore, its light weight, while maintaining the same bending and torsional strength, makes it widely used in the manufacture of mechanical parts and engineering structures. It is also commonly used in furniture and kitchenware.

Hardness

Stainless steel pipe is generally measured using the Brinell, Rockwell, and Vickers hardness scales.

Brinell Hardness

In stainless steel pipe standards, the Brinell hardness is the most widely used, often using the indentation diameter to indicate the material's hardness, which is both intuitive and convenient. However, it is not suitable for pipes made of harder or thinner steels.

Rockwell Hardness

The Rockwell hardness test for stainless steel pipe, like the Brinell hardness test, is an indentation test. The difference lies in measuring the indentation depth. The Rockwell hardness test is currently the most widely used method, with HRC being second only to the Brinell hardness (HB) in steel pipe standards. The Rockwell hardness test is suitable for measuring metals ranging from extremely soft to extremely hard. It addresses the shortcomings of the Brinell method and is simpler than the Brinell method, with the hardness value directly read from the hardness tester's dial. However, due to the smaller indentation, the hardness value is not as accurate as the Brinell method.

Vickers Hardness

The Vickers hardness test for stainless steel pipe is also an indentation test method, suitable for measuring the hardness of very thin metal materials and surface layers. It combines the key advantages of the Brinell and Rockwell methods while overcoming their fundamental disadvantages, but is less convenient than the Rockwell method and is rarely used in steel pipe standards.

Hardness Testing

Annealed stainless steel pipe with an inner diameter of 6.0 mm or greater and a wall thickness of 13 mm or less can be tested using the W-B75 Vickers hardness tester. This test is extremely fast and simple, making it suitable for rapid, non-destructive quality inspection of stainless steel pipes. Stainless steel pipe with an inner diameter greater than 30 mm and a wall thickness greater than 1.2 mm can be tested using a Rockwell hardness tester for HRB and HRC hardness. Stainless steel pipes with an inner diameter greater than 30mm and a wall thickness less than 1.2mm should be tested for HRT or HRN hardness using a Rockwell hardness tester. Stainless steel pipes with an inner diameter between 0mm and 4.8mm should be tested for HR15T hardness using a Rockwell hardness tester specifically designed for pipes. For stainless steel pipes with an inner diameter greater than 26mm, the inner wall hardness can also be tested using a Rockwell or Rockwell hardness tester.