Common problems in the production process of stainless steel pipes

There are corresponding causes and solutions for these problems. Like the Brinell hardness test, it is an indentation test method. But it is to measure the depth of the indentation. Rockwell hardness test is a widely used method at present, but the Rockwell hardness scale has three standards: A, B, and C, which are usually recorded as HRA, HRB, and HRC, and the expression method is hardness data + hardness symbol, such as 50HRC. Among them, HRC is second only to Brinell hardness HB in steel pipe standards. Rockwell hardness is suitable for measuring metal materials ranging from extremely soft to extremely hard, and the hardness value can be read directly from the dial of the hardness machine. But the hardness value is not as accurate as the Brinell method. When the tested sample is too small or the Brinell hardness (HB) is greater than 450, use the Rockwell hardness measurement instead.

The two commonly used stainless steel pipe materials are 201 stainless steel pipe and 304 stainless steel pipe. The main factor affecting the hardness of the two is the carbon content in the raw material. The carbon element in the stainless steel pipe mainly improves its hardness, but the higher the hardness, the better. The higher the carbon content, the lower the plasticity of the stainless steel pipe, and the easier it is to rust. Another factor that affects the hardness of 201 stainless steel pipes is the content of copper elements inside. 201 stainless steel pipes with high copper content have better toughness, enhanced plasticity, and softer pipes. What I want to talk about today is not there, but the wall thickness and ovality of stainless steel pipes. How many of these common problems do you know about stainless steel pipes?

1. The size of the stainless steel tube is out of tolerance, that is, the outer diameter and wall thickness of the stainless steel tube exceed the allowable deviation of the standard. Some people are used to calling the size out of tolerance "out of tolerance". This kind of equating the deviation with the tolerance is not strict, and should be called "deviation out of bounds". The deviation here may be "positive" or "negative". It is rare for the "positive and negative" deviations to exceed both in the same batch of stainless steel pipes.

2. The wall thickness of the stainless steel pipe is uneven, because the wall thickness of the stainless steel pipe cannot be the same everywhere, and there is an objective phenomenon of unequal wall thickness in its cross-section and longitudinal pipe body. In order to control this unevenness, some stainless steel pipe standards stipulate the allowable index of uneven wall thickness, which generally does not exceed 80% of the wall thickness tolerance, but in actual transactions, it is implemented after negotiation between the supplier and the buyer.

3. The ellipticity of the stainless steel pipe: there is a phenomenon of unequal outer diameter on the cross-section of the circular steel pipe, that is, there are large outer diameters and small outer diameters that are not necessarily perpendicular to each other, and the difference between the large outer diameter and the small outer diameter The difference is ovality (or out of roundness). In order to control ovality, some stainless steel pipe standards stipulate the allowable index of ovality, which is generally stipulated as not exceeding 80% of the outer diameter tolerance.