Issues regarding the material of pressure vessel flanges per NB/T47021~47023
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I’m new to the machinery industry. In the flange standards for pressure vessels, NB/T 47020–47027-2012, the first item under the classification and technical requirements for pressure vessel flanges states: Scope: Applicable to flanges for pressure vessels made of carbon steel and low-alloy steel. So, does this standard apply to flanges made of stainless steel or high-alloy steel as well? It seems that when designing and manufacturing them, they didn’t consider the material aspect, opting instead for standard sizes. They also never thought about the material of the studs and nuts; all of them are made of 35CrMoA/30CrMoA.
NB/T 47020~47027-2012 is mainly applicable to pressure vessel flanges made of carbon steel and low-alloy steel. For materials such as stainless steel or high-alloy steel, these standards may not be entirely applicable. When designing and manufacturing pressure vessel flanges made of stainless steel or high-alloy steel, relevant material standards and technical requirements should be referred to to ensure the performance and safety of the flanges. If you have doubts regarding the selection of materials, it is recommended to consult experienced engineers or refer to relevant professional standards to determine whether specific material specifications are required. For example, for stainless steel flanges, it may be necessary to refer to the specific regulations regarding stainless steel in international standards such as ASTM. As for the material of bolts and nuts, 35CrMoA/30CrMoA are commonly used in connections requiring high strength, but whether they are suitable also depends on the actual operating conditions and the material of the flange. If the flange is made of a high-alloy material, it may be necessary to use compatible high-alloy bolts and nuts to avoid issues such as corrosion caused by differences in materials. It is recommended to conduct appropriate material selection and testing when determining the material of the connectors. .
Stainless steel requires calculation; it cannot be selected directly
Using equipment flanges made of stainless steel is too wasteful; consider using linings or surfacing instead
A calculation sheet shall be prepared for stainless steel materials; other materials shall refer to this standard
Flange materials that are not within the standard range require calculation, and the choice of fastener material must be matched to the flange pressure rating, flange type, and gasket material. See Tables 2 to 5 for details
If Type A flanges as specified in the standard are used along with studs made of 35CrMoA, such a combination does not meet the material matching requirements outlined in the standard; therefore, strength calculations for the flanges are necessary. If flanges are made of stainless steel, they need to be calculated as custom flanges, while the flange dimensions can be selected from standard options.
For stainless steel container flanges, strength and stiffness calculations must be carried out as for custom flanges, while the flange dimensions are selected according to standards.