Issues when the maximum allowable operating pressure of the flanges on standard equipment is lower than the design pressure
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When reviewing the drawings of a certain manufacturing unit previously, a problem was identified: standard flanges in accordance with NB/T47023-2012 were used with a pressure rating of 4.0 MPa. Based on the material specifications for long-neck flanges and the tables indicating the maximum allowable operating pressure, the corresponding maximum allowable operating pressure for a nominal pressure of 4.0 MPa was indeed 4.0 MPa. However, the design pressure specified in the drawings was 4.5 MPa. Upon rechecking the flanges using SW6, it was found that these standard flanges also met the requirements at a design pressure of 4.5 MPa. Now there is a question: Is it acceptable to specify NB/T47023-2012 on the drawing (that is, to use standard flanges)? I think it’s possible, but it’s unreasonable. That is reasonable but illegal. Reason: When standard flanges are used, GB/T 150.3 specifies that calculations can be omitted; in such cases, the responsibility for the flange lies with the standard. The maximum allowable operating pressure specified for standard flanges is 4.0 MPa, so this value does not meet the requirements regarding design pressure. I believe the reasonable approach is to create drawings for the custom parts based on the dimensions of standard flanges at 4.0 MPa, and then prepare a design calculation report; in this case, all responsibility lies with the designer. What did you do in this situation?
The drawings for the non-standard parts should be prepared based on the dimensions of standard flanges at 4.0 MPa, and a design calculation report should also be issued; it is only then that it is reasonable for the designer to bear full responsibility.
I think the same. This drawing only lists the standard number; there are no part drawings provided either. Review comments were submitted, but it seems that the manufacturing unit is quite opposed to this. Perhaps the team believes that producing separate drawings represents a standard size, and it’s just a superficial change that wastes manpower and time. But I think that, although it’s the same old situation in disguise, what’s important is that the entity responsible has changed. In other words, if followed according to the factory’s drawings, it would be “reasonable but illegal””
Generally, standard flanges with a higher pressure rating are chosen.
Well, it is standard practice to choose a higher pressure rating, but from the perspective of cost reduction for the manufacturer, such a situation might indeed occur.
It can be done this way. But it must be reasonable and legal.
To achieve both cost savings and compliance with regulations, the only option is to design it as a non-standard flange; if standard flanges are chosen, then compliance must be adhered to according to the flange standards.
I often encounter such situations; I think it’s not necessary to include drawings. However, instead of writing down the standard names directly for the individual components, it’s sufficient to indicate that the dimensions, materials, manufacturing processes, and inspection requirements for the flanges meet the corresponding standards, as well as the standard requirements for equipment flanges. A calculation sheet should also be provided. That way there will be no problem. If it isn’t clearly stated that it is for use, it’s problematic; at the very least, it is technically inappropriate and prone to misunderstanding.
It’s not just about reducing costs; there are also size issues as well. When upgrading to a higher grade, there might be no equipment flanges available in the corresponding size, so this situation is quite common.
Hey, the original poster – I have a question: aren’t the standard pressures, design pressures, and maximum allowable operating pressures all determined by the design agency? As the manufacturing unit, design confirmation should be sought. While it is possible to avoid providing part drawings when standard components are used, I believe that when the manufacturing plant reviews the drawings and notices such discrepancies, design confirmation should be obtained to determine whether this specific specification is appropriate for the flange
You have it backwards. The procedure is as follows: the design unit sets out the bidding requirements, while the manufacturing unit prepares the construction drawings, which are then submitted to the design unit for joint review and inspection. The bidding specifications only include parameters such as operating pressure and design pressure; the pressure rating of the equipment flanges is determined by the personnel responsible for the detailed design (construction drawings).