For flanges of atmospheric-pressure vessels handling highly hazardous media, the pressure rating is 2.5 MPa; can the nominal pressure for manholes be reduced? Urgent need

There’s no rule stating that 1.6MPa cannot be used, right?

Of course. The pressure at the connection port is required to be 2.5 MPa, as this is necessary for the process piping; the pressure at the manhole can be reduced since it is not connected to the process piping. Although it is a container operating at atmospheric pressure, it poses a high level of hazard, so design should follow GB150 standards, as the standards for containers at atmospheric pressure are not applicable to those handling highly hazardous substances!

Of course, it’s possible. The pressure at the port is required to be 2.5 MPa, as that’s necessary for the process piping; the pressure can be reduced since the manhole isn’t connected to the process piping!

The minimum pressure rating shall be 1.6 MPa, and flanges with neck welding should be used.

According to HG/T20583-2011, for P437 materials that are classified as extremely hazardous or highly hazardous substances, as well as those with strong permeability, the nominal pressure rating of the flanges used on connections should be at least 2.0 MPa. Should the nominal pressure rating for manholes also be at least 2.0 MPa?

Is HG/T20583-2011 a mandatory standard? Besides, you’re at normal pressure – isn’t 1.6 enough for you? ! You should design in accordance with GB150 – I mean, as a reference, not by strictly following GB150! In other words, anything that is specified in GB150 but which you think should be added, such as testing requirements and technical specifications, can be included. In my opinion, for manhole flanges, this situation can definitely be reduced depending on the design of the process pipe outlet. Advocate: Safety first, save energy! In fact, this regulation exists because the connection is linked to a piping system, which involves piping loads, whereas manholes do not have such loads. If you look at the flange selection criteria in version 09 of the specifications, only the usage conditions for pipe flanges are specified. There are no equipment flanges, as there are no piping connections. It has no coercion! Standards should be applied flexibly; if the design you use is based on certain standards, then those standards must be followed. Is this standard indicated on your drawings? If it is, then it must be implemented. The above views are merely personal interpretations!

This post was last edited by fzujunru on 2016-10-10 at 10:50. It should work fine; the PN value for manhole fittings is often lower than that for process instrumentation connections. Manhole flanges are usually made in accordance with HG20592, while the flanges used for pipes are typically HG20615. The PN values for manholes are usually 2.5, 6, 10, 16, 25, 40, 63; the PN values for HG20615 flanges are 20, 50, 110. If a pipe flange with PN50 (CL300) is chosen, it’s not possible to use a manhole fitting with PN63

Just look at the design pressure; there should be no problem

The pipe outlet and the manhole are not the same; the pipe outlet is connected to the pipeline, and forces such as bending inevitably act on it, which can lead to slight leaks. The manhole is not connected to the pipeline, so it needs to be more resistant to stress. 20583 refers to the process pipe outlet; manholes do not have such requirements