Reasons for the increase in the pressure rating of instrument pipe ports
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As the title suggests: I’ve noticed that in the design of pressure vessels by some design institutes, the pressure rating of the instrument ports is one level higher than that of the other process ports. Have any of you sea friends encountered this situation? What exactly is the reason behind it? Thank you
It is also possible that uniform instrument specifications within the same project, resulting in a high interchangeability rate, were taken into consideration. Other main reasons include experienced sailors sharing their opinions, haha
Are flanges involved in this? When designing stainless steel equipment for a pressure of 1.0 MPa, if HG/T20592-2009 standard stainless steel flanges are used, it is necessary to select flanges with a maximum allowable working pressure of at least 1.6 MPa.
They are indeed a set of stainless steel flanges; the design pressure of the equipment is below 1.6 MPa, and the temperatures are not high either. However, the flange standard is HG/T20615-2009, so CLASS150 would have been sufficient; all the instrument connections use CLASS300
They are indeed a set of stainless steel flanges; the design pressure of the equipment is below 1.6 MPa, and the temperatures are not high either. However, the flange standard is HG/T20615-2009, so CLASS150 would have been sufficient; all the instrument connections use CLASS300
The owner who created the pressure vessel condition diagram for the process failed to specify the process pipe connections properly; if they had determined the size of the instruments first, they should have informed the manufacturer. If not, then configure it according to the equipment drawings.
That’s indeed the case. The pressure rating of the instrument port is slightly higher than that of ordinary ports. I asked colleagues in the instrumentation field, but I’m not entirely sure either. One reason is that the pressure ratings specified in their instrument selection manuals do not exactly match those in HG/T20592; another reason is related to the requirements regarding the instruments’ resistance to shock. There’s one more point that I consider to be a standard issue: the pipe connections are usually small in size, such as DN25, DN40, DN50, DN80. As for the flange grades, at PN40 and below, the dimensions for pipes smaller than DN50 are exactly the same. In other words, a pipe with DN50 size will have the same specifications whether it’s PN10, PN16, or PN25 – it’s just described differently on the drawings, but essentially it’s the same thing.
Currently, I am dealing with a batch of purchased finished flanges, and it is common for the effective thickness of these flanges to be below the specified value (in other words, the effective thickness does not meet the standard requirements). Additionally, the pressure rating of the instrument ports is one level higher than that of the other process ports, which fully meets the pressure and temperature requirements specified in the equipment design. So it’s a shame to scrap the stainless steel flange; on the other hand, reusing it directly is risky in case problems arise due to other unconsidered factors.
It’s possible that the instrument manufacturer selected a higher grade, and the pipe flanges on the equipment cannot be matched with theirs.
The same is true for our instrumentation field.