Why are some of the high-performance butt weld flanges of HG 20615 lacking an inner flange diameter?
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As the title suggests, butt-weld flanges all have an inner diameter
The reason why some of the butt-welded flanges specified in HG 20615 do not have their inner diameter indicated is that these flanges are primarily used for connecting pipelines, and their inner diameter generally matches that of the pipes they connect to. Therefore, for pipes of standard sizes, the inner diameter of the corresponding butt-welded flanges is already known, so it is not necessary to specify it separately. At the same time, the design of welded flanges focuses more on the pressure rating and size they can withstand, rather than the inner diameter. For butt-weld flanges of non-standard sizes, their inner diameter may be specified to facilitate purchasing by users. .
The inner diameter of standard flanges is designed according to the SCH 40 wall thickness series (as a general default); in special cases, such as with long-neck flanges, the wall thickness series of the connected pipes must be taken into consideration when preparing the purchase order. As an additional condition, the corresponding flange SCH series is proposed based on the inner diameter of the pipeline. Only in this way can the long-neck flange and the inside of the pipeline have the same inner diameter, facilitating welding.
For flat-face flanges, the pipe is inserted into the flange; in this case, the outer diameter of the pipe plays a role. For butt-face flanges, the outer diameter of the pipe is fixed, while the inner diameter depends on the pressure applied to the pipe
Isn’t it already explained in the chart above?
But flange butt welding per GB9124.1 PN is also available
For those without an inner diameter, it needs to be determined based on the actual thickness of the pipes in place. Even when an inner diameter is specified, it isn’t necessarily necessary to follow that value; for example, for 150LB DN300, the inner diameter is 303.5. If the outer diameter of the pipe in use is 12.7 mm, then the inner diameter of the flange should be set at 298.5.
For butt-weld flanges, the inner diameter of the flange matches the outer diameter of the pipe fitting; since the outer diameters of standard nominal pipes are fixed, the inner diameter of the butt-weld flange can be determined directly. For butt-welded flanges, the weld neck of such flanges is generally required to have the same wall thickness as the pipe connected to it; therefore, the inner diameter of the flange must be determined based on the wall thickness of the pipe being connected. This is also indicated in the tables provided in the standards – the inner diameter of the flange is determined by the wall thickness of the steel pipe. It is necessary to specify either the standard inner diameter of the flange or the wall thickness of the pipe when placing an order
It’s clearly stated below; why not take a look?
Because the eyes are meant to look at the sky; P
Because butt weld flanges need to be joined to pipes, and when the thicknesses of the pipes vary, the inner diameter of the butt weld flanges also changes. To determine the inner diameter of the butt-weld flange, the customer needs to provide the thickness of the pipe stub. Generally, for butt weld flanges that are subject to higher pressures, the customer is required to provide the thickness of the pipes connected to them, in order to determine the inner diameter of the flange.