Regarding the butt joint of large-diameter flanges and nozzles
Thread Content
Question: Section 1.0.4 of HG20623 states that the nominal diameter DN of the steel pipes applicable to this standard, as well as their outer diameter, are specified in Table 1.0.4. The issue is as follows: Currently, steel pipes with DN650 are being used, with an outer diameter of Φ660. The corresponding flanges are of the WN650-300 RF B series, and the outer diameter of the flange’s welded end is Φ665.2. If the same wall thickness is used, misalignment will occur on both the inner and outer sides of the pipe. How can this problem be resolved? For now, it is considered that pipes should be used instead of sheet metal
The flange should have its inner diameter set to that of the welded pipe during design. It’s fine to prepare a bevel here on the outer diameter before welding.
I think it’s right to specify the inner diameter when ordering flanges so that they match the corresponding fittings. But are there any requirements regarding the trimming of the outer diameter? Flanges with large diameters don’t have straight edges anyway
I think there are currently only 2 methods for large-diameter pipes: either make a groove and weld them together, or insert a pipe directly and weld it in two passes
Internal misalignment is trimmed at 7°. The exterior doesn’t differ much; just grind it after welding with a groove.
When ordering flanges, it should be specified that their inner diameter must match that of the steel pipe, while the outer diameter can be processed with transition sections in accordance with the relevant sections of GB50235.
Can a transition section be machined on the flange neck in accordance with GB50235?