Help needed! When the outer diameter of the flange weld end and the outer diameter of the pipe fitting are different, what type of welding groove should be used?
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This post was last edited by WallaceLee on 2020-9-5 at 21:29. As the title indicates, the flanges used are WN 850-150 RF steel pipe flanges from series HG/T 20623-2009 (B), as shown in the diagram. As depicted in the figure above, the outer diameter A of the flange’s welded end is Φ865.1 mm. The design institute, based on the strength verification calculations, determined that the outer diameter of the pipe fitting welded to the flange is Φ870mm. The outer diameter A of the flange weld end is different from the outer diameter of the pipe fitting! ! ! And when the outer diameter of the flange weld end differs from the outer diameter of the pipe fitting to which it is welded. There will be misalignment, leading to stress concentration. The current question is: 1. What type of welding groove should be used between the flange weld end and the pipe fitting in order to avoid stress concentration due to misalignment? 2. Are there any relevant standards that specify the welding groove shapes when the flange weld end and the outer diameter of the pipe fitting differ? I need the expertise of experts! ! !
I was wondering: does the design institute specify the outer diameter of the steel pipe for you? According to SHT 3405-2017, the outer diameter of the steel pipes used in the petrochemical industry in the DN850 size series is uniformly 864. Generally, design institutes select the nominal diameter based on requirements, and then determine the thickness of the steel pipe according to the pressure; there are dozens of different wall thickness options for DN850 pipes.
Yes, the outer diameter of the pipe fitting specified by the design institute is 870; it’s clearly stated in the drawings. I can’t possibly suggest that the design institute enforce stricter standards
From a design perspective, it is necessary to determine whether the wall thickness of the pipe fitting meets the requirements of the operating conditions. If its thickness is equal to that of the flange weld end, then the 150 series standard for thin-walled pipe fittings can be used as a reference
If the inner diameter of the fitting and the flange is equal, but the outer diameter of the fitting is larger, then the wall thickness of the fitting may have been taken into account to accommodate reinforcement for the opening; in such cases, it is necessary to determine what the calculated overhang height is for that reinforcement, as the wall thickness cannot be reduced within that overhang height
It is recommended to first check the dimensions of the joint as specified in the calculation sheet, determine the overhang height indicated there, and then appropriately use a butt-thinned structure of 150.4
As for stress concentration, the pressure in your equipment should not be high; after all, the pressure rating of the flange is only PN20. Unless it is a fatigue-prone container or subject to stress corrosion, other equipment should first meet the structural requirements specified in 150.4
This post was last edited by lmq881825 on 2020-9-6 at 16:08. The design institute provides rolled pipes; otherwise, where would pipes with a diameter of φ870 come from, right? If it’s a standard pipe flange as shown in the drawings, communicate with the design institute and ask them to clarify it.
Do you mean grinding of the welding groove shape?
Yes, it’s rolled plates. My problem now isn’t getting the design institute to modify the pipes and data; rather, it’s about how our own manufacturing plant can address this issue of different outer diameters from a production perspective.
First of all, if it is a standard steel pipe, there is no such specification as 870; then none of the remaining issues exist and there is no need to discuss them