The flanges at both ends of the valve are located at the mid-span; what is the specific acceptable value?
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As shown in attach://1392181.jpg, the bolt holes at both ends of the valve are not aligned in the center, yet many standards state that the flange holes should be arranged centrally. The flange connection should be concentric with the pipe, and the bolts should pass through freely. So: within what specific range of deviations does it count as being at the mid-span? (Standards are not required; it’s sufficient as long as there is a specific description), thank you very much!
Push it by yourself – does this fall under the mechanical processing standards?
Assuming the bolt hole diameter is 2 mm larger than the bolt diameter, then a misalignment of 1 mm between the two flanges results in an actual misalignment of 2 mm.
That’s the fact, but when I checked the inspection standards for valves, API598 and GB/T26480, along with all the manufacturing or design standards referenced in them, I couldn’t find any detailed requirements regarding this matter. Doesn’t that mean that if manufacturers process things arbitrarily, there’s nothing that can be done about it?
This HG20592/20593 is related to the pressure rating; it’s clear at a glance by checking the table； It seems the national standard ones are pretty much the same.
It’s not the coaxiality or parallelism of the flanges, but rather the issue of the centerline position of the flange bolt holes at both ends of the valve (see figure)
In GB/T50540, Code for Construction of Process Piping Projects in Oil and Gas Stations, there is a description of the backing plate.
If the deviation is not significant, a finer bolt with a higher strength can be used as a temporary substitute.
The offset of the flange bolt holes on the boiler from the center of the bolts shall satisfy the following requirement: ① When the outer diameter of the flange is ≤ 100 mm, the offset △a of the flange bolt holes shall be ≤ 1 mm； ②The outer diameter of the flange is >100–200 mm, and the offset of the flange bolt holes is △a ≤ 2 mm ； ③The outer diameter of the flange is >200 mm, and the offset of the flange bolt holes is △a ≤ 3 mm.