Which standard should be used for nuts on pressure vessel flanges?
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Which standard should be used for nuts on pressure vessel flanges? The standard numbers for pressure vessel flanges are JB/T4701-4703-2000, and there is also a standard for studs, namely JB/T4707-2000. However, only requirements are specified regarding the material of nuts; what standard can be chosen to match the studs? This is how we proceed with the design. When the stud material is Q235-A, select nut grade 8 according to GB/T6170-2000. When the stud material is 35CrMoA, use the special-grade nut HG20613 made of 30CrMo. Standard JB/T4700-2000 for pressure vessel flanges specifies that the hardness of the studs should be 20-30 higher than that of the nuts. I’ve also checked it – Q235-A is equivalent to grades below 8.8, while grade 8.8 corresponds to steel grade 35. When the stud material is Q235-A, selecting nuts of grade 8 according to GB/T6170-2000 does not meet the standard requirements; so what should I choose? By standard, the nut material is Q235-A. When the stud material is 35CrMoA, use the special-grade nut HG20613 made of 30CrMo. Someone on another forum said it simply can’t be tightened at all.
We are the same. When the stud material is of special grade, the nut is selected in accordance with GB/T6170-2000, and the material is chosen from Table 2 of JB/T4700-2000; however, 8.8 grade nuts are rarely used in equipment.
ASME B16.5-1996 Pipe Flanges and Flanged Fittings
Generally, nuts of grade 8 are used with bolts of grade 8.8
It seems that they always choose 4.8 grade bolts and 6.0 grade nuts
The grade of the nut should be lower than that of the bolt
Reply to 7# SlimShady313 with 6175
This post was last edited by happyhefei on 2011-4-14 09:47. The flange standard you mentioned is rarely used these days; indeed, I’ve never seen it in use alongside the JB4701–4703 standards. Nowadays, ASME B16.5 is the standard that’s generally used. The bolt standard is GB5783
Friend who rated me: I’m not quite sure what you mean, hehe! Is B16.5 also used as the national standard? In flange standards, no one uses the national standards, unless it is flanges such as manholes that are not connected to pipe flanges – in those cases the national standards are used. But how can you match other flanges with pipe flanges?
This is generally how we proceed: we first select high-strength studs based on the material specified for the pressure vessel flanges, and then choose the nut materials as recommended by the standards. Instead of matching the grades, we simply specify the material; the standard used is usually GB/T6170. Any company with manufacturing experience will ensure that the components are properly matched, so from a design perspective, this has never been considered an issue.