Usage limitations of bolts and studs
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Dear experts: According to the HG20634 standard, hex head bolts are specified to be used only at CL150. However, due to the special requirements of valves, especially butterfly valves, valves rated at CL300 and Cl600 often require the use of hex head bolts. Under the ASME standard as well, hex head bolts are limited to use at CL300. How should this contradiction be resolved?
For flange connections, single-headed bolts have never been used; instead, fully threaded double-headed bolts are employed.
I really don’t know. But I have used clamped check valves, with fully threaded bolt holes. During on-site installation, use 2 fully threaded double-ended studs, twist them in from 2 different directions, and then tighten the nuts in those 2 directions.
Thank you for your reply. If that’s the case, it will be difficult to unscrew these double-headed studs when removing and repairing the valve; this problem will still exist.
Oh, ours is a disposable tube. However, back at the shipyard, for wafer-type butterfly valves, there were often 4 bolt holes at the top and bottom that were fully threaded; I can’t quite remember how the work was carried out on site at that time.
After reading the above discussion, it seems that the \"hex head bolt\" is the type with a single-threaded head, while the other end is threaded on the valve flange. For butterfly valves manufactured in this way, their pressure resistance ratings are indeed not high.
It can be unscrewed by using two nuts
I’ve never seen hex bolts used in high-pressure applications. Some of the high-pressure butterfly valves in our systems use fully threaded bolts, with one end screwed into the valve seat and the other end having a nut. Is the poster in this situation?
I don’t quite understand how the double nuts can be unscrewed
In other words, for high-pressure applications, it’s not the hex head bolts with single threads that are used; instead, fully threaded studs are employed. One end of such a stud is screwed into the valve, and then a nut is screwed on the other end, right? But in this case, if the valve needs to be repaired, how can this stud be unscrewed out from inside the valve?
When two adjacent nuts are tightened, friction is generated between them.