Differences in bolt specifications between ASME B16.5 and HG/T20615
Thread Content
There is a foreign-made wafer-type butterfly valve on site (8’ CL150), with internal threads on its bolt holes; M20 bolts cannot be inserted into them. The flange standard specified at the time of design was ASME B16.5, but the bolts designed were of type HG/T20634 M20. I checked and found that B16.5 requires bolts with coarse threads according to AMSE B1.1. The design institute responded that B16.5 and HG/T20615 are interchangeable, so bolts based on HG/T20634 were used. I would appreciate it if someone could provide an analysis of this situation
If it is ASME B16.5, 3/4\" bolts are used, which are M20. The bolt won’t fit in; it’s related to the thread profile. It seems that B16.5 doesn’t specify any requirements for the bolt’s threaded hole
The bolt holes on the flanges are unthreaded. Now, the clamp-type butterfly valve between the two flanges also has 8 bolt holes, and these 8 bolt holes are threaded； B16.5 does not specify bolt holes for flanges, but it specifies the thread profile of the accompanying bolts
That’s the issue here: it’s necessary to clarify the standard for the threads on that bolt hole.
Strictly according to B16.5, the bolts use imperial threads； It needs to be fitted with British-style bolts in order to be used. The HG20615 bolt follows metric standards; this issue does not occur in flanged connections, as the bolt is used in combination with a nut ； B16.5 and HG20615 being generally applicable usually refers to this situation. The problem in your case lies with the butt-type design: the bolts and the valve body don’t match, as metric and imperial systems are incompatible.
Bolts and nuts smaller than M36 should use coarse thread, while those equal to or larger than M36 should use fine thread； . For nuts with a bolt diameter of M14, Type I (m=0.8d) should be used, while for the rest, Type II (m=1.0d) should be used; the technical requirements shall comply with the provisions of SH/T 3404.
The imported ANSI valves use ANSI bolts of type ASME_B18.2.1 and ASME B1.1-2003, which feature coarse thread profiles in imperial units; therefore, it is sufficient to purchase bolts of American standard. Domestically produced ones in metric system cannot be used.
Note that it is a bolt hole – the original through-hole, which now has threads.
The standard for HG is rounded up from the American standard; the bolts will be larger than the original ones, so you can use one size lower
I took a look at these two standards: does B18.2.1 determine parameters such as the type, length, and chamfer of the bolts, while B1.1 determines the thread specifications? It seems that bolt standards are much more complex than flange standards. . . It’s dizzying to watch. . .
One is a metric thread, and the other is an imperial thread; the main difference lies in the pitch. . The imperial system is complicated; there are also coarse and fine threads. . . Ask the relevant valve manufacturers about the standards for threads