Bolt Materials 1

I have referenced that Class II (specifically B7M) bolting may have a 20% reduction in tensile strength compared to Class I or standard bolting materials and may also reduce the allowable working pressure in some cases. Is there a rule of thumb or specific reference to determine acceptable design measures when utilizing B7M bolting versus standard B7 bolting for standard flange joint, flanged valves, compressor cylinders, and cooler connections?

 

[prex]

Your guess is correct: the allowable stress for ASME VIII Div.1 for B7M is 80% as that for B7 (at least at low temperature, didn't check the details). prex
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[CoryPad]

The fastener material requirements are listed in ASTM A 193/193M. The minimum mechanical properties are a function of fastener diameter, with B7 having higher properties for products under 4"/100 mm. Thus, you need to refer to this specification for material properties, then use those properties when determining joint requirements.