Replace B7 with B7M

[MATTChE11]

I know there are a few forums out there which discuss B7 and B7M bolting, however they seem to be geared a little differently.

I am constructing new pipespecs for our plants to follow (lucky me) and am specifying that our Carbon Steel Bolted Bonnet Gate, Globe, and Check Valves have API Trim 12 (316 Stainless Internals). Trim 12 is being specified to get rid of the lesser grades of stainless (400 series), which will give us a better defense against chloride stress cracking corrosion.

Too my question.... Most valve suppliers do not keep C.S. valves with Trim 12 in stock. However they do keep C.S. valves with Trim 12 NACE. Only difference is the B7 vs B7M bolting.

Are there any reasons why B7M bolting cannot be substituted for B7 bolting? I know there are a few slight differences (hardness, strength) but overall would I be ok specifying API Trim 12 with B7M bolting??

 

[btrueblood]

As long as the valves meet your expected pressure/temp. service conditions with the lower-hardness bolts, then I don't know why not.

 

[TVP]

B7M has minimum requirements that are ~ 25% lower for yield and tensile strength than B7. As long as your design can tolerate using lower strength bolts, then I agree with btrueblood.