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Re: Grade 8 Bolts

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>I'm not comfortable with this replacement.  So far as I can tell, the grade
>8 machine bolt is hard, tough, and *brittle*.  'Sounds like courting
>disaster to me...
>I recommended replacing the *new* bolts with A325, but the client is
>reluctant to spend money twice for the same work.
If they actually _are_ SAE grade 8 they comply with ASTM A354 grBD. Since 
they're OK for ASME code use they're fine for structural bolts and 
stronger than A-325 bolts. All quenched and tempered bolts are more 
brittle than low carbon structural steel--that's why you preload them. 
Basically just medium carbon alloy steel quenched and tempered. You 
should check the markings on the bolt heads--6 radial lines at each 

I'm inclined to agree--they either worked loose or failed in fatigue, 
probably the latter. If they were mounted vertically, they might have 
been jacked out of their holes and fallen to the ground, but that isn't 
likely. Depending on when they were replaced, there might be a few pieces 
on the ground under the connections. I'd look around real good, even at 
the risk of making an issue of it with the client.

2 caveats--
I rarely trust anyone to identify bolts for me; too many people are so 
clueless about what the markings mean that they aren't afraid to fake it. 

Verify that the bolts are correctly preloaded, that the nuts are suitable 
for use with high strength fasteners, and that hardened washers were 
used. This is a situation where the 'half-assed installation' limit state 
can easily govern.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)