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RE: Levelling plates or shims ?

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The true measure of hydrogen embrittlement potential is a measure of
Rockwell hardness.  But many specs relate it to minimum specified tensile
strength.  The ASCE Petrochemical Energy Committee puts a limit of 125 ksi
on the tensile strength for consideration of hydrogen embrittlement.  The
minimum specified tensile strength for F1554, 105 ksi anchor rods is 125 ksi
to 150 ksi.  That is why I like the duplex coating on anchor rods, or put
them in a bolt box filled with grease.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	HEATH MITCHELL [SMTP:hmitchell(--nospam--at)PCSAinc.com]
> Sent:	Wednesday, February 27, 2002 4:45 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Levelling plates or shims ?
>
> Harold-
>
> I believe that the "magic" number for hydrogen embrittlement is a tensile
> strength around 200 ksi. This is why A490 bolts (max tensile of 170 ksi)
> are
> not allowed to be galvanized. I would think that since most anchor rod
> material is 120 ksi and below, hydrogen embrittlement would not be a
> problem, at least for static loads. Is this a fatigue issue?
>
>
> Regards,
> Heath Mitchell
>
> > -----Original Message-----
> > From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> > Sent: Wednesday, February 27, 2002 12:00 PM
> > To: 'seaint(--nospam--at)seaint.org'
> > Subject: RE: Levelling plates or shims ?
> >
> > David,
> >
> > These structures are different.  You have access to the bottom nut, they
> > are
> > light weight, and they are generally isolated and not dependent on other
> > columns (for relative elevation).  There is nothing wrong with leveling
> > nuts
> > in those applications.
> >
> > I would caution however that in the high winds (that you get down in
> your
> > neck of the woods) to take into account the fatigue on the reduced
> section
> > of the anchor rod.  You can't preload to avoid stress cycles.
> >
> > The Australians did a study for glazing a while back that said for one
> > given
> > storm, they could get 10,000 cycles on elements.  This is the study that
> > fed
> > into the impact resistant glazing performance requirements.
> >
> > I would also urge caution on galvanizing high strength bolts.  You can
> > create a problem for hydrogen embrittlement.  This is not a pleasant
> mode
> > of
> > failure.  There is no warning.
> >
> > Do you hot dip galvanize the bolts in Florida?
> >
> > Regards,
> > Harold O. Sprague
> >
>
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