Return to index: [Subject] [Thread] [Date] [Author]

Re: Levelling plates or shims ?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Just adding to the below response, the hydrogen released during galvanizing
has mostly to do with the pickling process and not the zinc.  I have heard
that in Europe they galvanize A490 bolts by using a mechanical cleaning
process.

Thomas Hunt
Duke/Fluor Daniel




                    "David Sharp"
                    <Ausgang@e46fan       To:     <seaint(--nospam--at)seaint.org>
                    atics.com>            cc:
                                          Subject:     Re: Levelling plates or shims ?
                    02/28/02 09:41
                    AM
                    Please respond
                    to seaint






To add to Heath's observations about why ASTM forbids galvanizing of
A490s --- it is also due to concerns over hydrogen assisted
stress-corrosion
cracking in addition to other process-related or environmental-related
failures caused by hydrogen.

Not that a broken bolt cares where the hydrogen came from, but here is some
more detail on the topic as it relates to fasteners:

The phrase 'hydrogen embrittlement' is sometimes used as a general
catch-all
for all hydrogen-related fractures.  In recent years, ASTM's fastener
committee has adopted the use of different terms depending upon the source
of the hydrogen.  For example, in ASTM F1940 [Standard Test Method for
Process Control to Prevent Hydrogen Embrittlement in Plated or Coated
Fasteners], the document focuses on "Internal Hydrogen Embrittlement"
(IHE).

Thus, in F1940, we focus on evaluation of the processes by which fasteners
are plated or coated and the potential for hydrogen embrittlement caused
thereby.  Factors such as the chemistry of the cleaning and pickling media
to the plating solution or current density or baking temperatures and times
can be evaluated.

For hydrogen embrittlement caused by environmental exposure [EHE], ASTM's
fastener committee relies upon ASTM F1624.  This latter consideration is
the
more often forgotten one by fastener users.  All too frequently the focus
is
directed at obtaining 'hydrogen-free' fasteners ---- which eventually end
up
being used in an environment capable of providing sufficient hydrogen to
cause fracture anyway.  This is easier than often believed.   Consider a
highly stressed zinc-plated or galvanized fastener used to clamp aluminum
plates.  Add water and voila, hydrogen introduced via galvanic action.
Same
goes for galvanized fasteners used with stainless steel.  Or, try
galvanized
bolts with plain finish washers.

As Heath mentioned, fastener susceptibility to hydrogen-related failures is
highly correlated with higher tensile strengths (~180 to 200 ksi).  Keep in
mind, it is also highly correlated with actual induced fastener stress.
(See --- you knew loose bolts were good for something.)

Lastly, to be fair to the alchemists (or if you prefer, metallurgists),
materials are available that can push well beyond 200 ksi without undue
risk
of hydrogen related failures.  Conversely, fastener metallurgists love to
demonstrate how certainly readily available steels of much lower strength
are very susceptible to HE.


David Sharp
TurnaSure LLC




> 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
> >
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
>


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********





******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********