<font size=2 face="sans-serif">Hi:</font>
<br>
<br><font size=2 face="sans-serif">One thing which has come up a lot since
the solar industry really took off in the last 10 years is that of corrosion
and degradation of exposed metal on racks and modules.</font>
<br>
<br><font size=2 face="sans-serif">Corrosion due to dissimilar metals,
aka galvanic corrosion, is due to the natural characteristics of the metals.
</font>
<br>
<br><font size=2 face="sans-serif">To get a relative sense of the magnitude
of the problem, all the metals can be stacked up in table where at one
end are the metals which don't corrode and the other, the ones which do.</font>
<br>
<br><font size=2 face="sans-serif">With this layout, the farther apart
they are in table, the faster the corrodible metal will corrode. (This
shows that zinc is a good sacrificial metal for every other metal except
Magnesium).</font>
<br>
<br><img src=cid:_1_0CE4C3E00CE4BB140070104088257E54>
<br>
<br>
<br><font size=2 face="sans-serif">There is another effect which is at
least as, or in some cases even more significant. That is the dissimilar
coefficients of thermal expansion. The table below lists a bunch
of common metals. The units for the numbers are, micro-meters per
meter per degree Celsius.</font>
<br>
<table border=4>
<tr valign=top>
<td bgcolor=#4f81bd>
<div align=center><font size=4 color=white face="Calibri"><b>Most Expansive</b></font></div>
<td bgcolor=#4f81bd>
<div align=center><font size=4 color=white face="Calibri"><b>
</b></font></div>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Zinc</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">30</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Cadmium
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">30
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Lead
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">28
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Magnesium
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">25
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Tin
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">23
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Aluminium
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">22
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Silver
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">20
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Brass
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">19
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Copper
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">16
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Stainless Steel
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">16
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Gold
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">14
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Steel/Iron
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">11
</font>
<tr valign=top>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">Titanium
</font>
<td bgcolor=#d0d8e8><font size=1 face="Calibri">8
</font>
<tr valign=top>
<td bgcolor=#e9edf4><font size=1 face="Calibri">Graphite
</font>
<td bgcolor=#e9edf4><font size=1 face="Calibri">8
</font>
<tr valign=top>
<td bgcolor=#d0d8e8>
<div align=center><font size=4 face="Calibri">Least Expansive</font>
<br><font size=4 face="Calibri">
</font></div>
<td bgcolor=#d0d8e8>
<div align=center><font size=4 face="Calibri">
</font></div></table>
<br>
<br><font size=2 face="sans-serif">As in the previous table, the farther
apart the metals are the worse is the situation as the metals are cycled
through mid winter lows to high noon summer temperatures. You can
also see that steel/iron has an issue with almost every other metal.</font>
<br>
<br><font size=2 face="sans-serif">One way to deal with the galvanic corrosion
is by having a zinc coating or perhaps zinc anodes up in the framework
in such a place so that the zinc residue will run down the posts as the
zinc oxidizes.</font>
<br>
<br><font size=2 face="sans-serif">With the thermal expansion, the use
of rubber/plastic/nylon bushings will allow for thermal cycling without
allowing metal fatigue and/or damage. </font>
<br>
<br><font size=2 face="sans-serif">In the case of iron, the galvanic potential
between itself and aluminium is virtually non-existent. It's the
thermal expansion which messes things up. Using bushings gives flexibility
at the joint to allow for non-detrimental thermal expansion cycling.</font>
<br>
<br><font size=2 face="sans-serif">One other related thing to note is the
the thermal coefficient of expansion for masonry is in the range of 3-4.
That's a lot different than aluminium, so the "rubbery"
joints help a lot in this case.</font>
<br>
<br><font size=2 face="sans-serif">JARMO<br>
</font><font size=3 color=#008000>_____________________________________________________________________________________</font><font size=3>
<br>
</font><font size=1 face="Arial"><b><br>
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Schneider Electric </b></font><font size=1 face="Arial"><b> | Xantrex
Brand</b> | <b>CANADA</b> | <b>Sales Application
Engineer</b> <b><br>
Phone:</b> +604-422-2528 | <b>Tech Support:</b> 800-670-0707
| <b>Mobile:</b> +604-505-0291 <b><br>
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<br>
<br>
<table width=100%>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">From:</font>
<td><font size=1 face="sans-serif">RM You <solareagle@solareagle.com></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">To:</font>
<td><font size=1 face="sans-serif">RE-wrenches <re-wrenches@lists.re-wrenches.org>,
</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Date:</font>
<td><font size=1 face="sans-serif">05/28/2015 07:21 PM</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Subject:</font>
<td><font size=1 face="sans-serif">[RE-wrenches] iron & aluminum</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Sent by:</font>
<td><font size=1 face="sans-serif">"RE-wrenches" <re-wrenches-bounces@lists.re-wrenches.org></font></table>
<br>
<hr noshade>
<br>
<br>
<br><tt><font size=2>Hi Wrenches, I have had a couple of customers want
to fabricate their own PV pole mounts and racks out of iron. Aside from
the galvanic corrosion and weight issues is there anything else I should
caution these guys about? Any stories about failures etc? My druthers are
to stay with the engineered aluminum pole mounts but when you’re dealing
with someone with fabrication experience and the cost for pre-fab is high
then the obvious outcome occurs. If the unit is properly treated/painted
I imagine it could last many years. Is there a way to attach an anode to
such a rack or would simple non conductive insulation between panels and
rack be the best answer?<br>
<br>
Ron Young<br>
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