It was stainless but I do not know the grade. In a warm salt spray
environment, like Kwajalein, any grade of stainless will rust.
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: "Terry Gerdes" <terry@ab5k.net>
Cc: <TOWERTALK@CONTESTING.COM>
Sent: Monday, February 14, 2005 10:17 AM
Subject: Re: [TowerTalk] RADIAL WIRE, Aruba corrosion
> I would bet that the corroded clamp is not the proper grade of stainless
> if stainless at all.
>
> 73
> Gary K4FMX
>
> Terry Gerdes wrote:
> > Having spent 11 years working on radar systems in the Marshall Islands,
I'm
> > a bit of a expert of issues of maintaining antennas in tropical salt
> > conditions. In the case of the Marshall's, you are setting 8 degrees
north
> > of the equator. The temperature is a constant 80 degrees F (plus/minus
5
> > degrees) year round and there are constant trade winds blowing 10 months
of
> > the year coating all exterior surfaces with warm salt spray. Keeping
> > anything outdoors in this environment is a real challenge. For example,
a
> > new bicycle will last a couple of years and either the frame will rust
in to
> > or the spokes will rust out.
> >
> > On the antenna side, the real issue is the corrosion due to the
dissimilar
> > metals. Anywhere there is a dissimilar metal, there is a galvanic
reaction
> > and the stronger material will eat away the weaker material. For the
> > amateur antennas, you traditionally have stainless steel bolts holding
> > together aluminum elements. The aluminum will simply erode away where
it is
> > in contact with the stainless. Here is a picture of a less than
six-month
> > old Mosley antenna, http://www.ab5k.net/images/kwajant2.jpg. You can
see
> > on the aluminum phasing lines where the stainless bolts are attacking
it.
> >
> > You can see the Mosley boom at http://www.ab5k.net/images/kwajant1.jpg.
> > The stainless steel u-bolts are very rusty. They were treated with
> > never-seize before they went up. I believe the use of the never-seize
> > probably increased the rusting on the bolts due to adding more
dissimilar
> > metals. That is not really bad as a good coat of rust provides a
protective
> > coating which helps slow down the corrosion a bit.
> >
> > The corrosion issue is serious and is very hard to stop. Any antenna
taken
> > into a environment like this needs to be hardened. For example when
> > assembling aluminum elements use a aluminum pop rivet rather that a
> > stainless steel bolt or hose clamp. You will probably still have some
> > dissimilar metals due to different alloys in the aluminum but it will
slow
> > down the corrosion.
> >
> > On areas where you have to have dissimilar metals, due to structural
> > strength requirements, the use of a sacrificial washer works well.
Rather
> > than have the stainless bolt erode away the aluminum element, you place
a
> > sacrificial aluminum washer between the stainless bolt and the aluminum
> > element. That way most of the corrosion will take place on the
sacrificial
> > aluminum washer. The sacrificial aluminum washer can be replaced as
> > needed, assuming you can get the rusted bolt out.
> >
> > At work at the TRADEX radar, dissimilar metals also caused both major
and
> > minor repairs.
> > http://www.ab5k.net/images/tradex.jpg.
> > http://www.ab5k.net/images/TradexFeed.jpg
> > http://www.ab5k.net/images/TradexFeed2.jpg.
> >
> >
> > 73 Terry AB5K, ex KX6OI and V73AQ
> > www.ab5k.net
> >
> >
> >
> >
> >>Mike describes the effects of the severe Aruba ocean atmosphere on an
> >>aluminum vertical over 2 years. I wonder if an initial assembly using
> >>thorough greasing of all joints with Noalox or equiv, and periodic touch
> >
> > ups
> >
> >>could preserve the connection integrity for a significant period, or
> >
> > whether
> >
> >>even then, the attack by the salty air is not significantly slowed.
> >>73, DX, de Pat Barthelow AA6EG aa6eg@hotmail.com
> >>
> >>
> >>
> >>
> >>>From: "MIKE GREENWAY" <K4PI@peoplepc.com>
> >>>To: "Jim Lux" <jimlux@earthlink.net>, <TOWERTALK@CONTESTING.COM>
> >>>Subject: Re: [TowerTalk] RADIAL WIRE
> >>
> >>Snip;
> >>On the subject of
> >>
> >>>aluminum oxidizing , we had a Gap Challenger that was put up new in
Aruba
> >>>using the supplied hardware. In 2 years the aluminum started turning
to
> >>>white oxide powder where the screws go through the tubing. The holes
for
> >>>the screws go so big and the area around them got so brittle it had to
be
> >>>taken down 73 Mike K4PI
> >>
> >>
> >>_______________________________________________
> >>
> >>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> >
> > Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> > questions and ask for Sherman, W2FLA.
> >
> >>_______________________________________________
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> >>http://lists.contesting.com/mailman/listinfo/towertalk
> >>
> >
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
>
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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