[TowerTalk] RADIAL WIRE, Aruba corrosion

[Gary Schafer]

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 at hotmail.com
>>
>>
>>
>>
>>>From: "MIKE GREENWAY" <K4PI at peoplepc.com>
>>>To: "Jim Lux" <jimlux at earthlink.net>, <TOWERTALK at 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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> 
> 
> _______________________________________________
> 
> 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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