[TowerTalk] Fwd: N2JFS photos of bolts

[Hans Hammarquist]

I was recommended but Universal to use galvanized bolts as the SS are not available in high enough grade. (I don't remember now what grade they recommended.) In my mind I will replace the bolts in a few (maybe 10 - 15) years. That will also give me an idea what condition they are.


I don't know how important the grade issue is and in my case I think I already have both "belt and suspenders" as I have a self-supporting tower equipped with guy wires. (The tower should be able to sustain 135 mph even if the base gives in.)


SS bolts are not a panacea. Even if the bolt doesn't corrode, which it actually might anyhow, it might damage the surrounding aluminum. Has something to do with Redox potential. The problem is that the Redox potential is not stable for aluminum and SS steel, in other word, you can not predict what will corrode when you connect and aluminum piece to a SS piece. When dirt cover the two metals it will form the destructive electrolyte, which will cause the corrosion. Depending on what the dirt contain you will get different results (place of corrosion). If you can keep the dirt away (not necessary easy) you can prevent or slow the corrosion rate (needless to say, really).


As a final note: SS needs access to air to stay stainless. A thin oxide layer on the steel surface serves as the corrosion prevention. If you cover the steel and the protective layer get damaged the corrosion can set in very fast (know that from experience, not from a tower, though).


Hans - N2JFS



-----Original Message-----
From: john <john at kk9a.com>
To: towertalk <towertalk at contesting.com>
Sent: Thu, Jan 9, 2014 9:28 am
Subject: Re: [TowerTalk] N2JFS photos of bolts


I had the same bolt issue with my first Universal tower. I have never seen
corrosion of the base, except in Aruba and it was only surface rust. I had
filled the square tube with concrete too keep if from filling with water.
As I recall the supplied bolts were just poor quality zinc plated. 
Aluminum and galvanized steel touch in many areas of my tower systems with
no issues so I do not think it is a dissimilar metal problem. In fact, in
corrosive environments I have seem many instances were stainless steel
destroyed the aluminum it was in contact with so SS hardware has its
problems.

John KK9A - P40A


To:	towertalk at contesting.com
Subject:[TowerTalk] N2JFS photos of bolts
From:	kr2q at optimum.net
Date:	 Thu, 09 Jan 2014 12:31:15 +0000 (GMT)

Wow..those photos bring back lots of memories from the late 60's/early 70's..

I had an aluminum (Heights) crankup tower (84 feet?).

I noticed some "rust" one year and pulled out the bolt that came with the
tower.
They looked well on the way to what you showed in your photos.

Yeah...you can't use steel bolts on an aluminum tower..this happens every
time.

So I replaced all of the bolts with SS.  Worked great and let me sleep at
night.

However, I was always worried about the Al to Steel junction at the base.
Also, the steel
triangles at the top/bottom of each (telescopic) section "rusted" (dissimilar
metals - eaten
away) pretty badly.  I had SS triangles fabricated, but by the time they
arrived, I went off
to college and wen I returned, I found a greenhouse where my tower used to
be.
:-)

So I bought some taper sections and no longer had a crank up.  My dad was
kind
enough
to let me "move the tower" to the other side of the house...again using SS
bolts..but still had
the same issue with the base.

When I got my own place, I bought steel crankup towers.  Heavier but no
worries
about the
aluminum eating away the steel.

de Doug KR2Q

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