[TowerTalk] Fwd: Screw Anchor Experience

[K0DAN]

Hans...

In my experience this is not true. I have some photos of my failed 
galvanized screw anchor which I can send you. The failure was a good 3+ feet 
below the ground surface, however I expect the metal rod was probably 
compromised along its entire length.

The property I am on was once a working farm. I occasionally find gears and 
other metal parts from farm implements I believe to date from the 
1920's-1930's. This iron or steel parts are very solid and heavily rusted, 
and the rust protects it from deeper corrosion (think: ocean 
liner)...galvanized anchors, on the other hand, are not the same compound. 
(Metallurgists please chime in). I suspect that the steel underneath the 
galvanizing may be a very soft/cheap material (keep the costs down no matter 
what), and once the galvanizing is compromised it does not take long (15 
years in my case) for the actual metal to be totally compromised.

What you describe for poles, fence posts, etc., is true, but I suspect we 
are comparing apples and oranges. And again, we should not assume that all 
soils are created the same. What I have here in west central Missouri is 
probably much different than soils and ground water in other parts of the 
country.

As always YMMV.

73

Dan
K0DAN

-----Original Message----- 
From: Hans Hammarquist
Sent: June 20, 2013 11:38
To: towertalk at contesting.com
Subject: [TowerTalk] Fwd: Screw Anchor Experience

What I have seen, it is only the portion closest to the surface that 
corrodes. I have found iron pieces buried for hundred of years with only 
slight corrosion. Scrap iron, stored laying on the ground, has almost 
disappeared in no time. I believe it is a combination of water, "dirt", and 
air that is causing this.


When installing fence with steel poles, a concrete "plate" is made around 
the pole just at the surface. It is sloped on the top to allow water 
run-off. If you don't do that the pole will corrode at the surface and 
eventually break there.


The rebar in concrete is "protected" by the concrete but will corrode if too 
close to the surface. In the same way the fence pole is "protected" by the 
concrete plate.


Maybe some concrete poured around anchor can extend the life-expectancy of 
the anchor.


Next: What method or how would you inspect an anchor for corrosion damages? 
Just digging around it?


Hans - N2JFS



-----Original Message-----
From: Mark Robinson <markrob at mindspring.com>
To: Jim Thomson <jim.thom at telus.net>; towertalk <towertalk at contesting.com>
Sent: Thu, Jun 20, 2013 11:36 am
Subject: Re: [TowerTalk] Screw Anchor Experience


Jim wrote


> ##  why mess with screw in anchors ?  Only power company’s + telco’s use
> em. Even then
> they use eggs in the EHS guys.   A  40’ tall utlility pole is already 6
> feet into the ground. No
> anodes used.
>
> ##  The rohn type rod anchors are in contact with the soil, where it is
> trenched, so that portion
> of the rod needs to be coated with roofing tar pitch.  Those GAC series
> anchor rods involve
> excavating a huge hole, that is then trenched.  The concrete slab needs to
> be poured, then the
> entire mess is bakfilled with dirt.
>

I reply...

They weren't screw anchors. They were the Rohn supplied anchors set in
concrete per the Rohn specifcations (as you describee) BUT they are still
vulnerable to corrosion. I have read dubious accounts of using tar on the
buried metal parts - the tar can fail and then the corrosion will be
concentrated in the failed areas

My opinion/guess is that the sacrificial anodes are a better way to go but
only time will prove me right or wrong.



Mark N1UK


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